Power conversion method

Abstract

To provide a power conversion device in which switching loss is reduced, and a power conversion method.SOLUTION: A power conversion device comprises: a main circuit; an auxiliary circuit disposed between the main circuit and a power supply; and an inductor disposed between the main circuit and the auxiliary circuit. The main circuit comprises: a main-circuit high-side switch and a main-circuit low-side switch connected in series; a first capacitor; and a second capacitor. The auxiliary circuit comprises one or more diodes, and one or more switches. The inductor has one end connected to a connection point between the main-circuit high-side switch and the low-side switch, and the other end connected to the auxiliary circuit. The power conversion device flows current to the inductor by alternately turning on an auxiliary-circuit low-side switch disposed on a lower-side circuit of the auxiliary circuit and a high-side diode disposed on an upper-side circuit of the auxiliary circuit before turning on the main-circuit low-side switch, to adjust a change amount of an output current, and charges the first capacitor and the second capacitor.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for converting direct current power into alternating current power. ru

Background Art

[0002] FIG. 17 shows an output circuit diagram of one phase of a three-phase inverter of a conventionally known power conversion device. The power conversion device 100 is composed of a half-bridge circuit including a switching element arranged on the high side (upstream side, upper side) with respect to the load and a switching element arranged on the low side (downstream side, lower side) with respect to the load, and supplies power obtained by converting a direct current voltage into an alternating current voltage by driving these switching elements with their on / off timings shifted.

[0003] Switching losses occur in the switching element at the time of turn-on and turn-off when the switching state is switched. The switching loss increases as the operating frequency increases, and also increases as the power supply voltage and output current increase. In recent years, the demand for power conversion devices that supply high voltage and high current has been increasing, and various attempts have been made to reduce the switching loss for the purpose of improving the efficiency of the power conversion device.

[0004] Patent Document 1 discloses a power conversion device that suppresses the ringing of current while suppressing an increase in loss. The power conversion device of Patent Document 1 is a power conversion device including a high-side switch and a low-side switch composed of a wide-bandgap semiconductor, and includes a diode element reversely connected in parallel only to one of the switches, and a power conversion device in which a body diode is formed in the other switch. The diode element is composed of a narrow-bandgap semiconductor and has a characteristic that the frequency of current ringing generated when a recovery current flows through itself is lower than the frequency of current ringing generated when a recovery current flows through the body diode.

[0005] ​Patent Document 2 discloses a power conversion device equipped with a bridge circuit and a converter circuit between the AC end and the DC end. The control device of the power conversion device in Patent Document 2 defines a predetermined period within the AC voltage cycle as a stop period during which switching is stopped, in synchronization with the AC voltage cycle, thereby suppressing switching losses by reducing the number of switching cycles. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-54061 [Patent Document 2] Japanese Patent Publication No. 2013-255413 [Overview of the project] [Problems that the invention aims to solve]

[0007] One method to reduce switching losses in DC-DC converters and inverters, which are power conversion devices that supply high voltage and high current, is zero-volt switching, in which the switch-on and turn-off are performed when the voltage between the switching elements is zero volts. The present invention is for performing zero-volt switching. Electricity This invention was made with the goal of providing a method for converting force. [Means for solving the problem]

[0008] Power conversion device used in the power conversion method of the present inventionThe present invention relates to a power converter comprising a main circuit, an auxiliary circuit disposed between the main circuit and a power supply, and an inductor disposed between the main circuit and the auxiliary circuit. The power converter according to claim 1 comprises a main circuit high-side switch and a main circuit low-side switch connected in series, a first capacitor connected in parallel with the main circuit high-side switch, and a second capacitor connected in parallel with the main circuit low-side switch. The auxiliary circuit comprises one or more diodes and one or more switches. One end of the inductor is connected to the connection point between the main circuit high-side switch and the main circuit low-side switch, and the other end is connected to the auxiliary circuit.

[0009] electric The auxiliary circuit of the power converter preferably includes a high-side diode and a low-side diode connected in series, an auxiliary circuit high-side switch corresponding to the high-side diode, and an auxiliary circuit low-side switch corresponding to the low-side diode.

[0010] electric The auxiliary circuit of the power converter can consist of an auxiliary high-side switch located in the upper circuit and a low-side diode located in the lower circuit.

[0011] electric The auxiliary circuit of the power converter can consist of a high-side diode located in the upper circuit and an auxiliary low-side switch located in the lower circuit.

