Power conversion apparatus

Abstract

The present invention addresses the problem of performing soft switching more reliably. In a power conversion apparatus (100), if a control device (50) determines that resonance currents respectively passing through two or more switches (8) among a plurality of switches (8) simultaneously flow through a resonance inductor (L1) when a duty command value of one phase among duty command values of three phases in a two-phase modulation scheme is fixed at a constant value, the control device performs a first operation and further performs a second operation when one of two switches (8), among the two or more switches (8), corresponding one-to-one to two AC terminals (41) having load currents of the same polarity among a plurality of AC terminals (41) is defined as a first switch and the remaining one is defined as a second switch.

Description

Power conversion device

[0001] The present disclosure relates to a power conversion device, and more particularly to a power conversion device capable of converting DC power into AC power.

[0002] Patent Document 1 discloses a power conversion device that converts DC into polyphase AC.

[0003] The power conversion device disclosed in Patent Document 1 includes main switching means (power conversion circuit), two capacitors, one coil (resonance inductor), a plurality of auxiliary switch elements, and control means. The main switching means is composed of a pair of main switch elements connected in series between both terminals of a DC power supply, and a main switching circuit having the connection point between the pair of main switch elements as the output point of each phase is provided for each phase of the polyphase AC. The two capacitors divide the voltage of the DC power supply. One end of the coil is connected to the voltage division point by the two capacitors. The plurality of auxiliary switch elements connect between the other end of the coil and the output point of each phase. When the control means determines that a plurality of phase currents flow through the coil, the control means controls the plurality of auxiliary switch elements so that the current flowing through at least one phase becomes smaller than a preset magnitude.

[0004] In the power conversion device described in Patent Document 1, when the control means determines that a plurality of phase currents flow through the coil, the control means controls the plurality of auxiliary switch elements so that the current flowing through at least one phase becomes smaller than a preset magnitude. Therefore, soft switching of the main switch element corresponding to the at least one phase is not performed.

[0005] Japanese Unexamined Patent Application Publication No. 2010 - 233306

[0006] An object of the present disclosure is to provide a power conversion device capable of performing soft switching more reliably.

[0007] A power conversion device according to one embodiment of the present disclosure comprises a first DC terminal and a second DC terminal, a power conversion circuit, a plurality of AC terminals, a plurality of switches, a plurality of resonant capacitors, a resonant inductor, a regenerative capacitor, and a control device. The power conversion circuit has a plurality of first switching elements and a plurality of second switching elements. In the power conversion circuit, a plurality of switching circuits, each in which the plurality of first switching elements and the plurality of second switching elements are connected in series in a one-to-one relationship, are connected in parallel to each other. In the power conversion circuit, the plurality of first switching elements are connected to the first DC terminal, and the plurality of second switching elements are connected to the second DC terminal. The plurality of AC terminals correspond one-to-one to the plurality of switching circuits. Each of the plurality of AC terminals is connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit. The plurality of switches correspond one-to-one to the plurality of switching circuits. Each of the plurality of switches has its first end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit, and its second end is commonly connected to a common connection point. The resonant capacitors correspond one-to-one with the plurality of switches. Each of the plurality of resonant capacitors is connected between the first terminal and the second DC terminal of the corresponding switch. The resonant inductor has a third terminal and a fourth terminal. In the resonant inductor, the third terminal is connected to the common connection point. The regenerative capacitor has a fifth terminal and a sixth terminal. In the regenerative capacitor, the fifth terminal is connected to the first DC terminal or the second DC terminal. The control device generates a plurality of first PWM signals for controlling the plurality of first switching elements, a plurality of second PWM signals for controlling the plurality of second switching elements, and a plurality of control signals for controlling the plurality of switches. The control device generates the plurality of first PWM signals and the plurality of second PWM signals based on a three-phase duty cycle command value for a two-phase modulation scheme or a three-phase duty cycle command value for a three-phase modulation scheme.The control device sets a dead time period for each of the plurality of switching circuits between the high-level period of the first PWM signal to the first switching element and the high-level period of the second PWM signal to the second switching element, and sets the high-level period of the control signal to each of the plurality of switches based on the dead time period for the corresponding switching circuit among the plurality of switching circuits. A load current flows through each of the plurality of AC terminals through the first switching element or the second switching element of the corresponding switching circuit. When the control device determines that a resonant current flows simultaneously through two or more of the plurality of switches in the resonant inductor when the duty cycle command value of one phase of the three-phase duty cycle command value of the two-phase modulation method is fixed to a constant value, or when the duty cycle command value of one phase of the three-phase duty cycle command value of the three-phase modulation method is fixed to a constant value, the control device performs a first operation, and then performs a second operation, when one of the two or more switches that correspond one-to-one with two AC terminals in the plurality of AC terminals having the same polarity of load current is designated as the first switch, and the remaining one as the second switch. The first operation is to shorten the high-level period of the control signal to the first switch by a shortened period from a period that includes the resonant half-period determined by the capacitance of the resonant capacitor corresponding to the first switch among the plurality of resonant capacitors and the inductance of the resonant inductor, and an additional time determined by the voltage of the regenerative capacitor, the inductance of the resonant inductor and the load current value. The second operation is to shift the high-level period of the control signal to at least one of the first switch and the second switch such that the high-level period of the control signal to the first switch starts by a waiting period after the point in time when the current value of the resonant current passing through the second switch matches the current value of the load current flowing through the AC terminal corresponding to the second switch among the two or more AC terminals, after the current value of the resonant current passing through the second switch reaches an extreme value.

[0008] A power conversion device according to one embodiment of the present disclosure comprises a first DC terminal and a second DC terminal, a power conversion circuit, a plurality of AC terminals, a plurality of switches, a plurality of resonant capacitors, a resonant inductor, a regenerative capacitor, and a control device. The power conversion circuit has a plurality of first switching elements and a plurality of second switching elements. In the power conversion circuit, a plurality of switching circuits, each in which the plurality of first switching elements and the plurality of second switching elements are connected in series in a one-to-one relationship, are connected in parallel to each other. In the power conversion circuit, the plurality of first switching elements are connected to the first DC terminal, and the plurality of second switching elements are connected to the second DC terminal. The plurality of AC terminals correspond one-to-one to the plurality of switching circuits. Each of the plurality of AC terminals is connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit. The plurality of switches correspond one-to-one to the plurality of switching circuits. Each of the plurality of switches has its first end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit, and its second end is commonly connected to a common connection point. The resonant capacitors correspond one-to-one with the plurality of switches. Each of the plurality of resonant capacitors is connected between the first terminal and the second DC terminal of the corresponding switch. The resonant inductor has a third terminal and a fourth terminal. In the resonant inductor, the third terminal is connected to the common connection point. The regenerative capacitor has a fifth terminal and a sixth terminal. In the regenerative capacitor, the fifth terminal is connected to the first DC terminal or the second DC terminal. The control device generates a plurality of first PWM signals for controlling the plurality of first switching elements, a plurality of second PWM signals for controlling the plurality of second switching elements, and a plurality of control signals for controlling the plurality of switches. The control device generates the plurality of first PWM signals and the plurality of second PWM signals based on a three-phase duty cycle command value for a two-phase modulation scheme or a three-phase duty cycle command value for a three-phase modulation scheme.When the control device determines that a resonant current flows simultaneously through two or more of the switches in the resonant inductor when the duty cycle command value of one of the three phases of the two-phase modulation scheme is fixed to a constant value, or when the duty cycle command value of one of the three phases of the three-phase modulation scheme is fixed to a constant value, the control device performs shift control to shift the high-level period of the control signal to at least one of the two or more switches so that the resonant currents flowing through two or more of the switches in the resonant inductor do not flow simultaneously.

[0009] A power conversion device according to one embodiment of the present disclosure comprises a first DC terminal and a second DC terminal, a power conversion circuit, a plurality of AC terminals, a plurality of switches, a plurality of resonant capacitors, a resonant inductor, a regenerative capacitor, and a control device. The power conversion circuit has a plurality of first switching elements and a plurality of second switching elements. In the power conversion circuit, a plurality of switching circuits, each in which the plurality of first switching elements and the plurality of second switching elements are connected in series in a one-to-one relationship, are connected in parallel to each other. In the power conversion circuit, the plurality of first switching elements are connected to the first DC terminal, and the plurality of second switching elements are connected to the second DC terminal. The plurality of AC terminals correspond one-to-one to the plurality of switching circuits. Each of the plurality of AC terminals is connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit. The plurality of switches correspond one-to-one to the plurality of switching circuits. Each of the plurality of switches has its first end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit, and its second end is commonly connected to a common connection point. The resonant capacitors correspond one-to-one with the plurality of switches. Each of the plurality of resonant capacitors is connected between the first terminal and the second DC terminal of the corresponding switch. The resonant inductor has a third terminal and a fourth terminal. In the resonant inductor, the third terminal is connected to the common connection point. The regenerative capacitor has a fifth terminal and a sixth terminal. In the regenerative capacitor, the fifth terminal is connected to the first DC terminal or the second DC terminal. The control device generates a plurality of first PWM signals for controlling the plurality of first switching elements, a plurality of second PWM signals for controlling the plurality of second switching elements, and a plurality of control signals for controlling the plurality of switches. The control device generates the plurality of first PWM signals and the plurality of second PWM signals based on a three-phase duty cycle command value for a two-phase modulation scheme or a three-phase duty cycle command value for a three-phase modulation scheme.The control device can perform a first control operation and a second control operation when it determines that a resonant current flows simultaneously through two or more of the switches in the plurality of switches when the duty cycle command value of one of the three phases of the two-phase modulation scheme is fixed to a constant value, or when the duty cycle command value of one of the three phases of the three-phase modulation scheme is fixed to a constant value. The first control operation overlaps the high-level period of the control signal to each of the two or more switches with the dead time period corresponding to each of the two or more switching circuits connected to the two or more switches in the plurality of switching circuits for a predetermined period. The second control operation determines the start time of the high-level period of the control signal to at least one of the plurality of switches according to the load current of at least one phase flowing through the AC load connected to the plurality of AC terminals.

[0010] A power conversion device according to one embodiment of the present disclosure comprises a first DC terminal and a second DC terminal, a power conversion circuit, a plurality of AC terminals, a plurality of switches, a plurality of resonant capacitors, a resonant inductor, a regenerative capacitor, and a control device. The power conversion circuit has a plurality of first switching elements and a plurality of second switching elements. In the power conversion circuit, a plurality of switching circuits, each in which the plurality of first switching elements and the plurality of second switching elements are connected in series in a one-to-one relationship, are connected in parallel to each other. In the power conversion circuit, the plurality of first switching elements are connected to the first DC terminal, and the plurality of second switching elements are connected to the second DC terminal. The plurality of AC terminals correspond one-to-one to the plurality of switching circuits. Each of the plurality of AC terminals is connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit. The plurality of switches correspond one-to-one to the plurality of switching circuits. Each of the plurality of switches has its first end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit, and its second end is commonly connected to a common connection point. The resonant capacitors correspond one-to-one with the plurality of switches. Each of the plurality of resonant capacitors is connected between the first terminal and the second DC terminal of the corresponding switch. The resonant inductor has a third terminal and a fourth terminal. In the resonant inductor, the third terminal is connected to the common connection point. The regenerative capacitor has a fifth terminal and a sixth terminal. In the regenerative capacitor, the fifth terminal is connected to the first DC terminal or the second DC terminal. The control device generates a plurality of first PWM signals for controlling the plurality of first switching elements, a plurality of second PWM signals for controlling the plurality of second switching elements, and a plurality of control signals for controlling the plurality of switches. The control device generates the plurality of first PWM signals and the plurality of second PWM signals based on a three-phase duty cycle command value for a two-phase modulation scheme or a three-phase duty cycle command value for a three-phase modulation scheme.The control device sets a dead time period for each of the plurality of switching circuits between the high-level period of the first PWM signal to the first switching element and the high-level period of the second PWM signal to the second switching element, and sets the high-level period of the control signal to each of the plurality of switches based on the dead time period for the corresponding switching circuit among the plurality of switching circuits. A load current flows through each of the plurality of AC terminals through the first switching element or the second switching element of the corresponding switching circuit. When the duty cycle command value of one phase among the three phase duty cycle command values ​​of the two-phase modulation method is fixed to a constant value, or when the duty cycle command value of one phase among the three phase duty cycle command values ​​of the three-phase modulation method is fixed to a constant value, the control device performs a shortening control when it determines that a resonant current flows simultaneously through two or more of the plurality of switches when a control signal for a preset high-level period is applied to each of the plurality of switches. In the shortened control, the control device provides a control signal to a first switch, which is one of the two or more switches, with a shortened preset high-level period, and provides a control signal to a second switch, which is different from the first switch, with a preset high-level period.

[0011] Figure 1 is a circuit diagram of a system equipped with a power converter according to Embodiment 1. Figure 2 is an explanatory diagram illustrating the relationship between the duty cycle command value and the carrier signal generated by the top-stick two-phase modulation method in the control device of the power converter. Figure 3 is an explanatory diagram of the operation when the control device of the power converter performs basic operation when the load current > 0 and the resonant capacitor is charging. Figure 4 is an explanatory diagram of the operation when the control device of the power converter performs basic operation when the load current > 0 and the resonant capacitor is charging. Figure 5 is another explanatory diagram of the operation when the control device of the power converter performs basic operation when the load current > 0 and the resonant capacitor is charging. Figure 6 is an explanatory diagram of the first current threshold and second current threshold used in the control device of the power converter. Figure 7 is an explanatory diagram of the operation when the control device of the power converter performs basic operation when the load current > 0 and the resonant capacitor is discharging. Figure 8 is an explanatory diagram of the operation when the control device of the power converter performs basic operation when the load current < 0 and the resonant capacitor is discharging. Figure 9 is an explanatory diagram of the operation of the control device in the above power converter when the load current is < 0 and the resonant capacitor is being charged. Figure 10 is an explanatory diagram of the region in the above power converter where the three-phase duty cycle command values ​​are close together. Figure 11 is an explanatory diagram of the three-phase duty cycle command values ​​generated by the top-stick two-phase modulation method in the control device of the above power converter. Figure 12 is a timing chart for explaining the operation when the control device in the above power converter performs the first and second operations. Figure 13 is a circuit diagram of a system equipped with the power converter according to Embodiment 2. Figure 14 is a timing chart for explaining the operation of the control device in the above power converter. Figure 15 is a circuit diagram of a system equipped with the power converter according to Embodiment 3. Figure 16 is a timing chart when the control device in the above power converter performs the first control operation, the second control operation, and the third control operation. Figure 17 is a timing chart when the control device in the above power converter does not perform the first control operation, the second control operation, and the third control operation.Figure 18 is a circuit diagram of a system equipped with a power converter according to Embodiment 4. Figure 19 is a timing chart for explaining the operation of the control device in the same power converter when it determines that the resonant currents overlap. Figure 20 is a timing chart for explaining the operation of the control device in the same power converter when it performs shortening control. Figure 21 is a circuit diagram of a system equipped with a power converter according to Embodiment 5. Figure 22 is an explanatory diagram of the duty cycle command value generated by the bottom-stick two-phase modulation method in the control device of the same power converter. Figure 23 is a timing chart for explaining an example of boundary conditions for the same power converter when the V-phase resonant current and the W-phase resonant current do not overlap (do not flow simultaneously) and when they overlap (flow simultaneously). Figure 24 is a timing chart for explaining the operation of the control device in the same power converter when it performs the first operation and the second operation. Figure 25 is a circuit diagram of a system equipped with a power converter according to Embodiment 6. Figure 26 is an explanatory diagram of the duty cycle command value generated by the top-bottom-stick two-phase modulation method in the control device of the same power converter. Figure 27 is a timing chart illustrating the operation of the control device in the power converter described above when it performs the first and second operations. Figure 28 is a timing chart illustrating the operation of the control device in the power converter described above when it performs the first and second operations. Figure 29 is a circuit diagram of a system equipped with the power converter according to Embodiment 7. Figure 30 is an explanatory diagram illustrating the relationship between the duty cycle command value generated by a three-phase modulation scheme and the carrier signal in the control device of the power converter described above. Figure 31 is an explanatory diagram illustrating the duty cycle command value generated by a three-phase modulation scheme in the control device of the power converter described above. Figure 32 is a timing chart illustrating the operation of the control device in the power converter described above when it performs the first and second operations. Figure 33 is a timing chart illustrating the operation of the control device in the power converter described above when it performs the first and second operations.

[0012] (Embodiment 1) Below, the power conversion device 100 according to Embodiment 1 will be described with reference to Figures 1 to 12.

[0013] (1) Overall Configuration of the Power Converter The power converter 100 includes, for example, a first DC terminal 31 and a second DC terminal 32, and a plurality (for example, three) AC terminals 41, as shown in Figure 1. A DC power supply E1 is connected between the first DC terminal 31 and the second DC terminal 32, and an AC load RA1 is connected to the plurality of AC terminals 41. The AC load RA1 is, for example, a three-phase servo motor. The power converter 100 converts the DC output from the DC power supply E1 into AC power and outputs it to the AC load RA1. The DC power supply E1 includes, for example, an AC-DC converter, a DC-DC converter, a solar cell, or a fuel cell. In the power converter 100, if the plurality of AC terminals 41 are three AC terminals 41, the AC power is, for example, three-phase AC power having U-phase, V-phase, and W-phase.

[0014] The power converter 100 comprises a power conversion circuit 11, a plurality (for example, three) of switches 8, a plurality (for example, three) of resonant capacitors 9, a regenerative capacitor 15, a resonant inductor L1, and a control device 50. The power converter 100 further comprises a protection circuit 17 and a capacitor C10. Each of the plurality of switches 8 is, for example, a bidirectional switch.

[0015] The power conversion circuit 11 has a plurality (e.g., three) of first switching elements 1 and a plurality (e.g., three) of second switching elements 2. In the power conversion circuit 11, a plurality (e.g., three) of switching circuits 10, each consisting of a plurality of first switching elements 1 and a plurality of second switching elements 2 connected in a one-to-one series relationship, are connected in parallel to each other. In the power conversion circuit 11, the plurality of first switching elements 1 are connected to a first DC terminal 31, and the plurality of second switching elements 2 are connected to a second DC terminal 32. The plurality of AC terminals 41 correspond one-to-one to the plurality of switching circuits 10. Each of the plurality of AC terminals 41 is connected to the connection point 3 of the first switching element 1 and the second switching element 2 in the corresponding switching circuit 10. The plurality of switches 8 correspond one-to-one to the plurality of switching circuits 10. Each of the plurality of switches 8 has a first end 81 and a second end 82. The second end 82 of the plurality of switches 8 is connected to a common connection point 25. Each of the multiple switches 8 has its first end 81 connected to the connection point 3 of the first switching element 1 and the second switching element 2 in the corresponding switching circuit 10. The multiple resonant capacitors 9 correspond one-to-one with the multiple switches 8. Each of the multiple resonant capacitors 9 is connected between the first end 81 of the corresponding switch 8 and the second DC terminal 32. The resonant inductor L1 has a third end and a fourth end. In the resonant inductor L1, the third end of the resonant inductor L1 is connected to the common connection point 25. The regenerative capacitor 15 has a fifth end 153 and a sixth end 154. In the regenerative capacitor 15, the fifth end 153 is connected to the second DC terminal 32, and the sixth end 154 is connected to the common connection point 25 via the resonant inductor L1. The control device 50 generates multiple first PWM (Pulse Width Modulation) signals SU1, SV1, SW1 for controlling multiple first switching elements 1, multiple second PWM signals SU2, SV2, SW2 for controlling multiple second switching elements 2, and multiple control signals SU6, SU7, SV6, SV7, SW6, SW7 for controlling multiple switches 8.

[0016] (2) Details of the power converter In the following description, for the sake of convenience, the switching circuits 10 corresponding to the U-phase, V-phase, and W-phase may be referred to as switching circuit 10U, switching circuit 10V, and switching circuit 10W, respectively. Also, in the following description, the first switching element 1 and the second switching element 2 of switching circuit 10U may be referred to as the first switching element 1U and the second switching element 2U. Also, in the following description, the first switching element 1 and the second switching element 2 of switching circuit 10V may be referred to as the first switching element 1V and the second switching element 2V. Also, in the following description, the first switching element 1 and the second switching element 2 of switching circuit 10W may be referred to as the first switching element 1W and the second switching element 2W. Furthermore, in the following, the connection point 3 between the first switching element 1U and the second switching element 2U may be referred to as connection point 3U, the connection point 3 between the first switching element 1V and the second switching element 2V may be referred to as connection point 3V, and the connection point 3 between the first switching element 1W and the second switching element 2W may be referred to as connection point 3W. Furthermore, in the following, the AC terminal 41 connected to connection point 3U may be referred to as AC terminal 41U, the AC terminal 41 connected to connection point 3V may be referred to as AC terminal 41V, and the AC terminal 41 connected to connection point 3W may be referred to as AC terminal 41W. Furthermore, in the following, the resonant capacitor 9 connected in parallel to the second switching element 2U may be referred to as resonant capacitor 9U, the resonant capacitor 9 connected in parallel to the second switching element 2V may be referred to as resonant capacitor 9V, and the resonant capacitor 9 connected in parallel to the second switching element 2W may be referred to as resonant capacitor 9W. Furthermore, in the following, the switch 8 connected to connection point 3U may be referred to as switch 8U, the switch 8 connected to connection point 3V as switch 8V, and the switch 8 connected to connection point 3W as switch 8W.

[0017] The power converter 100 has the high-potential output terminal (positive terminal) of the DC power supply E1 connected to the first DC terminal 31, and the low-potential output terminal (negative terminal) of the DC power supply E1 connected to the second DC terminal 32. In addition, the power converter 100 has, for example, three AC terminals 41U, 41V, and 41W connected to the U-phase terminal, V-phase terminal, and W-phase terminal of the AC load RA1, respectively.

[0018] In the power conversion circuit 11, each of the multiple (e.g., three) first switching elements 1 and each of the multiple (e.g., three) second switching elements 2 has a control terminal, a first main terminal, and a second main terminal. The control terminals of the multiple first switching elements 1 and the multiple second switching elements 2 are connected to the control device 50. In each of the multiple switching circuits 10 of the power conversion device 100, the first main terminal of the first switching element 1 is connected to the first DC terminal 31, the second main terminal of the first switching element 1 is connected to the first main terminal of the second switching element 2, and the second main terminal of the second switching element 2 is connected to the second DC terminal 32. In each of the multiple switching circuits 10, the first switching element 1 is a high-side switching element (P-side switching element), and the second switching element 2 is a low-side switching element (N-side switching element). Each of the multiple first switching elements 1 and the multiple second switching elements 2 is, for example, an IGBT (Insulated Gate Bipolar Transistor). Therefore, the control terminal, first main terminal, and second main terminal of each of the multiple first switching elements 1 and the multiple second switching elements 2 are the gate terminal, collector terminal, and emitter terminal, respectively.

[0019] The power conversion circuit 11 further includes a plurality of first diodes 4 connected in antiparallel in a one-to-one relationship to a plurality of first switching elements 1 (three), and a plurality of second diodes 5 connected in antiparallel in a one-to-one relationship to a plurality of second switching elements 2 (three). In each of the plurality of first diodes 4, the anode of the first diode 4 is connected to the second main terminal (emitter terminal) of the first switching element 1 corresponding to the first diode 4, and the cathode of the first diode 4 is connected to the first main terminal (collector terminal) of the first switching element 1 corresponding to the first diode 4. In each of the plurality of second diodes 5, the anode of the second diode 5 is connected to the second main terminal (emitter terminal) of the second switching element 2 corresponding to the second diode 5, and the cathode of the second diode 5 is connected to the first main terminal (collector terminal) of the second switching element 2 corresponding to the second diode 5.

[0020] The connection point 3U between the first switching element 1U and the second switching element 2U is connected via AC terminal 41U to, for example, the U-phase terminal of the AC load RA1. The connection point 3V between the first switching element 1V and the second switching element 2V is connected via AC terminal 41V to, for example, the V-phase terminal of the AC load RA1. The connection point 3W between the first switching element 1W and the second switching element 2W is connected via AC terminal 41W to, for example, the W-phase terminal of the AC load RA1.

[0021] Multiple resonant capacitors 9 correspond one-to-one with multiple switches 8. Each of the multiple resonant capacitors 9 is connected between the first terminal 81 and the second DC terminal 32 of the corresponding switch 8. The power converter 100 has multiple resonant circuits. The multiple resonant circuits include a resonant circuit having a resonant capacitor 9U and a resonant inductor L1, a resonant circuit having a resonant capacitor 9V and a resonant inductor L1, and a resonant circuit having a resonant capacitor 9W and a resonant inductor L1. The resonant inductor L1 is common to all of the multiple resonant circuits.

[0022] Each of the multiple switches 8 has a third switching element 6 and a fourth switching element 7. Each of the multiple (three in the example of Figure 1) third switching elements 6 and each of the multiple (three in the example of Figure 1) fourth switching elements 7 has a control terminal, a first main terminal and a second main terminal. The control terminals of the multiple third switching elements 6 and the multiple fourth switching elements 7 are connected to the control device 50. Each of the multiple third switching elements 6 and the multiple fourth switching elements 7 is, for example, an IGBT. Therefore, the control terminal, first main terminal and second main terminal of each of the multiple third switching elements 6 and the multiple fourth switching elements 7 are the gate terminal, collector terminal and emitter terminal, respectively. In each of the multiple switches 8, the third switching element 6 and the fourth switching element 7 are connected in reverse series. In each of the multiple switches 8, the first main terminal (collector terminal) of the third switching element 6 is connected to the first main terminal (collector terminal) of the fourth switching element 7. In each of the multiple switches 8, the second main terminal (emitter terminal) of the third switching element 6 is connected to the connection point 3 of the corresponding switching circuit 10 among the multiple switching circuits 10, and the second main terminal (emitter terminal) of the fourth switching element 7 is connected to the resonant inductor L1. Furthermore, each of the multiple switches 8 has a diode 61 connected in antiparallel to the third switching element 6 and a diode 71 connected in antiparallel to the fourth switching element 7.

[0023] In the power converter 100, switch 8U is connected to the connection point 3U between the first switching element 1U and the second switching element 2U. Switch 8V is connected to the connection point 3V between the first switching element 1V and the second switching element 2V. Switch 8W is connected to the connection point 3W between the first switching element 1W and the second switching element 2W. For convenience of explanation, the third switching element 6 and the fourth switching element 7 of switch 8U may be referred to as the third switching element 6U and the fourth switching element 7U, respectively; the third switching element 6 and the fourth switching element 7 of switch 8V may be referred to as the third switching element 6V and the fourth switching element 7V, respectively; and the third switching element 6 and the fourth switching element 7 of switch 8W may be referred to as the third switching element 6W and the fourth switching element 7W, respectively.

[0024] Multiple switches 8 are controlled by the control device 50. In other words, the third switching element 6U, the fourth switching element 7U, the third switching element 6V, the fourth switching element 7V, the third switching element 6W, and the fourth switching element 7W are controlled by the control device 50.

[0025] The resonant inductor L1 has a third terminal and a fourth terminal. In the resonant inductor L1, the third terminal is connected to the common connection point 25. The fourth terminal of the resonant inductor L1 is connected to the sixth terminal 154 of the regenerative capacitor 15.

[0026] The regenerative capacitor 15 is connected between the fourth terminal of the resonant inductor L1 and the second DC terminal 32. The regenerative capacitor 15 is, for example, a film capacitor.

[0027] The protection circuit 17 includes a third diode 13 and a fourth diode 14. The third diode 13 is connected between the common connection point 25 and the first DC terminal 31. The anode of the third diode 13 is connected to the common connection point 25. Also, the cathode of the third diode 13 is connected to the first DC terminal 31. The fourth diode 14 is connected between the common connection point 25 and the second DC terminal 32. The anode of the fourth diode 14 is connected to the second DC terminal 32. Also, the cathode of the fourth diode 14 is connected to the common connection point 25. Therefore, the fourth diode 14 is connected in series with the third diode 13.

