ELECTRICAL POWER CONVERSION DEVICE

Abstract

A control device (50) is configured to perform a first control operation that controls a primary full-bridge circuit (30) such that a primary voltage at two levels is applied to a primary winding (22), and a secondary full-bridge circuit (40) such that a secondary voltage at three levels is applied to a series connection (24) of a secondary winding (33) and an inductor (L1). In the first control operation, the control device (50) is configured to output a required power by controlling the primary full-bridge circuit (30) and the secondary full-bridge circuit (40) such that a combination of a first phase difference and a second phase difference is achieved, allowing the output of a required power while satisfying condition 1 and condition 2.

Description

TECHNICAL AREA

[0001] The present disclosure relates to a power conversion device. BACKGROUND

[0002] Patent reference 1 discloses a power conversion device comprising a transformer, a primary full-bridge circuit, a secondary full-bridge circuit, and a control device. The transformer has a primary winding and a secondary winding. The primary full-bridge circuit has primary switching elements. The secondary full-bridge circuit has secondary switching elements. The control device controls the primary full-bridge circuit such that a primary voltage is applied to the primary winding at three levels. The control device controls the secondary full-bridge circuit such that a secondary voltage is applied to the secondary winding at three levels. The control device implements soft switching of the primary and secondary switching elements by controlling a phase difference between the primary and secondary voltages. Citation list patent literature

[0003] Patent literature 1: WO 2020 / 003 717 A SUMMARY OF THE INVENTION Technical Problem

[0004] If an equivalent voltage ratio, which is the ratio of an output voltage to an input voltage converted to a transformer turns ratio of 1.1, becomes a value close to 1, it may not be possible to achieve smooth switching of the primary and secondary switching elements. Solution to the problem

[0005] A power conversion device comprises a transformer with a primary winding and a secondary winding, an inductor connected to the primary winding in which the inductor and the primary winding form a series connection, a primary full-bridge circuit connected to the inductor and comprising primary switching elements, a secondary full-bridge circuit connected to the secondary winding and comprising secondary switching elements, and a control device configured to control the primary and secondary switching elements. Soft switching is performed on the primary switching elements under a condition designated as Condition 1, and soft switching is performed on the secondary switching elements under a condition defined as Condition 2.Condition 1 is that when at least one of the primary switching elements is switched between ON and OFF, the value of a current flowing through the primary winding in a forward direction through diodes connected in parallel to one or more of the primary switching elements being switched from OFF to ON is equal to or greater than an absolute value of a primary winding current threshold. Condition 2 is that when at least one of the secondary switching elements is switched between ON and OFF, the value of a current flowing through the secondary winding in a forward direction through diodes connected in parallel to one or more of the secondary switching elements being switched from OFF to ON is equal to or greater than an absolute value of a secondary winding current threshold.The control device is configured to perform a first control operation that controls the primary full-bridge circuit such that a primary voltage at two levels is applied to the series-connected core, and controls the secondary full-bridge circuit such that a secondary voltage at three levels is applied to the secondary winding. The primary and secondary voltages have waveforms of the same frequency, each inverted by a phase of 180 degrees. A difference between a first time at which the secondary voltage rises from a low level to a medium level and a second time at which the primary voltage rises from a low level to a high level is defined as a first phase difference. A difference between the first time and a third time at which the secondary voltage rises from a medium level to a high level is defined as a second phase difference.The control device is configured in the first control to output a required power by controlling the primary full bridge circuit and the secondary full bridge circuit in such a way as to realize a combination of the first phase difference and the second phase difference that allows the output of the required power while condition 1 and condition 2 are satisfied.

[0006] For soft switching to occur at the primary switching elements, condition 1 must be met. For soft switching to occur at the secondary switching elements, condition 2 must be met. If the equivalent voltage ratio, which is the ratio of the equivalent output voltage to the equivalent input voltage when the transformer winding ratio is converted to 1:1, is close to 1, the voltage applied to the inductor will be low. If the voltage applied to the inductor is low, even if the primary full-bridge circuit is controlled such that the primary voltage is applied to the series body at three levels, a small change in current may prevent soft switching from occurring.Conversely, if the voltage applied to the choke coil is low, the magnitude of the current change can be increased by controlling the secondary full-bridge circuit so that the secondary voltage is applied to the secondary winding at three levels. This allows for smooth switching of the primary and secondary switching elements.

[0007] A power conversion device comprises a transformer with a primary winding and a secondary winding, an inductor connected to the secondary winding, the inductor and the secondary winding forming a series connection, a primary full-bridge circuit connected to the primary winding and comprising primary switching elements, a secondary full-bridge circuit connected to the inductor and comprising secondary switching elements, and a control device configured to control the primary and secondary switching elements. Soft switching is performed on the primary switching elements under a condition defined as condition 1, and soft switching is performed on the secondary switching elements under a condition defined as condition 2.Condition 1 is that when at least one of the primary switching elements is switched between ON and OFF, the value of a current flowing through the primary winding in a forward direction through diodes connected in parallel to one or more of the primary switching elements being switched from OFF to ON is equal to or greater than an absolute value of a primary winding current threshold. Condition 2 is that when at least one of the secondary switching elements is switched between ON and OFF, the value of a current flowing through the secondary winding in a forward direction through diodes connected in parallel to one or more of the secondary switching elements being switched from OFF to ON is equal to or greater than an absolute value of a secondary winding current threshold.The control device is configured to perform a first control operation that controls the primary full-bridge circuit such that a primary voltage at three levels is applied to the primary winding, and controls the secondary full-bridge circuit such that a secondary voltage at two levels is applied to the series-connected body. The primary and secondary voltages have waveforms of the same frequency, each inverted by a phase of 180 degrees. A difference between a first time at which the primary voltage rises from a low level to a medium level and a second time at which the secondary voltage rises from a low level to a high level is defined as a first phase difference, and a difference between the first time and a third time at which the primary voltage rises from a medium level to a high level is defined as a second phase difference.The control device is configured to output a required power in the first control by controlling the primary full bridge circuit and the secondary full bridge circuit in such a way that a combination of the first phase difference and the second phase difference is achieved that allows the output of the required power while satisfying condition 1 and condition 2.