[0012] The present invention provides a power conversion method. The power conversion method of the present invention is a power conversion method for a power conversion device comprising a main circuit, an auxiliary circuit disposed between the main circuit and a power supply, and an inductor disposed between the main circuit and the auxiliary circuit. The main circuit of the power conversion device comprises a main circuit high-side switch and a main circuit low-side switch connected in series, a first capacitor connected in parallel with the main circuit high-side switch, and a second capacitor connected in parallel with the main circuit low-side switch. The auxiliary circuit comprises one or more diodes and one or more switches. The power conversion method of the present invention is characterized by adjusting the amount of change in output current by alternately turning on the auxiliary circuit high-side switch located in the upper circuit of the auxiliary circuit and the auxiliary circuit low-side switch located in the lower circuit of the auxiliary circuit before turning on the main circuit high-side switch, adjusting the period during which the auxiliary circuit high-side switch is turned on and the period during which the auxiliary circuit low-side switch is turned on until the first capacitor and the second capacitor are charged, and turning on the main circuit high-side switch after the voltage across the main circuit high-side switch becomes approximately 0V.

[0013] The present invention also provides an alternative power conversion method for turning on the main circuit high-side switch. The power conversion method of the present invention is a power conversion method for a power converter comprising a main circuit, an auxiliary circuit disposed between the main circuit and a power supply, and an inductor disposed between the main circuit and the auxiliary circuit. The main circuit of the power converter comprises a main circuit high-side switch and a main circuit low-side switch connected in series, a first capacitor connected in parallel with the main circuit high-side switch, and a second capacitor connected in parallel with the main circuit low-side switch, while the auxiliary circuit comprises one or more diodes and one or more switches. The alternative power conversion method of the present invention is characterized by adjusting the amount of change in output current by alternately turning on the auxiliary circuit high-side switch located in the upper circuit of the auxiliary circuit and the low-side diode located in the lower circuit of the auxiliary circuit before turning on the main circuit high-side switch, adjusting the period for turning on the auxiliary circuit high-side switch and the period for turning on the low-side diode until the first capacitor and the second capacitor are charged, and turning on the main circuit high-side switch after the voltage across the main circuit high-side switch becomes approximately 0V.

[0014] The present invention provides a further power conversion method. The power conversion method of the present invention is a power conversion method for a power conversion device comprising a main circuit, an auxiliary circuit disposed between the main circuit and a power source, and an inductor disposed between the main circuit and the auxiliary circuit. The main circuit of the power conversion device comprises a main circuit high-side switch and a main circuit low-side switch connected in series, a first capacitor connected in parallel with the main circuit high-side switch, and a second capacitor connected in parallel with the main circuit low-side switch. The auxiliary circuit comprises one or more diodes and one or more switches. The power conversion device of the present invention is characterized by adjusting the amount of change in output current by alternately turning on the auxiliary circuit low-side switch located in the lower circuit of the auxiliary circuit and the auxiliary circuit high-side switch located in the upper circuit of the auxiliary circuit before turning on the main circuit low-side switch, adjusting the period for turning on the auxiliary circuit low-side switch and the period for turning on the auxiliary circuit high-side switch until the first capacitor and the second capacitor are charged, and turning on the main circuit low-side switch after the voltage across the main circuit low-side switch becomes approximately 0V.

[0015] The present invention also provides an alternative power conversion method for turning on the main circuit low-side switch. The power conversion method of the present invention is a power conversion method for a power converter comprising a main circuit, an auxiliary circuit disposed between the main circuit and a power supply, and an inductor disposed between the main circuit and the auxiliary circuit. The main circuit of the power converter comprises a main circuit high-side switch and a main circuit low-side switch connected in series, a first capacitor connected in parallel with the main circuit high-side switch, and a second capacitor connected in parallel with the main circuit low-side switch, while the auxiliary circuit comprises one or more diodes and one or more switches. The power converter of the present invention is characterized by adjusting the amount of change in output current by alternately turning on the auxiliary circuit low-side switch located in the lower circuit of the auxiliary circuit and the high-side diode located in the upper circuit of the auxiliary circuit before turning on the main circuit low-side switch, adjusting the period for turning on the auxiliary circuit low-side switch and the period for turning on the high-side diode until the first and second capacitors are charged, and turning on the main circuit low-side switch after the voltage across the main circuit low-side switch becomes approximately 0V.

[0016] The power conversion method of the present invention can be applied to either or both cases: when current is passed from the power source to the main circuit, or when current is passed from the main circuit to the power source.

[0017] The power conversion method of the present invention can generate the turn-on timing of the main circuit high-side switch and the main circuit low-side switch by using the midpoint voltage between the main circuit high-side switch and the main circuit low-side switch, and the midpoint voltage of the auxiliary circuit high-side switch and the auxiliary circuit low-side switch as triggers. [Effects of the Invention]

[0018] Used in the power conversion method of the present inventionThe power conversion device includes an auxiliary circuit capable of reducing the switching loss of the main circuit. By achieving zero-voltage switching of the main circuit with the auxiliary circuit, it is possible to provide a power conversion device and a power conversion method that can operate with higher efficiency than conventional ones despite adding an auxiliary circuit.