[0028] Capacitor C10 is connected between the first DC terminal 31 and the second DC terminal 32, and is connected in parallel to the power conversion circuit 11. Capacitor C10 is, for example, an electrolytic capacitor.

[0029] The control device 50 controls a plurality of first switching elements 1, a plurality of second switching elements 2, and a plurality of switches 8. The execution entity of the control device 50 includes a computer system. The computer system has one or more computers. The computer system mainly consists of a processor and memory as hardware. The function of the control device 50 as the execution entity in this disclosure is realized by the processor executing a program recorded in the memory of the computer system. The program may be pre-recorded in the memory of the computer system, or it may be provided via a telecommunications line, or it may be recorded and provided on a non-temporary recording medium such as a memory card, optical disk, or hard disk drive (magnetic disk) that can be read by the computer system. The processor of the computer system is composed of one or more electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). The plurality of electronic circuits may be aggregated on a single chip or distributed across multiple chips. The plurality of chips may be aggregated on a single device or distributed across multiple devices.

[0030] The control device 50 outputs first PWM signals SU1, SV1, and SW1 to control the on / off state of each of the multiple first switching elements 1U, 1V, and 1W. Each of the first PWM signals SU1, SV1, and SW1 is a PWM signal whose potential level changes between, for example, a first potential level (hereinafter also referred to as a low level) and a second potential level (hereinafter also referred to as a high level) that is higher than the first potential level. The first switching elements 1U, 1V, and 1W are turned on when the first PWM signals SU1, SV1, and SW1 are at a high level and turned off when they are at a low level, respectively. The control device 50 also outputs second PWM signals SU2, SV2, and SW2 to control the on / off state of each of the multiple second switching elements 2U, 2V, and 2W. Each of the second PWM signals SU2, SV2, and SW2 is a PWM signal whose potential level changes between, for example, a first potential level (hereinafter also called the low level) and a second potential level (hereinafter also called the high level) that is higher than the first potential level. The second switching elements 2U, 2V, and 2W are turned on when the second PWM signals SU2, SV2, and SW2 are at a high level and turned off when they are at a low level, respectively.

[0031] The control device 50 generates a plurality of first PWM signals SU1, SV1, SW1 and a plurality of second PWM signals SU2, SV2, SW2 based on the three-phase duty command values ​​du, dv, dw of the two-phase modulation scheme (see Figure 2). In this embodiment, the two-phase modulation scheme is an over-stick two-phase modulation scheme. The middle section of Figure 2 shows the waveforms (modulated waves) of the three-phase duty command values ​​du, dv, dw of the two-phase modulation scheme, and the lower section of Figure 2 shows a magnified view of a part of the modulated wave.

[0032] The control device 50 generates a plurality of first PWM signals SU1, SV1, SW1 and a plurality of second PWM signals SU2, SV2, SW2 using three-phase duty cycle command values ​​du, dv, dw (see Figure 2) and a triangular wave carrier signal CA1 (see Figure 2). More specifically, the control device 50 generates the first PWM signal SU1 and the second PWM signal SU2 to be supplied to the first switching element 1U and the second switching element 2U, respectively, based on the carrier signal CA1 and the duty cycle command value du. The control device 50 also generates the first PWM signal SV1 and the second PWM signal SV2 to be supplied to the first switching element 1V and the second switching element 2V, respectively, based on the carrier signal CA1 and the V-phase duty cycle command value dv. Furthermore, the control device 50 generates a first PWM signal SW1 and a second PWM signal SW2 to be supplied to the first switching element 1W and the second switching element 2W, respectively, based on the carrier signal CA1 and the W-phase duty command value dw. In this embodiment, the control device 50 sets the maximum value of the carrier signal CA1 to 0.5 and the minimum value to -0.5. The control device 50 also sets the maximum value of each of the three-phase duty command values ​​du, dv, and dw to 0.5 and the minimum value to -0.5. Alternatively, the control device 50 may set the maximum value of the carrier signal CA1 to 1 and the minimum value to 0, and the maximum value of each of the three-phase duty command values ​​du, dv, and dw to 1 and the minimum value to 0. Alternatively, the control device 50 may set the maximum and minimum values ​​of the carrier signal CA1 to values ​​other than 1 and 0, respectively, and the maximum and minimum values ​​of each of the three-phase duty command values ​​du, dv, and dw to values ​​other than 1 and 0, respectively. Furthermore, the waveform of the carrier signal CA1 is not limited to a triangular wave; for example, it may be a sawtooth wave.

[0033] The duty cycles of the first PWM signal SU1 and the second PWM signal SU2, generated by the control device 50, change based on the duty cycle command value du. The control device 50 generates the first PWM signal SU1 by comparing the duty cycle command value du with the carrier signal CA1. More specifically, the control device 50 compares the duty cycle command value du with the carrier signal CA1 and generates the first PWM signal SU1 which is high level when the duty cycle command value du is greater than the carrier signal CA1 and low level when the duty cycle command value du is less than or equal to the carrier signal CA1. The control device 50 also generates the second PWM signal SU2 by inverting the first PWM signal SU1. Furthermore, the control device 50 sets a dead time period Td (see Figures 3 and 8) between the high-level period of the first PWM signal SU1 and the high-level period of the second PWM signal SU2 so that the ON period of the first switching element 1U and the ON period of the second switching element 2U do not overlap.

[0034] The duty cycles of the first PWM signal SV1 and the second PWM signal SV2, both generated by the control device 50, change based on the duty cycle command value dv. The control device 50 generates the first PWM signal SV1 by comparing the duty cycle command value dv with the carrier signal CA1. More specifically, the control device 50 compares the duty cycle command value dv with the carrier signal CA1 and generates the first PWM signal SV1 which is high level during periods when the duty cycle command value dv is greater than the carrier signal CA1, and low level during periods when the duty cycle command value dv is less than or equal to the carrier signal CA1. The control device 50 also generates the second PWM signal SV2 by inverting the first PWM signal SV1. Furthermore, the control device 50 sets a dead time period Td (see Figures 4 and 10) between the high-level period of the first PWM signal SV1 and the high-level period of the second PWM signal SV2 so that the ON period of the first switching element 1V and the ON period of the second switching element 2V do not overlap.

[0035] The duty cycles of the first PWM signal SW1 and the second PWM signal SW2, both generated by the control device 50, change based on the duty cycle command value dw. The control device 50 generates the first PWM signal SW1 by comparing the duty cycle command value dw with the carrier signal CA1. More specifically, the control device 50 compares the duty cycle command value dw with the carrier signal CA1 and generates the first PWM signal SW1 which is high level when the duty cycle command value dw is greater than the carrier signal CA1 and low level when the duty cycle command value dw is less than or equal to the carrier signal CA1. The control device 50 also generates the second PWM signal SW2 by inverting the first PWM signal SW1. Furthermore, the control device 50 sets a dead time period Td (see Figures 5 and 10) between the high-level period of the first PWM signal SW1 and the high-level period of the second PWM signal SW2 so that the ON period of the first switching element 1W and the ON period of the second switching element 2W do not overlap.

[0036] The control device 50, for example, uses the three-phase duty cycle reference values ​​du0, dv0, and dw0 (see Figure 2) of the three-phase modulation method to determine the three-phase duty cycle command values ​​du, dv, and dw of the two-phase modulation method. The U-phase modulated wave with the duty cycle reference value du0 as the instantaneous value, the V-phase modulated wave with the duty cycle reference value dv0 as the instantaneous value, and the W-phase modulated wave with the duty cycle reference value dw0 as the instantaneous value change in a sinusoidal manner with a phase difference of 120° from each other. The control device 50 determines the three-phase duty cycle command values ​​du, dv, and dw at each time by adding dcom to the three-phase duty cycle reference values ​​du0, dv0, and dw0 at each time. In this embodiment, as described above, the maximum value of the three-phase duty command values ​​du, dv, and dw is set to 0.5 and the minimum value to -0.5, and dcom is -max{du0, dv0, dw0} + 0.5. In other words, the control device 50 calculates the duty command value du for the two-phase modulation scheme by calculating du = du0 - max{du0, dv0, dw0} + 0.5. The control device 50 also calculates the duty command value dv for the two-phase modulation scheme by calculating dv = dv0 - max{du0, dv0, dw0} + 0.5. The control device 50 also calculates the duty command value dw for the two-phase modulation scheme by calculating dw = dw0 - max{du0, dv0, dw0} + 0.5.

[0037] The length of one cycle of each of the above-mentioned U-phase modulation wave, V-phase modulation wave, and W-phase modulation wave is the same. Also, the length of one cycle of each of the U-phase modulation wave, V-phase modulation wave, and W-phase modulation wave is longer than the length of one cycle of the carrier signal CA1.

[0038] Note that the control device 50 generates duty reference values du0, dv0, and dw0 of the three-phase modulation method based on information regarding the state of the AC load RA1. When the AC load RA1 is a three-phase servo motor, the information regarding the state of the AC load RA1 includes, for example, detection values from a plurality of current sensors that detect output currents (hereinafter also referred to as load currents) iU, iV, and iW flowing through the U-phase terminal, V-phase terminal, and W-phase terminal of the AC load RA1, respectively.

[0039] The control device 50 sets a dead time period Td between the high-level period of the first PWM signal to the first switching element 1 and the high-level period of the second PWM signal to the second switching element 2 for each of the plurality of switching circuits 10, and sets the high-level period of the control signal to each of the plurality of switches 8 based on the dead time period Td for the corresponding switching circuit 10 among the plurality of switching circuits 10. [[ID=IO]]

[0040] The plurality of switches 8, the resonance inductor L1, the plurality of resonance capacitors 9, and the regeneration capacitor 15 are provided to perform zero-voltage soft switching of the plurality of first switching elements 1 and the plurality of second switching elements 2.

[0041] In the power conversion device 100, the control device 50 controls the plurality of switches 8 in addition to the plurality of first switching elements 1 and the second switching elements 2 of the power conversion circuit 11.

[0042] The control device 50 generates control signals SU6, SU7, SV6, SV7, SW6, and SW7 for controlling the on / off states of the third switching element 6U, the fourth switching element 7U, the third switching element 6V, the fourth switching element 7V, the third switching element 6W, and the fourth switching element 7W respectively, and outputs them to the gate terminals of the third switching element 6U, the fourth switching element 7U, the third switching element 6V, the fourth switching element 7V, the third switching element 6W, and the fourth switching element 7W respectively.

[0043] The switch 8U can allow the charging current flowing through the path of the regeneration capacitor 15 - resonant inductor L1 - switch 8U - resonant capacitor 9U to pass when the third switching element 6U is in the on state and the fourth switching element 7U is in the off state. The charging current is the current that charges the resonant capacitor 9U. The switch 8U can allow the discharge current flowing through the path of the resonant capacitor 9U - switch 8U - resonant inductor L1 - regeneration capacitor 15 to pass when the third switching element 6U is in the off state and the fourth switching element 7U is in the on state. The discharge current is the current that discharges the charge of the resonant capacitor 9U.

[0044] The switch 8V can allow the charging current flowing through the path of the regeneration capacitor 15 - resonant inductor L1 - switch 8V - resonant capacitor 9V to pass when the third switching element 6V is in the on state and the fourth switching element 7V is in the off state. The charging current is the current that charges the resonant capacitor 9V. The switch 8V can allow the discharge current flowing through the path of the resonant capacitor 9V - switch 8V - resonant inductor L1 - regeneration capacitor 15 to pass when the third switching element 6V is in the off state and the fourth switching element 7V is in the on state. The discharge current is the current that discharges the charge of the resonant capacitor 9V.

[0045] Switch 8W can pass the charging current flowing through the path of regenerative capacitor 15 - resonant inductor L1 - switch 8W - resonant capacitor 9W when the third switching element 6W is ON and the fourth switching element 7W is OFF. The charging current is the current that charges the resonant capacitor 9W. Switch 8W can pass the discharge current flowing through the path of resonant capacitor 9W - switch 8W - resonant inductor L1 - regenerative capacitor 15 when the third switching element 6W is OFF and the fourth switching element 7W is ON. The discharge current is the current that discharges the charge from the resonant capacitor 9W.

[0046] (3) Operation of the power converter In the following, the current iL1 flowing through the resonant inductor L1 will be described as positive when flowing in the direction of the arrow in Figure 1, and negative when flowing in the opposite direction to the arrow in Figure 1. Furthermore, the load currents iU, iV, and iW flowing through the U-phase, V-phase, and W-phase terminals of the AC load RA1 will be described as positive when flowing in the direction of the arrow in Figure 1, and negative when flowing in the opposite direction to the arrow in Figure 1. Furthermore, the currents i9U, i9V, and i9W flowing through the resonant capacitors 9U, 9V, and 9W will be described as positive when flowing in the direction of the arrow in Figure 1, and negative when flowing in the opposite direction to the arrow in Figure 1. Therefore, in the discharge operation where the resonant capacitors 9U, 9V, and 9W are discharged, the polarity of the currents i9U, i9V, and i9W is positive, and in the charging operation where the resonant capacitors 9U, 9V, and 9W are charged, the polarity of the currents i9U, i9V, and i9W is negative. Furthermore, in the following explanation, the voltage value of the DC power supply E1 will be described as Vd (see Figures 3 to 5 and Figure 7).

[0047] In the power converter 100, for example, the third switching element 6U of the switch 8U may change from a state where a current iL1 flows in the resonant inductor L1 with positive polarity when the switch 8U is ON to a state where the third switching element 6U of the switch 8U is OFF. In this case, the current iL1 flowing through the resonant inductor L1 is regenerated to the power converter circuit 11 via the third diode 13 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero. Also, in the power converter 100, for example, the fourth switching element 7U of the switch 8U may change from a state where a current iL1 flows in the resonant inductor L1 with negative polarity when the switch 8U is ON to a state where the fourth switching element 7U is OFF. In this case, the current iL1 flowing through the resonant inductor L1 flows through the path of the fourth diode 14 - resonant inductor L1 - regenerative capacitor 15 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero.

[0048] Furthermore, in the power converter 100, for example, there are cases where the third switching element 6V of switch 8V is ON and a current iL1 flows through the resonant inductor L1 with positive polarity, and then the third switching element 6V of switch 8V changes to the OFF state. In this case, the current iL1 flowing through the resonant inductor L1 is regenerated to the power converter circuit 11 via the third diode 13 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero. Also, in the power converter 100, for example, there are cases where the fourth switching element 7V of switch 8V is ON and a current iL1 flows through the resonant inductor L1 with negative polarity, and then the fourth switching element 7V changes to the OFF state. In this case, the current iL1 flowing through the resonant inductor L1 flows through the path of the fourth diode 14 - resonant inductor L1 - regenerative capacitor 15 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero.

[0049] Furthermore, in the power converter 100, for example, there are cases where the third switching element 6W of switch 8W is turned ON and a current iL1 flows through the resonant inductor L1 in the positive polarity, and then the third switching element 6W of switch 8W is turned OFF. In this case, the current iL1 flowing through the resonant inductor L1 is regenerated to the power converter circuit 11 via the third diode 13 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero. Also, in the power converter 100, for example, there are cases where the fourth switching element 7W of switch 8W is turned ON and a current iL1 flows through the resonant inductor L1 in the negative polarity, and then the fourth switching element 7W is turned OFF. In this case, the current iL1 flowing through the resonant inductor L1 flows through the path of the fourth diode 14 - resonant inductor L1 - regenerative capacitor 15 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero.

[0050] The control device 50 sets a dead time period Td between the high-level period of the first PWM signals SU1, SV1, SW1 to the first switching elements 1U, 1V, 1W and the high-level period of the second PWM signals SU2, SV2, SW2 to the second switching elements 2U, 2V, 2W for each of the multiple switching circuits 10. The control device 50 also sets the high-level period of the control signal to each of the multiple switches 8 based on the dead time period Td for the corresponding switching circuit 10 among the multiple switching circuits 10. Here, the control device 50 sets the length of the high-level period of the control signal to each of the multiple switches 8 as, for example, the sum of the length of the first period and the length of the second period. The length of the first period is an integer (N) multiple of the resonant half-period determined by the capacitance of the resonant capacitor 9 corresponding to the switch 8 and the inductance of the resonant inductor L1. If the resonant period is Tres, the length of the first period is N × (Tres / 2). The end of the first period, that is, the end of an integer multiple of the resonant half-period, should preferably coincide with the end of the dead time period Td for the switching circuit 10 corresponding to the switch 8. For example, in the example in Figure 3, N=1, the length of the first period is the length between time t2 and time t3 of the high-level period of the control signal SU6. More specifically, the length of the first period is designed so that Tres / 2 = the length of the dead time period Td, with N=1. In other words, Figure 3 is an example in which the capacitance of the resonant capacitor 9 and the inductance of the resonant inductor L1 are selected so that Tres / 2 matches the length of the dead time period Td. The length of the second period is, as an example, an additional time Tau determined by the voltage of the regenerative capacitor 15, the inductance of the resonant inductor L1, and the load current value. The length of the first period described above is an ideal design example, and may be 90% to 110% of the length of N × (Tres / 2). Furthermore, the length of the second period described above is an ideal design example, and may be 90% to 110% of the additional time (additional time Tau in the example of Figure 3) determined by the voltage of the regenerative capacitor 15, the inductance of the resonant inductor L1, and the load current value.

[0051] The following describes the basic operation of zero-voltage soft switching for each of the multiple first switching elements 1 and the multiple second switching elements 2, with reference to Figures 3 to 9. The basic operation is the operation when resonant current does not flow simultaneously through two or more of the multiple switches 8 in the resonant inductor L1. After describing the basic operation, the operation when the control device 50 determines that resonant current flows simultaneously through two or more of the multiple switches 8 will be described.

[0052] (3.1) Basic Operation In zero-voltage soft switching of the first switching element 1, it is necessary to set the voltage across the first switching element 1 to zero immediately before the first switching element 1 that is the target of zero-voltage soft switching is turned on. Similarly, in zero-voltage soft switching of the second switching element 2, it is necessary to set the voltage across the second switching element 2 to zero immediately before the second switching element 2 that is the target of zero-voltage soft switching is turned on. Hereafter, the switching element that is the target of zero-voltage soft switching (first switching element 1 or second switching element 2) will also be referred to as the target switching element.

[0053] The basic operation of the control device 50 differs depending on the polarity (positive / negative) of the load current flowing through the AC terminal 41 connected to the target switching element and the operation (charging / discharging) of the resonant capacitor 9 connected in series or parallel to the target switching element. The load current is positive when it flows from the AC terminal 41 toward the AC load RA1, and negative when it flows from the AC load RA1 toward the AC terminal 41. During the charging operation of the resonant capacitor 9, the voltage across the resonant capacitor 9 increases. Conversely, during the discharging operation of the resonant capacitor 9, the voltage across the resonant capacitor 9 decreases. The voltage across each of the multiple second switching elements 2 is the same as the voltage across the resonant capacitor 9 connected in parallel to the second switching elements 2.

[0054] (3.1.1) When the load current > 0, the operation control device 50 for soft-switching the first switching element turns on the third switching element 6 corresponding to the first switching element 1 if the target of soft-switching is the first switching element 1 (hereinafter also referred to as the target first switching element 1) and the polarity of the load current flowing through the AC terminal 41 connected to the target first switching element 1 is positive. As a result, the control device 50 causes the resonant inductor L1 and the resonant capacitor 9 connected to the target first switching element 1 to resonate, charging the resonant capacitor 9 from the regenerative capacitor 15 and making the voltage across the target first switching element 1 zero. As a result, the power converter 100 can achieve zero-voltage soft-switching of the target first switching element 1.

[0055] Figure 3 shows the first PWM signal SU1, the second PWM signal SU2, the control signal SU6, the load current iU, the current iL1, the voltage V1u across the first switching element 1U, and the voltage V2u across the second switching element 2U, in the case where the target first switching element is the first switching element 1U of the switching circuit 10U. Figure 3 also shows the additional time Tau set for the control signal SU6 in the control device 50. The additional time Tau will be described later.

[0056] Figure 4 shows the first PWM signal SV1, the second PWM signal SV2, the control signal SV6, the load current iV, the current iL1, the voltage V1v across the first switching element 1V, and the voltage V2v across the second switching element 2V, in the case where the target first switching element is the first switching element 1V of the switching circuit 10V. Figure 4 also shows the additional time Tav set for the control signal SV6 in the control device 50. The additional time Tav will be described later.

[0057] Figure 5 shows the first PWM signal SW1, the second PWM signal SW2, the control signal SW6, the load current iW, the current iL1, the voltage V1w across the first switching element 1W, and the voltage V2w across the second switching element 2W, in the case where the target first switching element is the first switching element 1W of the switching circuit 10W. Figure 5 also shows the additional time Taw set for the control signal SW6 in the control device 50. The additional time Taw will be described later.

[0058] The above-mentioned additional time Tau is set to achieve soft switching of the target switching element (first switching element 1U) regardless of the value of the load current iU, by making the start time t1 of the high-level period of the control signal SU6 earlier than the start time t2 of the dead time period Td, as shown in Figure 3, and making the high-level period of the control signal SU6 longer than the half-period of resonance (dead time period Td in this embodiment). The length of the additional time Tau is set based on the value of the load current iU. In order to start LC resonance from the start time t2 of the dead time period Td, it is desirable that the value of the current iL1 matches the value of the load current iU at the start time t2 of the dead time period Td. This is because, as long as iL1 < iU, the entire current iL1 flows to the AC load RA1, and therefore the resonant capacitor 9U cannot be charged. The end time of the high-level period of the control signal SU6 can be the same as or later than the end time t3 of the dead time period Td. Figure 3 shows an example where the end time of the high-level period of the control signal SU6 is set to be the same as the end time t3 of the dead time period Td. The control device 50 sets the high-level period of the control signal SU6 to Tau + Td, for example. That is, the control device 50 sets N = 1 and Tres / 2 = length of the dead time period Td, so that the length of the first period is N × Tres / 2 = Td. In the switching circuit 10U, the voltage V2u across the second switching element 2U becomes Vd at the end time t3 of the dead time period Td, and the voltage V1u across the first switching element 1U becomes zero at the end time t3 of the dead time period Td. In the example in Figure 3, the current iL1 flowing through the resonant inductor L1 starts flowing from the start time t1 of the high-level period of the control signal SU6 and becomes zero at time t4, after an additional time Tau has elapsed from the end time t3 of the dead time period Td. Regarding the current iL1, from the time t2 when the dead time period Td begins, iL1 ≥ iU, and the current iL1 in the shaded region of the fourth current waveform from the top in Figure 3 flows into the resonant capacitor 9U, causing LC resonance to occur.The current iL1 is regenerated to the power conversion circuit 11 via the third diode 13, which is directly connected to the resonant inductor L1, after the end of the dead time period Td at time t3.

[0059] As described above, the control device 50 determines the additional time Tau based on the load current iU so that iL1 = iU at time t2 when the dead time period Td begins, in order to start LC resonance at time t2 when the dead time period Td begins and end the half-cycle of resonance at time t3 when the dead time period Td ends. More specifically, the control device 50 determines the additional time Tau by calculating Tau = iU × (L / V15) using, for example, the detection result of the load current iU by a current sensor or its signal processing value, or an estimated value of the load current iU, the inductance L of the resonant inductor L1 which is stored in advance, and the detection result of the voltage V15 of the regenerative capacitor 15 (potential V15 at the sixth terminal 154 of the regenerative capacitor 15). The detection result of the load current iU or its signal processing value at this time is the detection value at the carrier cycle in which the additional time Tau is added, or at the timing closest to that carrier cycle. Furthermore, the estimated value of the load current iU at this time is the estimated value of the load current iU at the carrier period in which the additional time Tau is added. In the case of basic operation, the resonant half-period is half of the resonant period, which is the reciprocal of the resonant frequency of the resonant circuit including the resonant inductor L1 and one resonant capacitor 9. Therefore, if the inductance of the resonant inductor L1 is L and the capacitance of the resonant capacitor 9 is C, then the resonant half-period is π × (L・C) １／２ In the control device 50, the resonant half-period during basic operation is set to be the same as, for example, the length of the dead time period Td.

[0060] The above-mentioned additional time Tav is set to achieve soft switching of the target switching element (first switching element 1V) regardless of the value of the load current iV, by making the start time t5 of the high-level period of the control signal SV6 earlier than the start time t6 of the dead time period Td, as shown in Figure 4, and making the high-level period of the control signal SV6 longer than the half-period of resonance (dead time period Td in this embodiment). The length of the additional time Tav is set based on the value of the load current iV. In order to start LC resonance from the start time t6 of the dead time period Td, it is desirable that the value of the current iL1 at the start time t6 of the dead time period Td matches the value of the load current iV. This is because, as long as iL1 < iV, the entire current iL1 flows to the AC load RA1, and therefore the resonant capacitor 9V cannot be charged. The end time of the high-level period of the control signal SV6 can be the same as or later than the end time t7 of the dead time period Td. Figure 4 shows an example where the end of the high-level period of the control signal SV6 is set to the same time as the end of the dead time period Td, t7. The control device 50 sets the high-level period of the control signal SV6 to Tab + Td. That is, the control device 50 sets N = 1 and Tres / 2 = length of the dead time period Td, so the length of the first period is N × Tres / 2 = Td. In the switching circuit 10V, the voltage V2v across the second switching element 2V becomes Vd at the end of the dead time period Td, t7, and the voltage V1v across the first switching element 1V becomes zero at the end of the dead time period Td, t7. In the example in Figure 4, the current iL1 flowing through the resonant inductor L1 starts flowing from the start of the high-level period of the control signal SV6, t5, and becomes zero at t8, after the additional time Tab has elapsed from the end of the dead time period Td, t7. Regarding the current iL1, from time t6 when the dead time period Td begins, iL1 ≥ iV, and the current iL1 in the shaded region of the fourth current waveform from the top in Figure 4 flows into the resonant capacitor 9V, causing LC resonance to occur.The current iL1 is regenerated to the power conversion circuit 11 via the third diode 13, which is directly connected to the resonant inductor L1, after the end of the dead time period Td at time t7.

[0061] As described above, the control device 50 determines the additional time Tav based on the load current iv such that iL1 = iv at time t6 when the dead time period Td begins, in order to start LC resonance at time t6 when the dead time period Td begins and end the half-cycle of resonance at time t7 when the dead time period Td ends. More specifically, the control device 50 determines the additional time Tav by calculating Tav = iv × (L / V15) using, for example, the detection result of the load current iv by the current sensor or its signal processing value, or an estimated value of the load current iv, the inductance L of the resonant inductor L1 which is stored in advance, and the detection result of the voltage V15 of the regenerative capacitor 15. The detection result of the load current iv or its signal processing value at this time is the detection value at the carrier period in which the additional time Tav is added, or the timing closest to that carrier period. The estimated value of the load current iv at this time is the value estimated from the load current iv at the carrier period in which the additional time Tav is added.