[0008] For soft switching to occur at the primary switching elements, condition 1 must be met. For soft switching to occur at the secondary switching elements, condition 2 must be met. If the equivalent voltage ratio, that is, the ratio of the equivalent output voltage to the equivalent input voltage applied to a transformer with a 1:1 turns ratio, is close to 1, the voltage applied to the inductor will be low. If the voltage applied to the inductor is low, even if the secondary full-bridge circuit is controlled such that the secondary voltage is applied to the series body at three levels, a small change in current may prevent soft switching from occurring.Conversely, if the voltage applied to the choke coil is low, the rate of change in the current can be increased by controlling the primary full-bridge circuit so that the primary voltage is applied to the primary winding at three levels. This allows for smooth switching of the primary and secondary switching elements. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 shows a circuit diagram of a power conversion device according to a first embodiment. Fig. Figure 2 shows a representation illustrating a relationship between an equivalent voltage ratio and control modes. Fig. Figure 3 shows a representation illustrating a primary voltage and a secondary voltage in a first buck-shift phase-lag mode according to the first embodiment. Fig. Figure 4 shows a representation illustrating the primary voltage and the secondary voltage in a first buck-set phase-equalization mode according to the first embodiment. Fig. Figure 5 shows a representation illustrating the primary voltage and the secondary voltage in a buck-shift phase-adjustment mode according to the first embodiment. Fig. Figure 6 shows a flowchart illustrating a switching control carried out by a control device. Fig. Figure 7 shows a representation illustrating a primary current and a secondary current in the first buck-shift phase-lag mode according to the first embodiment. Fig. Figure 8 shows a representation illustrating the primary voltage and the secondary voltage in a first boost phase-lag mode according to the first embodiment. Fig. Figure 9 shows a representation illustrating the primary voltage and the secondary voltage in a first boost phase-equalization mode according to the first embodiment. Fig. Figure 10 shows a representation illustrating the primary voltage and the secondary voltage in a first boost phase advance mode according to the first embodiment. Fig. Figure 11 shows a representation illustrating the primary voltage and the secondary voltage in a second buck-shift phase-lag mode according to the first embodiment. Fig. Figure 12 shows a representation illustrating the primary voltage and the secondary voltage in a second buck-set phase-equalization mode according to the first embodiment. Fig. Figure 13 shows a representation illustrating the primary voltage and the secondary voltage in a second buck-shift phase-adjustment mode according to the first embodiment. Fig. Figure 14 shows a representation illustrating a relationship between an equivalent voltage ratio and an output current of the power conversion device according to the first embodiment. Fig. Figure 15 shows a circuit diagram of a power conversion device according to a second embodiment. Fig. Figure 16 shows a representation illustrating a primary voltage and a secondary voltage in a first buck-shift phase-lag mode according to the second embodiment. Fig. Figure 17 shows a representation illustrating the primary voltage and the secondary voltage in a first buck-set phase-equalization mode according to the second embodiment. Fig. Figure 18 shows a representation illustrating the primary voltage and the secondary voltage in a first buck phase advance mode according to the second embodiment. Fig. Figure 19 shows a representation illustrating the primary voltage and the secondary voltage in a first boost phase-lag mode according to the second embodiment. Fig. Figure 20 shows a representation illustrating the primary voltage and the secondary voltage in a first boost phase-equalization mode according to the second embodiment. Fig. Figure 21 shows a representation illustrating the primary voltage and the secondary voltage in a first boost phase advance mode according to the second embodiment. Fig. Figure 22 shows a representation illustrating the primary voltage and the secondary voltage in a second boost phase-lag mode according to the second embodiment. Fig. Figure 23 shows a representation illustrating the primary voltage and the secondary voltage in a second boost phase-equalization mode according to the second embodiment. Fig. Figure 24 shows a representation illustrating the primary voltage and the secondary voltage in a second boost phase advance mode according to the second embodiment. Fig. Figure 25 shows a representation that establishes a relationship between an equivalent voltage ratio and an output current of the

[0009] Power conversion device illustrated according to the second embodiment. DESCRIPTION OF EXAMPLES OF EXECUTION [First example of execution]

[0010] A first embodiment of a power conversion device is described below.

[0011] As it is in Fig. As shown in Figure 1, a power supply system 100 comprises a DC power supply 110, a load 120, and a power conversion device 10. The DC power supply 110 supplies DC power to the power conversion device 10. The DC power supply 110 is, for example, a battery or a power supply circuit. The power supply circuit is, for example, an AC / DC converter that converts AC power to DC power and outputs the DC power. The load 120 is, for example, a rechargeable battery that charges and discharges the DC power. The rechargeable battery is, for example, a rechargeable lithium-ion battery or a lead-acid battery. <leistungsumwandlungsvorrichtung>

[0012] The power conversion device 10 is a dual active bridge DC / DC converter. The power conversion device 10 is located between the DC power supply 110 and the load 120. The power conversion device 10 is configured to convert the DC power from the DC power supply 110 and output the converted DC power to the load 120. In the following description, the primary side is the input and the secondary side is the output. In other words, the power conversion device 10 converts the DC voltage from the DC power supply 110 and outputs the converted DC voltage to the load 120.

[0013] The power conversion device 10 has two primary terminals 11 and 12 and two secondary terminals 13 and 14. The DC power supply 110 is electrically connected to the primary terminals 11 and 12. The load 120 is electrically connected to the secondary terminals 13 and 14.

[0014] The power conversion device 10 comprises a transformer 20. The transformer 20 is of an insulated design. The transformer 20 has a magnetic core 21, a primary winding 22, and a secondary winding 23. The primary winding 22 and the secondary winding 23 are wound around the core 21. The transformer 20 has an inductor L1. The inductor L1 can be a protective choke or a leakage inductor of the primary winding 22 and the secondary winding 23. The inductor L1 is connected to the primary winding 22.

[0015] The power conversion device 10 has a primary full-bridge circuit 30. The primary full-bridge circuit 30 has a first leg 31 and a second leg 32. The first leg 31 and the second leg 32 are connected to the primary terminals 11 and 12 in parallel. Accordingly, the primary full-bridge circuit 30 is electrically connected to the DC power supply 110 via the primary terminals 11 and 12. The first leg 31 has a first switching element Q1, a second switching element Q2, diodes D1 and D2, and capacitors C1 and C2. The first switching element Q1 and the second switching element Q2 are connected in series. The second leg 32 has a third switching element Q3, a fourth switching element Q4, diodes D3 and D4, and capacitors C3 and C4. The third switching element Q3 and the fourth switching element Q4 are connected in series with each other.The first switching element Q1 and the third switching element Q3 form an upper branch. The second switching element Q2 and the fourth switching element Q4 form a lower branch.

[0016] The first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 are primary switching elements Q1, Q2, Q3, and Q4. Each of the primary switching elements Q1 to Q4 is, for example, an n-type metal-oxide-semiconductor field-effect transistor (MOSFET). Each of the primary switching elements Q1 to Q4 can be a p-type MOSFET, an insulated-gate bipolar transistor (IGBT), or a high-electrode mobility GaN transistor (HEMT).

[0017] Diodes D1 to D4 and capacitors C1 to C4 are each connected in parallel to the corresponding primary circuit elements Q1 to Q4. Diodes D1 to D4 can be parasitic diodes or discrete elements. Capacitors C1 to C4 can be parasitic capacitors, discrete elements, or a combination of both.

[0018] A connection point between the first switching element Q1 and the second switching element Q2 is connected to the primary winding 22 via the inductor L1. A connection point between the third switching element Q3 and the fourth switching element Q4 is also connected to the primary winding 22. Accordingly, the primary full-bridge circuit 30 is connected to the primary winding 22. The primary winding 22 and the inductor L1 form a series circuit 24.

[0019] The power conversion device 10 has a primary voltage sensor 32. The primary voltage sensor 37 detects the input voltage Vin, which is fed from the DC power supply 110 into the primary full bridge circuit 30.

[0020] The power conversion device 10 has a secondary full-bridge circuit 40. The secondary full-bridge circuit 40 has a third leg 41 and a fourth leg 42. The third leg 41 and the fourth leg 42 are connected to the secondary terminals 13 and 14 in parallel. Accordingly, the secondary full-bridge circuit 40 is electrically connected to the load 120. The third leg 41 has a fifth switching element Q5, a sixth switching element Q6, diodes D5 and D6, and capacitors C5 and C6. The fifth switching element Q5 and the sixth switching element Q6 are connected in series. The fourth leg 42 has a seventh switching element Q7, an eighth switching element Q8, diodes D7 and D8, and capacitors C7 and C8. The seventh switching element Q7 and the eighth switching element Q8 are connected in series.The fifth switching element Q5 and the seventh switching element Q7 form an upper branch. The sixth switching element Q6 and the eighth switching element Q8 form a lower branch.

[0021] The fifth switching element Q5, the sixth switching element Q6, the seventh switching element Q7, and the eighth switching element Q8 are secondary switching elements Q5, Q6, Q7, and Q8. Each of the secondary switching elements Q5 to Q8 is, for example, an n-MOSFET. Each of the secondary switching elements Q5 to Q8 can be a p-MOSFET, an IGBT, or a GaN HEMT.

[0022] Diodes D5 to D8 and capacitors C5 to C8 are each connected in parallel to the secondary switching elements Q5 to Q8. Diodes D5 to D8 can be parasitic diodes or discrete components. Capacitors C5 to C8 can be parasitic capacitors, discrete components, or a combination of both.