[0019] Used in the power conversion method of the present invention The power conversion device includes an auxiliary circuit capable of reducing the switching loss of the main circuit. The auxiliary circuit has a short energization time and can be made smaller in size compared to the main circuit. Therefore, by achieving zero-voltage switching of the main circuit with the auxiliary circuit, it is possible to provide a power conversion device and a power conversion method that are less expensive than conventional ones despite adding an auxiliary circuit.

Brief Description of Drawings

[0020] [Figure 1] FIG. 1 is a circuit diagram showing an outline of the basic circuit configuration of a power conversion device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the control contents of the current and voltage of each part of the power conversion device in a time series when supplying power from a power source to a load. [Figure 3] FIG. 3 is a diagram showing the control contents of the current and voltage of each part in a time series during the period of switching from the on state of the main circuit low-side switch to the on state of the main circuit high-side switch of the power conversion device. [Figure 4] FIG. 4 is a diagram showing the control contents of the current and voltage of each part in a time series during the period of switching from the on state of the main circuit high-side switch to the on state of the main circuit low-side switch of the power conversion device. [Figure 5] FIG. 5 is a diagram showing the path of the current passing through the power conversion device with arrows. [Figure 6] FIG. 6 is a diagram showing the path of the current passing through the power conversion device with arrows. [Figure 7] FIG. 7 is a diagram showing the path of the current passing through the power conversion device with arrows. <L [Figure 8]Figure 8 is a circuit diagram of a first alternative example of a power converter. [Figure 9] Figure 9 is a diagram showing the current and voltage control of each part of a power converter in chronological order when power is supplied to the main circuit from an external source. [Figure 10] Figure 10 is a diagram showing the time-series current and voltage control of each part during the period when the main circuit high-side switch of the power converter is switched from the ON state to the ON state of the main circuit low-side switch. [Figure 11] Figure 11 is a time-series diagram showing the current and voltage control of each part during the period when the main circuit low-side switch of the power converter is switched from the ON state to the ON state of the main circuit high-side switch. [Figure 12] Figure 12 is a diagram showing the path of the current passing through the power converter, indicated by arrows. [Figure 13] Figure 13 is a diagram showing the path of current passing through a power converter, indicated by arrows. [Figure 14] Figure 14 is a diagram showing the path of the current passing through the power converter, indicated by arrows. [Figure 15] Figure 15 is a circuit diagram of a second alternative example of a power converter. [Figure 16] Figure 16 shows an example of a circuit that generates switch-on timing using the midpoint voltage of the main circuit switch and the midpoint voltage of the auxiliary circuit switch as triggers. [Figure 17] Figure 17 is a circuit diagram showing an overview of the basic circuit configuration of a conventional power conversion device. [Modes for carrying out the invention]

[0021] The present invention is described below. Used A preferred embodiment of the power converter 1 will be described with reference to the drawings. Figure 1 shows the basic circuit configuration of the power converter 1. The power converter 1 is a device placed between a DC power source 2 and a load 3 supplied with AC power, and comprises a main circuit 11 and an auxiliary circuit 12 placed between the main circuit 11 and the power source 2. An inductor L1 is placed between the main circuit 11 and the auxiliary circuit 12.

[0022] The main circuit 11 includes a main circuit high-side switch Q1 and a main circuit low-side switch Q2 connected in series. The main circuit also includes a first capacitor C1 connected in parallel with the main circuit high-side switch Q1 and a second capacitor C2 connected in parallel with the main circuit low-side switch Q2.

[0023] In this embodiment, the auxiliary circuit 12 includes a high-side diode D1 and a low-side diode D2 connected in series. Furthermore, it includes an auxiliary circuit high-side switch Q3 corresponding to the high-side diode D1 and an auxiliary circuit low-side switch Q4 corresponding to the low-side diode D2.

[0024] Inductor L1 has one end connected to the connection point between the main circuit high-side switch Q1 and the main circuit low-side switch Q2, and the other end connected to the connection point between the auxiliary circuit diodes D1 and D2.

[0025] The main circuit high-side switch Q1, the main circuit low-side switch Q2, the auxiliary circuit high-side switch Q3, and the auxiliary circuit low-side switch Q4 can be transistors such as MOSFETs. All switching elements in the main and auxiliary circuits are controlled by control means (not shown) for on / off timing.