[0062] The above-mentioned additional time Taw is set to achieve soft switching of the target switching element (first switching element 1W) regardless of the value of the load current iW, by making the start time t9 of the high-level period of the control signal SW6 earlier than the start time t10 of the dead time period Td, as shown in Figure 5, and making the high-level period of the control signal SW6 longer than the half-cycle of resonance (dead time period Td in this embodiment). The length of the additional time Taw is set based on the value of the load current iW. In order to start LC resonance from the start time t10 of the dead time period Td, it is desirable that the value of the current iL1 matches the value of the load current iW at the start time t10 of the dead time period Td. This is because, as long as iL1 < iW, the entire current iL1 flows to the AC load RA1, and therefore the resonant capacitor 9W cannot be charged. The end time of the high-level period of the control signal SW6 can be the same as or later than the end time t11 of the dead time period Td. Figure 5 shows an example where the end of the high-level period of the control signal SW6 is set to be the same as the end of the dead time period Td, which is t11. The control device 50 sets the high-level period of the control signal SW6 to Taw + Td. That is, the control device 50 sets N = 1 and Tres / 2 = length of the dead time period Td, so the length of the first period is N × Tres / 2 = Td. In the switching circuit 10W, the voltage V2w across the second switching element 2W becomes Vd at the end of the dead time period Td, t11, and the voltage V1w across the first switching element 1W becomes zero at the end of the dead time period Td, t11. In the example in Figure 5, the current iL1 flowing through the resonant inductor L1 starts flowing from the start of the high-level period of the control signal SW6, t9, and becomes zero at t12, after the additional time Taw has elapsed from the end of the dead time period Td, t11. Regarding the current iL1, from the time t10 when the dead time period Td begins, iL1 ≥ iW, and the current iL1 in the shaded region of the fourth current waveform from the top in Figure 5 flows into the resonant capacitor 9W, causing LC resonance to occur.The current iL1 is regenerated to the power conversion circuit 11 via the third diode 13, which is directly connected to the resonant inductor L1, after the end of the dead time period Td at time t11.

[0063] As described above, the control device 50 determines the additional time Taw based on the load current iW such that iL1 = iW at the time t10 when the dead time period Td begins, in order to start LC resonance at the time t10 when the dead time period Td ends and to end the half-cycle of resonance at the time t11 when the dead time period Td ends. More specifically, the control device 50 determines the additional time Taw by calculating Taw = iW × (L / V15) using, for example, the detection result of the load current iW by a current sensor or its signal processing value, or an estimated value of the load current iW, the inductance L of the resonant inductor L1 which is stored in advance, and the detection result of the voltage V15 of the regenerative capacitor 15. The detection result of the load current iW at this time or its signal processing value is the detection value at the carrier cycle in which the additional time Taw is added, or the timing closest to that carrier cycle. The estimated value of the load current iW at this time is the value estimated from the load current iW at the carrier cycle in which the additional time Taw is added.

[0064] (3.1.2) The control device 50 for soft-switching the second switching element when the load current > 0 compares the current value of the load current with the first current threshold I1 (= Ith, see Figure 6) when the target of soft-switching is the second switching element 2 (hereinafter also referred to as the target second switching element 2) and the polarity of the load current (load current iU, load current iV, or load current iW) flowing through the AC terminal 41 connected to the target second switching element 2 is positive. As an example of the design of the operation of the control device 50, the control device 50 does not turn on the switch 8 when the current value of the load current is greater than the first current threshold I1, and turns on the switch 8 during the dead time period Td when the current value of the load current is less than the first current threshold I1. Here, as in section (3.1.1), it is assumed that the resonant half-period is set to be the same as the length of the dead time period Td, for example. In the power converter 100, when the load current value is greater than the first current threshold I1, the control device 50 can discharge the resonant capacitor 9U connected in parallel to the target second switching element 2 using the load current iU without turning on the switch 8 corresponding to the target second switching element 2. As a result, the power converter 100 can achieve zero-voltage soft switching of the target second switching element 2.

[0065] Figure 7 shows the first PWM signal SU1, the second PWM signal SU2, the control signal SU7, the load current iU, the current i9U, and the voltage V2u across the second switching element 2U when the target second switching element 2 is the second switching element 2U of the switching circuit 10U and the load current value is greater than the first current threshold I1. Also in Figure 7, the additional time Tau set in the control device 50 for the control signal SU7 of the fourth switching element 7U of the switch 8U.

[0066] The control device 50 does not provide a high-level period for the control signal SU7 when the load current iU is greater than the first current threshold I1. In this case, in the power converter 100, current i9U starts flowing from the resonant capacitor 9U at time t22 when the dead time period Td begins, and the current i9U drops to zero before time t23 when the dead time period Td ends, so that the voltage V2u across the second switching element 2U becomes zero before time t23 when the dead time period Td ends. As a result, in the power converter 100, when the second PWM signal SU2 changes from a low level to a high level at time t23 when the dead time period Td ends, the second switching element 2U is soft-switched to zero voltage.

[0067] When the load current iU is less than the first current threshold I1, the control device 50 provides a high-level period for the control signal SU7, for example, as shown by the dashed line in Figure 7. The start time of the high-level period for the control signal SU7 is, for example, the same as the start time t22 of the dead time period Td. The end time of the high-level period for the control signal SU7 is the same as the end time t23 of the dead time period Td. As a result, in the power converter 100, the voltage V2u across the second switching element 2U becomes zero before the end time t23 of the dead time period Td. Therefore, in the power converter 100, when the second PWM signal SU2 changes from low level to high level at the end time t23 of the dead time period Td, the second switching element 2U is zero-voltage soft-switched. The start time of the high-level period for the control signal SU7 may be a time t21 that is earlier by an additional time Tau than the start time of the dead time period Td. The end of the high-level period of the control signal SU7 may be a time t24 that is later than the end of the dead time period Td (t23) by an additional time Tau. The time before and after the period overlapping with the dead time period Td in the high-level period is not limited to the additional time Tau, but may be any other set time. Furthermore, the relationship between the first current threshold I1 of the load current and the method for determining the high-level period of the control signal to switch 8, as described above, is an ideal design example and is not limited to this example. For example, the control device 50 may set the high-level period of the control signal for switch 8 so that switch 8 turns on during the dead time period Td, even if the load current value is greater than the first current threshold I1. Also, the control device 50 does not need to turn on switch 8 during the dead time period Td, even if the load current value is less than the first current threshold I1. Furthermore, the control device 50 may set the high-level period of the control signal for switch 8 so that switch 8 is always turned on during the dead time period Td, regardless of the first current threshold I1. Furthermore, the control device 50 may keep the switch 8 always in the off state regardless of the first current threshold I1. Also, the control device 50 may combine the operations described in (3.1.2) as appropriate.Furthermore, the control device 50 does not need to match the high-level period of the control signal to the switch 8 with the dead time period Td. In one design example, for example, the high-level period of the control signal to the switch 8 may be designed to be different from the length of the dead time period Td, depending on the design time of the resonant half-period.

[0068] (3.1.3) When the load current is less than 0, the control device 50 for soft-switching the second switching element turns on the fourth switching element 7 corresponding to the second switching element 2 if the polarity of the load current (load current iU, load current iV, or load current iW) flowing through the AC terminal 41 connected to the target second switching element 2 is negative. As a result, the control device 50 causes the resonant capacitor 9 and the resonant inductor L1 connected to the target second switching element 2 to resonate, causing the resonant capacitor 9 to discharge and the voltage across the target second switching element 2 to become zero. As a result, the power converter 100 can achieve zero-voltage soft switching of the target second switching element 2.

[0069] Figure 8 shows the first PWM signal SU1, the second PWM signal SU2, the control signal SU7, the load current iU, the current iL1, and the voltage V2u across the second switching element 2U, in the case where the target second switching element 2 is the second switching element 2U of the switching circuit 10U. Figure 8 also shows the additional time Tau that the control device 50 sets for the control signal SU7 of the fourth switching element 7U of the switch 8U. The end time of the high-level period of the control signal SU7 can be the same as or after the end time t33 of the dead time period Td. In Figure 8, an example is shown where the end time of the high-level period of the control signal SU7 is set to be the same as the end time t33 of the dead time period Td. The control device 50 sets the high-level period of the control signal SU7 to Tau + Td, for example. In the switching circuit 10U, the voltage V2u across the second switching element 2U becomes zero at time t33, when the dead time period Td ends. In the example in Figure 8, the current iL1 flowing through the resonant inductor L1 begins to flow from time t31, when the high-level period of the control signal SU7 begins, and becomes zero at time t34, when an additional time Tau has elapsed from time t33, when the dead time period Td ends. With respect to the current iL1, iL1 ≤ iU occurs from time t32, when the dead time period Td begins, causing LC resonance to occur and a resonant current (discharge current of the resonant capacitor 9U) to flow from the resonant capacitor 9U towards the resonant inductor L1. After time t33, when the dead time period Td ends, the current iL1 is regenerated to the power conversion circuit 11 via the fourth diode 14, which is directly connected to the resonant inductor L1.

[0070] The control device 50 determines the additional time Tau based on the load current iU so that iL1 = iU at the start of the dead time period Td (t32), in order to start LC resonance at the start of the dead time period Td (t32) and end the half-cycle of resonance at the end of the dead time period Td (t33). More specifically, the control device 50 determines the additional time Tau by calculating Tau = |iU| × (L / V15), using, for example, the detection result of the output current iU by a current sensor or its signal processing value, or an estimated value of the load current iU, the inductance L of the resonant inductor L1 which is stored in advance, and the detection result of the voltage V15 of the regenerative capacitor 15. The load current value at this time (the detection result of the load current iU or its signal processing value) is the detection value at the carrier cycle in which the additional time Tau is added, or at the timing closest to that carrier cycle. Furthermore, the estimated value of the load current iU at this time is the estimated value of the load current iU at the carrier period in which the additional time Tau is added. In the case of basic operation, the resonant half-period is half of the resonant period, which is the reciprocal of the resonant frequency of the resonant circuit including the resonant inductor L1 and one resonant capacitor 9. Therefore, if the inductance of the resonant inductor L1 is L and the capacitance of the resonant capacitor 9 is C, then the resonant half-period is π × (L・C) １／２ In the control device 50, the resonant half-period during basic operation is set to be the same as, for example, the length of the dead time period Td.

[0071] (3.1.4) The operation control device 50 for soft-switching the first switching element when the load current < 0 compares the current value of the load current (load current iU, load current iV, or load current iW) flowing through the AC terminal 41 connected to the target first switching element 1 with the second current threshold I2 (= -Ith, see Figure 6) if the polarity of the load current is negative. As an example of the operation design of the control device 50, the control device 50 does not turn on the switch 8 if the current value of the load current is less than the second current threshold I2, and turns on the switch 8 during the dead time period Td if the current value of the load current is greater than the second current threshold I2. Here, as in section (3.1.1), it is assumed that the resonant half-period is set to be the same as the length of the dead time period Td, for example. When the load current value is smaller than the second current threshold I2, the power converter 100 can charge the resonant capacitor 9U connected in series with the target first switching element 1 using the load current without the control device 50 turning on the switch 8 corresponding to the target first switching element 1. As a result, the power converter 100 can achieve zero-voltage soft switching of the target first switching element 1.

[0072] Figure 9 shows the first PWM signal SU1, the second PWM signal SU2, the control signal SU6, the load current iU, the current i9U, the voltage V1u across the first switching element 1U, and the voltage V2u across the second switching element 2U when the target first switching element 1 is the first switching element 1U of the switching circuit 10U, and the current value of the load current is greater than the second current threshold I2 (in other words, when the absolute value of the load current is less than the absolute value of the second current threshold I2).

[0073] The control device 50 does not provide a high-level period for the control signal SU6 when the load current value is smaller than the second current threshold (in other words, when the absolute value of the load current is larger than the absolute value of the second current threshold). In this case, in the power converter 100, current i9U starts flowing through the resonant capacitor 9U at time t41 when the dead time period Td begins. As a result, in the power converter 100, the resonant capacitor 9U is charged and the voltage V2u across the second switching element 2U increases, the current i9U becomes zero before time t42 when the dead time period Td ends, and the voltage V1u across the first switching element 1U becomes zero before time t42 when the dead time period Td ends. As a result, in the power converter 100, when the first PWM signal SU1 changes from a low level to a high level at time t42 when the dead time period Td ends, the first switching element 1U is zero-voltage soft-switched.

[0074] The control device 50, when the load current value is greater than the second current threshold I2 (in other words, when the absolute value of the load current is less than the absolute value of the second current threshold), sets a high-level period for the control signal SU6, as shown by the dashed line in Figure 9. The start time of the high-level period for the control signal SU6 is the same as the start time t41 of the dead time period Td. The end time of the high-level period for the control signal SU6 is the same as the end time t42 of the dead time period Td. As a result, in the power converter 100, the voltage V1u across the first switching element 1U becomes zero before the end time t42 of the dead time period Td. Therefore, in the power converter 100, when the first PWM signal SU1 changes from a low level to a high level at the end time t42 of the dead time period Td, the first switching element 1U is soft-switched to zero voltage. Furthermore, the relationship between the second current threshold I2 of the load current and the method for determining the high-level period of the control signal to switch 8, as described above, is an ideal design example and is not limited to the above design example. For example, the control device 50 may set the high-level period of the control signal to switch 8 so that switch 8 is turned on, for example, during the dead time period, even when the current value of the load current is smaller than the second current threshold I2. Also, the control device 50 does not have to turn on switch 8 during the dead time period Td even when the current value of the load current is larger than the second current threshold I2. Also, the control device 50 may set the high-level period of the control signal to switch 8 so that switch 8 is always turned on, for example, during the dead time period Td, regardless of the second current threshold I2. Also, the control device 50 may keep switch 8 always in the off state, regardless of the second current threshold I2. Also, the control device 50 may combine the operations described in (3.1.3) as appropriate. Also, the control device 50 does not have to make the high-level period of the control signal to switch 8 coincide with the dead time period Td as described above. For example, depending on the design time of the resonant half-period, the high-level period of the control signal to switch 8 may be designed to be other than the length of the dead time period Td.

[0075] (3.2) When the first and second operation control device 50 determines that a resonant current flows simultaneously through two of the multiple switches 8 to the resonant inductor L1 when the duty cycle command value of one of the three phase duty cycle command values ​​du, dv, dw (see Figure 2) of the two-phase modulation method is fixed to a constant value, the device performs the first operation and the second operation when it determines that one of the two switches 8 corresponds one-to-one to two AC terminals 41 where the polarity of the load current is the same (in this embodiment, the polarity is negative) at the multiple AC terminals 41, and the other switch 8 is designated as the first switch and the remaining switch as the second switch. "When the duty cycle command value of one of the three phases of duty cycle command values ​​du, dv, and dw in the two-phase modulation scheme is fixed to a constant value" means, in this embodiment, when the duty cycle command value of one of the three phases of duty cycle command values ​​du, dv, and dw in the top-stick two-phase modulation scheme is fixed to a constant value (maximum value), and in the example of Figure 2, it means when the duty cycle command value of one phase is fixed to 0.5. "When it is determined that resonant current flows simultaneously through two of the multiple switches 8" means when it is estimated in advance that resonant current flows simultaneously through the two switches 8 in the resonant inductor L1.

[0076] In the first operation, the high-level period of the control signal to the first switch is shortened by a shortening period Tred (see Figure 12) from the period which includes the resonant half-period determined by the capacitance C of the resonant capacitor 9 corresponding to the first switch and the inductance L of the resonant inductor L1, and the additional time determined by the voltage V15 of the regenerative capacitor 15, the inductance L of the resonant inductor L1, and the load current value. If Tres is the resonant period of the resonant circuit between the inductance L of the resonant inductor L1 and the capacitance C of the resonant capacitor 9 corresponding to the first switch, then Tres = 1 / {2π(L・C)} １／２The resonant half-period is Tres / 2. If the additional time is Tad and the load current flowing through the AC terminal 41 corresponding to the first switch is i, then Tad is expressed as Tad = L × i / V15. Regarding the load current i, when the first switch is switch 8U, it is the load current iU; when the first switch is switch 8V, it is the load current iv; and when the first switch is switch 8W, it is the load current iW. Regarding the additional time Tad, when the first switch is switch 8U, it is the additional time Tau as described above; when the first switch is switch 8V, it is the additional time Tav as described above; and when the first switch is switch 8W, it is the additional time Taw as described above.

[0077] In the second operation, the high-level period of the control signal to one of the first or second switches is shifted so that the high-level period of the control signal to the first switch begins a delay of Tdef (see Figure 12) from the point in time when the current value of the resonant current passing through the second switch reaches its extreme value and then matches the current value of the load current flowing through the AC terminal 41 corresponding to the second switch among the two AC terminals 41.

[0078] (3.2.1) Determination of whether two-phase resonant currents flow simultaneously The power converter 100 generates three first PWM signals SU1, SV1, SW1 and three second PWM signals SU2, SV2, SW2 based on the control device 50's three-phase duty command values ​​du, dv, dw (see Figures 2 and 11) of the top-stick two-phase modulation method. As a result, the two-phase duty command values ​​approach each other at electrical angles of 60° (see regions A11, A12, and A13 in Figure 11), and the duty cycles of the two-phase control signals become the same or close to each other. In region A11 of Figure 11, the duty command values ​​dv and dw are each -0.25 or close to -0.25. In region A12 of Figure 11, the duty command values ​​du and dw are each -0.25 or close to -0.25. In region A13 of Figure 11, the duty cycle command values ​​du and dv are both -0.25 or close to -0.25. The polarity of the resonant current is the same as the polarity of the current iL1, and in each of regions A11, A12, and A13, the polarity of the resonant current is negative. For example, in region A11, during one period of the carrier signal CA1, the time difference between the start of the high-level period of the control signal SW7 applied to the fourth switching element 7W at t51 (see Figure 10) and the start of the high-level period of the control signal SV7 applied to the fourth switching element 7V at t61 (see Figure 10) becomes shorter, and the W-phase resonant current and the V-phase resonant current may flow simultaneously through the resonant inductor L1. Similarly, in region A12, the U-phase resonant current and the W-phase resonant current may flow simultaneously through the resonant inductor L1. Similarly, in region A13, the resonant current of the U-phase and the resonant current of the V-phase may flow simultaneously through the resonant inductor L1.

[0079] If we assume that the capacitance of each of the multiple resonant capacitors 9U, 9V, and 9W is C, then if the W-phase current and the V-phase current flow simultaneously through the resonant inductor L1, the equivalent circuit will have a capacitor with a combined capacitance of resonant capacitor 9W and resonant capacitor 9V (= 2 × C) connected in series with the resonant inductor L1. Therefore, in the power converter 100, if two-phase current flows simultaneously through the resonant inductor L1, the resonant frequency of the resonant circuit including the resonant inductor L1 will change compared to the case where one-phase current flows through the resonant inductor L1, and there is a possibility that zero-voltage soft switching will not be achieved.

[0080] Figure 10 shows an example of boundary conditions for the cases where the resonant currents of the W phase and the V phase do not overlap (do not flow simultaneously) and overlap (flow simultaneously). These boundary conditions will be explained with reference to Figure 10.

[0081] In the power converter 100, if the time difference ΔTvw is Tres / 2 or greater, the resonant current of the U phase and the resonant current of the V phase do not overlap, and if the time difference ΔTvw is less than Tres / 2, the resonant current of the W phase and the resonant current of the V phase overlap. The time difference ΔTvw is the time difference between the start of the high-level period of the second PWM signal SW2 at time t53 and the start of the high-level period of the second PWM signal SV2 at time t63.

[0082] The control device 50 sets a threshold value for the time difference ΔTvw to Tres / 2 (in this embodiment, the dead time period Td = Tres / 2). The control device 50 estimates (determines) that the W-phase resonant current and the V-phase resonant current flow simultaneously in the resonant inductor L1 if the time difference ΔTvw is less than Tres / 2. The above threshold setting is just an example, and it may be set to a different value. For example, considering errors in the value of Tres / 2, the threshold may be set to a value even larger than Tres / 2. The threshold may also be set to Tav + Taw + Td. Furthermore, the method for calculating the time difference ΔTvw used to determine whether the two-phase resonant currents flow simultaneously is not limited to the above example, and other calculation methods are acceptable as long as they can calculate a time difference equivalent to the time difference ΔTvw. For example, the time difference ΔTvw used to determine whether or not two-phase resonant currents flow simultaneously may be the time difference between the end of the high-level period of the first PWM signal SW1 and the end of the high-level period of the first PWM signal SV1.

[0083] In the power converter 100, if the time difference ΔTuw is Tres / 2 or greater, the resonant current of the U phase and the resonant current of the W phase do not overlap in the resonant inductor L1, and if the time difference ΔTuw is less than Tres / 2, the resonant current of the U phase and the resonant current of the W phase overlap. The time difference ΔTuw is the time difference between the start of the high-level period of the second PWM signal SU2 and the start of the high-level period of the second PWM signal SW2.

[0084] The control device 50 has a threshold value set to Tres / 2 for the time difference ΔTuw. The time difference ΔTuw is the time difference between the start of the high-level period of the second PWM signal SW2 at time t53 and the start of the high-level period of the second PWM signal SU2 at time t33 (see Figure 8). The control device 50 estimates (determines) that the resonant current of the U phase and the resonant current of the W phase flow simultaneously in the resonant inductor L1 if the time difference ΔTuw is less than Tres / 2. The above threshold setting is just an example, and it may be set to a different value. For example, considering errors in the value of Tres / 2, the threshold may be set to a value even larger than Tres / 2. Also, the threshold may be set to Tau + Taw + Td. Furthermore, the method for calculating the time difference ΔTuw used to determine whether the two-phase resonant currents flow simultaneously is not limited to the above example, and other calculation methods are acceptable as long as they can calculate a time difference equivalent to the time difference ΔTuw. For example, the time difference ΔTuw used to determine whether or not two-phase resonant currents flow simultaneously may be the time difference between the end of the high-level period of the first PWM signal SU1 at time t32 (see Figure 8) and the end of the high-level period of the first PWM signal SW1 at time t52 (see Figure 10).

[0085] In the power converter 100, if the time difference ΔTuv is Tres / 2 or greater, the resonant current of the U phase and the resonant current of the V phase do not overlap in the resonant inductor L1, and if the time difference ΔTuv is less than Tres / 2, the resonant current of the U phase and the resonant current of the V phase overlap. The time difference ΔTuv is the time difference between the start of the high-level period of the second PWM signal SU2 at time t33 (see Figure 8) and the start of the high-level period of the second PWM signal SV2 at time t63 (see Figure 10).

[0086] The control device 50 has a threshold value set to Tres / 2 for the time difference ΔTuv. The time difference ΔTuv is the time difference between the start of the high-level period of the second PWM signal SU2 at time t33 (see Figure 8) and the start of the high-level period of the second PWM signal SV2 at time t63 (see Figure 10). The control device 50 estimates (determines) that the resonant current of the U-phase and the resonant current of the V-phase flow simultaneously in the resonant inductor L1 if the time difference ΔTuv is less than Tres / 2. The above threshold setting is an example, and it may be set to other values. For example, considering errors in the value of Tres / 2, the above threshold may be set to a value even larger than Tres / 2. Also, the above threshold may be set to Tau + Tav + Td. Furthermore, the method for calculating the time difference ΔTuv used to determine whether the two-phase resonant currents flow simultaneously is not limited to the example described above; any other calculation method that can calculate a time difference equivalent to the time difference ΔTuw is acceptable. For example, the time difference ΔTuv used to determine whether the two-phase resonant currents flow simultaneously may be the time difference between the end of the high-level period of the first PWM signal SU1 at time t32 (see Figure 8) and the end of the high-level period of the first PWM signal SV1 at time t62 (see Figure 10).

[0087] (3.2.2) When the first and second operation control device 50 determines that two-phase resonant currents are flowing simultaneously, for example, when it determines that the resonant currents passing through each of the two switches 8 are flowing simultaneously through the resonant inductor L1, it performs the first and second operations to shorten the period during which the resonant currents passing through each of the two switches 8 are flowing simultaneously through the resonant inductor L1.

[0088] When the control device 50 performs the first and second operations, it performs the first and second operations in such a way that the length of the dead time period Td between the high-level period of the first PWM signal supplied to the first switching element 1 of the two switching circuits 10 corresponding to the two switches 8 and the high-level period of the second PWM signal supplied to the second switching element 2 does not change. Furthermore, for example, in the second operation, when the control device 50 shifts the high-level period of the control signal SU7 supplied to the switch 8U, it shifts the high-level periods of the first PWM signal SU1 and the second PWM signal SU2, respectively, but does not change the duty cycles of the first PWM signal SU1 and the second PWM signal SU2 in one cycle of the carrier signal CA1. Furthermore, when the control device 50 shifts the high-level period of the control signal SV7 supplied to switch 8V, it shifts the high-level periods of the first PWM signal SV1 and the second PWM signal SV2, but does not change the duty cycles of the first PWM signal SV1 and the second PWM signal SV2 in one cycle of the carrier signal CA1. Similarly, when the control device 50 shifts the high-level period of the control signal SW7 supplied to switch 8W, it shifts the high-level periods of the first PWM signal SW1 and the second PWM signal SW2, but does not change the duty cycles of the first PWM signal SW1 and the second PWM signal SW2 in one cycle of the carrier signal CA1. For the sake of explanation, in the following, the shift time of the high-level period of the control signal SU7 supplied to switch 8U will be denoted as Tsu. Furthermore, when shifting the high-level period of the control signal SV7 for switch 8V, let Tsv be the shift time of the high-level period of the control signal SV7. Also, when shifting the high-level period of the control signal SW7 for switch 8W, let Tsw be the shift time of the high-level period of the control signal SW7.

[0089] The upper part of Figure 12 shows a timing chart when the control device 50 has determined in advance that the resonant currents of the two phases, the V phase and the W phase, will flow simultaneously during the period corresponding to region A11 in Figure 11. Here, the upper part of Figure 12 shows the timing charts of the first PWM signal SU1, the first PWM signal SV1, the second PWM signal SV2, the first PWM signal SW1, the second PWM signal SW2, the control signals SV7, SW7, the load current iV, the load current iW, and the current iL1 before the shift. The lower part of Figure 12 shows a timing chart when the control device 50 has performed both the first and second operations during the period corresponding to region A11 in Figure 11 (hereinafter also referred to as "after the shift"). In the lower part of Figure 12, the timing charts of the shifted first PWM signal SV1, second PWM signal SV2, first PWM signal SW1, second PWM signal SW2, control signals SV7, SW7, load current iV, load current iW, current iL1, voltage V2v across the second switching element 2V, and voltage V2w across the second switching element 2W are shown. In the example of Figure 12, the polarity of the load currents iV and iW flowing through the two AC terminals 41V and 41W connected to the two switches 8V and 8W is negative, and the absolute value of the load current iV is smaller than the absolute value of the load current iW.

[0090] In the example shown in Figure 12, when the control device 50 performs the first operation, it compares the absolute value of the load current iV with the absolute value of the load current iW, and shortens the high-level period of the control signal SV7 to switch 8V, which has a smaller absolute value of load current among the two AC terminals 41V and 41W, by the shortening period Tred. In the example shown in Figure 12, the control device 50 sets the length of the shortening period Tred so that the length of the high-level period of the control signal SV7 is the length of the resonant half-period (= Tres / 2). Therefore, in the example shown in Figure 12, the length of the shortening period Tred is the same as the length of the additional time Tav.

[0091] Furthermore, when the control device 50 performs the second operation, it shifts the high-level period of the control signal SV7 in the direction of delaying by a shift time Tsv. At this time, the control device 50 takes time ta as the start of the high-level period of the control signal SW7 to switch 8W, and shifts the high-level period of the control signal SV7 to switch 8V, the high-level period of the first PWM signal SV1 to the first switching element 1V, and the high-level period of the second PWM signal SV2 to the second switching element 2V, each by a shift time Tsv in the direction of delaying, so that the high-level period of the control signal SV7 to switch 8V starts at time tc, which is a time Tdef after time tb, when the current value of the resonant current (current iL1) passing through switch 8W reaches an extreme value (minimum value in the example of Figure 12) and coincides with the current value of the load current iW flowing to the AC terminal 41V corresponding to switch 8W. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current iV flowing through the AC terminal 41V corresponding to switch 8V. The control device 50 determines the standby period Tdef by the calculation Tdef = L × |iW - iV| / V15. The control device 50 determines the shift time Tsv by the calculation Tsv = ΔT + Tdef. In the example in Figure 12, ΔT is the time difference between the start of the high-level period of the second PWM signal SW2 to the second switching element 2W corresponding to switch 8W and the end of the high-level period of the first PWM signal SV1 to the first switching element 1V corresponding to switch 8V. As a result, the current value of the resonant current (current iL1) at time tc when the standby period Tdef ends is equal to the absolute value of the load current iV. Therefore, in the power converter 100, zero-voltage soft switching of the second switching element 2V is possible if the high-level period of the control signal SV7 to the switch 8V is the same as the resonant half-period (Tres / 2), even if it does not include the additional time Tav.