[0023] A connection point between the fifth switching element Q5 and the sixth switching element Q6, and a connection point between the seventh switching element Q7 and the eighth switching element Q8, are each connected to the secondary winding 23. Accordingly, the secondary full-bridge circuit 40 is connected to the secondary winding 23.

[0024] The output power of the secondary full bridge circuit 40 is supplied to the load 120.

[0025] The power conversion device 10 has a secondary voltage sensor 47. The secondary voltage sensor 47 detects the output voltage Vout of the power conversion device 10.

[0026] The power conversion device 10 comprises a control unit 50. The control unit 50 comprises a processor and memory. The processor is, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The memory comprises random access memory (RAM) and read-only memory (ROM). The memory stores program code or instructions configured to cause the processor to execute processes. The memory, which is a computer-readable medium, comprises some type of medium accessible by a general-purpose or specialized computer. The control unit 50 may include a hardware circuit such as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA).The control device 50, which is a processing circuit, can execute programs and may have one or more processors, one or more hardware circuits (for example, ASIC or FPGA) or a combination of these.

[0027] The control unit 50 converts the input voltage Vin into the output voltage Vout by controlling the primary switching elements Q1 to Q4 and the secondary switching elements Q5 to Q8. <Erste Steuerung>

[0028] The control device 50 performs a first control operation such that one of the primary full-bridge circuits 30 and the secondary full-bridge circuit 40, through which an excitation current flows, is controlled at three levels, and the other of the primary full-bridge circuit 30 and the secondary full-bridge circuit 40, through which no excitation current flows, is controlled at two levels. The one of the primary full-bridge circuits 30 and the secondary full-bridge circuit 40, through which an excitation current flows, is not connected to the inductor L1. The one of the primary full-bridge circuits 30 and the secondary full-bridge circuit 40, through which no excitation current flows, is connected to the inductor L1. According to the present embodiment, the primary full-bridge circuit 30 is controlled at two levels, and the secondary full-bridge circuit 40 is controlled at three levels.

[0029] The three-level control switches the voltage applied to the secondary winding 23 into three levels: positive, negative, and zero. The two-level control switches the voltage applied to the primary winding 22 and the series terminal 24 of the choke coil L1 into two levels: positive and negative. In the three-level control, the positive voltage applied to the secondary winding 23 is called the high level, the zero voltage applied to the secondary winding 23 is called the medium level, and the negative voltage applied to the secondary winding 23 is called the low level. In the two-level control, the positive voltage applied to the series terminal 24 is called the high level, and the negative voltage applied to the series terminal 24 is called the low level.The voltage applied to the primary winding 22 and the series connection body 24 of the choke coil L1 is called the primary voltage V1, and the voltage applied to the secondary winding 23 is called the secondary voltage V2. The primary voltage V1 is the potential difference between the junction of the first switching element Q1 and the second switching element Q2, and between the junction of the third switching element Q3 and the fourth switching element Q4. The secondary voltage V2 is the potential difference between the junction of the fifth switching element Q5 and the sixth switching element Q6, and between the junction of the seventh switching element Q7 and the eighth switching element Q8. A voltage related to the primary voltage V1 and the secondary voltage V2 is shown in the diagram. Fig. The added arrow indicates the positive direction. During normal operation, with the output unchanged, the primary voltage V1 and the secondary voltage V2 exhibit waveforms of the same frequency, each inverted by 180 degrees in phase.

[0030] When two-level control is performed on the primary full-bridge circuit 30, the control device 50 controls the first leg 31 and the second leg 32 in cooperation. The control device 50 switches the first switching element Q1 and the fourth switching element Q4 ON ​​simultaneously. The control device 50 switches the second switching element Q2 and the third switching element Q3 ON simultaneously. Switching patterns of the primary full-bridge circuit 30 have a first pattern and a second pattern.

[0031] The first pattern is a switching pattern in which the first switching element Q1 is ON, the second switching element Q2 is OFF, the third switching element Q3 is OFF, and the fourth switching element Q4 is ON.

[0032] The second pattern is a switching pattern in which the first switching element Q1 is OFF, the second switching element Q2 is ON, the third switching element Q3 is ON, and the fourth switching element Q4 is OFF.

[0033] When three-level control is performed on the secondary full-bridge circuit 40, the control device 50 independently controls the third leg 41 and the fourth leg 42. The switching patterns of the secondary full-bridge circuit 40 include a third pattern, a fourth pattern, a fifth pattern, and a sixth pattern.

[0034] The third pattern is a switching pattern in which the fifth switching element Q5 is ON, the sixth switching element Q6 is OFF, the seventh switching element Q7 is OFF, and the eighth switching element Q8 is ON.

[0035] The fourth pattern is a switching pattern in which the fifth switching element Q5 is ON, the sixth switching element Q6 is OFF, the seventh switching element Q7 is ON, and the eighth switching element Q8 is OFF.

[0036] The fifth pattern is a switching pattern in which the fifth switching element Q5 is OFF, the sixth switching element Q6 is ON, the seventh switching element Q7 is ON, and the eighth switching element Q8 is OFF.

[0037] The sixth pattern is a switching pattern in which the fifth switching element Q5 is OFF, the sixth switching element Q6 is ON, the seventh switching element Q7 is OFF, and the eighth switching element Q8 is ON.

[0038] The control device 50 outputs the output voltage Vout from the secondary full bridge circuit 40 by a combination of one of the first pattern and the second pattern of the primary full bridge circuit 30 and one of the third to sixth patterns of the secondary full bridge circuit 40.

[0039] The number of turns in the primary windings 22 of the transformer 20 is N1, and the number of turns in the secondary winding 23 is N2. The ratio between the input voltage Vin, which is input to the primary full-bridge circuit 30, and the output voltage Vout, which is output from the secondary full-bridge circuit 40, is a voltage ratio. The equivalent voltage ratio, which is the voltage ratio when the turns ratio of the transformer 20 is converted to 1:1, is expressed as (Vout × N1) / (Vin × N2). Vin × N2 is an equivalent input voltage converted to a transformer turns ratio of 1:1. Vout × N1 is an equivalent output voltage converted to a transformer turns ratio of 1:1. The control device 50 has a first buck mode and a first boost mode as its primary control modes.The first buck mode is a control mode for reducing the equivalent voltage ratio to less than 1. The first boost mode is a control mode for increasing the equivalent voltage ratio to greater than 1.

[0040] For example, if the turns ratio of transformer 20 is 1:2, the input voltage Vin is 200 V, and the output voltage Vout is 400 V, the equivalent voltage ratio (Vout×1) / (Vin×2) is 1 when the turns ratio is converted to 1:1. Thus, if the turns ratio of transformer 20 is 1:2 and the input voltage Vin is 200 V, the transformer operates in buck mode when the output voltage Vout is less than 400 V and in boost mode when the output voltage Vout is greater than 400 V. In the following description, the turns ratio is assumed to be 1:1 unless otherwise specified. <Erster Tiefsetzmodus>

[0041] As it is in Fig. As shown in Figure 2, the first buck mode has a first buck lag mode, a first buck equal phase mode, and a first buck lead mode.

[0042] As it is in Fig. As shown in Figure 3, the first buck-start phase-tracking mode is a first buck-start mode in which the secondary voltage V2 first rises from a low level to a medium level, the primary voltage V1 then rises from a low level to a high level, and subsequently the secondary voltage V2 rises from the medium level to the high level. The first buck-start phase-tracking mode is a first buck-start mode that outputs a small amount of power corresponding to the power required for load 120.