[0026] Next, the power conversion method of the present invention will be described. Figure 2 is a diagram showing the control of the current and voltage of each part of the power converter 1 in chronological order when power is supplied from power source 2 to load 3. The top graph in Figure 2 shows the control of the source-drain voltage V2 and current value A2 of the main circuit low-side switch Q2. The second graph from the top in Figure 2 shows the control of the source-drain voltage V1 and current value A1 of the main circuit high-side switch Q1. The third graph from the top in Figure 2 shows the voltage V3 at the connection point of the auxiliary circuit high-side switch Q3 and auxiliary circuit low-side switch Q4 and the current value A3 of the inductor L1. The bottom graph shows the voltage V4 at the connection point of the main circuit high-side switch Q1 and main circuit low-side switch Q2 and the output current value A4 of the power converter 1.

[0027] In the following explanation of the power conversion method, the control content for each period will be described as follows: Period 1 is the period during which the main circuit low-side switch Q2 is switched on to the main circuit high-side switch Q1 is switched on; Period 2 is the period during which power is continuously supplied to the load from the main circuit high-side switch Q1; Period 3 is the period during which the main circuit high-side switch Q1 is switched on to the main circuit low-side switch Q2 is switched on; and Period 4 is the period during which power is supplied from the main circuit low-side switch Q2. Figure 3 shows the control content of the current and voltage of each part of the power converter 1 in Period 1 in chronological order. Figure 4 shows the control content of the current and voltage of each part of the power converter 1 in Period 3 in chronological order.

[0028] In period 1, the control details of soft switching that reduce switching losses when the main circuit high-side switch Q1 is turned on will be explained with reference to the drawings. During the period indicated by reference numeral 1-1 in Figure 3, the main circuit high-side switch Q1 is off, and current is output to the load from the main circuit low-side switch Q2 side (Figure 5(a)). In order to reduce switching losses when the main circuit high-side switch Q1 is turned on, it is necessary to charge the first capacitor C1 and the second capacitor C2 of the main circuit 11 with the surplus current supplied from the main circuit low-side switch Q2 side and the current supplied from the auxiliary circuit 12.

[0029] To charge the first capacitor C1 and the second capacitor C2 of the main circuit 11, the auxiliary circuit high-side switch Q3 and the auxiliary circuit low-side switch Q4 are alternately switched on and off. The ON period of the auxiliary circuit high-side switch Q3 is indicated by the period indicated by 1-2 in Figure 3, and the ON period of the auxiliary circuit low-side switch Q4 is indicated by the period indicated by 1-3 in Figure 3. The alternating switching of the auxiliary circuit high-side switch Q3 and the auxiliary circuit low-side switch Q4 energizes the inductor L1. The power output from the auxiliary circuit 12 through the inductor L1 charges the first capacitor C1 and the second capacitor C2 of the main circuit 11 until the power supply voltage reaches the voltage required to turn on the main circuit high-side switch Q1. Figure 5(b) shows the power supply state when the auxiliary circuit high-side switch Q3 is ON, and Figure 6(a) shows the power supply state when the auxiliary circuit low-side switch Q4 is ON.

[0030] When the auxiliary circuit high-side switch Q3 is turned on, current is supplied to the load 3 from the auxiliary circuit high-side switch Q3 through the inductor L1. When the supply of current from inductor L1 begins, the load 3 is supplied with current from both the main circuit low-side switch Q2 and inductor L1. As a result, the current in the main circuit low-side switch Q2 decreases by the amount that inductor L1 is energized. When the current supplied through inductor L1 exceeds the current supplied through the load 3, charging of the first capacitor C1 and the second capacitor C2 begins.

[0031] When the charging voltages of the first capacitor C1 and the second capacitor C2 are equal to 1 / 2, the auxiliary circuit high-side switch Q3 and the main circuit low-side switch Q2 are turned off, and the auxiliary circuit low-side switch Q4 is turned on. From the start of charging of the first capacitor C1 and the second capacitor C2, the first capacitor C1 and the second capacitor C2 and the inductor L1 can be considered to be in LC resonance, so the energy of the inductor L1 is used to charge the first capacitor C1 and the second capacitor C2, and when the charging of the first capacitor C1 and the second capacitor C2 is complete, the current in the inductor L1 becomes 0. At this point, the auxiliary circuit low-side switch Q4 is turned off.

[0032] Once the first capacitor C1 and the second capacitor C2 have finished charging, the voltage across the main circuit high-side switch Q1 becomes approximately 0V. By turning on the main circuit high-side switch Q1, the soft switching of the main circuit high-side switch Q1 is completed. Figure 6(b) shows the power supply state when the main circuit high-side switch Q1 is in the ON state. Control of the power converter 1 moves to a period 2 in which a predetermined voltage is maintained, and power is supplied to the load 3.