[0092] As can be seen from the waveforms of current iL1 in the upper and lower parts of Figure 12, in the power converter 100, if the control device 50 determines in advance that the resonant currents of the V-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the V-phase and the W-phase by performing the first and second operations. Similarly, in the power converter 100, if the control device 50 determines in advance that the resonant currents of the U-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the W-phase by performing the first and second operations. Furthermore, in the power converter 100, if the control device 50 determines in advance that the resonant currents of the U-phase and V-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the V-phase by performing the first and second operations.

[0093] In the power converter 100, if the control device 50 does not perform the first and second operations, the voltages V2v and V2w across the second switching elements 2V and 2W do not decrease to zero at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends, respectively). As a result, in the power converter 100, the switching of the second switching elements 2U and 2V becomes hard switching.

[0094] In contrast, when the control device 50 performs the first and second operations, as shown in the lower part of Figure 12, the voltages V2v and V2w across the second switching elements 2V and 2W respectively decrease to zero at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends). Therefore, in the power converter 100, when the control device 50 performs the first and second operations, the switching of the second switching elements 2V and 2W becomes zero-voltage soft switching.

[0095] Figure 12 above shows an example in which the control device 50 executes the first and second operations when it has previously determined that the V-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, but it is not limited to this. For example, if the control device 50 has previously determined that the U-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, or if it has previously determined that the U-phase resonant current and the V-phase resonant current flow simultaneously through the resonant inductor L1, the control device 50 will execute the first and second operations, thereby enabling zero-voltage soft switching.

[0096] The first and second operations of the control device 50 can be generalized as follows.

[0097] When the control device 50 performs the first operation, it shortens the high-level period of the control signal to the first switch, which has a smaller absolute value of the corresponding load current, by a shortening period Tred. When the control device 50 performs the second operation, it shifts the high-level period of the control signal to the first switch in the direction of delaying by a shift time. At this time, the control device 50 sets time ta as the start of the high-level period of the control signal to the second switch, and shifts the high-level period of the control signal to the first switch to start at time tc, which is a waiting period Tdef after time tb, when the current value of the resonant current (current iL1) passing through the second switch reaches an extreme value and then matches the current value of the load current flowing through the AC terminal 41 corresponding to the second switch. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch. If the length of the standby period Tdef is set to be the same as the length of the additional time Tad in the control signal to the first switch, the current value of the resonant current (current iL1) at time tc will be equal to the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch.

[0098] (4) Advantages In the power converter 100 according to Embodiment 1, when the control device 50 determines that a resonant current flows simultaneously through two of the multiple switches 8 to the resonant inductor L1 when the duty cycle command value of one of the three phase duty cycle command values ​​du, dv, and dw of the two-phase modulation method is fixed to a constant value, the control device 50 performs a first operation and then a second operation. In the first operation, when one of the two switches 8 is designated as the first switch and the other as the second switch, the high-level period of the control signal to the first switch is shortened by a shortened period Tred from a period that includes the resonant half-period (Tres / 2) determined by the capacitance C of the resonant capacitor 9 corresponding to the first switch and the inductance L of the resonant inductor L1, and the additional time Tad determined by the voltage V15 of the regenerative capacitor 15, the inductance L of the resonant inductor L1, and the load current value. In the second operation, the high-level period of the control signal to the first switch is shifted so that the high-level period of the control signal to the first switch begins after a standby period Tdef from the point in time when the current value of the resonant current passing through the second switch reaches its extreme value and then matches the current value of the load current flowing through the AC terminal 41 corresponding to the second switch.

[0099] With the above configuration, the power converter 100 can more reliably achieve soft switching. Furthermore, in the power converter 100, the control device 50 generates multiple control signals based on the three-phase duty cycle command values ​​du, dv, and dw of the two-phase modulation method, which makes it possible to reduce switching losses.

[0100] In the power converter 100, the length of the shortening period Tred only needs to be less than or equal to the length of the additional time Tad. This allows the power converter 100 to perform soft switching even if the length of the shortening period Tred varies.

[0101] Furthermore, in the power converter 100, when the control device 50 performs the second operation, it shifts either the high-level period of the control signal to the first switch or the high-level period of the control signal to the second switch. This makes it possible to suppress changes in the line voltage. For example, the control device 50 may be configured to perform the shift of the high-level period of the control signal to the first switch and the shift of the high-level period of the control signal to the second switch alternately or in any ratio. This makes it possible for the power converter 100 to reduce the bias in the fluctuation of the line voltage ripple. In addition, the power converter 100 makes it possible to distribute the period during which the resonant current flows through the resonant inductor L1, thereby reducing the thermal load on the resonant inductor L1.

[0102] (5) Modified Examples (5.1) Modified Example 1 In Modified Example 1, when the control device 50 performs the first operation, it shortens the high-level period of the control signal to the first switch, which has a larger absolute value of the corresponding load current, by a shortening period Tred. Also in Modified Example 1, when the control device 50 performs the second operation, it shifts the high-level period of the control signal to the first switch in the direction of delaying it, and shifts the high-level period of the control signal to the second switch in the direction of advancing it. At this time, the control device 50 sets time ta as the start of the high-level period of the control signal to the second switch, and shifts the high-level period of the control signal to the first switch and the high-level period of the control signal to the first switch in opposite directions so that the high-level period of the control signal to the first switch starts at time tc, which is a waiting period Tdef after time tb, when the current value of the resonant current (current iL1) passing through the second switch reaches an extreme value and coincides with the current value of the load current flowing to the AC terminal 41 corresponding to the second switch. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch. If the length of the standby period Tdef is set to be the same as the length of the additional time Tad in the control signal to the first switch, the current value of the resonant current (current iL1) at time tc becomes equal to the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch. As a result, the power converter 100 of Modified Example 1 can more reliably achieve soft switching.

[0103] Furthermore, in the power conversion device 100 according to Modification 1, when the control device 50 performs the first and second operations, it shortens the high-level period of one of the control signals to the two switches 8, and shifts the high-level periods of the respective control signals to the two switches 8 in opposite directions. As a result, the power conversion device 100 according to Modification 1 can be made to operate at a higher frequency and can handle shorter carrier cycles.

[0104] (5.2) Modification 2 Modification 2 differs from Embodiment 1 only in that the control device 50 delays the end of the high-level period of the control signal by the clamp period (the length of the clamp period is the length of the additional time Tad) compared to the end of the dead time period Td.

[0105] (Embodiment 2) Hereinafter, a power converter 100A according to Embodiment 2 will be described based on Figures 13 and 14.

[0106] (1) Configuration of the power converter The power converter 100A according to Embodiment 2 differs from the power converter 100 according to Embodiment 1 in that, as shown in Figure 13, it is equipped with a control device 50A instead of the control device 50 of the power converter 100 according to Embodiment 1. With respect to the power converter 100A according to Embodiment 2, the same reference numerals are used for components that are the same as those in the power converter 100 according to Embodiment 1, and their descriptions are omitted.

[0107] The control device 50A differs from the control device 50 of Embodiment 1 in its operation when it determines that two-phase resonant currents are flowing simultaneously.

[0108] (2) Operation of the power converter (2.1) Basic operation The basic operation of the control device 50A is the same as the basic operation of the control device 50 described in Embodiment 1, so the explanation is omitted.

[0109] (2.2) When the shift control operation control device 50A determines that a resonant current flows simultaneously through two of the three phase duty command values ​​du, dv, and dw of the two-phase modulation scheme (see Figures 2 and 11), and that the duty command value of one phase is fixed to a constant value, the device performs shift control to shift the high-level period of the control signal to at least one of the two switches 8 so that the resonant currents flowing through each of the two switches 8 simultaneously do not flow through the resonant inductor L1. "When it determines that a resonant current flows simultaneously through two of the multiple switches 8" means when it is estimated in advance that a resonant current flowing through each of the two switches 8 simultaneously flows through the resonant inductor L1.

[0110] (2.2.1) Determination of whether two-phase resonant currents flow simultaneously The power converter 100A generates three first PWM signals SU1, SV1, SW1 and three second PWM signals SU2, SV2, SW2 based on the control device 50A's three-phase duty command values ​​du, dv, dw (see Figures 2 and 11) of the upper-stick two-phase modulation method. As shown in Figure 11, the two-phase duty command values ​​approach each other every 60° of electrical angle (see regions A11, A12, and A13 in Figure 11), and the duty cycles of the two-phase control signals become the same or close to each other.

[0111] The operation in control device 50A to "determine whether or not two-phase resonant currents flow simultaneously" is the same as the operation in control device 50 to "determine whether or not two-phase resonant currents flow simultaneously," so the explanation is omitted.

[0112] (2.2.2) When the shift control device 50A determines that two-phase resonant currents are flowing simultaneously, it performs shift control to shift the high-level period of the control signals to the two switches 8 so that the resonant currents passing through each of the two switches 8 do not flow simultaneously through the resonant inductor L1.

[0113] When the control device 50A performs shift control, it shifts the high-level period of the control signals to the two switches 8 so that the length of the high-level period of the first PWM signal and the second PWM signal supplied to the first switching element 1 and the second switching element 2 of the two switching circuits 10 corresponding to the two switches 8 does not change. For example, when the control device 50A shifts the high-level period of the control signal SU7 supplied to switch 8U, it shifts the high-level periods of the first PWM signal SU1 and the second PWM signal SU2, respectively, but does not change the duty cycles of the first PWM signal SU1 and the second PWM signal SU2 in one cycle of the carrier signal CA1. Furthermore, when the control device 50A shifts the high-level period of the control signal SV7 supplied to switch 8V, it shifts the high-level periods of the first PWM signal SV1 and the second PWM signal SV2, but does not change the duty cycles of the first PWM signal SV1 and the second PWM signal SV2 in one cycle of the carrier signal CA1. Similarly, when the control device 50A shifts the high-level period of the control signal SW7 supplied to switch 8W, it shifts the high-level periods of the first PWM signal SW1 and the second PWM signal SW2, but does not change the duty cycles of the first PWM signal SW1 and the second PWM signal SW2 in one cycle of the carrier signal CA1. For the sake of explanation, in the following, the shift time of the high-level period of the control signal SU7 supplied to switch 8U will be denoted as Tsu. Furthermore, when shifting the high-level period of the control signal SV7 for switch 8V, let Tsv be the shift time of the high-level period of the control signal SV7. Also, when shifting the high-level period of the control signal SW7 for switch 8W, let Tsw be the shift time of the high-level period of the control signal SW7.

[0114] (2.2.3) When the operation control device 50A for soft switching the second switching element performs shift control, it shifts the high-level periods of each of the control signals to the two switches 8 in opposite directions. When the control device 50A performs shift control, it first compares the duty cycles of the control signals to the two first switching elements 1 that correspond to the two switches 8, from among the plurality of first switching elements 1, when the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switches 8 is negative. Then, the control device 50A shifts the high-level period of the control signal given to the switch 8 corresponding to the first switching element 1 that is given a control signal with a relatively large duty cycle in the direction of delaying, and shifts the high-level period of the control signal given to the switch 8 corresponding to the first switching element 1 that is given a control signal with a relatively small duty cycle in the direction of advancing.

[0115] Figure 14 shows an example of operation when shift control is performed during the period corresponding to region A11 in Figure 11. In the upper part of Figure 14, the timing chart of the first PWM signal SU1, first PWM signal SV1, second PWM signal SV2, first PWM signal SW1, second PWM signal SW2, control signal SV6, control signal SV7, control signal SW6, control signal SW7, load current iV, load current iW, load current iW and current iL1 is shown for the case when the control device 50A determines that the resonant currents of the two phases, the V phase and the W phase, are flowing simultaneously, before the shift (when no shift control is performed). Furthermore, the lower part of Figure 14 shows a timing chart of the first PWM signal SV1, second PWM signal SV2, first PWM signal SW1, second PWM signal SW2, control signals SV6, control signals SV7, control signals SW6, control signals SW7, load current iv, load current iW, and current iL1 when the control signals SV7 and SW7 are shifted so that the total shift time of the high-level period shift time of the high-level period shift time of the control signal SV7 and the high-level period shift time of the control signal SW7 becomes a predetermined period. In the example of Figure 14, the control device 50A shifts the start time of the high-level period of the control signal SV7 to switch 8V by a shift time Tvs, and shifts the high-level period of the control signal SW7 to switch 8W by a shift time Tsw.

[0116] The control device 50A sets the predetermined period to be longer than or equal to the overlap period Tov (Tov_vw in the example of Figure 14) of the two-phase resonant currents when it is determined that the two-phase resonant currents are flowing simultaneously.

[0117] In the example in Figure 14, where the time margin is ΔT, the control device 50A is shown as having set the predetermined period to Tov + ΔT. In other words, in the example in Figure 14, the control device 50A is set to ΔT = 0 and the predetermined period = Tov + ΔT = Tsv + Tsw.

[0118] In the example shown in Figure 14, the polarity of the load currents iV and iW flowing through the two AC terminals 41V and 41W connected to the two switches 8V and 8W is negative. In this case, the control device 50A compares the duty cycles of the first PWM signals SV1 and SW1 for the two first switching elements 1V and 1W, which correspond one-to-one with the two switches 8V and 8W. The control device 50A then shifts the high-level period of the control signal SW7 given to switch 8W, which corresponds to the first switching element 1W that provides the first PWM signal SW1 with a relatively large duty cycle, by delaying it by a shift time Tsw, and shifts the high-level period of the control signal SV7 given to switch 8V, which corresponds to the first switching element 1V that provides the first PWM signal SV1 with a relatively small duty cycle, by advancing it by a shift time Tsv.

[0119] As can be seen from the waveform of current iL1 in Figure 14, in the power converter 100A, if the control device 50A determines in advance that the resonant currents of the V-phase and W-phase will flow simultaneously, it can avoid the overlap of the resonant currents of the V-phase and W-phase by performing shift control (see current iL1 in the lower part of Figure 14). Similarly, in the power converter 100A, if the control device 50A determines that the resonant currents of the U-phase and W-phase will flow simultaneously, it can avoid the overlap of the resonant currents of the U-phase and W-phase by performing shift control. Furthermore, in the power converter 100A, if the control device 50A determines that the resonant currents of the U-phase and V-phase will flow simultaneously, it can avoid the overlap of the resonant currents of the U-phase and V-phase by performing shift control.

[0120] In the power converter 100A, if the control device 50A does not perform shift control, the voltages V1v and V1w across the first switching elements 1V and 1W do not rise to Vd at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the end of the dead time period Td corresponding to the V-phase and W-phase, respectively). In other words, if the control device 50A does not perform shift control, the discharge of the resonant capacitors 9V and 9W is not completed at the end of the dead time period Td corresponding to the V-phase and W-phase, respectively. Therefore, if shift control is not performed, the voltages V2v and V2w across the second switching elements 2V and 2W do not decrease to zero at the end of the dead time period Td corresponding to the V-phase and W-phase, respectively. As a result, in the power converter 100A, the switching of the second switching elements 2V and 2W becomes hard switching.

[0121] In contrast, when the control device 50A performs shift control, as shown in Figure 14, the voltages V1v and V1w across the first switching elements 1V and 1W rise to Vd at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the end of the dead time period Td corresponding to the V-phase and W-phase, respectively). In other words, when the control device 50A performs shift control, the discharge of the resonant capacitors 9V and 9W ends at the end of the dead time period Td corresponding to the V-phase and W-phase, respectively. For this reason, in the power converter 100A, when the control device 50A performs shift control, the switching of the second switching elements 2V and 2W becomes zero-voltage soft switching.

[0122] Figure 14 above shows an example of shift control when the control device 50A has previously determined that the V-phase resonant current and the W-phase resonant current will flow simultaneously through the resonant inductor L1, but it is not limited to this. For example, if the control device 50A has previously determined that the U-phase resonant current and the W-phase resonant current will flow simultaneously through the resonant inductor L1, or if it has previously determined that the U-phase resonant current and the V-phase resonant current will flow simultaneously through the resonant inductor L1, the control device 50A can perform shift control, thereby enabling zero-voltage soft switching.

[0123] (3) Advantages In the power converter 100A according to Embodiment 2, when the control device 50A determines that a resonant current flows simultaneously through two of the multiple switches 8 to the resonant inductor L1 when the duty cycle command value of one of the three phases of the two-phase modulation scheme, du, dv, and dw, is fixed to a constant value, the control device 50A performs control to shift the high-level period of the control signal to each of the two switches 8 so that the resonant currents flowing through each of the two switches 8 to the resonant inductor L1 do not flow simultaneously.

[0124] With the above configuration, the power converter 100A can more reliably achieve soft switching.

[0125] Furthermore, in the power converter 100A according to Embodiment 2, when the control device 50A performs shift control, it shifts the high-level period of the control signals to each of the two switches 8 so that the length of the high-level period of the control signals given to the first switching element 1 and the second switching element 2 of the switching circuit 10 connected to the two switches 8 among the plurality of switching circuits 10 does not change. As a result, the power converter 100A according to Embodiment 2 can suppress changes in line voltage.

[0126] Furthermore, in the power converter 100A according to Embodiment 2, when the control device 50A performs shift control, it shifts the high-level period of each of the control signals to the two switches 8 in different directions. As a result, the power converter 100A according to Embodiment 2 can be made to operate at a higher frequency.

[0127] Furthermore, in the power converter 100A according to Embodiment 2, when the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switches 8 is negative, the control device 50A compares the duty cycles of the first PWM signals to the two first switching elements 1 corresponding to the two switches 8. The control device 50A then shifts the high-level period of the control signal given to the switch 8 corresponding to the first switching element 1 that provides the first PWM signal with a relatively large duty cycle toward a slower period, and shifts the high-level period of the control signal given to the switch 8 corresponding to the first switching element 1 that provides the first PWM signal with a relatively small duty cycle toward an earlier period. As a result, the power converter 100A according to Embodiment 2 can be made to operate at a higher frequency.

[0128] Furthermore, the power converter 100 according to Embodiment 1 can reduce the shift amount more effectively than the power converter 100A according to Embodiment 2. Therefore, the power converter 100 of Embodiment 1 can improve the current distortion of the load current and increase the frequency of the carrier signal CA1 compared to the power converter 100A according to Embodiment 2.

[0129] (4) Modified Examples (4.1) Modified Example 1 When the control device 50A performs shift control, it shifts the high-level period of each of the control signals to the two switches 8 in opposite directions. When the control device 50A performs shift control, first, when the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switches 8 is negative, it compares the duty cycles of the first PWM signals for the two first switching elements 1 that correspond to the two switches 8 from among the plurality of first switching elements 1. Then, the control device 50A shifts the high-level period of the control signal given to the switch 8 corresponding to the first switching element 1 that gives a first PWM signal with a relatively large duty cycle in the direction of advancing, and shifts the high-level period of the control signal given to the switch 8 corresponding to the first switching element 1 that gives a first PWM signal with a relatively small duty cycle in the direction of delaying.

[0130] In the power converter 100A of the modified example 1, if the control device 50A determines in advance that the resonant currents of the U-phase and V-phase flow simultaneously, it can avoid the overlap of the resonant currents of the U-phase and V-phase by performing shift control. Similarly, in the power converter 100A, if the control device 50 determines that the resonant currents of the U-phase and W-phase flow simultaneously, it can avoid the overlap of the resonant currents of the U-phase and W-phase by performing shift control. Furthermore, in the power converter 100A, if the control device 50A determines that the resonant currents of the V-phase and W-phase flow simultaneously, it can avoid the overlap of the resonant currents of the V-phase and W-phase by performing shift control.

[0131] (4.2) Modification 2 In Modification 2 of Embodiment 2, the control device 50A combines the shift control of the control device 50A of Modification 1 of Embodiment 2 with the shift control of the control device 50A of Embodiment 2, and is configured to execute the shift control of the control device 50A of Modification 1 of Embodiment 2 and the shift control of the control device 50A of Embodiment 2 alternately or in an arbitrary ratio. As a result, the power converter 100A according to Modification 2 can reduce the bias in the fluctuation of line voltage ripple compared to the power converter 100A according to Embodiment 2 and the power converter 100A according to Modification 1 of Embodiment 2. Furthermore, the power converter 100A according to Modification 2 can distribute the period during which the resonant current flows through the resonant inductor L1 compared to the power converter 100A according to Embodiment 2 and the power converter 100A according to Modification 1 of Embodiment 2, thereby reducing the thermal load on the resonant inductor L1.

[0132] (Embodiment 3) Hereinafter, a power converter 100B according to Embodiment 3 will be described with reference to Figure 15.

[0133] (1) Configuration of the power converter The power converter 100B according to Embodiment 3 differs from the power converter 100 according to Embodiment 1 in that, as shown in Figure 15, it is equipped with a control device 50B instead of the control device 50 of the power converter 100 according to Embodiment 1. With respect to the power converter 100B according to Embodiment 3, the same reference numerals are used for components that are the same as those in the power converter 100 according to Embodiment 1, and their descriptions are omitted.

[0134] The control device 50B differs from the control device 50 of Embodiment 1 in its operation when it determines that two-phase resonant currents are flowing simultaneously.

[0135] (2) Operation of the power converter (2.1) Basic operation The basic operation of the control device 50B is the same as the basic operation of the control device 50 described in Embodiment 1, so the explanation is omitted.

[0136] (2.2) When the operation control device 50B determines that two-phase resonant currents are flowing simultaneously, it can perform the first control operation, the second control operation, and the third control operation when it determines that resonant currents are flowing simultaneously through two of the multiple switches 8 when the duty cycle command value of one of the three-phase duty cycle command values ​​du, dv, dw (see Figures 2 and 11) of the two-phase modulation method are fixed to a constant value. "When it determines that resonant currents are flowing simultaneously through two of the multiple switches 8" means when it is estimated in advance that resonant currents are flowing simultaneously through two of the two switches 8 through the resonant inductor L1.

[0137] (2.2.1) Determination of whether two-phase resonant currents flow simultaneously The power converter 100B generates three first PWM signals SU1, SV1, SW1 and three second PWM signals SU2, SV2, SW2 based on the control device 50B's three-phase duty command values ​​du, dv, dw (see Figures 2 and 11) of the top-stick two-phase modulation method. As shown in Figure 11, the two-phase duty command values ​​approach each other every 60° of electrical angle (see regions A11, A12, and A13 in Figure 11), and the duty cycles of the two-phase control signals become the same or close to each other.

[0138] The operation in control device 50B to "determine whether or not two-phase resonant currents flow simultaneously" is the same as the operation in control device 50 to "determine whether or not two-phase resonant currents flow simultaneously," so the explanation is omitted.

[0139] (2.2.2) In the first control operation, the control device 50B overlaps the high-level period of the control signal to each of the two switches 8 with the dead time period Td corresponding to each of the two switching circuits 10 connected to the two switches 8 for a predetermined period of time.

[0140] In the second control operation, the control device 50B determines the start time of the high-level period of the control signal to at least one of the multiple switches 8 according to the load current flowing through the AC load RA1. Here, in the second control operation of the control device 50B, the start time of the high-level period of the control signals to two of the multiple switches 8 is changed according to the sum of the two-phase load currents flowing through each of the two AC terminals 41 connected to those two switches 8. In the example in Figure 16, the start time of the high-level period of the control signals SV7 and SW7 to the two switches 8 is changed according to the sum of the V-phase load current iV flowing through AC terminal 41V and the W-phase load current iW flowing through AC terminal 41W.

[0141] In the third control operation, the control device 50B can perform a third control operation that makes the dead time period corresponding to each of the two switching circuits 10 connected to the two switches 8 among the multiple switching circuits 10 longer than a predetermined dead time period Td by an additional time Tad. The predetermined dead time period Td is the dead time period Td in the case of the basic operation.

[0142] Figure 16 shows the timing chart of the power converter 100B when the control device 50B performs the first control operation, the second control operation, and the third control operation, and Figure 17 shows the timing chart of the power converter 100B when the control device 50B does not perform the first control operation, the second control operation, and the third control operation. The predetermined period is, for example, at least a portion of the resonant half-period of a resonant circuit including a resonant inductor L1 and two resonant capacitors 9 (here, resonant capacitors 9V, 9W). For example, if the resonant half-period of a resonant circuit including two resonant capacitors 9 is Tr2 (in other words, when the current iL1 flowing through the resonant inductor L1 includes a two-phase resonant current), then the resonant half-period Tr2 is half of the resonant period, which is the reciprocal of the resonant frequency of the resonant circuit including the resonant inductor L1 and the two resonant capacitors 9. If the resonant circuit includes two resonant capacitors 9, and the inductance of the resonant inductor L1 is L, and the capacitance of each of the two resonant capacitors 9 is C, then the resonant half-period Tr2 of the resonant circuit is Tr2 = 2 １／２ ×π×(L・C) １／２ In the example shown in Figure 16, the predetermined period is the entire duration of the resonant half-period Tr2. In other words, the length of the predetermined period is 100% of the length of the resonant half-period Tr2.

[0143] The operation of the control device 50B will be explained in more detail below.

[0144] If the control device 50B determines that the resonant currents overlap, it executes the first, second, and third steps in the order of the first, second, and third steps. In the following example, we will describe the case where it is estimated that the resonant current flowing through the V-phase switch 8V and the resonant current flowing through the W-phase switch 8W in the resonant inductor L1 overlap, but the same applies to the cases of U-phase and W-phase, and U-phase and V-phase.

[0145] In the first step, the first PWM signals SV1 and SV2 of the V phase are synchronized with the first PWM signals SW1 and SV2 of the W phase. In the example in Figure 16, the first PWM signals SV1 and SV2 of the V phase are synchronized with the first PWM signals SW1 and SV2 of the W phase by shifting the end of the high-level period of the first PWM signal SW1 of the W phase and the start of the high-level period of the second PWM signal SW2 of the W phase by ΔT1. In the power converter 100B according to Embodiment 3, the first step corresponds to the first control operation of the control device 50B. In the first step, the first PWM signal SV1 and the second PWM signal SV2 of the V phase may be synchronized with the first PWM signal SW1 and the second PWM signal SW2 of the W phase by shifting the high-level period of each of the V phase first PWM signal SV1 and the second PWM signal SV2 by delaying it by ΔT1. Alternatively, in the first step, the first PWM signal SV1 and the second PWM signal SV2 of the V phase may be synchronized with the first PWM signal SW1 and the second PWM signal SW2 of the W phase by shifting them together by a total of ΔT1.

[0146] In the second step, an additional time Tad corresponding to the sum of the two-phase load currents iV and iW is added to the high-level period of the control signals SV7 and SW7 to the two-phase switch 8, which correspond to the dead time period Td of each of the two phases. The control device 50B determines the additional time Tad by calculating Tad = L × |iU + iV| / V15, using, for example, the detection results of the load currents iV and iW from the current sensor, or their signal processing values, or estimated values ​​of the load currents iV and iW, the inductance L of the resonant inductor L1 which is stored in advance, and the detection result of the potential V15 at the sixth terminal 154 of the regenerative capacitor 15. In the power converter 100B according to Embodiment 3, the second step corresponds to the second control operation of the control device 50B.

[0147] In the third step, the lengths of the high-level period and dead time period Td of the two control signals SV7 and SW7 are set to the resonant half-period Tr2 = 2 of the resonant circuit. １／２ ×π×(L・C) １／２The settings are changed accordingly. More specifically, the control device 50B sets the length of the period obtained by subtracting the additional time Tad from the high-level period of each of the two control signals SV7 and SW7 to the resonant half-period Tr2 of the resonant circuit, and changes the dead time period Td to a dead time period Td1 equal to the resonant half-period Tr2 of the resonant circuit. In the power converter 100B according to Embodiment 3, the third step corresponds to the third control operation of the control device 50B. Note that the end of the high-level period of each of the two control signals SV7 and SW7 may be after the end of the resonant half-period Tr2.