[0043] In the first buck-shift mode, the difference between a first time T1, at which the secondary voltage V2 rises from the low level to the medium level, and a second time T2, at which the primary voltage V1 rises from the low level to the high level, is defined as a first phase difference θ1. The difference between the first time T1 and a third time T3, at which the secondary voltage V2 rises from the medium level to the high level, is defined as a second phase difference θ2.

[0044] As described above, during normal operation, with the output unchanged, the primary voltage V1 and the secondary voltage V2 exhibit waveforms of the same frequency, each inverted by a phase of 180 degrees. Accordingly, the time it takes for the secondary voltage V2 to fall from the high level to the mid-level is also the first time T1, the time it takes for the primary voltage V1 to fall from the high level to the low level is also the second time T2, and the time it takes for the secondary voltage V2 to fall from the mid-level to the low level is also the third time T3.

[0045] As it is in Fig. As shown in Figure 4, the first buck-step mode is a first buck-step mode in which the secondary voltage V2 rises from a low level to a medium level, and simultaneously the primary voltage V1 rises from a low level to a high level, and then the secondary voltage V2 rises from the medium level to a high level. In the first buck-step mode, the first time T1 and the second time T2 are the same. Accordingly, the first phase difference θ1 is zero. The first buck-step mode is a first buck-step mode that outputs a medium amount of power corresponding to the power required for load 120. The medium amount of power is greater than the small amount of power.

[0046] As it is in Fig. As shown in Figure 5, the first buck-start phase-adjustment mode is a first buck-start mode in which the primary voltage V1 rises from a low level to a high level, the secondary voltage V2 then rises from a low level to a medium level, and subsequently the secondary voltage V2 rises from the medium level to a high level. The first buck-start phase-adjustment mode is a first buck-start mode that outputs a high magnitude of power corresponding to the power required for load 120. The high magnitude of power is greater than the medium magnitude of power.

[0047] The first buck-delay phase lag mode is an example of a light-load mode. The first buck-delay phase lead mode is an example of a heavy-load mode. The first buck-delay phase equal mode is an example of a mode for switching between the light-load and heavy-load modes.

[0048] The following describes a switching control operation performed by the control unit 50 in the first buck-shift mode. The switching control outputs the output voltage Vout by switching the primary switching elements Q1 to Q4 and the secondary switching elements Q5 to Q8.

[0049] As it is in Fig. 6 and Fig. As shown in Figure 7, in step S1 the control device 50 defines a soft-switching region. The soft-switching region is set for a primary current I1 and a secondary current I2. The primary current I1 is the current flowing through the primary winding 22. The secondary current I2 is the current flowing through the secondary winding 23. Arrows pointing to the primary current I1 and the primary current I2 in Fig. Added values ​​of 1 indicate a positive direction.

[0050] The condition for soft switching of the primary switching elements Q1 to Q4 is that, when at least one of the primary switching elements Q1 to Q4 is switched between ON and OFF, the value of the primary current I1 flowing in the forward direction of the diodes connected in parallel to one or more of the primary switching elements Q1 to Q4 being switched from OFF to ON is equal to or greater than an absolute value of a primary winding current threshold TI1. This condition is referred to below as Condition 1. The region satisfying Condition 1 is the soft-switching region of the primary current I1. The time at which at least one of the primary switching elements Q1 to Q4 is switched between ON and OFF is the time at which at least one of the primary switching elements of the switching elements Q1 to Q4 is switched from ON to OFF or from OFF to ON.In the first control according to the present embodiment, the time at which at least one of the primary switching elements Q1 to Q4 is switched between ON and OFF is the same as the second time T2 at which the primary voltage V1 rises or falls.

[0051] The condition for soft switching of the secondary switching elements Q5 to Q8 is that, when at least one of the secondary switching elements Q5 to Q8 is switched between ON and OFF, the value of the secondary current I2 flowing in the forward direction of the diodes connected in parallel to one or more of the secondary switching elements Q5 to Q8 being switched from OFF to ON is equal to or greater than an absolute value of a secondary winding current threshold TI2. This condition is referred to below as Condition 2. The region satisfying Condition 2 is a soft-switching region of the secondary current I2. The time at which at least one of the secondary switching elements Q5 to Q8 is switched between ON and OFF is the time at which at least one of the switching elements of the switching elements Q5 to Q8 is switched from ON to OFF or from OFF to ON.In the first control system according to the present embodiment, the time when at least one of the secondary switching elements Q5 to Q8 is switched between ON and OFF is the same as the first time T1 or the third time T3. The first time T1 is when the secondary voltage V2 rises from the low level to the medium level, or when the secondary voltage V2 falls from the high level to the medium level. The third time is when the secondary voltage V2 rises from the medium level to the high level, or when the secondary voltage V2 falls from the medium level to the low level.

[0052] As described above, the primary voltage V1 and the secondary voltage V2 exhibit waveforms of the same frequency, each inverted by a phase of 180 degrees, and are only inverted in polarity between positive and negative as the voltage rises and falls. Thus, only one of these voltages is described. The description below focuses on the rising transition.

[0053] Fig. Figure 7 shows an example where the primary current I1 and the secondary current I2 are in the first buck-set phase-lag mode. As can be seen from a comparison with the voltage waveform of Fig. 3 emerges, in the Fig. In the example shown, the switching pattern of the secondary full-bridge circuit 40 switches from the fifth pattern to the fourth pattern at the first time T1. Therefore, at the third time T3, the switching pattern of the secondary full-bridge circuit 40 switches from the fourth pattern to the third pattern. A soft switching of the secondary switching elements Q5 to Q8 is successful if condition 2 is met at the first time T1 and the third time T3. At the second time T2, the switching pattern of the primary full-bridge circuit 30 switches from the second pattern to the first pattern. A soft switching of the primary switching elements Q1 to Q4 is successful if condition 1 is met.

[0054] The primary winding current threshold TI1 is expressed as the following equation (1). [Equation 1] TI1=−k1V12C01L

[0055] In the equation, TI1 represents the primary winding current threshold, k1 represents a coefficient, V1 represents the primary voltage, L represents the inductance of the choke L1, and C01 represents the capacitance corresponding to a switching element with respect to the total capacitance of capacitors C1 to C4, which are connected in parallel to switching elements Q1 to Q4 of the full bridge circuit 30. If the capacitance of capacitor C1 is C11, the capacitance of capacitor C2 is C12, the capacitance of capacitor C3 is C13, and the capacitance of capacitor C4 is C14, then C01 = (C11 + C12 + C13 + C14) / 4 is satisfied. If Cx is the largest capacitance of C11 to C14, then C01 = Cx. In the same way, the secondary winding current threshold TI2 is also defined by replacing each value with a corresponding value on the secondary side. In this way, the soft-switching region is determined.

[0056] In step S2, the control unit 50 then determines a target current. The target current is a current value that outputs the power required for the load 120 and fulfills conditions 1 and 2.

[0057] In this control mode, the switching elements of the primary switching elements Q1 to Q4, which are switched from OFF to ON at the second time T2, are the first switching element Q1 and the fourth switching element Q4. The first switching element Q1 and the fourth switching element Q4 are primary switching elements that are switched from OFF to ON when the switching pattern changes from the second pattern to the first pattern.

[0058] To satisfy condition 1, the value of the primary current I1 at the second time T2, the value of the current flowing forward through diodes D1 and D4, which are connected in parallel to the first switching element Q1 and the fourth switching element Q4, which are switched from OFF to ON, is equal to or greater than the absolute value “|TI1|” of the primary winding current threshold TI1. The value of the current is in Fig. 1 is represented as “-I1”. As it is in Fig. As shown in 7, since the primary current I1 has a negative value at the second time T2, “-I1” becomes a positive value.