[0033] Here, after turning off the auxiliary circuit high-side switch Q3 and auxiliary circuit low-side switch Q4, a residual loop current is generated that charges the auxiliary circuit 11 from the main circuit high-side switch Q1 through the inductor L1, as shown in Figure 7(a). To reduce the residual loop current, it is effective to turn on the auxiliary circuit high-side switch Q3 at the timing when the source-drain voltages of the auxiliary circuit high-side switch Q3 and the auxiliary circuit low-side switch Q4 are equal, thereby fixing the current value to 0. Using switch elements with small capacitance for the auxiliary circuit high-side switch Q3 and auxiliary circuit low-side switch Q4, and adding an inductance L1 are also effective.

[0034] Next, we will explain the soft switching control that reduces switching losses when turning on the main circuit low-side switch Q2 during period 3, which is the period when switching from the main circuit high-side switch Q1 to the main circuit low-side switch Q2, with reference to the drawings. At the beginning of the period indicated by reference numeral 3-1 in Figure 4, the main circuit low-side switch Q2 remains off, and current is output to the load from the main circuit high-side switch Q1 side (Figure 6(b)). In order to reduce switching losses when turning on the main circuit low-side switch Q2, it is necessary to discharge the first capacitor C1 and the second capacitor C2 of the main circuit 11 with the load current and the current supplied to the auxiliary circuit 12.

[0035] To discharge the first capacitor C1 and the second capacitor C2 of the main circuit 11, the on and off states of the auxiliary circuit high-side switch Q3 and the auxiliary circuit low-side switch Q4 are alternately switched. The on period of the auxiliary circuit low-side switch Q4 is indicated by the period indicated by 3-2 in Figure 4, and the on period of the auxiliary circuit high-side switch Q3 is indicated by the period indicated by 3-3 in Figure 4. The alternating switching energizes the inductor L1. The power input to the auxiliary circuit 12 via the inductor L1 allows the first capacitor C1 and the second capacitor C2 of the main circuit 11 to discharge until the ground voltage that turns on the main circuit low-side switch Q2 is reached. The power supply state when the auxiliary circuit low-side switch Q4 is on is shown in Figure 7(b), and the power supply state when the auxiliary circuit high-side switch Q3 is on is shown in Figure 7(c).

[0036] When the main circuit high-side switch Q1 is turned off and the auxiliary circuit low-side switch Q4 is turned on, current is supplied from the first capacitor C1 and the second capacitor C2 through the inductor L1 to the auxiliary circuit low-side switch Q4 and the load, causing the discharge of the first capacitor C1 and the second capacitor C2 to begin.

[0037] When the discharge voltages of the first capacitor C1 and the second capacitor C2 are equal to 1 / 2, the auxiliary circuit low-side switch Q4 is turned off and the auxiliary circuit high-side switch Q3 is turned on. From the start of discharge of the first capacitor C1 and the second capacitor C2, the first capacitor C1 and the second capacitor C2 and the inductor L1 can be considered to be in LC resonance, so the first capacitor C1 and the second capacitor C2 discharge using the energy of the inductor L1, and when the discharge of the first capacitor C1 and the second capacitor C2 is complete, the current in the inductor L1 becomes 0. At this point, the auxiliary circuit high-side switch Q3 is turned off.

[0038] Once the discharge of the first capacitor C1 and the second capacitor C2 is complete, the voltage across the main circuit low-side switch Q2 becomes approximately 0V. By turning on the main circuit low-side switch Q2, the soft switching of the main circuit low-side switch Q2 is completed. Figure 5(a) shows the power supply state when the main circuit low-side switch Q2 is turned on. Control of the power converter 1 moves to a period 4 in which a predetermined voltage is maintained, and power is supplied to the load 3.

[0039] However, when power is supplied from the main circuit high-side switch Q1, the current supplied to the load itself contributes to bringing the voltage across the main circuit low-side switch Q2 to approximately 0V. Therefore, depending on the amount of power supplied, the operation of the auxiliary circuit 12 during period 3 may not be necessary.

[0040] Thus, the power conversion method using the power conversion device 1 of this embodiment allows for alternating soft switching of the main circuit high-side switch Q1 and the main circuit low-side switch Q2, enabling highly efficient power supply to the load 3.

[0041] Figure 8 shows an example of an alternative power converter when outputting current from power source 2 to load 3. In power converter 21, the low-side switch Q4 of the auxiliary circuit is replaced with a low-side diode D2. Also, the high-side diode D1 is omitted. In such a power converter 21, zero detection of the inductor L1 current is unnecessary. Power converter 21 can automatically perform zero-crossing (ZCS) operation where the current becomes zero, making it easy to control. Furthermore, since diodes have lower power loss than common switching elements such as MOSFETs, more efficient power conversion is possible.