[0148] In the power converter 100B, if the control device 50B does not perform the first, second, and third control operations, as shown in Figure 17, the voltages V2v and V2w across the second switching elements 2V and 2W have not decreased to zero at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the end of the dead time period Td corresponding to the V-phase and W-phase, respectively). In other words, in the power converter 100B, if the control device 50B does not perform the first, second, and third control operations, the discharge of the resonant capacitors 9V and 9W has not finished at the end of the dead time period Td corresponding to the V-phase and W-phase, respectively. For this reason, in the power converter 100B, if the control device 50B does not perform the first, second, and third control operations, the switching of the second switching elements 2U and 2V becomes hard switching.

[0149] In contrast, when the control device 50B performs the first, second, and third control operations, as shown in Figure 16, the voltages V2v and V2w across the second switching elements 2V and 2W become zero at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the end of the dead time period Td1 corresponding to the V-phase and W-phase, respectively). In other words, when the control device 50B performs the first, second, and third control operations, the discharge of the resonant capacitors 9V and 9W ends at the end of the dead time period Td1 corresponding to the V-phase and W-phase, respectively. For this reason, in the power converter 100B, when the control device 50B performs the first, second, and third control operations, the switching of the second switching elements 2V and 2W becomes zero-voltage soft switching.

[0150] (3) Advantages In the power converter 100B according to Embodiment 3, the control device 50B can perform a first control operation and a second control operation when it determines that a resonant current flows simultaneously through two of the multiple switches 8 when the duty cycle command value of one of the three phase duty cycle command values ​​du, dv, and dw of the two-phase modulation scheme is fixed to a constant value. The first control operation overlaps the high-level period of the control signal to each of the two switches 8 with the dead time period corresponding to each of the two or more switching circuits 10 connected to two or more of the multiple switching circuits 10. The second control operation determines the start time of the high-level period of the control signal to at least one of the multiple switches 8 according to the load current of at least one phase flowing through the AC load RA1 connected to the multiple AC terminals 41.

[0151] With the above configuration, the power converter 100B can more reliably achieve soft switching. In addition, the power converter 100B can increase the frequency of the carrier signal CA1.

[0152] Furthermore, in the power converter 100B according to Embodiment 3, the predetermined period is the entire duration of the resonant half-cycle. This makes it possible for the power converter 100B according to Embodiment 3 to more reliably achieve zero-voltage soft switching.

[0153] Furthermore, in the second control operation of the control device 50B according to Embodiment 3, the power converter 100B changes the start time of the high-level period of the control signal to at least one of the multiple switches 8 according to the sum of the two-phase load currents flowing through each of the two AC terminals 41 connected to the two switches 8. This makes it possible for the power converter 100B to initiate resonance at the start of the dead time period.

[0154] Furthermore, in the power converter 100B according to Embodiment 3, the control device 50B can perform a third control operation that extends the dead time period corresponding to each of the two switching circuits 10 connected to the two switches 8 from among the plurality of switching circuits 10 by an additional time Td compared to a predetermined dead time period Td. As a result, the power converter 100B can achieve zero-voltage soft switching even when the resonant half-period Tr2 is longer than the dead time period Td.

[0155] (4) Modified Examples (4.1) Modified Example 1 In the power converter 100B according to Modified Example 1, a part of the operation of the control device 50B when it is determined that the two-phase resonant currents overlap differs from the operation of the control device 50B in Embodiment 3.

[0156] In the first control operation, the control device 50B overlaps the high-level period of the control signal to each of the two switches 8 with the dead time period Td corresponding to each of the two switching circuits 10 connected to the two switches 8 among the plurality of switching circuits 10 for a predetermined period. The predetermined period is, for example, a portion of the resonant half-period Tr2 of the resonant circuit, which includes the resonant inductor L1 and the two resonant capacitors 9 connected to each of the two switches 8. The predetermined period is 60% of the resonant half-period Tr2. In other words, the length of the predetermined period is 60% of the length of the resonant half-period.

[0157] In the power converter 100B according to Modification 1, when the control device 50B performs the first control operation and the second control operation, the switching of the first switching elements 1U and 1V becomes somewhat incomplete soft switching, but losses and noise can be reduced compared to when complete hard switching occurs.

[0158] (4.2) Modification 2 The circuit configuration of the power converter 100B according to Modification 2 of Embodiment 3 is the same as that of the power converter 100B according to Embodiment 3 (see Figure 15), so the illustration and description are omitted.

[0159] In the power converter 100B according to the modified example 2, the resonant half-period during basic operation is half the dead time period Td during basic operation, and a part of the operation of the control device 50B when it is determined that the two-phase resonant currents overlap differs from the operation of the control device 50B in Embodiment 3.

[0160] In modified example 2, the resonant half-period in the basic operation is Td / 2. The predetermined period is, for example, the entire duration of the resonant half-period Tr2 of the resonant circuit, which includes the resonant inductor L1 and the two resonant capacitors 9 connected to the two switches 8, respectively. The resonant half-period Tr2 is Tr2 = 2 １／２ It is set to ×Td / 2. In Modification 2, the length of the resonant half-period Tr2 is shorter than the length of the dead time period Td, and the period excluding the additional time Tad in the high-level period of each of the two control signals overlaps with the entire resonant half-period Tr2. In Modification 2, if the resonant half-period Tr2 is within the dead time period Td in the basic operation, it is not necessary to make the dead time period Td longer than the dead time period Td in the basic operation in the first control operation.

[0161] (4.3) Modification 3 The circuit configuration of the power converter 100B according to Modification 3 of Embodiment 3 is the same as that of the power converter 100B according to Embodiment 3 (see Figure 15), so the illustration and description are omitted.

[0162] In the power converter 100B of the modified example 3, when the control device 50B determines that the two-phase resonant currents overlap, it is not necessary to completely overlap the high-level periods of the control signals to each of the two-phase switches 8. For example, it is sufficient to output a control signal that causes one of the two-phase switches 8 to conduct until the current iL1 flowing through the resonant inductor L1 reaches the sum of the two-phase load currents.

[0163] In the power converter 100B according to the modified example 3, a part of the operation of the control device 50B when it is determined that the two-phase resonant currents overlap differs from the operation of the control device 50B in embodiment 3.

[0164] (Embodiment 4) Hereinafter, a power converter 100C according to Embodiment 4 will be described with reference to Figure 18.

[0165] (1) Configuration of the power converter The power converter 100C according to Embodiment 4 differs from the power converter 100 according to Embodiment 1 in that, as shown in Figure 18, it is equipped with a control device 50C instead of the control device 50 of the power converter 100 according to Embodiment 1. With respect to the power converter 100C according to Embodiment 4, the same reference numerals are used for components that are the same as those in the power converter 100 according to Embodiment 1, and their descriptions are omitted.

[0166] The control device 50C differs from the control device 50 of Embodiment 1 in its operation when it determines that two-phase resonant currents are flowing simultaneously.

[0167] (2) Operation of the power converter (2.1) Basic operation The basic operation of the control device 50C is the same as the basic operation of the control device 50 described in Embodiment 1, so the explanation is omitted. In this embodiment, it is assumed that the length of the dead time period Td is set to be longer than the half-period of resonance.

[0168] (2.2) The operation control device 50C for shortening the time is determined to perform shortening control when the duty cycle command value of one of the three phase duty cycle command values ​​du, dv, dw (see Figures 2 and 11) of the two-phase modulation method is fixed to a constant value, and the control device determines that resonant currents flow simultaneously through two of the multiple switches 8 to the resonant inductor L1. In shortening control, the control device 50C provides a control signal to the first switch, which is one of the two switches 8, with a preset high-level period shortened, and provides a control signal to the second switch, which is different from the first switch, with a preset high-level period. When the control device 50C determines that "resonant currents flow simultaneously through two of the multiple switches 8 to the resonant inductor L1," it means when it has been estimated in advance that resonant currents flow simultaneously through both of the two switches 8 to the resonant inductor L1.

[0169] (2.2.1) Determination of whether two-phase resonant currents flow simultaneously The power converter 100C generates three first PWM signals SU1, SV1, SW1 and three second PWM signals SU2, SV2, SW2 based on the control device 50C's three-phase duty command values ​​du, dv, dw (see Figures 2 and 11) of the upper-stick two-phase modulation method. As shown in Figure 11, the two-phase duty command values ​​approach each other at electrical angles of 60° (see regions A11, A12, and A13 in Figure 11), and the duty cycles of the two-phase control signals become the same or close to each other.

[0170] The operation in control device 50C to "determine whether or not two-phase resonant currents flow simultaneously" is the same as the operation in control device 50 to "determine whether or not two-phase resonant currents flow simultaneously," so the explanation is omitted.

[0171] (2.2.2) When the control device 50C determines that two-phase resonant currents are flowing simultaneously, in shortening control, it provides a control signal to the first switch, which is one of the two switches 8, with a preset high-level period shortened, and provides a control signal to the second switch, which is different from the first switch, with a preset high-level period. When the control device 50C performs shortening control, the first switch is the switch 8 among the two switches 8 that corresponds to the switching circuit 10 in the plurality of switching circuits 10, where the absolute value of the load current flowing through each of the two switching circuits 10 corresponding to the two switches 8 is the largest.

[0172] The operation of the shortening control when the control device 50C has previously determined that the resonant currents of the V-phase and W-phase flow simultaneously during the period corresponding to region A11 in Figure 11 will be explained below with reference to Figures 19 and 20.

[0173] Figure 19 shows the timing chart of the first PWM signal SU1, first PWM signal SV1, second PWM signal SV2, first PWM signal SW1, second PWM signal SW2, control signal SV7, control signal SW7, load current iV, load current iW, current iL1, and the voltages V2v and V2w across the two second switching elements 2V and 2W, respectively, before the control device 50C determines that the resonant current of the V phase and the resonant current of the W phase are flowing simultaneously and performs shortening control. Furthermore, Figure 20 shows the first PWM signal SU1, first PWM signal SV1, second PWM signal SV2, first PWM signal SW1, second PWM signal SW2, control signal SV7, control signal SW7, load current iV, load current iW, current iL1, and the voltages V2v and V2w across the two second switching elements 2V and 2W, respectively, when the control device 50C performs shortening control.Figures 19 and 20 show the timing chart for a portion of the period within one cycle of the carrier signal CA1 (see Figure 2).

[0174] In the power converter 100C, if the control device 50C does not perform shortening control, as shown in Figure 19, the voltages V2u and V2v across the two second switching elements 2V and 2W do not decrease to zero at the point when the two second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the end of the dead time period Td corresponding to the V-phase and W-phase, respectively). In other words, if the control device 50C does not perform shortening control, the discharge of the resonant capacitors 9V and 9W is not completed at the end of the dead time period Td corresponding to the V-phase and W-phase, respectively. For this reason, in the power converter 100C, if the control device 50C does not perform shortening control, the switching of the second switching elements 2V and 2W becomes hard switching.

[0175] The control device 50C compares the absolute value of the load current iV with the absolute value of the load current iW, and shortens the high-level period of the control signal SW7 to the switch 8W, which has a larger absolute value of the load current iW, by the shortening period Tredw. Specifically, the control device 50C shortens the high-level period of the control signal SW7 by the shortening period Tredw so that the control signal SV7 and the control signal SW7 do not overlap. In the example in Figure 20, the control device 50C sets the length of the shortening period Tredw to be the length of the overlap period Tov (see Figure 19) between the high-level period of the control signal SV7 before the shortening control and the control signal SW7 before the shortening control. In the example in Figure 19, the length of the overlap period Tov is the time difference between the start of the high-level period of the control signal SV7 and the end of the high-level period of the control signal SW7. Therefore, in the example in Figure 20, the length of the shortening period Tredw is the same as the length of the overlap period Tov. In the example shown in Figure 20, the control device 50C shortens the high-level period of the control signal SW7 in a way that advances the end of the high-level period of the control signal SW7 before the shortening control by the shortening period Tredw.

[0176] As can be seen from the waveform of current iL1 in Figure 19 and the waveform of current iL1 in Figure 20, in the power converter 100C, the control device 50C shortens the overlap period between the resonant current of the V-phase and the resonant current of the W-phase by performing shortening control when it has determined in advance that the resonant currents of the two phases, the V-phase and the W-phase, will flow simultaneously. Furthermore, from the voltages V2v and V2w across the two second switching elements 2V and 2W in Figure 19 and the voltages V2v and V2w across the two second switching elements 2V and 2W in Figure 20, it can be seen that in the power converter 100C, the hard switching of the second switching element 2V is mitigated, and the hard switching of the second switching element 2W is also mitigated. Mitigation of the hard switching of the second switching element 2V means that zero-voltage soft switching of the second switching element 2V is realized, or the value of the voltage V2v across the second switching element 2V when the second switching element 2V is turned on is reduced. For each of the other switching elements 2U and 2W, "the hard switching of the switching element is relaxed" has the same meaning as when the hard switching of the second switching element 2V is relaxed. In other words, when the hard switching of a switching element is relaxed, it means that zero-voltage soft switching of the switching element is achieved or the value of the voltage across the switching element when the switching element is turned on is reduced.

[0177] Similarly, in the power converter 100C, if the control device 50C determines in advance that the resonant currents of the U-phase and W-phase flow simultaneously, it performs shortening control to shorten the overlap period between the resonant currents of the U-phase and the W-phase, and to alleviate the hard switching of the second switching element 2U and the second switching element 2W.

[0178] Furthermore, in the power converter 100C, if the control device 50C determines in advance that the resonant currents of the U-phase and V-phase flow simultaneously, it performs shortening control, thereby shortening the overlap period between the resonant currents of the U-phase and the V-phase, and mitigating the hard switching of the second switching element 2U and the second switching element 2V.

[0179] (3) Advantages In the power converter 100C according to Embodiment 4, the control device 50C sets a dead time period Td between the high-level period of the control signal to the first switching element 1 and the high-level period of the control signal to the second switching element 2 for each of the plurality of switching circuits 10, and sets the high-level period of the control signal to each of the plurality of switches 8 based on the dead time period Td for the corresponding switching circuit 10 among the plurality of switching circuits 10. Furthermore, when the control device 50C determines that a resonant current flows simultaneously through two of the plurality of switches 8 through the resonant inductor L1 when the duty command value of one of the three phase duty command values ​​du, dv, and dw of the two-phase modulation method is fixed to a constant value, it performs shortening control. In shortening control, the control device 50C provides a control signal to the first switch, which is one of the two switches 8, with a shortened preset high-level period, and provides a control signal to the second switch, which is different from the first switch among the two switches 8, with a preset high-level period.

[0180] With the above configuration, zero-voltage soft switching is possible, and switching losses can be reduced.

[0181] Furthermore, in the power converter 100C, when the control device 50C performs shortening control, the first switch is the switch 8 among the two switches 8 that corresponds to the switching circuit 10 in the plurality of switching circuits 10, where the absolute value of the load current flowing through each of the two switching circuits 10 corresponding to the two switches 8 is the largest.

[0182] According to the above configuration, the number of switches 8 that mitigate hard switching among the multiple switches 8 is equalized.

[0183] (4) Modified Examples (4.1) Modified Example 1 The circuit configuration of the power converter 100C according to Modified Example 1 of Embodiment 4 is the same as that of the power converter 100C according to Embodiment 4 (see Figure 18), so the illustration and description are omitted.

[0184] In the power converter 100C according to the modified example 1 of Embodiment 4, the only difference is how the first switch and the second switch are determined when the control device 50C performs shortening control.

[0185] In the modified example 1, when the control device 50C performs shortening control, the first switch is the switch 8 among the two switches 8 that corresponds to the switching circuit 10 in the plurality of switching circuits 10 where the absolute value of the voltage command value for each of the two switching circuits 10 corresponding to the two switches 8 is the largest.

[0186] (4.2) Modification 2 The circuit configuration of the power converter 100C according to Modification 2 of Embodiment 4 is the same as that of the power converter 100C according to Embodiment 4 (see Figure 18), so the illustration and description are omitted.

[0187] In the power converter 100C according to the modified example 2 of Embodiment 4, the method for determining the first switch and the second switch when the control device 50C performs shortening control is different.

[0188] In the modified example 2, when the control device 50C performs shortening control, the first switch is the switch 8 among the two switches 8 that corresponds to the switching circuit 10 in the plurality of switching circuits 10, the one in which the absolute value of the load current flowing through each of the two switching circuits 10 corresponding to the two switches 8 is smallest.

[0189] In the modified power converter 100C of the second modification, the control device 50C shortens the overlap period between the resonant currents of the V-phase and W-phase by performing shortening control when it determines in advance that the resonant currents of the two phases, the V-phase and the W-phase, are flowing simultaneously. Furthermore, in the modified power converter 100C of the second modification, the hard switching of the second switching element 2V is mitigated, and zero-voltage soft switching of the second switching element 2W is realized.

[0190] Similarly, in the power converter 100C of the modified example 2, if the control device 50C determines in advance that the resonant currents of the U-phase and W-phase flow simultaneously, it performs shortening control, thereby shortening the overlap period between the resonant currents of the U-phase and the W-phase, and mitigating the hard switching of one of the second switching elements 2U and 2W, while realizing zero-voltage soft switching of the other.

[0191] Furthermore, in the modified power converter 100C of the second example, if the control device 50C determines in advance that the resonant currents of the U-phase and V-phase flow simultaneously, it performs shortening control, thereby shortening the overlap period between the resonant currents of the U-phase and the V-phase. Additionally, hard switching of one of the second switching elements 2U and 2V is mitigated, while zero-voltage soft switching of the other is realized.

[0192] (4.3) Modification 3 The circuit configuration of the power converter 100C according to Modification 3 of Embodiment 4 is the same as that of the power converter 100C according to Embodiment 4 (see Figure 18), so the illustration and description are omitted.

[0193] In the power converter 100C according to the modified example 3 of Embodiment 4, the only difference is how the first and second switches are determined when the control device 50C performs shortening control.

[0194] When the control device 50C performs shortening control, the first switch is the switch 8 among the two switches 8 that corresponds to the switching circuit 10 in the plurality of switching circuits 10 where the absolute value of the voltage command value for each of the two switching circuits 10 corresponding to the two switches 8 is smallest.

[0195] (Embodiment 5) Hereinafter, a power converter 100D according to Embodiment 5 will be described based on Figure 21.

[0196] (1) Configuration of the power converter The power converter 100D according to Embodiment 5 differs from the power converter 100 according to Embodiment 1 in that, as shown in Figure 21, it is equipped with a control device 50D instead of the control device 50 of the power converter 100 according to Embodiment 1. With respect to the power converter 100D according to Embodiment 5, the same reference numerals are used for components that are the same as those in the power converter 100 according to Embodiment 1, and their descriptions are omitted.

[0197] In this embodiment, the control device 50D generates a plurality of first PWM signals SU1, SV1, SW1 and a plurality of second PWM signals SU2, SV2, SW2 based on three-phase duty command values ​​du, dv, dw (see Figure 22) of a two-phase modulation scheme. This embodiment differs from Embodiment 1 in that the two-phase modulation scheme is a bottom-tagged two-phase modulation scheme.

[0198] The control device 50D generates a plurality of first PWM signals SU1, SV1, SW1 and a plurality of second PWM signals SU2, SV2, SW2 using three-phase duty cycle command values ​​du, dv, dw (see Figure 22) and a triangular wave carrier signal CA1 (see Figure 2). More specifically, the control device 50D generates the first PWM signal SU1 and the second PWM signal SU2 to be supplied to the first switching element 1U and the second switching element 2U, respectively, based on the carrier signal CA1 and the duty cycle command value du. The control device 50D also generates the first PWM signal SV1 and the second PWM signal SV2 to be supplied to the first switching element 1V and the second switching element 2V, respectively, based on the carrier signal CA1 and the V-phase duty cycle command value dv. Furthermore, the control device 50D generates a first PWM signal SW1 and a second PWM signal SW2 to be supplied to the first switching element 1W and the second switching element 2W, respectively, based on the carrier signal CA1 and the W-phase duty command value dw. In this embodiment, the control device 50D, like the control device 50, sets the maximum value of the carrier signal CA1 to 0.5 and the minimum value to -0.5. Also, like the control device 50, the control device 50D sets the maximum value of each of the three-phase duty command values ​​du, dv, and dw to 0.5 and the minimum value to -0.5. Alternatively, the control device 50D may set the maximum value of the carrier signal CA1 to 1 and the minimum value to 0, and the maximum value of each of the three-phase duty command values ​​du, dv, and dw to 1 and the minimum value to 0. Furthermore, the control device 50D may set the maximum and minimum values ​​of the carrier signal CA1 to values ​​other than 1 and 0, respectively, and the maximum and minimum values ​​of the three-phase duty cycle command values ​​du, dv, and dw to values ​​other than 1 and 0, respectively. Also, the waveform of the carrier signal CA1 is not limited to a triangular wave, but may be a sawtooth wave, for example.

[0199] The control device 50D, like the control device 50, uses the three-phase duty cycle reference values ​​du0, dv0, and dw0 (see Figure 2) for the three-phase modulation scheme to determine the three-phase duty cycle command values ​​du, dv, and dw for the two-phase modulation scheme.

[0200] The control device 50D sets a dead time period Td between the high-level period of the first PWM signal to the first switching element 1 and the high-level period of the second PWM signal to the second switching element 2 for each of the plurality of switching circuits 10, and sets the high-level period of the control signal to each of the plurality of switches 8 based on the dead time period Td for the corresponding switching circuit 10 among the plurality of switching circuits 10.

[0201] (2) Operation of the power converter (2.1) Basic operation The basic operation of the control device 50D is the same as the basic operation of the control device 50 described in Embodiment 1, so the explanation is omitted.

[0202] (2.2) When the operation control device 50D determines that two-phase resonant currents are flowing simultaneously, it can perform the first control operation, the second control operation, and the third control operation when it determines that resonant currents are flowing simultaneously through two of the multiple switches 8 when the duty cycle command value of one of the three-phase duty cycle command values ​​du, dv, and dw of the two-phase modulation method is fixed to a constant value. "When it determines that resonant currents are flowing simultaneously through two of the multiple switches 8" means when it is estimated in advance that resonant currents are flowing simultaneously through two of the two switches 8 through the resonant inductor L1.

[0203] (2.2.1) Determination of whether two-phase resonant currents flow simultaneously The power converter 100D generates three first PWM signals SU1, SV1, SW1 and three second PWM signals SU2, SV2, SW2 based on the three-phase duty command values ​​du, dv, dw of the bottom-stick two-phase modulation method, as shown in Figure 22, the two-phase duty command values ​​approach each other every 60° of electrical angle (see regions A21, A22, and A23 in Figure 22), and the duty cycles of the two-phase control signals become the same or close to each other.

[0204] Figure 23 shows an example of boundary conditions for the cases where the resonant currents of the W phase and the V phase do not overlap (do not flow simultaneously) and overlap (flow simultaneously). These boundary conditions will be explained with reference to Figure 23.

[0205] In the power converter 100D, if the time difference ΔTvw is Tres / 2 or greater, the resonant current of the W phase and the resonant current of the V phase do not overlap, and if the time difference ΔTvw is less than Tres / 2, the resonant current of the W phase and the resonant current of the V phase overlap. The time difference ΔTvw is the time difference between the start of the high-level period of the first PWM signal SW1 at time t11 and the start of the high-level period of the first PWM signal SV1 at time t7.

[0206] The control device 50D has a threshold value set to Tres / 2 for the time difference ΔTvw (in this embodiment, the dead time period Td = Tres / 2). The control device 50D estimates (determines) that the W-phase resonant current and the V-phase resonant current flow simultaneously in the resonant inductor L1 if the time difference ΔTvw is less than Tres / 2. The above threshold setting is just an example, and it may be set to a different value. For example, considering errors in the value of Tres / 2, the threshold may be set to a value even larger than Tres / 2. Furthermore, the method for calculating the time difference ΔTvw used to determine whether the two-phase resonant currents flow simultaneously is not limited to the above example, and other calculation methods are acceptable as long as they can calculate a time difference equivalent to the time difference ΔTvw. For example, the time difference ΔTvw used to determine whether or not the two-phase resonant currents flow simultaneously may be the time difference between the end of the high-level period of the second PWM signal SW2 at time t10 and the end of the high-level period of the second PWM signal SV2 at time t6.

[0207] In the power converter 100D, if the time difference ΔTuw is Tres / 2 or greater, the resonant current of the U phase and the resonant current of the W phase do not overlap in the resonant inductor L1, and if the time difference ΔTuw is less than Tres / 2, the resonant current of the U phase and the resonant current of the W phase overlap. The time difference ΔTuw is the time difference between the start of the high-level period of the first PWM signal SU1 at time t3 (see Figure 3) and the start of the high-level period of the first PWM signal SW1 at time t11.

[0208] The control device 50D has a threshold value set to Tres / 2 for the time difference ΔTuw. The control device 50D estimates (determines) that the resonant current of the U phase and the resonant current of the W phase flow simultaneously in the resonant inductor L1 if the time difference ΔTuw is less than Tres / 2. The above threshold setting is just an example, and it may be set to a different value. For example, considering errors in the value of Tres / 2, the threshold may be set to a value even larger than Tres / 2. Also, the method for calculating the time difference ΔTuw used to determine whether the two-phase resonant currents flow simultaneously is not limited to the above example, and any other calculation method that can calculate a time difference equivalent to the time difference ΔTuw may be used. For example, the time difference ΔTuw used to determine whether or not the two-phase resonant currents flow simultaneously may be the time difference between the end of the high-level period of the second PWM signal SU2 (see Figure 3) and the end of the high-level period of the second PWM signal SW2 (see Figure 23).

[0209] In the power converter 100D, if the time difference ΔTuv is Tres / 2 or greater, the resonant current of the U-phase and the resonant current of the V-phase do not overlap in the resonant inductor L1, and if the time difference ΔTuv is less than Tres / 2, the resonant current of the U-phase and the resonant current of the V-phase overlap. The time difference ΔTuv is the time difference between the start of the high-level period of the first PWM signal SU1 at time t3 (see Figure 3) and the start of the high-level period of the first PWM signal SV1 at time t7 (see Figure 23).

[0210] The control device 50D has a threshold value set to Tres / 2 for the time difference ΔTuv. The control device 50D estimates (determines) that the resonant current of the U phase and the resonant current of the V phase flow simultaneously in the resonant inductor L1 if the time difference ΔTuv is less than Tres / 2. The above threshold setting is just an example, and it may be set to a different value. For example, considering errors in the value of Tres / 2, the threshold may be set to a value even larger than Tres / 2. Furthermore, the method for calculating the time difference ΔTuv used to determine whether the two-phase resonant currents flow simultaneously is not limited to the above example, and any other calculation method that can calculate a time difference equivalent to the time difference ΔTuv may be used. For example, the time difference ΔTuv used to determine whether or not the two-phase resonant currents flow simultaneously may be the time difference between the end of the high-level period of the second PWM signal SU2 (see Figure 3) and the end of the high-level period of the second PWM signal SV2 (see Figure 23).

[0211] (2.2.2) When the first and second operation control device 50D determines that two-phase resonant currents are flowing simultaneously, for example, when it determines that the resonant currents passing through each of the two switches 8 are flowing simultaneously through the resonant inductor L1, it performs the first and second operations to shorten the period during which the resonant currents passing through each of the two switches 8 are flowing simultaneously through the resonant inductor L1.