[0059] In this control mode, the secondary current I2 at the first time T1 and the third time T3 is taken into account to satisfy condition 2. The absolute value in this control mode is smaller at the first time T1 than at the third time T3. Thus, the secondary current I2 at the first time T1 is taken into account. Accordingly, to satisfy condition 2, the secondary current I2 at the first time T1, the value of the current flowing in the forward direction through diode D5, which is connected in parallel to the fifth switching element Q5, which is switched from OFF to ON, is equal to or greater than the absolute value “|TI2|” of the secondary winding current threshold value TI2. The value of the current is denoted as “+I2” in Fig. 1 represents. The fifth switching element Q5 is a secondary switching element that switches from OFF to ON when the switching pattern changes from the fifth pattern to the fourth pattern. As shown in Fig. As shown in Figure 7, since the secondary current I2 has a positive value at the first time T1, “+I2” also assumes a positive value. Furthermore, the time of the first time T1 and the third time T3, at which the absolute value of the secondary current is smaller, varies according to the control mode.

[0060] In practice, condition 2 can be satisfied by comparing a secondary winding current threshold value TI2, which is converted to the primary side (TI2'), with the primary current I1 at the first time T1, or vice versa. In this case, one of the primary currents I1 and I2 is taken into account. Furthermore, the inductance L of the choke coil L1 can be preset such that if one of condition 1 and condition 2 is satisfied, the other of condition 1 and condition 2 is also satisfied.

[0061] In this way, a combination of target currents can be obtained that allows the output of the power required for load 120 while fulfilling both condition 1 and condition 2. If there is no combination of target currents that allows the output of the required power while fulfilling both condition 1 and condition 2, soft switching below the required power and control mode cannot be performed.

[0062] In step S3, the control unit 50 then determines a combination of the first phase difference θ1 and the second phase difference θ2 based on the obtained target current. The combination of the first phase difference θ1 and the second phase difference θ2 is obtained such that it follows the target current calculated at the first time T1 and the target current calculated at the second time T2. In other words, the combination of the first phase difference θ1 and the second phase difference θ2 allows the output of the power required for the power 120 and fulfills condition 1 and condition 2.

[0063] In step S4, the control device 50 controls the primary full bridge circuit 30 and the secondary full bridge circuit 40 in such a way that the first phase difference θ1 and the second phase difference θ2, which were determined in step S3, are realized.

[0064] The required power and the first phase difference θ1 and the second phase difference θ2 can be determined if necessary, or can be determined in advance and stored in a diagram (characteristic map) or the like. <Erster Hochsetzmodus>

[0065] As it is in Fig. As shown in Figure 2, the first boost mode has a first boost phase lag mode, a first boost phase equal mode, and a first boost phase lead mode.

[0066] As it is in Fig. As shown in Figure 8, the first boost phase-tracking mode is a first boost mode in which the secondary voltage V2 first rises from a low level to a mid-level, then the primary voltage V1 rises from a low level to a high level, and subsequently the secondary voltage V2 rises from the mid-level to a high level. The first boost phase-tracking mode is a first boost mode that outputs a small amount of power corresponding to the power required for load 120. The first boost phase-tracking mode differs from the first buck phase-tracking mode in that the high level of the secondary voltage V2 is higher than the high level of the primary voltage V1. Furthermore, the first boost phase-lag mode differs from the first buck phase-lag mode in that the low level of the secondary voltage V2 is lower than the low level of the primary voltage V1.

[0067] In the first buck-shift mode, the difference between a first time T11, at which the secondary voltage V2 rises from the low level to the medium level, and a second time T12, at which the primary voltage V1 rises from the low level to the high level, is defined as a first phase difference θ11. The difference between the first time T11 and a third time T13, at which the secondary voltage V2 rises from the medium level to the high level, is defined as a second phase difference θ12.

[0068] As described above, during a normal state where the output is unchanged, the primary voltage V1 and the secondary voltage V2 exhibit waveforms of the same frequency, each inverted by a phase of 180 degrees. Thus, the time at which the secondary voltage V2 falls from the high level to the mid-level is also the first time T11, the time at which the primary voltage V1 falls from the high level to the low level is also the second time T12, and the time at which the secondary voltage V2 falls from the mid-level to the low level is also the third time T13.

[0069] As it is in Fig. As shown in Figure 9, the first boost-equal phase mode is a first boost mode in which the secondary voltage V2 rises from the low level to the mid-level, and the primary voltage V1 simultaneously rises from the low level to the high level, and then the secondary voltage V2 rises from the mid-level to the high level. In the first boost-equal phase mode, the first time T11 and the second time T12 are the same. Accordingly, the first phase difference θ11 is zero. The first boost-equal phase mode is the first boost mode that outputs a mid-level power corresponding to the power required for load 120. The mid-level power is greater than the low-level power. The first boost-equal phase mode differs from the first buck-equal phase mode in that the high level of the secondary voltage V2 is higher than the high level of the primary voltage V1.Furthermore, the first boost phase-equal mode differs from the first buck phase-equal mode in that the low level of the secondary voltage V2 is lower than the low level of the primary voltage V1.

[0070] As it is in Fig. As shown in Figure 10, the first boost phase-adjustment mode is a first boost mode in which the primary voltage V1 first rises from a low level to a high level, the secondary voltage V2 then rises from a low level to a medium level, and subsequently the secondary voltage V2 rises from the medium level to a high level. The first boost phase-adjustment mode is a first boost mode that delivers a high level of power corresponding to the power required for load 120. The first boost phase-adjustment mode differs from the first buck phase-adjustment mode in that the high level of the secondary voltage V2 is higher than the high level of the primary voltage V1. Furthermore, the first boost phase-adjustment mode differs from the first buck phase-adjustment mode in that the low level of the secondary voltage V2 is lower than the low level of the primary voltage V1.

[0071] The first boost phase-lag mode is an example of a light-load mode. The first boost phase-advance mode is an example of a heavy-load mode. The first boost phase-align mode is a mode for switching between the light-load and heavy-load modes.

[0072] The switching control performed by the control device 50 in the case of the first boost mode is the same as in the first buck mode. In other words, the control device 50 determines a combination of the first phase difference θ11 and the second phase difference θ12 that allows the required power output. This combination satisfies conditions 1 and 2. Furthermore, the control device 50 outputs the required power by controlling the primary full-bridge circuit 30 and the secondary full-bridge circuit 50 such that the determined first phase difference θ11 and the determined second phase difference θ12 are achieved. <Zweite Steuerung>

[0073] The control unit 50 performs a second control operation. In the second control operation, the control unit 50 controls the primary full-bridge circuit 30 such that the primary voltage V1 is applied to the series-connected body 24 at three levels, and controls the secondary full-bridge circuit 40 such that the secondary voltage V2 is applied to the secondary winding 23 at two levels.

[0074] According to the first embodiment, the control device 50 performs the second control operation when the equivalent voltage ratio is less than the predetermined threshold, i.e., less than 1. The control device 50 performs the first control operation when the equivalent voltage ratio is equal to or greater than the predetermined threshold.

[0075] When implementing three-level control on the primary full-bridge circuit 30, the control device 50 independently controls the first limb 31 and the second limb 32. The switching patterns of the primary full-bridge circuit 30 include a seventh pattern, an eighth pattern, a ninth pattern, and a tenth pattern.

[0076] The seventh pattern is a switching pattern where the first switching element Q1 is ON, the second switching element Q2 is OFF, the third switching element Q3 is OFF, and the fourth switching element Q4 is ON.

[0077] The eighth pattern is a switching pattern where the first switching element Q1 is ON, the second switching element Q2 is OFF, the third switching element Q3 is ON, and the fourth switching element Q4 is OFF.

[0078] The ninth pattern is a switching pattern where the first switching element Q1 is OFF, the second switching element Q2 is ON, the third switching element Q3 is ON, and the fourth switching element Q4 is OFF.

[0079] The tenth pattern is a switching pattern where the first switching element Q1 is OFF, the second switching element Q2 is ON, the third switching element Q3 is OFF, and the fourth switching element Q4 is ON.