[0042] Next, the operation of the power converter 1 when supplying power from external source 2 to the main circuit will be explained with reference to the drawings. Figure 9 is a diagram showing the current and voltage control of each part of the power converter 1 in chronological order. The top graph in Figure 9 shows the control of the source-drain voltage V2, current value A2, and gate voltage G2 of the main circuit low-side switch Q2. The second graph from the top in Figure 2 shows the control of the source-drain voltage V1, current value A1, and gate voltage G1 of the main circuit high-side switch Q1. The third graph from the top in Figure 2 shows the voltage V3 at the connection point between the auxiliary circuit high-side switch Q3 and the auxiliary circuit low-side switch Q4, the current value A3 of the inductor L1, and the gate voltage G3. The bottom graph shows the voltage V4 at the connection point between the main circuit high-side switch Q1 and the main circuit low-side switch Q2, and the output current value A4 of the power converter 1.

[0043] In the following explanation of the power conversion method, the control content for each period will be described as follows: Period 5 is the period during which the main circuit high-side switch Q1 is switched on to the main circuit low-side switch Q2 is switched on; Period 6 is the period during which the main circuit low-side switch Q2 remains in the ON state; Period 7 is the period during which the main circuit low-side switch Q2 is switched on to the main circuit high-side switch Q1 is switched on; and Period 8 is the period during which power is supplied from the main circuit low-side switch Q2. Figure 10 shows the control content of the current and voltage of each part of the power converter 1 in chronological order during Period 5. Figure 11 shows the control content of the current and voltage of each part of the power converter 1 in chronological order during Period 6.

[0044] The control details of soft switching to reduce switching losses during the period 5 when switching from the ON state of the main circuit high-side switch Q1 to the ON state of the main circuit low-side switch Q2 will be explained with reference to the drawings. During the period indicated by reference numeral 5-1 in Figure 10, the main circuit low-side switch Q2 is OFF, and current is output to the load from the main circuit high-side switch Q1 side (Figure 12(a)). In order to reduce switching losses when turning on the main circuit low-side switch Q2, it is necessary to charge the first capacitor C1 and the second capacitor C2 of the main circuit 11 with the current supplied from the main circuit high-side switch Q1 side and the current from the auxiliary circuit 12. For charging, the ON and OFF states of the auxiliary circuit high-side switch Q3 and the ON and OFF states of the auxiliary circuit low-side switch Q4 are alternately switched. The ON period of the auxiliary circuit low-side switch Q4 is indicated by reference numeral 5-2 in Figure 10, and the ON period of the auxiliary circuit high-side switch Q3 is indicated by reference numeral 5-3 in Figure 10. The power passing alternately through the auxiliary circuit high-side switch Q3 and the auxiliary circuit low-side switch Q4 charges the first capacitor C1 and the second capacitor C2 of the main circuit 11 until the power supply voltage reaches 0V, which turns on the main circuit low-side switch Q2. Figure 12(b) shows the power supply state when the auxiliary circuit low-side switch Q3 is ON, and Figure 13(a) shows the power supply state when the auxiliary circuit high-side switch Q4 is ON.

[0045] When the first capacitor C1 and the second capacitor C2 have finished charging, the voltage across the main circuit low-side switch Q2 becomes approximately 0V, and by turning on the main circuit low-side switch Q2, the soft switching of the main circuit low-side switch Q2 is completed. Figure 13(b) shows the power supply state when the main circuit low-side switch Q2 is in the ON state. Control of the power converter 1 moves to period 6, during which a predetermined voltage is maintained.

[0046] Here, after turning off the auxiliary circuit high-side switch Q3 and auxiliary circuit low-side switch Q4, a residual loop current is generated that flows from the auxiliary circuit low-side switch Q4 through the inductor L1 to the main circuit low-side switch Q2, as shown in Figure 14(a). To reduce the residual loop current, it is effective to turn on the auxiliary circuit low-side switch Q4 at the timing when the source-drain voltages of the auxiliary circuit high-side switch Q3 and auxiliary circuit low-side switch Q4 are equal, thereby fixing the current value to 0. Using switch elements with small capacitance for the auxiliary circuit high-side switch Q3 and auxiliary circuit low-side switch Q4, and adding an inductance L1 are also effective.