[0212] When the control device 50D performs the first and second operations, it performs the first and second operations in such a way that the length of the dead time period Td between the high-level period of the first PWM signal supplied to the first switching element 1 of the two switching circuits 10 corresponding to the two switches 8 and the high-level period of the second PWM signal supplied to the second switching element 2 does not change. Furthermore, for example, in the second operation, when the control device 50D shifts the high-level period of the control signal SU6 supplied to the switch 8U, it shifts the high-level periods of the first PWM signal SU1 and the second PWM signal SU2, respectively, but does not change the duty cycles of the first PWM signal SU1 and the second PWM signal SU2 in one cycle of the carrier signal CA1 (see Figure 2). Furthermore, when the control device 50D shifts the high-level period of the control signal SV6 supplied to switch 8V, it shifts the high-level periods of the first PWM signal SV1 and the second PWM signal SV2, but does not change the duty cycles of the first PWM signal SV1 and the second PWM signal SV2 in one cycle of the carrier signal CA1. Similarly, when the control device 50D shifts the high-level period of the control signal SW6 supplied to switch 8W, it shifts the high-level periods of the first PWM signal SW1 and the second PWM signal SW2, but does not change the duty cycles of the first PWM signal SW1 and the second PWM signal SW2 in one cycle of the carrier signal CA1. For the sake of explanation, in the following, the shift time of the high-level period of the control signal SU6 supplied to switch 8U will be denoted as Tsu. Furthermore, when shifting the high-level period of the control signal SV6 for switch 8V, let Tsv be the shift time of the high-level period of the control signal SV6. Also, when shifting the high-level period of the control signal SW6 for switch 8W, let Tsw be the shift time of the high-level period of the control signal SW6.

[0213] The upper part of Figure 24 shows the timing chart when the control device 50D has determined in advance that the resonant currents of the V-phase and W-phase flow simultaneously during the period corresponding to region A23 in Figure 22. Here, the upper part of Figure 24 shows the timing chart of the second PWM signal SU2, the first PWM signal SV1, the second PWM signal SV2, the first PWM signal SW1, the second PWM signal SW2, the control signal SV6, the control signal SW6, the load current iV, the load current iW, and the current iL1 before the shift. The lower part of Figure 24 shows the timing chart when the control device 50D has performed both the first and second operations (hereinafter also referred to as "after the shift") during the period corresponding to region A23 in Figure 22. In the lower part of Figure 24, the timing charts of the shifted first PWM signal SV1, second PWM signal SV2, first PWM signal SW1, second PWM signal SW2, control signal SV6, control signal SW6, load current iV, load current iW, current iL1, voltage V2v across the second switching element 2V, and voltage V2w across the second switching element 2W are shown. In the example of Figure 24, the polarity of the load currents iV and iW flowing through the two AC terminals 41V and 41W connected to the two switches 8V and 8W is positive, and the absolute value of the load current iV is smaller than the absolute value of the load current iW.

[0214] In the example shown in Figure 24, when the control device 50D performs the first operation, it compares the absolute value of the load current iV with the absolute value of the load current iW, and shortens the high-level period of the control signal SV6 to switch 8V, which has a smaller absolute value of load current among the two AC terminals 41V and 41W, by the shortening period Tred. In the example shown in Figure 24, the control device 50D sets the length of the shortening period Tred so that the length of the high-level period of the control signal SV6 is the length of the resonant half-period (= Tres / 2). Therefore, in the example shown in Figure 24, the length of the shortening period Tred is the same as the length of the additional time Tav.

[0215] Furthermore, when the control device 50D performs the second operation, it shifts the high-level period of the control signal SV6 in the direction of delaying by a shift time Tsv. At this time, the control device 50D takes time ta as the start of the high-level period of the control signal SW6 to the switch 8W, and shifts the high-level period of the control signal SV6 to the switch 8V in the direction of delaying by a shift time Tsv, such that the high-level period of the control signal SV6 to the switch 8V starts at time tc, which is a time Tdef after time tb, when the current value of the resonant current (current iL1) passing through the switch 8W reaches an extreme value (maximum value in the example of Figure 24) and coincides with the current value of the load current iW flowing through the AC terminal 41V corresponding to the switch 8W. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current iV flowing through the AC terminal 41V corresponding to switch 8V. The control device 50D determines the standby period Tdef by the calculation Tdef = L × |iW - iV| / V15. The control device 50D determines the shift time Tsv by the calculation Tsv = ΔT + Tdef. In the example in Figure 24, ΔT is the time difference between the start of the high-level period of the first PWM signal SW1 to the first switching element 1W corresponding to switch 8W and the end of the high-level period of the second PWM signal SV2 to the second switching element 2V corresponding to switch 8V. As a result, the current value of the resonant current (current iL1) at time tc when the standby period Tdef ends is equal to the absolute value of the load current iV. Therefore, in the power converter 100D, zero-voltage soft switching of the first switching element 1V is possible if the high-level period of the control signal SV6 to the switch 8V is the same as the resonant half-period (Tres / 2), even if it does not include the additional time Tav.

[0216] As can be seen from the waveforms of current iL1 in the upper and lower parts of Figure 24, in the power converter 100D, if the control device 50D determines in advance that the resonant currents of the V-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the V-phase and the W-phase by performing the first and second operations. Similarly, in the power converter 100D, if the control device 50D determines in advance that the resonant currents of the U-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the W-phase by performing the first and second operations. Furthermore, in the power converter 100D, if the control device 50D determines in advance that the resonant currents of the U-phase and V-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the V-phase by performing the first and second operations.

[0217] In the power converter 100D, if the control device 50D does not perform the first and second operations, the voltages V1v and V1w across the first switching elements 1V and 1W do not decrease to zero at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends, respectively). As a result, in the power converter 100D, the switching of the first switching elements 1U and 1V becomes hard switching.

[0218] In contrast, when the control device 50D performs the first and second operations, as shown in the lower part of Figure 24, at the point when the first PWM signals SV1 and SW1 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends), the voltages V2v and V2w across the second switching elements 2V and 2W increase to Vd, respectively, so that the voltages V1v and V1w across the first switching elements 1V and 1W decrease to zero. Therefore, in the power converter 100D, when the control device 50D performs the first and second operations, the switching of the first switching elements 1V and 1W becomes zero-voltage soft switching.

[0219] Figure 24 above shows an example in which the control device 50D executes the first and second operations when it has previously determined that the V-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, but it is not limited to this. For example, if the control device 50D has previously determined that the U-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, or if it has previously determined that the U-phase resonant current and the V-phase resonant current flow simultaneously through the resonant inductor L1, the control device 50D can also execute the first and second operations, thereby enabling zero-voltage soft switching.

[0220] The first and second operations of the control device 50D can be generalized as follows:

[0221] When the control device 50D performs the first operation, it shortens the high-level period of the control signal to the first switch, which has a smaller absolute value of the corresponding load current, by a shortening period Tred. When the control device 50D performs the second operation, it shifts the high-level period of the control signal to the first switch in the direction of delaying by a shift time. At this time, the control device 50D sets time ta as the start of the high-level period of the control signal to the second switch, and shifts the high-level period of the control signal to the first switch to start at time tc, which is a waiting period Tdef after time tb, when the current value of the resonant current (current iL1) passing through the second switch reaches an extreme value and then matches the current value of the load current flowing through the AC terminal 41 corresponding to the second switch. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch. If the length of the standby period Tdef is set to be the same as the length of the additional time Tad in the control signal to the first switch, the current value of the resonant current (current iL1) at time tc will be equal to the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch.

[0222] (3) Advantages In the power converter 100D according to Embodiment 5, when the control device 50D determines that a resonant current flows simultaneously through two of the multiple switches 8 to the resonant inductor L1 when the duty cycle command value of one of the three phase duty cycle command values ​​du, dv, and dw of the two-phase modulation method is fixed to a constant value, the control device 50D performs a first operation and then a second operation. In the first operation, when one of the two switches 8 is designated as the first switch and the other as the second switch, the high-level period of the control signal to the first switch is shortened by a shortened period Tred from a period that includes the resonant half-period (Tres / 2) determined by the capacitance C of the resonant capacitor 9 corresponding to the first switch and the inductance L of the resonant inductor L1, and the additional time Tad determined by the voltage V15 of the regenerative capacitor 15, the inductance L of the resonant inductor L1, and the load current value. In the second operation, the high-level period of the control signal to the first switch is shifted so that the high-level period of the control signal to the first switch begins after a standby period Tdef from the point when the current value of the resonant current passing through the second switch reaches its extreme value and then matches the current value of the load current flowing through the AC terminal 41 corresponding to the second switch. This makes it possible for the power converter 100D to achieve soft switching more reliably.

[0223] In the power converter 100D, the length of the shortening period Tred only needs to be less than or equal to the length of the additional time Tad. This allows the power converter 100D to perform soft switching even if the length of the shortening period Tred varies.

[0224] Furthermore, in the power converter 100D, the control device 50D shifts either the high-level period of the control signal to the first switch or the high-level period of the control signal to the second switch when performing the second operation. This makes it possible to suppress changes in the line voltage. For example, the control device 50D may be configured to alternately perform the shift of the high-level period of the control signal to the first switch and the shift of the high-level period of the control signal to the second switch, or at any ratio. This makes it possible for the power converter 100D to reduce the bias in the fluctuation of the line voltage ripple. In addition, the power converter 100D makes it possible to distribute the period during which the resonant current flows through the resonant inductor L1, thereby reducing the thermal load on the resonant inductor L1.

[0225] (Embodiment 6) Hereinafter, a power converter 100E according to Embodiment 6 will be described with reference to Figure 25.

[0226] (1) Configuration of the power converter The power converter 100E according to Embodiment 6 differs from the power converter 100 according to Embodiment 1 (see Figure 1) in that, as shown in Figure 25, it is equipped with a control device 50E instead of the control device 50. With respect to the power converter 100E according to Embodiment 6, the same reference numerals are used for components that are the same as those in the power converter 100 according to Embodiment 1, and their descriptions are omitted.

[0227] In this embodiment, the control device 50E generates a plurality of first PWM signals and a plurality of second PWM signals based on the three-phase duty command values ​​du, dv, and dw of the two-phase modulation scheme (see Figure 26). This embodiment differs from Embodiment 1 in that the two-phase modulation scheme is an upper and lower fixed two-phase modulation scheme.

[0228] The control device 50E generates a plurality of first PWM signals SU1, SV1, SW1 and a plurality of second PWM signals SU2, SV2, SW2 using three-phase duty cycle command values ​​du, dv, dw (see Figure 26) and a triangular wave carrier signal CA1 (see Figure 2). More specifically, the control device 50E generates the first PWM signal SU1 and the second PWM signal SU2 to be supplied to the first switching element 1U and the second switching element 2U, respectively, based on the carrier signal CA1 and the duty cycle command value du. The control device 50E also generates the first PWM signal SV1 and the second PWM signal SV2 to be supplied to the first switching element 1V and the second switching element 2V, respectively, based on the carrier signal CA1 and the V-phase duty cycle command value dv. Furthermore, the control device 50E generates a first PWM signal SW1 and a second PWM signal SW2 to be supplied to the first switching element 1W and the second switching element 2W, respectively, based on the carrier signal CA1 and the W-phase duty command value dw. In this embodiment, the control device 50E sets the maximum value of the carrier signal CA1 to 0.5 and the minimum value to -0.5, similar to the control device 50 of Embodiment 1 (see Figure 1). Also, the control device 50E sets the maximum value of each of the three-phase duty command values ​​du, dv, and dw to 0.5 and the minimum value to -0.5, similar to the control device 50 of Embodiment 1 (see Figure 1). Alternatively, the control device 50E may set the maximum value of the carrier signal CA1 to 1 and the minimum value to 0, and the maximum value of each of the three-phase duty command values ​​du, dv, and dw to 1 and the minimum value to 0. Furthermore, the control device 50E may set the maximum and minimum values ​​of the carrier signal CA1 to values ​​other than 1 and 0, respectively, and the maximum and minimum values ​​of the three-phase duty cycle command values ​​du, dv, and dw to values ​​other than 1 and 0, respectively. Also, the waveform of the carrier signal CA1 is not limited to a triangular wave, but may be a sawtooth wave, for example.

[0229] The control device 50E, like the control device 50 of Embodiment 1 and the control device 50D of Embodiment 5 (see Figure 21), uses the three-phase duty reference values ​​du0, dv0, and dw0 of the three-phase modulation method (see Figure 2) to determine the three-phase duty command values ​​du, dv, and dw of the two-phase modulation method.

[0230] The control device 50E sets a dead time period Td for each of the multiple switching circuits 10 between the high-level period of the first PWM signal to the first switching element 1 and the high-level period of the second PWM signal to the second switching element 2, and sets the high-level period of the control signal to each of the multiple switches 8 based on the dead time period Td for the corresponding switching circuit 10 among the multiple switching circuits 10.

[0231] (2) Operation of the power converter (2.1) Basic operation The basic operation of the control device 50E is the same as the basic operation of the control device 50 described in Embodiment 1, so the explanation is omitted.

[0232] (2.2) When the operation control device 50E determines that two-phase resonant currents are flowing simultaneously, it can perform the first control operation, the second control operation, and the third control operation when it determines that resonant currents are flowing simultaneously through two of the multiple switches 8 when the duty cycle command value of one of the three-phase duty cycle command values ​​du, dv, and dw of the two-phase modulation method is fixed to a constant value. "When it determines that resonant currents are flowing simultaneously through two of the multiple switches 8" means when it is estimated in advance that resonant currents are flowing simultaneously through two of the two switches 8 through the resonant inductor L1.

[0233] (2.2.1) Determination of whether two-phase resonant currents flow simultaneously The power converter 100E generates three first PWM signals SU1, SV1, SW1 and three second PWM signals SU2, SV2, SW2 based on the control device 50E's three-phase duty command values ​​du, dv, dw (see Figure 26) of the upper and lower fixed two-phase modulation method. As shown in Figure 26, the two-phase duty command values ​​approach each other at electrical angles of 60° (see regions A31, A32, A33, A34, A35, and A36 in Figure 26), and the duty cycles of the two-phase control signals become the same or close to each other. Each waveform (modulated wave) of the three-phase duty command values ​​du, dv, dw of the upper and lower fixed two-phase modulation method has a first linear portion that is constant at the maximum value and a second linear portion that is constant at the minimum value.

[0234] The boundary conditions for whether the two-phase (V-phase and W-phase) resonant currents overlap in region A32 can be determined in the same way as for region A11 in Embodiment 1 (see Figure 11). The diagram illustrating an example of the boundary conditions for the cases where the W-phase resonant current and the V-phase resonant current do not overlap (do not flow simultaneously) and overlap (flow simultaneously) is the same as Figure 10 explained in Embodiment 1, so the explanation is omitted. The boundary conditions for whether the two-phase (U-phase and W-phase) resonant currents overlap in region A34 can be determined in the same way as for region A12 in Embodiment 1 (see Figure 11). Similarly, the boundary conditions for whether the two-phase (U-phase and V-phase) resonant currents overlap in region A36 can be determined in the same way as for region A13 in Embodiment 1 (see Figure 11).

[0235] The boundary conditions for whether the two-phase (V-phase and W-phase) resonant currents overlap in region A35 can be determined in the same way as for region A23 in Embodiment 5 (see Figure 22). The diagram illustrating an example of the boundary conditions for the cases where the W-phase resonant current and the V-phase resonant current do not overlap (do not flow simultaneously) and overlap (flow simultaneously) is the same as Figure 23 explained in Embodiment 5, so the explanation is omitted. The boundary conditions for whether the two-phase (U-phase and W-phase) resonant currents overlap in region A31 can be determined in the same way as for region A21 in Embodiment 5 (see Figure 22). Similarly, the boundary conditions for whether the two-phase (U-phase and V-phase) resonant currents overlap in region A33 can be determined in the same way as for region A22 in Embodiment 5 (see Figure 22).

[0236] (2.2.2) When the first and second operation control device 50E determines that two-phase resonant currents are flowing simultaneously, for example, when it determines that the resonant currents passing through each of the two switches 8 are flowing simultaneously through the resonant inductor L1, it performs the first and second operations to shorten the period during which the resonant currents passing through each of the two switches 8 are flowing simultaneously through the resonant inductor L1.

[0237] (2.2.2.1) When the polarity of the current flowing through the resonant inductor L1 is negative, the control device 50E performs the first and second operations in such a way that the length of the dead time period Td between the high-level period of the first PWM signal supplied to the first switching element 1 of the two switching circuits 10 corresponding to the two switches 8 and the high-level period of the second PWM signal supplied to the second switching element 2 does not change. Furthermore, for example, in the second operation, when the control device 50E shifts the high-level period of the control signal SU7 supplied to the switch 8U, it shifts the high-level periods of the first PWM signal SU1 and the second PWM signal SU2, respectively, but does not change the duty cycles of the first PWM signal SU1 and the second PWM signal SU2 in one cycle of the carrier signal CA1. Furthermore, when the control device 50E shifts the high-level period of the control signal SV7 supplied to switch 8V, it shifts the high-level periods of the first PWM signal SV1 and the second PWM signal SV2, respectively, but does not change the duty cycles of the first PWM signal SV1 and the second PWM signal SV2 in one cycle of the carrier signal CA1. Furthermore, when the control device 50E shifts the high-level period of the control signal SW7 supplied to switch 8W, it shifts the high-level periods of the first PWM signal SW1 and the second PWM signal SW2, respectively, but does not change the duty cycles of the first PWM signal SW1 and the second PWM signal SW2 in one cycle of the carrier signal CA1.

[0238] The upper part of Figure 27 shows a timing chart when the control device 50E has determined in advance that the resonant currents of the V-phase and W-phase flow simultaneously during the period corresponding to region A32 in Figure 26. Here, the upper part of Figure 27 shows the timing charts of the first PWM signal SU1, the first PWM signal SV1, the second PWM signal SV2, the first PWM signal SW1, the second PWM signal SW2, the control signal SV7, the control signal SW7, the load current iV, the load current iW, and the current iL1 before the shift. The lower part of Figure 27 shows a timing chart when the control device 50E has performed both the first and second operations (hereinafter also referred to as "after the shift") during the period corresponding to region A32 in Figure 26. In the lower part of Figure 27, the timing charts of the shifted first PWM signal SV1, second PWM signal SV2, first PWM signal SW1, second PWM signal SW2, control signal SV7, control signal SW7, load current iV, load current iW, current iL1, voltage V2v across the second switching element 2V, and voltage V2w across the second switching element 2W are shown. In the example of Figure 27, the polarity of the load currents iV and iW flowing through the two AC terminals 41V and 41W connected to the two switches 8V and 8W is negative, and the absolute value of the load current iV is smaller than the absolute value of the load current iW.

[0239] In the example shown in Figure 27, when the control device 50E performs the first operation, it compares the absolute value of the load current iV with the absolute value of the load current iW, and shortens the high-level period of the control signal SV7 to switch 8V, which has a smaller absolute value of load current among the two AC terminals 41V and 41W, by the shortening period Tred. In the example shown in Figure 27, the control device 50E sets the length of the shortening period Tred so that the length of the high-level period of the control signal SV7 is the length of the resonant half-period (= Tres / 2). Therefore, in the example shown in Figure 27, the length of the shortening period Tred is the same as the length of the additional time Tav.

[0240] Furthermore, when the control device 50E performs the second operation, it shifts the high-level period of the control signal SV7 in the direction of delaying by a shift time Tsv. At this time, the control device 50E takes time ta as the start of the high-level period of the control signal SW7 to switch 8W, and shifts the high-level period of the control signal SV7 to switch 8V, the high-level period of the first PWM signal SV1 to the first switching element 1V, and the high-level period of the second PWM signal SV2 to the second switching element 2V, each by a shift time Tsv in the direction of delaying, so that the high-level period of the control signal SV7 to switch 8V starts at time tc, which is a time Tdef after time tb, when the current value of the resonant current (current iL1) passing through switch 8W reaches an extreme value (minimum value in the example of Figure 27) and coincides with the current value of the load current iW flowing to the AC terminal 41V corresponding to switch 8W. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current iV flowing through the AC terminal 41V corresponding to switch 8V. The control device 50E determines the standby period Tdef by the calculation Tdef = L × |iW - iV| / V15. The control device 50E determines the shift time Tsv by the calculation Tsv = ΔT + Tdef. In the example in Figure 27, ΔT is the time difference between the start of the high-level period of the second PWM signal SW2 to the second switching element 2W corresponding to switch 8W and the end of the high-level period of the first PWM signal SV1 to the first switching element 1V corresponding to switch 8V. As a result, the current value of the resonant current (current iL1) at time tc when the standby period Tdef ends is equal to the absolute value of the load current iV. Therefore, in the power converter 100E, zero-voltage soft switching of the second switching element 2V is possible if the high-level period of the control signal SV7 to the switch 8V is the same as the resonant half-period (Tres / 2), even if it does not include the additional time Tav.

[0241] As can be seen from the waveforms of current iL1 in the upper and lower parts of Figure 27, in the power converter 100E, if the control device 50E determines in advance that the resonant currents of the V-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the V-phase and the W-phase by performing the first and second operations. Similarly, in the power converter 100E, if the control device 50E determines in advance that the resonant currents of the U-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the W-phase by performing the first and second operations. Furthermore, in the power converter 100E, if the control device 50E determines in advance that the resonant currents of the U-phase and V-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the V-phase by performing the first and second operations.

[0242] In the power converter 100E, if the control device 50E does not perform the first and second operations, the voltages V2v and V2w across the second switching elements 2V and 2W do not decrease to zero at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends, respectively). As a result, in the power converter 100E, the switching of the second switching elements 2U and 2V becomes hard switching.

[0243] In contrast, when the control device 50E performs the first and second operations, as shown in the lower part of Figure 27, the voltages V2v and V2w across the second switching elements 2V and 2W respectively decrease to zero at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends). Therefore, in the power converter 100E, when the control device 50E performs the first and second operations, the switching of the second switching elements 2V and 2W becomes zero-voltage soft switching.

[0244] Figure 27 above shows an example in which the control device 50E executes the first and second operations when it has previously determined that the V-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, but it is not limited to this. For example, if the control device 50E has previously determined that the U-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, or if it has previously determined that the U-phase resonant current and the V-phase resonant current flow simultaneously through the resonant inductor L1, the control device 50E can also execute the first and second operations, thereby enabling zero-voltage soft switching.

[0245] The first and second operations of the control device 50E can be generalized as follows:

[0246] When the control device 50E performs the first operation, it shortens the high-level period of the control signal to the first switch, which has a smaller absolute value of the corresponding load current, by a shortening period Tred. When the control device 50E performs the second operation, it shifts the high-level period of the control signal to the first switch in the direction of delaying by a shift time. At this time, the control device 50E sets time ta as the start of the high-level period of the control signal to the second switch, and shifts the high-level period of the control signal to the first switch to start at time tc, which is a waiting period Tdef after time tb, when the current value of the resonant current (current iL1) passing through the second switch reaches an extreme value and then matches the current value of the load current flowing through the AC terminal 41 corresponding to the second switch. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch. If the length of the standby period Tdef is set to be the same as the length of the additional time Tad in the control signal to the first switch, the current value of the resonant current (current iL1) at time tc will be equal to the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch.

[0247] (2.2.2.2) When the polarity of the current flowing through the resonant inductor L1 is positive, the control device 50E performs the first and second operations in such a way that the length of the dead time period Td between the high-level period of the first PWM signal supplied to the first switching element 1 of the two switching circuits 10 corresponding to the two switches 8 and the high-level period of the second PWM signal supplied to the second switching element 2 does not change. Furthermore, for example, in the second operation, when the control device 50E shifts the high-level period of the control signal SU6 supplied to the switch 8U, it shifts the high-level periods of the first PWM signal SU1 and the second PWM signal SU2, respectively, but does not change the duty cycles of the first PWM signal SU1 and the second PWM signal SU2 in one period of the carrier signal CA1 (see Figure 2). Furthermore, when the control device 50E shifts the high-level period of the control signal SV6 supplied to switch 8V, it shifts the high-level periods of the first PWM signal SV1 and the second PWM signal SV2, but does not change the duty cycles of the first PWM signal SV1 and the second PWM signal SV2 in one cycle of the carrier signal CA1. Similarly, when the control device 50E shifts the high-level period of the control signal SW6 supplied to switch 8W, it shifts the high-level periods of the first PWM signal SW1 and the second PWM signal SW2, but does not change the duty cycles of the first PWM signal SW1 and the second PWM signal SW2 in one cycle of the carrier signal CA1. For the sake of explanation, in the following, the shift time of the high-level period of the control signal SU6 supplied to switch 8U will be denoted as Tsu. Furthermore, when shifting the high-level period of the control signal SV6 for switch 8V, let Tsv be the shift time of the high-level period of the control signal SV6. Also, when shifting the high-level period of the control signal SW6 for switch 8W, let Tsw be the shift time of the high-level period of the control signal SW6.

[0248] The upper part of Figure 28 shows the timing chart when the control device 50E has determined in advance that the resonant currents of the two phases, the V phase and the W phase, will flow simultaneously during the period corresponding to region A35 in Figure 26. Here, the upper part of Figure 28 shows the timing chart of the second PWM signal SU2, the first PWM signal SV1, the second PWM signal SV2, the first PWM signal SW1, the second PWM signal SW2, the control signal SV6, the control signal SW6, the load current iV, the load current iW, and the current iL1 before the shift. The lower part of Figure 28 shows the timing chart when the control device 50E has performed both the first and second operations (hereinafter also referred to as "after the shift") during the period corresponding to region A35 in Figure 26. In the lower part of Figure 28, the timing charts of the shifted first PWM signal SV1, second PWM signal SV2, first PWM signal SW1, second PWM signal SW2, control signal SV6, control signal SW6, load current iV, load current iW, current iL1, voltage V2v across the second switching element 2V, and voltage V2w across the second switching element 2W are shown. In the example of Figure 28, the polarity of the load currents iV and iW flowing through the two AC terminals 41V and 41W connected to the two switches 8V and 8W is positive, and the absolute value of the load current iV is smaller than the absolute value of the load current iW.

[0249] In the example shown in Figure 28, when the control device 50E performs the first operation, it compares the absolute value of the load current iV with the absolute value of the load current iW, and shortens the high-level period of the control signal SV6 to switch 8V, which has a smaller absolute value of load current among the two AC terminals 41V and 41W, by the shortening period Tred. In the example shown in Figure 28, the control device 50E sets the length of the shortening period Tred so that the length of the high-level period of the control signal SV6 is the length of the resonant half-period (= Tres / 2). Therefore, in the example shown in Figure 28, the length of the shortening period Tred is the same as the length of the additional time Tav.

[0250] Furthermore, when the control device 50E performs the second operation, it shifts the high-level period of the control signal SV6 in the direction of delaying it by a shift time Tsv. At this time, the control device 50E takes time ta as the start of the high-level period of the control signal SW6 to switch 8W, and shifts the high-level period of the control signal SV6 to switch 8V, the high-level period of the first PWM signal SV1 to the first switching element 1V, and the high-level period of the second PWM signal SV2 to the second switching element 2V, each by a shift time Tsv in the direction of delaying them, so that the high-level period of the control signal SV6 to switch 8V starts at time tc, which is a time Tdef after time tb, when the current value of the resonant current (current iL1) passing through switch 8W reaches an extreme value (maximum value in the example of Figure 28) and coincides with the current value of the load current iW flowing to the AC terminal 41V corresponding to switch 8W. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current iV flowing through the AC terminal 41V corresponding to switch 8V. The control device 50E determines the standby period Tdef by the calculation Tdef = L × |iW - iV| / V15. The control device 50E determines the shift time Tsv by the calculation Tsv = ΔT + Tdef. In the example in Figure 28, ΔT is the time difference between the start of the high-level period of the first PWM signal SW1 to the first switching element 1W corresponding to switch 8W and the end of the high-level period of the second PWM signal SV2 to the second switching element 2V corresponding to switch 8V. As a result, the current value of the resonant current (current iL1) at time tc when the standby period Tdef ends is equal to the absolute value of the load current iV. Therefore, in the power converter 100E, zero-voltage soft switching of the first switching element 1V is possible if the high-level period of the control signal SV6 to the switch 8V is the same as the resonant half-period (Tres / 2), even if it does not include the additional time Tav.