[0080] When implementing two-level control on the secondary full-bridge circuit 40, the control device 50 controls the third leg 41 and the fourth leg 42 in cooperation. The control device 50 simultaneously switches the fifth switching element Q5 and the eighth switching element Q8 ON. The control device 50 simultaneously switches the sixth switching element Q6 and the seventh switching element Q7 ON. The switching patterns of the secondary full-bridge circuit 40 have an eleventh pattern and a twelfth pattern.

[0081] The eleventh pattern is a switching pattern where the fifth switching element Q5 is ON, the sixth switching element Q6 is OFF, the seventh switching element Q7 is OFF, and the eighth switching element Q8 is ON.

[0082] The twelfth pattern is a switching pattern in which the fifth switching element Q5 is OFF, the sixth switching element Q6 is ON, the seventh switching element Q7 is ON, and the eighth switching element Q8 is OFF.

[0083] The control device 50 outputs the output voltage Vout from the secondary full bridge circuit 40 by combining one of the seventh to tenth patterns of the primary full bridge circuit 30 with one of the eleventh and twelfth patterns of the secondary full bridge circuit 40. <Zweiter Tiefsetzmodus>

[0084] The control device 50 has a second buck-shift mode as a control mode of the second control. The second buck-shift mode is a control mode that has an equivalent voltage ratio of less than 1. The second buck-shift mode has a second buck-shift phase-lag mode, a second buck-shift phase-align mode, and a second buck-shift phase-advance mode.

[0085] As it is in Fig. As shown in Figure 11, the second buck-start phase-tracking mode is a second buck-start mode in which the primary voltage V1 first rises from a low level to a medium level, the secondary voltage V2 then rises from the low level to a high level, and subsequently the primary voltage V1 rises from the medium level to a high level. The second buck-start phase-tracking mode is a second buck-start mode that outputs a small amount of power corresponding to the power required for load 120.

[0086] In the second control, the difference between a first time T21, at which the primary voltage V1 rises from the low level to the medium level, and a second time T22, at which the secondary voltage V2 rises from the low level to the high level, is defined as a first phase difference θ21. The difference between the first time T21 and a third time T23, at which the primary voltage V1 rises from the medium level to the high level, is defined as a second phase difference θ22.

[0087] As described above, during normal operation with an unchanged output, the primary voltage V1 and the secondary voltage V2 exhibit waveforms of the same frequency, each inverted by a phase of 180 degrees. Accordingly, the time it takes for the primary voltage V1 to fall from the high level to the mid-level is also the first time T21, the time it takes for the secondary voltage V2 to fall from the high level to the low level is also the second time T22, and the time it takes for the primary voltage V1 to fall from the mid-level to the low level is also the third time T23.

[0088] As it is in Fig. As shown in Figure 12, the second buck-step mode is a second buck-step mode in which the primary voltage V1 first rises from the low level to the medium level, then the secondary voltage V2 rises from the low level to the high level, and simultaneously the primary voltage V1 rises from the medium level to the high level. In the second buck-step mode, the first time T21 and the second time T22 are the same. Thus, the first phase difference θ21 and the second phase difference θ22 are the same value. The second buck-step mode is a second buck-step mode that outputs an average amount of power corresponding to the power required for the load 120.

[0089] As it is in Fig. As shown in Figure 13, the second buck-start phase-adjustment mode is a second buck-start mode in which the primary voltage V1 first rises from the low level to the medium level, then from the medium level to the high level, and subsequently the secondary voltage V2 rises from the low level to the high level. The second buck-start phase-adjustment mode is a second buck-start mode that outputs a high level of power corresponding to the power required for load 120. The high level of power is greater than the medium level of power.

[0090] The second buck-phase lag mode is an example of a light-load mode. The second buck-phase lead mode is an example of a heavy-load mode. The second buck-phase equal mode is a mode for switching between the light-load and heavy-load modes.

[0091] In the second buck-shift mode, the control unit 50 performs switching control by controlling the first phase difference θ21 and the second phase difference θ22. The control unit 50 determines a combination of the first phase difference θ21 and the second phase difference θ22 that allows the required power output. This combination is the condition for performing soft switching at the primary switching elements Q1 to Q4, which fulfills the same condition as condition 1 of the first control, and is also the condition for performing soft switching at the secondary switching elements Q5 to Q8, which fulfills the same condition as condition 2 of the first control.

[0092] In the second control, the time when at least one of the primary switching elements Q1 to Q4 is switched between ON and OFF refers to the point in time at which at least one of the primary switching elements of Q1 to Q4 switches from ON to OFF or from OFF to ON. This point in time is the same as the first time T21 or the third time T23. The first time T21 is the time at which the primary voltage V1 rises from the low level to the medium level, or the time at which the primary voltage V1 falls from the high level to the medium level. The third time T23 is the time at which the primary voltage V1 rises from the medium level to the high level, or the time at which the primary voltage V1 falls from the medium level to the low level.Furthermore, in the second control, the time at which at least one of the secondary switching elements Q5 to Q8 is switched from ON to OFF is the same as the time at which at least one of the switching elements of the secondary switching elements Q5 to Q8 is switched from ON to OFF or from OFF to ON. This time is the same as when the secondary voltage V2 rises from the low level to the high level, or the second time T22 is the same as when the secondary voltage V2 falls from the high level to the low level.

[0093] The control device 50 outputs the required power by controlling the primary full bridge circuit 30 and the secondary full bridge circuit 40 in such a way that the specific first phase difference θ21 and the specific second phase difference θ22 are achieved. [Operation according to the first embodiment]

[0094] Fig. Figure 14 shows a relationship between the equivalent voltage ratio and the output current. Line L12 is a boundary line where the heavy-duty and light-duty modes are switched when the second control is performed. Region A2 is an operating range where soft switching cannot be performed when the second control is performed. As shown in Fig. As shown in Figure 14, region A2 has the equivalent voltage ratio of 1. Therefore, soft switching cannot be performed in region A2, which has the equivalent voltage ratio of 1, in the second controller, even in heavy-duty mode.

[0095] In the second buck mode, the primary full-bridge circuit 30 is controlled such that the primary voltage V1 is applied to the series core 24 at three levels. The voltage applied to the inductor L1 is a value obtained by subtracting the voltage applied to the primary winding 22 from the primary voltage V1. When the equivalent voltage ratio is close to 1, the voltage applied to the inductor L1 decreases. If the voltage applied to the inductor L1 is low, the small change in current may prevent soft switching, even when the primary full-bridge circuit 30 is controlled to apply the primary voltage V1 at three levels to the series core 24. In other words, there may be cases where the primary current I1 and the secondary current I2 cannot be changed to values ​​within the soft-switching region.

[0096] When the voltage applied to the choke coil L1 is low, the rate of change in the current can be increased by controlling the secondary full-bridge circuit 40 such that the secondary voltage V2 is applied to the secondary winding 23 at three levels. This allows for smooth switching of the primary switching elements Q1 to Q4 and the secondary switching elements Q5 to Q8.

[0097] A line L11 in Fig. 14 is a boundary line where the heavy-duty and light-duty modes are switched when the first control is executed. Region A1 is an operating range where soft shifting is not performed when the first control is executed. In this way, the region where soft shifting cannot be performed shifts from region A2 under the second control to region A1 under the first control. Region A1, where soft shifting cannot be performed under the first control, does not overlap with region A2, where soft shifting cannot be performed under the second control. Thus, even though soft shifting cannot be performed under the second control, soft shifting can still be performed in region A2 under the first control.