[0047] Next, the soft switching control details for reducing switching losses during period 7, which is the period when the main circuit low-side switch Q2 is turned on and the main circuit high-side switch Q1 is turned on, will be explained with reference to the drawings. At the beginning of the period indicated by reference numeral 7-1 in Figure 11, the main circuit high-side switch Q1 remains off, and current is output to the load from the main circuit low-side switch Q2 side (Figure 13(b)). In order to reduce switching losses when the main circuit high-side switch Q1 is turned on, it is necessary to discharge the first capacitor C1 and the second capacitor C2 of the main circuit 11 with current supplied from an external source.

[0048] To discharge the first capacitor C1 and the second capacitor C2 of the main circuit 11, the on and off states of the auxiliary circuit high-side switch Q3 and the auxiliary circuit low-side switch Q4 are alternately switched. The on period of the auxiliary circuit high-side switch Q3 is indicated by the period indicated by 7-2 in Figure 11, and the on period of the auxiliary circuit low-side switch Q4 is indicated by the period indicated by 7-3 in Figure 11. By switching alternately, the inductor L1 is energized, and the power input to the auxiliary circuit 12 via the inductor L1 allows the first capacitor C1 and the second capacitor C2 of the main circuit 11 to discharge until the ground voltage that turns on the main circuit high-side switch Q1 is reached. The power supply state when the auxiliary circuit low-side switch Q4 is on is shown in Figure 14(b), and the power supply state when the auxiliary circuit high-side switch Q3 is on is shown in Figure 14(c).

[0049] Current is supplied from the first capacitor C1 and the second capacitor C2 through the inductor L1 to the auxiliary circuit high-side switch Q3, and the discharge of the first capacitor C1 and the second capacitor C2 begins. When the discharge voltage of the first capacitor C1 and the second capacitor C2 is equal to 1 / 2, the auxiliary circuit low-side switch Q4 is turned off and the auxiliary circuit high-side switch Q3 is turned on. From the start of the discharge of the first capacitor C1 and the second capacitor C2, the first capacitor C1 and the second capacitor C2 and the inductor L1 can be considered to be in LC resonance, so the first capacitor C1 and the second capacitor C2 discharge using the energy of the inductor L1, and when the discharge of the first capacitor C1 and the second capacitor C2 is complete, the current in the inductor L1 becomes 0. At this point, the auxiliary circuit low-side switch Q4 is turned off.

[0050] Once the discharge of the first capacitor C1 and the second capacitor C2 is complete, the voltage across the main circuit high-side switch Q1 becomes approximately 0V. By turning on the main circuit high-side switch Q1, the soft switching of the main circuit high-side switch Q1 is completed. Control of the power converter 1 then moves to a period 8 during which a predetermined voltage is maintained.

[0051] Thus, the power conversion method using the power conversion device 1 of this embodiment allows for the alternating soft switching of the main circuit high-side switch Q1 and the main circuit low-side switch Q2, enabling highly efficient power supply from an external source to the main circuit side.

[0052] Figure 15 shows an example of an alternative power converter when outputting current from an external source 2 to the main circuit 11. In the power converter 31, the high-side switch Q3 of the auxiliary circuit is replaced with a high-side diode D1. The low-side diode D2 is omitted. In such a power converter 31, zero detection of the inductor L1 current is unnecessary. The power converter 31 can automatically perform zero-crossing (ZCS) operation where the current becomes zero, making it easy to control. Furthermore, since diodes have lower power loss than common switching elements such as MOSFETs, more efficient power conversion is possible.

[0053] Figure 16 shows an example of a logic circuit for generating the timing of the main circuit high-side switch, the main circuit low-side switch, the auxiliary circuit high-side switch, and the auxiliary circuit low-side switch, using the midpoint voltage between the main circuit high-side switch and the main circuit low-side switch, and the midpoint voltage of the auxiliary circuit high-side switch and the auxiliary circuit low-side switch as triggers. Adding this logic circuit makes it easier to control the on and off timing of the switching elements. [Industrial applicability]

[0054] The power conversion device of the present invention can be applied to step-up / step-down converters, three-phase AC inverters, single-phase inverters, motors that rotate in both directions or single-phase motors, step-down DC-DC converters, step-up DC-DC converters, and the like. In particular, a power conversion device that supplies power from the power source to the load in only one direction is suitably applied to step-down converters and grounded single-phase motors. In the case of a power conversion device that supplies power to the main circuit from an external source, it is suitably applied to step-up converters and single-phase motors connected to a power source. [Explanation of Symbols]

[0055] 1. Power converter 2 power supply 3 load 11 Main circuit 12 Auxiliary circuit L1 Inductor Q1 Main circuit high-side switch Q2 Main circuit low-side switch Q3 Auxiliary circuit high-side switch Q4 Auxiliary circuit low-side switch C1 First capacitor C2 Second capacitor C2 D1, D2 diodes