[0251] As can be seen from the waveforms of current iL1 in the upper and lower parts of Figure 28, in the power converter 100E, if the control device 50E determines in advance that the resonant currents of the V-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the V-phase and the W-phase by performing the first and second operations. Similarly, in the power converter 100E, if the control device 50E determines in advance that the resonant currents of the U-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the W-phase by performing the first and second operations. Furthermore, in the power converter 100E, if the control device 50E determines in advance that the resonant currents of the U-phase and V-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the V-phase by performing the first and second operations.

[0252] In the power converter 100E, if the control device 50E does not perform the first and second operations, the voltages V1v and V1w across the first switching elements 1V and 1W do not decrease to zero at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends, respectively). As a result, in the power converter 100E, the switching of the first switching elements 1U and 1V becomes hard switching.

[0253] In contrast, when the control device 50E performs the first and second operations, as shown in the lower part of Figure 28, at the point when the first PWM signals SV1 and SW1 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends), the voltages V2v and V2w across the second switching elements 2V and 2W increase to Vd, respectively, so that the voltages V1v and V1w across the first switching elements 1V and 1W decrease to zero. Therefore, in the power converter 100E, when the control device 50E performs the first and second operations, the switching of the first switching elements 1V and 1W becomes zero-voltage soft switching.

[0254] Figure 28 above shows an example in which the control device 50E executes the first and second operations when it has previously determined that the V-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, but it is not limited to this. For example, if the control device 50E has previously determined that the U-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, or if it has previously determined that the U-phase resonant current and the V-phase resonant current flow simultaneously through the resonant inductor L1, the control device 50E can also execute the first and second operations, thereby enabling zero-voltage soft switching.

[0255] The first and second operations of the control device 50E can be generalized as follows:

[0256] When the control device 50E performs the first operation, it shortens the high-level period of the control signal to the first switch, which has a smaller absolute value of the corresponding load current, by a shortening period Tred. When the control device 50E performs the second operation, it shifts the high-level period of the control signal to the first switch in the direction of delaying by a shift time. At this time, the control device 50E sets time ta as the start of the high-level period of the control signal to the second switch, and shifts the high-level period of the control signal to the first switch to start at time tc, which is a waiting period Tdef after time tb, when the current value of the resonant current (current iL1) passing through the second switch reaches an extreme value and then matches the current value of the load current flowing through the AC terminal 41 corresponding to the second switch. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch. If the length of the standby period Tdef is set to be the same as the length of the additional time Tad in the control signal to the first switch, the current value of the resonant current (current iL1) at time tc will be equal to the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch.

[0257] (3) Advantages In the power converter 100E according to Embodiment 6, when the control device 50E determines that a resonant current flows simultaneously through two of the multiple switches 8 to the resonant inductor L1 when the duty cycle command value of one of the three phase duty cycle command values ​​du, dv, and dw of the two-phase modulation method is fixed to a constant value, it performs a first operation and then a second operation. In the first operation, when one of the two switches 8 is designated as the first switch and the other as the second switch, the high-level period of the control signal to the first switch is shortened by a shortened period Tred from a period that includes the resonant half-period (Tres / 2) determined by the capacitance C of the resonant capacitor 9 corresponding to the first switch and the inductance L of the resonant inductor L1, and the additional time Tad determined by the voltage V15 of the regenerative capacitor 15, the inductance L of the resonant inductor L1, and the load current value. In the second operation, the high-level period of the control signal to the first switch is shifted so that the high-level period of the control signal to the first switch begins after a standby period Tdef from the point when the current value of the resonant current passing through the second switch reaches its extreme value and then matches the current value of the load current flowing through the AC terminal 41 corresponding to the second switch. This makes it possible for the power converter 100E to achieve soft switching more reliably.

[0258] (Embodiment 7) The power converter 100F according to Embodiment 7 will be described below with reference to Figure 29.

[0259] (1) Configuration of the power converter The power converter 100F according to Embodiment 7 differs from the power converter 100 according to Embodiment 1 (see Figure 1) in that it is equipped with a control device 50F instead of the control device 50, as shown in Figure 29. With respect to the power converter 100F according to Embodiment 7, the same reference numerals are used for components that are the same as those in the power converter 100 according to Embodiment 1, and their descriptions are omitted.

[0260] In this embodiment, the control device 50F generates a plurality of first PWM signals SU1, SV1, SW1 and a plurality of second PWM signals SU2, SV2, SW2 based on three-phase duty command values ​​du, dv, dw of a three-phase modulation scheme as shown in Figure 30.

[0261] The control device 50F, similar to the control device 50, generates a first PWM signal SU1 and a second PWM signal SU2 to be supplied to the first switching element 1U and the second switching element 2U, respectively, based on the carrier signal CA1 (see Figure 2) and the duty cycle command value du. The control device 50F also generates a first PWM signal SV1 and a second PWM signal SV2 to be supplied to the first switching element 1V and the second switching element 2V, respectively, based on the carrier signal CA1 and the duty cycle command value dv of the V phase. Furthermore, the control device 50F generates a first PWM signal SW1 and a second PWM signal SW2 to be supplied to the first switching element 1W and the second switching element 2W, respectively, based on the carrier signal CA1 and the duty cycle command value dw of the W phase.

[0262] The control device 50F compares the duty cycle command value du with the carrier signal CA1 and generates a first PWM signal SU1 that is high level when the duty cycle command value du is greater than the carrier signal CA1 and low level when the duty cycle command value du is less than or equal to the carrier signal CA1. The control device 50F also inverts the first PWM signal SU1 to generate a second PWM signal SU2. Furthermore, the control device 50F sets a dead time period Td (see Figures 3 and 7) between the high-level period of the first PWM signal SU1 and the high-level period of the second PWM signal SU2 so that the on-periods of the first switching element 1U and the on-periods of the second switching element 2U do not overlap.

[0263] The control device 50F compares the duty cycle command value dv with the carrier signal CA1 and generates a first PWM signal SV1 that is high level when the duty cycle command value dv is greater than the carrier signal CA1 and low level when the duty cycle command value dv is less than or equal to the carrier signal CA1. The control device 50F also inverts the first PWM signal SV1 to generate a second PWM signal SV2. Furthermore, the control device 50F sets a dead time period Td (see Figures 4 and 10) between the high-level period of the first PWM signal SV1 and the high-level period of the second PWM signal SV2 so that the on-period of the first switching element 1V and the on-period of the second switching element 2V do not overlap.

[0264] The control device 50F compares the duty cycle command value dw with the carrier signal CA1 and generates a first PWM signal SW1 that is high level when the duty cycle command value dw is greater than the carrier signal CA1 and low level when the duty cycle command value dw is less than or equal to the carrier signal CA1. The control device 50F also inverts the first PWM signal SW1 to generate a second PWM signal SW2. Furthermore, the control device 50F sets a dead time period Td (see Figures 5 and 10) between the high-level period of the first PWM signal SW1 and the high-level period of the second PWM signal SW2 so that the on-periods of the first switching element 1W and the on-periods of the second switching element 2W do not overlap.

[0265] (2.1) The basic operation of the basic operation control device 50F is the same as the basic operation of the control device 50 described in Embodiment 1, so the explanation is omitted.

[0266] (2.2) When the operation control device 50F determines that two-phase resonant currents are flowing simultaneously, for example, when the duty cycle command value of one of the three-phase duty cycle command values ​​du, dv, and dw of the three-phase modulation method is fixed to a constant value due to a change in the state of the AC load RA1 (hereinafter also referred to as overmodulation), the control device 50F can perform the first control operation, the second control operation, and the third control operation when it determines that resonant currents are flowing simultaneously through two of the multiple switches 8 in the resonant inductor L1. "When it determines that resonant currents are flowing simultaneously through two of the multiple switches 8" means when it is estimated in advance that resonant currents are flowing simultaneously through two of the two switches 8 in the resonant inductor L1.

[0267] (2.2.1) Determination of whether two-phase resonant currents flow simultaneously In the power converter 100F, during overmodulation, as shown in Figure 31, each waveform (modulated wave) of the three-phase duty command values ​​du, dv, and dw has a first linear section where it is constant at the maximum value and a second linear section where it is constant at the minimum value, and the two-phase duty command values ​​approach each other at electrical angles of 60° (see regions A31, A32, A33, A34, A35, and A36 in Figure 31), and the duty cycles of the two-phase control signals become the same or close to each other. Therefore, during overmodulation, each waveform (modulated wave) of the three-phase duty command values ​​du, dv, and dw becomes a waveform similar to each waveform (modulated wave) of the three-phase duty command values ​​du, dv, and dw in the upper and lower fixed two-phase modulation method (see Figure 26).

[0268] The boundary conditions for whether the two-phase (V-phase and W-phase) resonant currents overlap in region A32 can be determined in the same way as for region A11 in Embodiment 1 (see Figure 11). The diagram illustrating an example of the boundary conditions for the cases where the W-phase resonant current and the V-phase resonant current do not overlap (do not flow simultaneously) and overlap (flow simultaneously) is the same as Figure 10 explained in Embodiment 1, so the explanation is omitted. The boundary conditions for whether the two-phase (U-phase and W-phase) resonant currents overlap in region A34 can be determined in the same way as for region A12 in Embodiment 1 (see Figure 11). Similarly, the boundary conditions for whether the two-phase (U-phase and V-phase) resonant currents overlap in region A36 can be determined in the same way as for region A13 in Embodiment 1 (see Figure 11).

[0269] The boundary conditions for whether the two-phase (V-phase and W-phase) resonant currents overlap in region A35 can be determined in the same way as for region A23 in Embodiment 5 (see Figure 22). The diagram illustrating an example of the boundary conditions for the cases where the W-phase resonant current and the V-phase resonant current do not overlap (do not flow simultaneously) and overlap (flow simultaneously) is the same as Figure 23 explained in Embodiment 5, so the explanation is omitted. The boundary conditions for whether the two-phase (U-phase and W-phase) resonant currents overlap in region A31 can be determined in the same way as for region A21 in Embodiment 5 (see Figure 22). Similarly, the boundary conditions for whether the two-phase (U-phase and V-phase) resonant currents overlap in region A33 can be determined in the same way as for region A22 in Embodiment 5 (see Figure 22).

[0270] (2.2.2) When the first and second operation control device 50F determines that two-phase resonant currents are flowing simultaneously, for example, when it determines that the resonant currents passing through each of the two switches 8 are flowing simultaneously through the resonant inductor L1, it performs the first and second operations to shorten the period during which the resonant currents passing through each of the two switches 8 are flowing simultaneously through the resonant inductor L1.

[0271] (2.2.2.1) When the polarity of the current flowing through the resonant inductor L1 is negative, the control device 50F performs the first and second operations in such a way that the length of the dead time period Td between the high-level period of the first PWM signal supplied to the first switching element 1 of the two switching circuits 10 corresponding to the two switches 8 and the high-level period of the second PWM signal supplied to the second switching element 2 does not change. Furthermore, for example, in the second operation, when the control device 50F shifts the high-level period of the control signal SU7 supplied to the switch 8U, it shifts the high-level periods of the first PWM signal SU1 and the second PWM signal SU2, respectively, but does not change the duty cycles of the first PWM signal SU1 and the second PWM signal SU2 in one cycle of the carrier signal CA1. Furthermore, when the control device 50F shifts the high-level period of the control signal SV7 supplied to switch 8V, it shifts the high-level periods of the first PWM signal SV1 and the second PWM signal SV2, respectively, but does not change the duty cycles of the first PWM signal SV1 and the second PWM signal SV2 in one cycle of the carrier signal CA1. Furthermore, when the control device 50F shifts the high-level period of the control signal SW7 supplied to switch 8W, it shifts the high-level periods of the first PWM signal SW1 and the second PWM signal SW2, respectively, but does not change the duty cycles of the first PWM signal SW1 and the second PWM signal SW2 in one cycle of the carrier signal CA1.

[0272] The upper part of Figure 32 shows the timing chart when the control device 50F has determined in advance that the resonant currents of the V-phase and W-phase flow simultaneously during the period corresponding to region A32 in Figure 31. The lower part of Figure 32 shows the timing chart when the control device 50F has performed both the first and second operations (hereinafter also referred to as "after shift") during the period corresponding to region A32 in Figure 31. The way to read Figure 32 is the same as for Figure 27, so the explanation is omitted.

[0273] In the example shown in Figure 32, when the control device 50F performs the first operation, it compares the absolute value of the load current iV with the absolute value of the load current iW, and shortens the high-level period of the control signal SV7 to switch 8V, which has a smaller absolute value of load current among the two AC terminals 41V and 41W, by the shortening period Tred. In the example shown in Figure 32, the control device 50F sets the length of the shortening period Tred so that the length of the high-level period of the control signal SV7 is the length of the resonant half-period (= Tres / 2). Therefore, in the example shown in Figure 32, the length of the shortening period Tred is the same as the length of the additional time Tav.

[0274] Furthermore, when the control device 50F performs the second operation, it shifts the high-level period of the control signal SV7 in the direction of delaying by a shift time Tsv. At this time, the control device 50F takes time ta as the start of the high-level period of the control signal SW7 to switch 8W, and shifts the high-level period of the control signal SV7 to switch 8V, the high-level period of the first PWM signal SV1 to the first switching element 1V, and the high-level period of the second PWM signal SV2 to the second switching element 2V in the direction of delaying by a shift time Tsv, so that the high-level period of the control signal SV7 to switch 8V starts at time tc, which is a time Tdef after time tb, when the current value of the resonant current (current iL1) passing through switch 8W reaches an extreme value (minimum value in the example of Figure 32) and coincides with the current value of the load current iW flowing to the AC terminal 41V corresponding to switch 8W. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current iV flowing through the AC terminal 41V corresponding to switch 8V. The control device 50F determines the standby period Tdef by the calculation Tdef = L × |iW - iV| / V15. The control device 50F determines the shift time Tsv by the calculation Tsv = ΔT + Tdef. In the example in Figure 32, ΔT is the time difference between the start of the high-level period of the second PWM signal SW2 to the second switching element 2W corresponding to switch 8W and the end of the high-level period of the first PWM signal SV1 to the first switching element 1V corresponding to switch 8V. As a result, the current value of the resonant current (current iL1) at time tc when the standby period Tdef ends is equal to the absolute value of the load current iV. Therefore, in the power converter 100F, if the high-level period of the control signal SV7 to the switch 8V is the same as the resonant half-period (Tres / 2), even if it does not include the additional time Tav, zero-voltage soft switching of the second switching element 2V becomes possible.

[0275] As can be seen from the waveforms of current iL1 in the upper and lower parts of Figure 32, in the power converter 100F, if the control device 50F determines in advance that the resonant currents of the V-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the V-phase and the W-phase by performing the first and second operations. Similarly, in the power converter 100F, if the control device 50F determines in advance that the resonant currents of the U-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the W-phase by performing the first and second operations. Furthermore, in the power converter 100F, if the control device 50F determines in advance that the resonant currents of the U-phase and V-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the V-phase by performing the first and second operations.

[0276] In the power converter 100F, if the control device 50F does not perform the first and second operations, the voltages V2v and V2w across the second switching elements 2V and 2W do not decrease to zero at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends, respectively). As a result, in the power converter 100F, the switching of the second switching elements 2U and 2V becomes hard switching.

[0277] In contrast, when the control device 50F performs the first and second operations, as shown in the lower part of Figure 32, the voltages V2v and V2w across the second switching elements 2V and 2W respectively decrease to zero at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends). Therefore, in the power converter 100F, when the control device 50F performs the first and second operations, the switching of the second switching elements 2V and 2W becomes zero-voltage soft switching.

[0278] Figure 32 above shows an example in which the control device 50F executes the first and second operations when it has previously determined that the V-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, but it is not limited to this. For example, if the control device 50F has previously determined that the U-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, or if it has previously determined that the U-phase resonant current and the V-phase resonant current flow simultaneously through the resonant inductor L1, the control device 50F will execute the first and second operations, thereby enabling zero-voltage soft switching.

[0279] The first and second operations of the control device 50F can be generalized as follows.

[0280] When the control device 50F performs the first operation, it shortens the high-level period of the control signal to the first switch, which has a smaller absolute value of the corresponding load current, by a shortening period Tred. When the control device 50F performs the second operation, it shifts the high-level period of the control signal to the first switch in the direction of delaying by a shift time. At this time, the control device 50F sets time ta as the start of the high-level period of the control signal to the second switch, and shifts the high-level period of the control signal to the first switch to start at time tc, which is a waiting period Tdef after time tb, when the current value of the resonant current (current iL1) passing through the second switch reaches an extreme value and then matches the current value of the load current flowing through the AC terminal 41 corresponding to the second switch. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch. If the length of the standby period Tdef is set to be the same as the length of the additional time Tad in the control signal to the first switch, the current value of the resonant current (current iL1) at time tc will be equal to the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch.

[0281] (2.2.2.2) When the polarity of the current flowing through the resonant inductor L1 is positive, the control device 50F performs the first and second operations in such a way that the length of the dead time period Td between the high-level period of the first PWM signal supplied to the first switching element 1 of the two switching circuits 10 corresponding to the two switches 8 and the high-level period of the second PWM signal supplied to the second switching element 2 does not change. Furthermore, for example, in the second operation, when the control device 50F shifts the high-level period of the control signal SU6 supplied to the switch 8U, it shifts the high-level periods of the first PWM signal SU1 and the second PWM signal SU2, respectively, but does not change the duty cycles of the first PWM signal SU1 and the second PWM signal SU2 in one cycle of the carrier signal CA1. Furthermore, when the control device 50F shifts the high-level period of the control signal SV6 supplied to switch 8V, it shifts the high-level periods of the first PWM signal SV1 and the second PWM signal SV2, but does not change the duty cycles of the first PWM signal SV1 and the second PWM signal SV2 in one cycle of the carrier signal CA1. Furthermore, when the control device 50F shifts the high-level period of the control signal SW6 supplied to switch 8W, it shifts the high-level periods of the first PWM signal SW1 and the second PWM signal SW2, but does not change the duty cycles of the first PWM signal SW1 and the second PWM signal SW2 in one cycle of the carrier signal CA1.

[0282] The upper part of Figure 33 shows the timing chart when the control device 50F has determined in advance that the resonant currents of the V-phase and W-phase flow simultaneously during the period corresponding to region A35 in Figure 31. The lower part of Figure 33 shows the timing chart when the control device 50F has performed both the first and second operations (hereinafter also referred to as "after shift") during the period corresponding to region A35 in Figure 31. The way to read Figure 33 is the same as Figure 28, so the explanation will be omitted.

[0283] In the example shown in Figure 33, when the control device 50F performs the first operation, it compares the absolute value of the load current iV with the absolute value of the load current iW, and shortens the high-level period of the control signal SV6 to switch 8V, which has a smaller absolute value of load current among the two AC terminals 41V and 41W, by the shortening period Tred. In the example shown in Figure 33, the control device 50F sets the length of the shortening period Tred so that the length of the high-level period of the control signal SV6 is the length of the resonant half-period (= Tres / 2). Therefore, in the example shown in Figure 33, the length of the shortening period Tred is the same as the length of the additional time Tav.

[0284] Furthermore, when the control device 50F performs the second operation, it shifts the high-level period of the control signal SV6 in the direction of delaying by a shift time Tsv. At this time, the control device 50F takes time ta as the start of the high-level period of the control signal SW6 to switch 8W, and shifts the high-level period of the control signal SV6 to switch 8V, the high-level period of the first PWM signal SV1 to the first switching element 1V, and the high-level period of the second PWM signal SV2 to the second switching element 2V in the direction of delaying by a shift time Tsv, so that the high-level period of the control signal SV6 to switch 8V starts at time tc, which is a time Tdef after time tb, when the current value of the resonant current (current iL1) passing through switch 8W reaches an extreme value (maximum value in the example of Figure 33) and coincides with the current value of the load current iW flowing to the AC terminal 41V corresponding to switch 8W. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current iV flowing through the AC terminal 41V corresponding to switch 8V. The control device 50F determines the standby period Tdef by the calculation Tdef = L × |iW - iV| / V15. The control device 50F determines the shift time Tsv by the calculation Tsv = ΔT + Tdef. In the example in Figure 33, ΔT is the time difference between the start of the high-level period of the first PWM signal SW1 to the first switching element 1W corresponding to switch 8W and the end of the high-level period of the second PWM signal SV2 to the second switching element 2V corresponding to switch 8V. As a result, the current value of the resonant current (current iL1) at time tc when the standby period Tdef ends is equal to the absolute value of the load current iV. Therefore, in the power converter 100F, zero-voltage soft switching of the first switching element 1V is possible if the high-level period of the control signal SV6 to the switch 8V is the same as the resonant half-period (Tres / 2), even if it does not include the additional time Tav.

[0285] As can be seen from the waveforms of current iL1 in the upper and lower parts of Figure 33, in the power converter 100F, if the control device 50F determines in advance that the resonant currents of the V-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the V-phase and the W-phase by performing the first and second operations. Similarly, in the power converter 100F, if the control device 50F determines in advance that the resonant currents of the U-phase and W-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the W-phase by performing the first and second operations. Furthermore, in the power converter 100F, if the control device 50F determines in advance that the resonant currents of the U-phase and V-phase will flow simultaneously, it can shorten the overlap period between the resonant currents of the U-phase and the V-phase by performing the first and second operations.

[0286] In the power converter 100F, if the control device 50F does not perform the first and second operations, the voltages V1v and V1w across the first switching elements 1V and 1W do not decrease to zero at the point when the second PWM signals SV2 and SW2 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends, respectively). As a result, in the power converter 100F, the switching of the first switching elements 1U and 1V becomes hard switching.

[0287] In contrast, when the control device 50F performs the first and second operations, as shown in the lower part of Figure 33, at the point when the first PWM signals SV1 and SW1 change from a low-level period to a high-level period (the point at which the dead time period Td corresponding to the V-phase and W-phase ends), the voltages V2v and V2w across the second switching elements 2V and 2W increase to Vd, respectively, so that the voltages V1v and V1w across the first switching elements 1V and 1W decrease to zero. Therefore, in the power converter 100F, when the control device 50F performs the first and second operations, the switching of the first switching elements 1V and 1W becomes zero-voltage soft switching.

[0288] Figure 33 above shows an example in which the control device 50F executes the first and second operations when it has previously determined that the V-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, but it is not limited to this. For example, zero-voltage soft switching is possible when the control device 50F has previously determined that the U-phase resonant current and the W-phase resonant current flow simultaneously through the resonant inductor L1, or when it has previously determined that the U-phase resonant current and the V-phase resonant current flow simultaneously through the resonant inductor L1, by executing the first and second operations.

[0289] The first and second operations of the control device 50F can be generalized as follows.

[0290] When the control device 50F performs the first operation, it shortens the high-level period of the control signal to the first switch, which has a smaller absolute value of the corresponding load current, by a shortening period Tred. When the control device 50F performs the second operation, it shifts the high-level period of the control signal to the first switch in the direction of delaying by a shift time. At this time, the control device 50F sets time ta as the start of the high-level period of the control signal to the second switch, and shifts the high-level period of the control signal to the first switch to start at time tc, which is a waiting period Tdef after time tb, when the current value of the resonant current (current iL1) passing through the second switch reaches an extreme value and then matches the current value of the load current flowing through the AC terminal 41 corresponding to the second switch. The absolute value of the resonant current (current iL1) at time tb is greater than the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch. If the length of the standby period Tdef is set to be the same as the length of the additional time Tad in the control signal to the first switch, the current value of the resonant current (current iL1) at time tc will be equal to the absolute value of the load current flowing through the AC terminal 41 corresponding to the first switch.

[0291] (3) Advantages In the power converter 100F according to Embodiment 7, when the control device 50F determines that a resonant current flows simultaneously through two of the multiple switches 8 to the resonant inductor L1 when the duty cycle command value of one of the three phases of the three-phase modulation scheme, du, dv, and dw, is fixed to a constant value, it performs a first operation and then a second operation. In the first operation, when one of the two switches 8 is designated as the first switch and the other as the second switch, the high-level period of the control signal to the first switch is shortened by a shortened period Tred from a period that includes the resonant half-period (Tres / 2) determined by the capacitance C of the resonant capacitor 9 corresponding to the first switch and the inductance L of the resonant inductor L1, and the additional time Tad determined by the voltage V15 of the regenerative capacitor 15, the inductance L of the resonant inductor L1, and the load current value. In the second operation, the high-level period of the control signal to the first switch is shifted so that the high-level period of the control signal to the first switch begins after a standby period Tdef from the point when the current value of the resonant current passing through the second switch reaches its extreme value and then matches the current value of the load current flowing through the AC terminal 41 corresponding to the second switch. This makes it possible for the power converter 100F to achieve soft switching more reliably.

[0292] (Other Modifications) Embodiments 1 to 7 described above are merely one of many embodiments of this disclosure. Embodiments 1 to 7 described above can be modified in various ways depending on the design, etc., as long as the objectives of this disclosure are achieved.

[0293] In power converters 100, 100A to 100F, control devices 50, 50A to 50F shorten the high-level period of the control signal to the switch 8 corresponding to the switching circuit 10 of the phase where the duty cycle command value is fixed, in the case of three-phase duty cycle command values ​​du, dv, dw in the two-phase modulation method or three-phase duty cycle command values ​​du, dv, dw in the three-phase modulation method. This makes it possible to reduce losses in the switch 8 corresponding to the switching circuit 10 of the phase where the duty cycle command value is fixed. The shortened high-level period may be zero. Furthermore, shortening the high-level period of the control signal to the switch 8 corresponding to the switching circuit 10 of the phase where the duty cycle command value is fixed is not essential.

[0294] Furthermore, each of the control devices 50D to 50F may apply one of the control operations of control devices 50A to 50C as an operation when it determines that the resonant currents overlap.

[0295] In control devices 50, 50A to 50F, the operation of "determining that multiple resonant currents are flowing simultaneously" is not limited to the operation described in Embodiment 1, which determines that "multiple resonant currents are flowing simultaneously" when the time difference is less than a threshold.

[0296] For example, control devices 50, 50A to 50F may determine that a two-phase resonant current flows simultaneously when any one of the following is less than a current difference threshold: the current difference between the U-phase load current iU and the V-phase load current iV, the current difference between the V-phase load current iV and the W-phase load current iW, or the current difference between the W-phase load current iW and the U-phase load current iU.

[0297] Furthermore, control devices 50, 50A to 50F may determine that the three-phase resonant current flows simultaneously when the current difference between the U-phase load current iU and the V-phase load current iV, the current difference between the V-phase load current iV and the W-phase load current iW, and the current difference between the W-phase load current iW and the U-phase load current iU is all below a current difference threshold.

[0298] Furthermore, each of the multiple first switching elements 1 and the multiple second switching elements 2 is not limited to IGBTs, but may also be a MOSFET. In this case, each of the multiple first diodes 4 may be replaced with a parasitic diode of the MOSFET constituting the corresponding first switching element 1. Similarly, each of the multiple second diodes 5 may be replaced with a parasitic diode of the MOSFET constituting the corresponding second switching element 2. The MOSFETs are, for example, Si-based MOSFETs or SiC-based MOSFETs. Each of the multiple first switching elements 1 and the multiple second switching elements 2 may also be, for example, a bipolar transistor or a GaN-based GIT.

[0299] Furthermore, in power converters 100, 100A to 100F, if the capacitance of each of the multiple resonant capacitors 9 is relatively small, instead of externally mounting multiple resonant capacitors 9, the parasitic capacitance between the ends of the multiple second switching elements 2 may serve as the multiple resonant capacitors 9.

[0300] Furthermore, the length of the dead time period Td is not limited to being set to be the same as the resonant half-period; it may also be set to a length different from the resonant half-period.