[0098] As described above, the control device 50 performs the second control when the equivalent voltage ratio is less than the predetermined threshold, which is less than 1. The threshold can, for example, be any value less than the lower limit of the equivalent voltage ratio represented by region A2 and greater than the upper limit of the equivalent voltage ratio represented by region A1. In other words, the threshold can be set such that the second control is performed in region A1 and such that the first control is performed in region A2. [Advantages of the first embodiment] (1-1) When the equivalent voltage ratio is close to 1, the voltage applied to the inductor L1 is low. When the voltage applied to the inductor L1 is low, even if the primary full-bridge circuit 30 is controlled such that the primary voltage V1 is applied to the series body 24 at three levels, there are cases where soft switching cannot be performed because the change in the magnitude of the current is small (region A2). When the voltage applied to the inductor L1 is low, the magnitude of the change in the current is increased by controlling the secondary full-bridge circuit 40 such that the secondary voltage V2 is applied to the secondary winding 23 at three levels. Accordingly, even if the equivalent voltage ratio is close to 1, soft switching can be performed at the primary switching elements Q1 to Q4 and the secondary switching elements Q5 to Q8. (1-2) The control unit 50 performs the second control operation when the equivalent voltage ratio is less than the threshold, and performs the first control operation when the equivalent voltage ratio is equal to or greater than the threshold. When the equivalent voltage ratio is less than the threshold, there are cases in which soft switching cannot be performed with the first control operation (region A1). In such a case, the execution of the second control operation allows soft switching to be performed, even if soft switching cannot be performed with the first control operation. When the equivalent voltage ratio is equal to or greater than the threshold, there are cases in which soft switching cannot be performed with the second control operation (region A2).In such a case, the execution of the first control allows a soft switching operation to be carried out, even if the soft switching operation cannot be carried out with the second control. [Second embodiment]

[0099] A second embodiment of the power conversion device is described below.

[0100] As it is in Fig. As shown in Figure 15, the second embodiment differs from the first embodiment in that an inductor L2 is connected to the secondary winding 23 instead of the primary winding 22, and that the implementation of the three-level control and the two-level control is reversed between the primary and secondary sides. The secondary winding 23 and the inductor L2 form a series circuit 25. <Erste Steuerung>

[0101] The first control according to the second embodiment controls the primary full bridge circuit 30 in three levels and controls the secondary full bridge circuit 40 in two levels.

[0102] The three-level control switches the voltage applied to the primary winding 22 into three levels: positive, negative, and zero. The two-level control switches the voltage applied to the series terminal 25 of the secondary winding 23 and the inductor L2 into two levels: positive and negative. In the three-level control, the positive voltage applied to the primary winding 22 is called the high level, the zero voltage applied to the primary winding 22 is called the medium level, and the negative voltage applied to the primary winding 22 is called a low level. In the two-level control, the positive voltage applied to the series terminal 25 is called the high level, and the negative voltage applied to the series terminal 25 is called a low level.

[0103] The control device 50 outputs the output voltage Vout from the primary full bridge circuit 30 by combining one of the seventh to tenth patterns of the primary full bridge circuit 30 with one of the eleventh and twelfth patterns of the secondary full bridge circuit 40.

[0104] According to the second embodiment, the control device 50 has a first down-setting mode and a first up-setting mode as control modes of the first control. <Erster Tiefsetzmodus>

[0105] The first buck mode includes a first buck phase lag mode, a first buck phase equal mode, and a first buck phase lag mode.

[0106] As it is in Fig. As shown in Figure 16, the first buck-start phase-tracking mode is a first buck-start mode in which the primary voltage V1 first rises from the low level to the medium level, the secondary voltage V2 then rises from the low level to the high level, and the primary voltage V1 subsequently rises from the medium level to the high level. The first buck-start phase-tracking mode is a first buck-start mode that outputs a small amount of power corresponding to the power required for load 120.

[0107] The difference between a first time T31, at which the primary voltage V1 rises from the low level to the medium level, and a second time T32, at which the secondary voltage V2 rises from the low level to the high level, is defined as a first phase difference θ31. The difference between the first time T31 and a third time T33, at which the primary voltage V1 rises from the medium level to the high level, is defined as a second phase difference θ32.

[0108] During normal operation with an unchanged output, the primary voltage V1 and the secondary voltage V2 exhibit waveforms of the same frequency, each inverted by 180 degrees in phase. Thus, the time it takes for the primary voltage V1 to fall from the high level to the mid-level is also the first time T31, the time it takes for the secondary voltage V2 to fall from the high level to the low level is also the second time T32, and the time it takes for the primary voltage V1 to fall from the mid-level to the low level is also the third time T33.

[0109] As it is in Fig. As shown in Figure 17, the first buck-step mode is a first buck-step mode in which the primary voltage V1 first rises from the low level to the medium level, then from the medium level to the high level, and simultaneously the secondary voltage V2 rises from the low level to the high level. In the first buck-step mode, the second time T32 and the third time T33 are the same. Thus, the first phase difference θ31 and the second phase difference θ32 are the same value. The first buck-step mode is a first buck-step mode that outputs an average amount of power corresponding to the power required for load 120.

[0110] As it is in Fig. As shown in Figure 18, a first buck-start phase-adjustment mode is a first buck-start mode in which the primary voltage V1 first rises from a low level to a medium level, then from a medium level to a high level, and subsequently the secondary voltage V2 rises from a low level to a high level. The first buck-start phase-adjustment mode is a first buck-start mode that outputs a high amount of power corresponding to the power required for load 120.

[0111] In the first step-down mode, the control device 50 performs switching control by controlling the first phase difference θ31 and the second phase difference θ32, in the same manner as in the first embodiment. The control device 50 determines a combination of the first phase difference θ31 and the second phase difference θ32 that allows the output of the required power. This combination is the condition for performing soft switching at the primary switching elements Q1 to Q4, which is the same condition as operation 1 of the first control, and is also a condition for performing soft switching at the secondary switching elements Q5 to Q8, which is the same condition as condition 2 of the first control.

[0112] In the case of the first control according to the present embodiment, the time when at least one of the primary switching elements Q1 to Q4 is switched between ON and OFF refers to the time at which at least one of the primary switching elements of switching elements Q1 to Q4 switches from ON to OFF or from OFF to ON. This time is the same as the first time T31 or the third time T33. The first time T31 is the time at which the primary voltage V1 rises from the low level to the medium level, or the time at which the primary voltage V1 falls from the high level to the medium level. The third time T33 is the time at which the primary voltage V1 rises from the medium level to the high level, or the time at which the primary voltage V1 falls from the medium level to the low level.Furthermore, in the case of the first control according to the exemplary embodiment, the time at which at least one of the secondary switching elements Q5 to Q8 is switched between ON and OFF refers to the time at which at least one of the switching elements of the switching elements Q5 to Q8 switches from ON to OFF or from OFF to ON. This time is the same as the time when the secondary voltage V2 rises from the low level to the high level, or the second time T32, when the secondary voltage V2 falls from the high level to the low level.

[0113] Furthermore, the control device 50 outputs the required power by controlling the primary full bridge circuit 50 and the secondary full bridge circuit 50 in such a way that the specific first phase difference θ31 and the specific second phase difference θ32 are achieved. <Erster Hochsetzmodus>

[0114] A first boost mode according to the second embodiment has a first boost phase-lag mode, a first boost phase-align mode and a boost phase-lag mode.

[0115] As it is in Fig. As shown in Figure 19, the first boost phase-tracking mode is a first boost mode in which the primary voltage V1 first rises from the low level to the mid-level, the secondary voltage V2 then rises from the low level to the high level, and subsequently the primary voltage V1 rises from the mid-level to the high level. The first boost phase-tracking mode is a first boost mode that outputs a small amount of power corresponding to the power required for load 120. The first boost phase-tracking mode differs from the first buck phase-tracking mode in that a high level of the secondary voltage V2 is higher than a high level of the primary voltage V1. Furthermore, the first boost phase-tracking mode differs from the first buck phase-tracking mode in that a low level of the secondary voltage V2 is lower than a low level of the primary voltage V1.