Claims

1. A power conversion method for a power conversion device comprising a main circuit, an auxiliary circuit disposed between the main circuit and a power supply, and an inductor disposed between the main circuit and the auxiliary circuit, The main circuit comprises a main circuit high-side switch and a main circuit low-side switch connected in series, a first capacitor connected in parallel with the main circuit high-side switch, and a second capacitor connected in parallel with the main circuit low-side switch. The auxiliary circuit comprises one or more diodes and one or more switches. Before turning on the main circuit high-side switch, the auxiliary circuit high-side switch located in the upper circuit of the auxiliary circuit and the auxiliary circuit low-side switch located in the lower circuit of the auxiliary circuit are alternately turned on to energize the inductor and adjust the amount of change in the output current. The period during which the auxiliary circuit high-side switch is turned on and the period during which the auxiliary circuit low-side switch is turned on are adjusted until the first capacitor and the second capacitor are charged. A power conversion method characterized by turning on the main circuit high-side switch after the voltage applied to the main circuit high-side switch becomes approximately 0V.

2. A power conversion method for a power conversion device comprising a main circuit, an auxiliary circuit disposed between the main circuit and a power supply, and an inductor disposed between the main circuit and the auxiliary circuit, The main circuit comprises a main circuit high-side switch and a main circuit low-side switch connected in series, a first capacitor connected in parallel with the main circuit high-side switch, and a second capacitor connected in parallel with the main circuit low-side switch. The auxiliary circuit comprises one or more diodes and one or more switches. Before turning on the main circuit high-side switch, the auxiliary circuit high-side switch located in the upper circuit of the auxiliary circuit and the low-side diode located in the lower circuit of the auxiliary circuit are alternately turned on to energize the inductor and adjust the amount of change in the output current. The period during which the auxiliary circuit high-side switch is turned on and the period during which the low-side diode is turned on are adjusted until the first capacitor and the second capacitor are charged. A power conversion method characterized by turning on the main circuit high-side switch after the voltage applied to the main circuit high-side switch becomes approximately 0V.

3. A power conversion method for a power conversion device comprising a main circuit, an auxiliary circuit disposed between the main circuit and a power supply, and an inductor disposed between the main circuit and the auxiliary circuit, The main circuit comprises a main circuit high-side switch and a main circuit low-side switch connected in series, a first capacitor connected in parallel with the main circuit high-side switch, and a second capacitor connected in parallel with the main circuit low-side switch. The auxiliary circuit comprises one or more diodes and one or more switches. Before turning on the main circuit low-side switch, the auxiliary circuit low-side switch located in the lower circuit of the auxiliary circuit and the auxiliary circuit high-side switch located in the upper circuit of the auxiliary circuit are alternately turned on to energize the inductor and adjust the amount of change in the output current. The period during which the auxiliary circuit low-side switch is turned on and the period during which the auxiliary circuit high-side switch is turned on are adjusted until the first capacitor and the second capacitor are charged. A power conversion method characterized by turning on the main circuit low-side switch after the voltage applied to the main circuit low-side switch becomes approximately 0V.

4. A power conversion method for a power conversion device comprising a main circuit, an auxiliary circuit disposed between the main circuit and a power supply, and an inductor disposed between the main circuit and the auxiliary circuit, The main circuit comprises a main circuit high-side switch and a main circuit low-side switch connected in series, a first capacitor connected in parallel with the main circuit high-side switch, and a second capacitor connected in parallel with the main circuit low-side switch. The auxiliary circuit comprises one or more diodes and one or more switches. Before turning on the main circuit low-side switch, the auxiliary circuit low-side switch located in the lower circuit of the auxiliary circuit and the high-side diode located in the upper circuit of the auxiliary circuit are alternately turned on to energize the inductor and adjust the amount of change in the output current. Furthermore, the period for which the auxiliary circuit low-side switch is turned on and the period for which the high-side diode is turned on are adjusted until the first capacitor and the second capacitor are charged. A power conversion method characterized by turning on the main circuit low-side switch after the voltage applied to the main circuit low-side switch becomes approximately 0V.

5. The power conversion method according to claim 1 or 2, characterized in that it is applicable when current is supplied from the power source to the main circuit.

6. The power conversion method according to claim 3 or 4, characterized in that it is applicable when current is passed from the main circuit in the direction of the power supply.

7. The midpoint voltage between the main circuit high-side switch and the main circuit low-side switch, The power conversion method according to claim 1 or 3, characterized in that the timing of the main circuit high-side switch, the main circuit low-side switch, the auxiliary circuit high-side switch, and the auxiliary circuit low-side switch is generated by using the midpoint voltage of the auxiliary circuit high-side switch and the auxiliary circuit low-side switch as triggers.

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