[0301] The dead time period Td may be set by a dead time generation circuit, such as a gate driver IC (Integrated Circuit), which is provided separately from the control devices 50, 50A to 50F. Alternatively, the control device 50 may include a gate driver IC, and the dead time generation circuit of the gate driver IC may set the dead time period Td.

[0302] Furthermore, in the example of Embodiment 1, the control device 50 performs the calculation of shift time (for example, Tsu) = ΔT + Tdef, but the result is not limited to the result obtained by this calculation formula. Any other formula may be used as long as approximately soft switching can be achieved compared to before the shift, and there may be variations from the result obtained by the above calculation formula.

[0303] Regarding the method for determining the additional times Tau, Tav, and Taw described in the "(3.1) Basic Example" section of Embodiment 1, the calculation formula is an ideal design example and is not limited to always performing calculations using such a formula. In some cases, it is not a problem to set the additional times Tau, Tav, and Taw to 0 or another fixed time. Furthermore, if the purpose of the additional times Tau, Tav, and Taw can be achieved, values ​​obtained by calculations using other formulas are also acceptable. For example, in the basic example, the calculation Tau = iU × (L / V15) is performed, but it is not limited to this; Tau may be set to 0, set between 0 and iU × (L / V15), always set to a constant additional time, calculated using another formula, or a combination of these may be used.

[0304] In each of the multiple switches 8, the second main terminal (emitter terminal) of the third switching element 6 is connected to the second main terminal (emitter terminal) of the fourth switching element 7, the first main terminal (collector terminal) of the third switching element 6 is connected to the connection point 3 of the corresponding switching circuit 10 among the multiple switching circuits 10, and the first main terminal (collector terminal) of the fourth switching element 7 is connected to the common connection point 25. In this case, each of the multiple switches 8 further has a diode antiparallel connected to the third switching element 6 and a diode antiparallel connected to the fourth switching element 7.

[0305] Furthermore, each of the third switching element 6 and the fourth switching element 7 may be replaced with a MOSFET or a bipolar transistor.

[0306] In each of the multiple switches 8, the third switching element 6 and the fourth switching element 7 may be connected in antiparallel. Furthermore, each of the multiple switches 8 may further include a diode connected in antiparallel to the third switching element 6 and a diode connected in antiparallel to the fourth switching element 7.

[0307] Furthermore, in each of the multiple switches 8, the third switching element 6 and the fourth switching element 7 may be MOSFETs.

[0308] The operation of control devices 50A to 50F is, for example, the same as the operation of control device 50 in Embodiment 1, but is not limited to this. It may also be the same as the operation of control device 50 in any of the modified examples 1 and 2 of Embodiment 1, or these operations may be combined as appropriate.

[0309] Each of the multiple switches 8 may be a dual-gate type GaN-based GIT having a first source terminal, a first gate terminal, a second gate terminal, and a second source terminal. In this case, a control signal SU6 is applied between the first gate terminal and the first source terminal of the dual-gate type GaN-based GIT constituting switch 8U, and a control signal SU7 is applied between the second gate terminal and the second source terminal. Similarly, a control signal SV6 is applied between the first gate terminal and the first source terminal of the dual-gate type GaN-based GIT constituting switch 8V, and a control signal SV7 is applied between the second gate terminal and the second source terminal. Furthermore, a control signal SW6 is applied between the first gate terminal and the first source terminal of the dual-gate type GaN-based GIT constituting switch 8W, and a control signal SW7 is applied between the second gate terminal and the second source terminal.

[0310] Each of the power converters 100, 100A to 100F may further include a capacitor connected between the fourth end of the resonant inductor L1 and the first DC terminal 31. In this case, each of the power converters 100, 100A to 100F has a series circuit of the capacitor and the regenerative capacitor 15 connected between the first DC terminal 31 and the second DC terminal 32.

[0311] (Aspects) The following aspects are disclosed herein.

[0312] The power conversion device (100; 100D; 100E; 100F) according to the first embodiment includes a first DC terminal (31) and a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant capacitors (9), a resonant inductor (L1), a regenerative capacitor (15), and a control device (50; 50D; 50E; 50F). The power conversion circuit (11) has a plurality of first switching elements (1) and a plurality of second switching elements (2). In the power conversion circuit (11), a plurality of switching circuits (10), each of which a plurality of first switching elements (1) and a plurality of second switching elements (2) are connected in series in a one-to-one relationship, are connected in parallel with each other. In the power conversion circuit (11), multiple first switching elements (1) are connected to a first DC terminal (31), and multiple second switching elements (2) are connected to a second DC terminal (32). Multiple AC terminals (41) correspond one-to-one with multiple switching circuits (10). Each of the multiple AC terminals (41) is connected to the connection point (3) of the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10). Multiple switches (8) correspond one-to-one with multiple switching circuits (10). Each of the multiple switches (8) has its first end (81) connected to the connection point (3) of the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10), and its second end (82) is commonly connected to a common connection point (25). Resonant capacitors (9) correspond one-to-one with multiple switches (8). Each of the multiple resonant capacitors (9) is connected between the first terminal (81) and the second DC terminal (32) of the corresponding switch (8). The resonant inductor (L1) has a third terminal and a fourth terminal. In the resonant inductor (L1), the third terminal of the resonant inductor (L1) is connected to the common connection point (25). The regenerative capacitor (15) has a fifth terminal (153) and a sixth terminal (154). In the regenerative capacitor (15), the fifth terminal (153) is connected to the first DC terminal (31) or the second DC terminal (32).The control devices (50; 50D; 50E; 50F) generate a plurality of first PWM signals to control a plurality of first switching elements (1), a plurality of second PWM signals to control a plurality of second switching elements (2), and a plurality of control signals to control a plurality of switches (8). The control devices (50; 50D; 50E; 50F) generate a plurality of first PWM signals and a plurality of second PWM signals based on a three-phase duty cycle command value for a two-phase modulation scheme or a three-phase duty cycle command value for a three-phase modulation scheme. The control devices (50; 50D; 50E; 50F) set a dead time period (Td) between the high-level period of the first PWM signal to the first switching element (1) and the high-level period of the second PWM signal to the second switching element (2) for each of the plurality of switching circuits (10), and set the high-level period of the control signal to each of the plurality of switches (8) based on the dead time period (Td) for the corresponding switching circuit (10) among the plurality of switching circuits (10). A load current flows through each of the multiple AC terminals (41) through the first switching element (1) or second switching element (2) of the corresponding switching circuit (10). When the control device (50; 50D; 50E; 50F) determines that a resonant current flows simultaneously through two or more of the multiple switches (8) in the resonant inductor (L1) when the duty cycle command value of one phase of the three-phase duty cycle command values ​​of the two-phase modulation method is fixed to a constant value, or when the duty cycle command value of one phase of the three-phase duty cycle command values ​​of the three-phase modulation method is fixed to a constant value, the control device (50; 50D; 50E; 50F) determines that a resonant current flows simultaneously through two or more of the multiple switches (8) through each of the multiple switches (8), then, among the two or more switches (8), it sets one of the two switches (8) that correspond one-to-one to two AC terminals (41) whose load current polarity is the same at the multiple AC terminals (41) as the first switch, and the remaining one as the second switch, and then performs the first operation, and then performs the second operation.The first operation is to shorten the high-level period of the control signal to the first switch by a shortened period (Tred) from a period that includes the resonant half-period determined by the capacitance of the resonant capacitor (9) corresponding to the first switch among the multiple resonant capacitors (9) and the inductance of the resonant inductor (L1), and an additional time (Tad) determined by the voltage (V15) of the regenerative capacitor (15), the inductance of the resonant inductor (L1), and the load current value. The second operation is to shift the high-level period of the control signal to at least one of the first switch and the second switch so that the high-level period of the control signal to the first switch starts by a waiting period (Tdef) after the point in time when the current value of the resonant current passing through the second switch matches the current value of the load current flowing through the AC terminal (41) corresponding to the second switch among the two or more AC terminals (41) mentioned above.

[0313] This embodiment makes it possible to perform soft switching more reliably.

[0314] The power conversion device (100A; 100D; 100E; 100F) according to the second embodiment comprises a first DC terminal (31) and a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant capacitors (9), a resonant inductor (L1), a regenerative capacitor (15), and a control device (50A; 50D; 50E; 50F). The power conversion circuit (11) has a plurality of first switching elements (1) and a plurality of second switching elements (2). In the power conversion circuit (11), a plurality of switching circuits (10), each of which a plurality of first switching elements (1) and a plurality of second switching elements (2) are connected in series one-to-one, are connected in parallel to each other. In the power conversion circuit (11), multiple first switching elements (1) are connected to a first DC terminal (31), and multiple second switching elements (2) are connected to a second DC terminal (32). Multiple AC terminals (41) correspond one-to-one with multiple switching circuits (10). Each of the multiple AC terminals (41) is connected to the connection point (3) of the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10). Multiple switches (8) correspond one-to-one with multiple switching circuits (10). Each of the multiple switches (8) has its first end (81) connected to the connection point (3) of the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10), and its second end (82) is commonly connected to a common connection point (25). Resonant capacitors (9) correspond one-to-one with multiple switches (8). Each of the multiple resonant capacitors (9) is connected between the first terminal (81) and the second DC terminal (32) of the corresponding switch (8). The resonant inductor (L1) has a third terminal and a fourth terminal. In the resonant inductor (L1), the third terminal of the resonant inductor (L1) is connected to the common connection point (25). The regenerative capacitor (15) has a fifth terminal (153) and a sixth terminal (154). In the regenerative capacitor (15), the fifth terminal (153) is connected to the first DC terminal (31) or the second DC terminal (32).The control devices (50A; 50D; 50E; 50F) generate a plurality of first PWM signals to control a plurality of first switching elements (1), a plurality of second PWM signals to control a plurality of second switching elements (2), and a plurality of control signals to control a plurality of switches (8). The control devices (50A; 50D; 50E; 50F) generate a plurality of first PWM signals and a plurality of second PWM signals based on a three-phase duty cycle command value for a two-phase modulation scheme or a three-phase duty cycle command value for a three-phase modulation scheme. When the control device (50A; 50D; 50E; 50F) determines that a resonant current flows simultaneously through two or more switches (8) to the resonant inductor (L1) when the duty cycle command value of one of the three phases of duty cycle command values ​​in a two-phase modulation system is fixed to a constant value, or when the duty cycle command value of one of the three phases of duty cycle command values ​​in a three-phase modulation system is fixed to a constant value, the control device performs shift control to shift the high-level period of the control signal to at least one of the two or more switches (8) so that the resonant currents flowing through two or more switches (8) to the resonant inductor (L1) do not flow simultaneously through the resonant inductor (L1).

[0315] This embodiment makes it possible to perform soft switching more reliably.

[0316] The power conversion device (100B; 100D; 100E; 100F) according to the third embodiment comprises a first DC terminal (31) and a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant capacitors (9), a resonant inductor (L1), a regenerative capacitor (15), and a control device (50B; 50D; 50E; 50F). The power conversion circuit (11) has a plurality of first switching elements (1) and a plurality of second switching elements (2). In the power conversion circuit (11), a plurality of switching circuits (10), each of which a plurality of first switching elements (1) and a plurality of second switching elements (2) are connected in series one-to-one, are connected in parallel to each other. In the power conversion circuit (11), multiple first switching elements (1) are connected to a first DC terminal (31), and multiple second switching elements (2) are connected to a second DC terminal (32). Multiple AC terminals (41) correspond one-to-one with multiple switching circuits (10). Each of the multiple AC terminals (41) is connected to the connection point (3) of the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10). Multiple switches (8) correspond one-to-one with multiple switching circuits (10). Each of the multiple switches (8) has its first end (81) connected to the connection point (3) of the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10), and its second end (82) is commonly connected to a common connection point (25). Resonant capacitors (9) correspond one-to-one with multiple switches (8). Each of the multiple resonant capacitors (9) is connected between the first terminal (81) and the second DC terminal (32) of the corresponding switch (8). The resonant inductor (L1) has a third terminal and a fourth terminal. In the resonant inductor (L1), the third terminal of the resonant inductor (L1) is connected to the common connection point (25). The regenerative capacitor (15) has a fifth terminal (153) and a sixth terminal (154). In the regenerative capacitor (15), the fifth terminal (153) is connected to the first DC terminal (31) or the second DC terminal (32).The control devices (50B; 50D; 50E; 50F) generate a plurality of first PWM signals to control a plurality of first switching elements (1), a plurality of second PWM signals to control a plurality of second switching elements (2), and a plurality of control signals to control a plurality of switches (8). The control devices (50B; 50D; 50E; 50F) generate a plurality of first PWM signals and a plurality of second PWM signals based on a three-phase duty cycle command value for a two-phase modulation scheme or a three-phase duty cycle command value for a three-phase modulation scheme. The control devices (50B; 50D; 50E; 50F) can perform a first control operation and a second control operation when they determine that a resonant current flows simultaneously through two or more switches (8) of the plurality of switches (8) when the duty cycle command value of one of the three phases of duty cycle command values ​​in a two-phase modulation scheme is fixed to a constant value, or when the duty cycle command value of one of the three phases of duty cycle command values ​​in a three-phase modulation scheme is fixed to a constant value. The first control operation overlaps the high-level period of the control signal to each of the two or more switches (8) with the dead time period (Td) corresponding to each of the two or more switching circuits (10) connected to two or more switches (8) of the plurality of switching circuits (10) for a predetermined period. The second control operation determines the start time of the high-level period of the control signal to at least one of the plurality of switches (8) according to the load current of at least one phase flowing through the AC load (RA1) connected to the plurality of AC terminals (41).

[0317] This embodiment makes it possible to perform soft switching more reliably.

[0318] The power conversion device (100C; 100D; 100E; 100F) according to the fourth embodiment comprises a first DC terminal (31) and a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant capacitors (9), a resonant inductor (L1), a regenerative capacitor (15), and a control device (50C; 50D; 50E; 50F). The power conversion circuit (11) has a plurality of first switching elements (1) and a plurality of second switching elements (2). In the power conversion circuit (11), a plurality of switching circuits (10), each of which a plurality of first switching elements (1) and a plurality of second switching elements (2) are connected in series in a one-to-one relationship, are connected in parallel to each other. In the power conversion circuit (11), multiple first switching elements (1) are connected to a first DC terminal (31), and multiple second switching elements (2) are connected to a second DC terminal (32). Multiple AC terminals (41) correspond one-to-one with multiple switching circuits (10). Each of the multiple AC terminals (41) is connected to the connection point (3) of the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10). Multiple switches (8) correspond one-to-one with multiple switching circuits (10). Each of the multiple switches (8) has its first end (81) connected to the connection point (3) of the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10), and its second end (82) is commonly connected to a common connection point (25). Resonant capacitors (9) correspond one-to-one with multiple switches (8). Each of the multiple resonant capacitors (9) is connected between the first terminal (81) and the second DC terminal (32) of the corresponding switch (8). The resonant inductor (L1) has a third terminal and a fourth terminal. In the resonant inductor (L1), the third terminal of the resonant inductor (L1) is connected to the common connection point (25). The regenerative capacitor (15) has a fifth terminal (153) and a sixth terminal (154). In the regenerative capacitor (15), the fifth terminal (153) is connected to the first DC terminal (31) or the second DC terminal (32).The control devices (50C; 50D; 50E; 50F) generate a plurality of first PWM signals to control a plurality of first switching elements (1), a plurality of second PWM signals to control a plurality of second switching elements (2), and a plurality of control signals to control a plurality of switches (8). The control devices (50C; 50D; 50E; 50F) generate a plurality of first PWM signals and a plurality of second PWM signals based on a three-phase duty cycle command value for a two-phase modulation scheme or a three-phase duty cycle command value for a three-phase modulation scheme. The control devices (50C; 50D; 50E; 50F) set a dead time period (Td) between the high-level period of the first PWM signal to the first switching element (1) and the high-level period of the second PWM signal to the second switching element (2) for each of the multiple switching circuits (10), and set the high-level period of the control signal to each of the multiple switches (8) based on the dead time period (Td) for the corresponding switching circuit (10) among the multiple switching circuits (10). A load current flows through each of the multiple AC terminals (41) through the first switching element (1) or the second switching element (2) of the corresponding switching circuit (10). The control devices (50C; 50D; 50E; 50F) perform shortening control when, in the case of a two-phase modulation scheme, the duty cycle command value of one phase of the three-phase modulation scheme is fixed to a constant value, or in the case of a three-phase modulation scheme, the duty cycle command value of one phase of the three-phase modulation scheme is fixed to a constant value, and a control signal with a preset high-level period is applied to each of the multiple switches (8). If the control devices determine that a resonant current flows simultaneously through two or more of the multiple switches (8) to the resonant inductor (L1), then shortening control is performed. In shortening control, the control devices (50C; 50D; 50E; 50F) apply a control signal with a preset high-level period shortened to the first switch, which is one of the two or more switches (8), and apply a control signal with a preset high-level period to the second switch, which is different from the first switch.

[0319] This embodiment makes it possible to perform soft switching more reliably. Furthermore, this embodiment makes it possible to perform zero-voltage soft switching and reduce switching losses.

[0320] The power converter (100; 100A; 100B; 100C; 100D; 100E; 100F) according to the fifth embodiment is based on any one of the first to fourth embodiments. The control device (50; 50A; 50B; 50C; 50D; 50E; 50F) shortens the high-level period of the control signal to the switch (8) among the plurality of switches (8) that corresponds to the switching circuit (10) of the phase in which the duty cycle command value is fixed in the three-phase duty cycle command value (du, dv, dw) of the two-phase modulation method or the three-phase duty cycle command value (du, dv, dw) of the three-phase modulation method.

[0321] According to this embodiment, it is possible to reduce losses in the switch (8) corresponding to the switching circuit (10) of the phase in which the duty cycle command value is fixed.

[0322] 1 First switching element 2 Second switching element 3 Connection point 8 Switch 9 Resonant capacitor 10 Switching circuit 11 Power conversion circuit 15 Regenerative capacitor 153 Fifth terminal 154 Sixth terminal 31 First DC terminal 32 Second DC terminal 41 AC terminals 50, 50A, 50B, 50C, 50D, 50E, 50F Control device 100, 100A, 100B, 100C, 100D, 100E, 100F Power converter iU, iv, iW Output current (load current) L1 Resonant inductor RA1 AC load SU1, SV1, SW1 First PWM signal SU2, SV2, SW2 Second PWM signal SU6, SU7, SV6, SV7, SW6, SW7 Control signal Tad Additional time Tred, Reduced period Tdef, Standby period Tres, Resonance period Tr2, Resonance half-period V15, Voltage

Claims

1. A power conversion circuit having a first DC terminal and a second DC terminal, a plurality of first switching elements and a plurality of second switching elements, wherein a plurality of switching circuits are connected in parallel to each other, with the plurality of first switching elements and the plurality of second switching elements connected in one-to-one series, the plurality of first switching elements connected to the first DC terminal and the plurality of second switching elements connected to the second DC terminal, a plurality of AC terminals corresponding one-to-one to the plurality of switching circuits, each connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit, a plurality of switches corresponding one-to-one to the plurality of switching circuits, each having its first end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit and its second end commonly connected to a common connection point, a plurality of resonant capacitors corresponding one-to-one to the plurality of switches, each connected between the first end and the second DC terminal of the corresponding switch, and a resonant inductor having a third end and a fourth end, the third end of which is connected to the common connection point, A regenerative capacitor having a fifth and a sixth terminal, the fifth terminal of which is connected to the first DC terminal or the second DC terminal; a control device that generates a plurality of first PWM signals for controlling the plurality of first switching elements, a plurality of second PWM signals for controlling the plurality of second switching elements, and a plurality of control signals for controlling the plurality of switches, wherein the control device generates the plurality of first PWM signals and the plurality of second PWM signals based on a three-phase duty cycle command value of a two-phase modulation scheme or a three-phase duty cycle command value of a three-phase modulation scheme; sets a dead time period between the high-level period of the first PWM signal to the first switching element and the high-level period of the second PWM signal to the second switching element for each of the plurality of switching circuits; sets the high-level period of the control signal to each of the plurality of switches based on the dead time period for the corresponding switching circuit among the plurality of switching circuits;A load current flows through each of the plurality of AC terminals through the first switching element or the second switching element of the corresponding switching circuit, and the control device determines that a resonant current flows simultaneously through two or more of the plurality of switches when the duty cycle command value of one phase of the three-phase duty cycle command value of the two-phase modulation method is fixed to a constant value, or when the duty cycle command value of one phase of the three-phase duty cycle command value of the three-phase modulation method is fixed to a constant value, and the control device determines that a resonant current flows simultaneously through two or more of the plurality of switches, then, when one of the two or more switches corresponds one-to-one with two AC terminals in the plurality of AC terminals whose load current polarity is the same, is designated as the first switch, and the remaining one as the second switch, the control device performs a first operation to shorten the high-level period of the control signal to the first switch by a shortened period from a period including the resonant half-period determined by the capacitance of the resonant capacitor corresponding to the first switch among the plurality of resonant capacitors and the inductance of the resonant inductor, and an additional time determined by the voltage of the regenerative capacitor, the inductance of the resonant inductor and the load current value. Furthermore, a power converter that performs a second operation to shift the high-level period of the control signal to at least one of the first switch and the second switch, such that the high-level period of the control signal to the first switch begins a delay of a certain waiting period from the point in time when the current value of the resonant current passing through the second switch reaches an extreme value and then matches the current value of the load current flowing through the AC terminal corresponding to the second switch among the two or more AC terminals.

2. A power conversion circuit having a first DC terminal and a second DC terminal, a plurality of first switching elements and a plurality of second switching elements, wherein a plurality of switching circuits are connected in parallel to each other, with the plurality of first switching elements and the plurality of second switching elements connected in one-to-one series, the plurality of first switching elements connected to the first DC terminal and the plurality of second switching elements connected to the second DC terminal, a plurality of AC terminals corresponding one-to-one to the plurality of switching circuits, each connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit, a plurality of switches corresponding one-to-one to the plurality of switching circuits, each having its first end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit and its second end commonly connected to a common connection point, a plurality of resonant capacitors corresponding one-to-one to the plurality of switches, each connected between the first end and the second DC terminal of the corresponding switch, and a resonant inductor having a third end and a fourth end, the third end of which is connected to the common connection point, The regenerative capacitor has a fifth and a sixth terminal, the fifth terminal of which is connected to the first DC terminal or the second DC terminal; and a control device that generates a plurality of first PWM signals for controlling the plurality of first switching elements, a plurality of second PWM signals for controlling the plurality of second switching elements, and a plurality of control signals for controlling the plurality of switches, wherein the control device generates the plurality of first PWM signals and the plurality of second PWM signals based on a three-phase duty cycle command value of a two-phase modulation scheme or a three-phase duty cycle command value of a three-phase modulation scheme.A power converter that, when it is determined that a resonant current flows simultaneously through two or more of the switches in the resonant inductor when the duty cycle command value of one of the three phases of the two-phase modulation scheme is fixed to a constant value, or when the duty cycle command value of one of the three phases of the three-phase modulation scheme is fixed to a constant value, performs shift control to shift the high-level period of the control signal to at least one of the two or more switches so that the resonant currents flowing through two or more of the switches in the resonant inductor do not flow simultaneously.

3. A power conversion circuit having a first DC terminal and a second DC terminal, a plurality of first switching elements and a plurality of second switching elements, wherein a plurality of switching circuits are connected in parallel to each other, with the plurality of first switching elements and the plurality of second switching elements connected in one-to-one series, the plurality of first switching elements being connected to the first DC terminal and the plurality of second switching elements being connected to the second DC terminal, a plurality of AC terminals corresponding one-to-one to the plurality of switching circuits, each connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit, a plurality of switches corresponding one-to-one to the plurality of switching circuits, each having its first end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit and its second end commonly connected to a common connection point, a plurality of resonant capacitors corresponding one-to-one to the plurality of switches, each connected between the first end and the second DC terminal of the corresponding switch, and a resonant inductor having a third end and a fourth end, the third end being connected to the common connection point, The regenerative capacitor has a fifth and a sixth terminal, the fifth terminal of which is connected to the first DC terminal or the second DC terminal, and the control device generates a plurality of first PWM signals for controlling the plurality of first switching elements, a plurality of second PWM signals for controlling the plurality of second switching elements, and a plurality of control signals for controlling the plurality of switches, wherein the control device generates the plurality of first PWM signals and the plurality of second PWM signals based on a three-phase duty cycle command value of a two-phase modulation scheme or a three-phase duty cycle command value of a three-phase modulation scheme, and determines that a resonant current flows simultaneously through two or more of the plurality of switches through the resonant inductor when the duty cycle command value of one phase of the three-phase duty cycle command value of the two-phase modulation scheme is fixed to a constant value or when the duty cycle command value of one phase of the three-phase duty cycle command value of the three-phase modulation scheme is fixed to a constant value,A power converter capable of performing a first control operation that overlaps the high-level period of the control signal to each of the two or more switches with the dead time period corresponding to each of the two or more switching circuits connected to the two or more switches among the plurality of switching circuits for a predetermined period of time, and a second control operation that determines the start time of the high-level period of the control signal to at least one of the plurality of switches according to the load current of at least one phase flowing through the AC load connected to the plurality of AC terminals.

4. A power conversion circuit having a first DC terminal and a second DC terminal, a plurality of first switching elements and a plurality of second switching elements, wherein a plurality of switching circuits are connected in parallel to each other, with the plurality of first switching elements and the plurality of second switching elements connected in one-to-one series, the plurality of first switching elements connected to the first DC terminal and the plurality of second switching elements connected to the second DC terminal, a plurality of AC terminals corresponding one-to-one to the plurality of switching circuits, each connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit, a plurality of switches corresponding one-to-one to the plurality of switching circuits, each having its first end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit and its second end commonly connected to a common connection point, a plurality of resonant capacitors corresponding one-to-one to the plurality of switches, each connected between the first end and the second DC terminal of the corresponding switch, and a resonant inductor having a third end and a fourth end, the third end connected to the common connection point, A regenerative capacitor having a fifth and a sixth terminal, the fifth terminal of which is connected to the first DC terminal or the second DC terminal; a control device that generates a plurality of first PWM signals for controlling the plurality of first switching elements, a plurality of second PWM signals for controlling the plurality of second switching elements, and a plurality of control signals for controlling the plurality of switches, wherein the control device generates the plurality of first PWM signals and the plurality of second PWM signals based on a three-phase duty cycle command value of a two-phase modulation scheme or a three-phase duty cycle command value of a three-phase modulation scheme; the control device sets a dead time period between the high-level period of the first PWM signal to the first switching element and the high-level period of the second PWM signal to the second switching element for each of the plurality of switching circuits, and sets the high-level period of the control signal to each of the plurality of switches based on the dead time period for the corresponding switching circuit among the plurality of switching circuits.A load current flows through each of the plurality of AC terminals through the first switching element or the second switching element of the corresponding switching circuit. The control device performs a shortening control when it determines that a resonant current flows simultaneously through two or more of the switches when a control signal for a preset high-level period is given to each of the plurality of switches, either when the duty cycle command value of one of the three phases of the two-phase modulation scheme is fixed to a constant value or when the duty cycle command value of one of the three phases of the three-phase modulation scheme is fixed to a constant value, and a resonant current flows through two or more of the switches simultaneously through each of the plurality of switches. In the shortening control, a control signal with a shortened preset high-level period is given to a first switch, which is one of the two or more switches, and a control signal with a preset high-level period is given to a second switch, which is different from the first switch among the two or more switches.

5. The power conversion device according to any one of claims 1 to 4, wherein the control device shortens the high-level period of the control signal for a switch among the plurality of switches that corresponds to a switching circuit of a phase in which the duty command value is fixed in the three-phase duty command value of the two-phase modulation method or the three-phase duty command value of the three-phase modulation method.

Images