[0116] The difference between a first time T41, at which the primary voltage V1 rises from the low level to the medium level, and a second time T42, at which the secondary voltage V2 rises from the low level to the high level, is defined as a first phase difference θ41. The difference between the first time T41 and a third time T43, at which the primary voltage V1 rises from the medium level to the high level, is defined as a second phase difference θ42.

[0117] As described above, during normal operation with an unchanged output, the primary voltage V1 and the secondary voltage V2 exhibit waveforms of the same frequency, each inverted by a phase of 180 degrees. Thus, the time it takes for the primary voltage V1 to fall from the high level to the mid-level is also the first time T41, the time it takes for the secondary voltage V2 to fall from the high level to the low level is also the second time T42, and the time it takes for the primary voltage V1 to fall from the mid-level to the low level is also the third time T43.

[0118] As it is in Fig. As shown in Figure 20, the first boost-equal phase mode is a first boost mode in which the primary voltage V1 first rises from the low level to the medium level, then from the medium level to the high level, and simultaneously the secondary voltage V2 rises from the low level to the high level. In the first boost-equal phase mode, the second time T42 and the third time T43 are the same. Thus, the first phase difference θ41 and the second phase difference θ42 are the same value. The first boost-equal phase mode is a first boost mode that outputs a medium amount of power corresponding to the power required for the load 120. The first boost-equal phase mode differs from the first buck-equal phase mode in that the high level of the secondary voltage V2 is higher than the high level of the primary voltage V1.Furthermore, the first boost phase-equal mode differs from the first buck phase-equal mode in that the low level of the secondary voltage V2 is lower than the low level of the primary voltage V1.

[0119] As it is in Fig. As shown in Figure 21, the first boost phase-adjustment mode is a first boost mode in which the primary voltage V1 first rises from the low level to the medium level, then from the medium level to the high level, and subsequently the secondary voltage V2 rises from the low level to the high level. The first boost phase-adjustment mode is a first boost mode that delivers a high level of power corresponding to the power required for load 120. The first boost phase-adjustment mode differs from the first buck phase-adjustment mode in that the high level of the secondary voltage V2 is higher than the high level of the primary voltage V1. Furthermore, the first boost phase-adjustment mode differs from the first buck phase-adjustment mode in that the low level of the secondary voltage V2 is lower than the low level of the primary voltage V1.

[0120] The switching control performed by the control device 50 in the case of the first boost mode is the same as in the first buck mode. In other words, the control device 50 determines a combination of the first phase difference θ41 and the second phase difference θ42 that allows the output of the required power. This combination satisfies conditions 1 and 2. Furthermore, the control device 50 outputs the required power by controlling the primary full-bridge circuit 30 and the secondary full-bridge circuit 40 such that the specified first phase difference θ41 and the specified second phase difference θ42 are achieved. <Zweite Steuerung>

[0121] The control device 50 performs the second control operation. According to the second embodiment, the second control operation controls the primary full-bridge circuit 30 such that the primary voltage V1 is applied to the primary winding 22 at two levels, and controls the secondary full-bridge circuit 40 such that the secondary voltage V2 is applied to the series-connected body 25 at three levels. According to the second embodiment, the control device 50 performs the second control operation when the equivalent voltage ratio is greater than the predetermined threshold, i.e., greater than 1. The control device 50 performs the first control operation when the equivalent voltage ratio is equal to or less than the predetermined threshold.

[0122] The control device 50 outputs the output voltage Vout from the secondary full bridge circuit 40 by combining one of the first pattern and the second pattern of the primary full bridge circuit 30 with one of the third to sixth patterns of the secondary full bridge circuit 40. <Zweiter Hochsetzmodus>

[0123] The control device 50 has a second boost mode as a control mode of the second controller. The second boost mode is a control mode for when the equivalent voltage ratio is greater than 1. The second boost mode has a second boost phase-advantage mode, a second boost phase-equalization mode, and a second boost phase-delay mode.

[0124] As it is in Fig. As shown in Figure 22, the second boost phase-tracking mode is a second boost mode in which the secondary voltage V2 first rises from the low level to the medium level, the primary voltage V1 then rises from the low level to the high level, and subsequently the secondary voltage V2 rises from the medium level to the high level. The second boost phase-tracking mode is a second boost mode that outputs a small amount of power corresponding to the power required for load 120.

[0125] In the second control, the difference between a first time T51, at which the secondary voltage V2 rises from the low level to the medium level, and a second time T52, at which the primary voltage V1 rises from the low level to the high level, is defined as a first phase difference θ51. The difference between the first time T51 and a third time T53, at which the secondary voltage V2 rises from the medium level to the high level, is defined as the second phase difference θ52.

[0126] As described above, during normal operation with an unchanged output, the primary voltage V1 and the secondary voltage V2 exhibit waveforms of the same frequency, each inverted by a phase of 180 degrees. Thus, the time it takes for the secondary voltage V2 to fall from the high level to the mid-level is also the first time T51, the time it takes for the primary voltage V1 to fall from the high level to the low level is also the second time T52, and the time it takes for the secondary voltage V2 to fall from the mid-level to the low level is also the third time T53.

[0127] As it is in Fig. As shown in Figure 23, the second boost-equal phase mode is a second boost mode in which the secondary voltage V2 first rises from the low level to the medium level, and the primary voltage V1 simultaneously rises from the low level to the high level, and the secondary voltage V2 then rises from the medium level to the high level. In the second boost-equal phase mode, the first time T51 and the second time T52 are the same. Accordingly, the first phase difference θ51 is zero. The second boost-equal phase mode is a second boost mode that outputs an average amount of power corresponding to the power required for load 120.

[0128] As it is in Fig. As shown in Figure 24, the second boost phase-adjustment mode is a second boost mode in which the primary voltage V1 first rises from the low level to the high level, the secondary voltage V2 then rises from the low level to the medium level, and subsequently the secondary voltage V2 rises from the medium level to the high level. The second boost phase-adjustment mode is a second boost mode that outputs a high amount of power corresponding to the power required for load 120.

[0129] The second boost phase-lag mode is an example of a light-load mode. The second boost phase-advance mode is an example of a heavy-load mode. The second boost phase-align mode is a mode for switching between the light-load and heavy-load modes.

[0130] In the second boost mode, the control unit 50 performs switching control by controlling the first phase difference θ51 and the second phase difference θ52. The control unit 50 determines a combination of the first phase difference θ51 and the second phase difference θ52 that allows the output of the required power. This combination is the condition for performing soft switching at the primary switching elements Q1 to Q4, which fulfills the same condition as condition 1 of the first control, and is also the condition for performing soft switching at the secondary switching elements Q5 to Q8, which fulfills the same condition as condition 2 of the first control.

[0131] In the second control, the time at which at least one of the primary switching elements Q1 to Q4 is switched between ON and OFF is the time at which at least one of the primary switching elements of Q1 to Q4 switches from ON to OFF or from OFF to ON. This time is the same as the time when the primary voltage V1 rises from the low level to the high level, or the second time T52, when the primary voltage V1 falls from the high level to the low level. Furthermore, in the second control, the time at which at least one of the secondary switching elements Q5 to Q8 is switched between ON and OFF is the time at which at least one of the switching elements of Q5 to Q8 switches from ON to OFF or from OFF to ON. This time is the same as the first time T51 or the third time T53.The first time, T51, is the time when the secondary voltage V2 rises from the low level to the medium level, or the time when the secondary voltage V2 falls from the high level to the low level. The third time, T53, is the time when the secondary voltage V2 rises from the medium level to the high level, or the time when the secondary voltage V2 falls from the medium level to the low level.

[0132] Furthermore, the control device 50 outputs the required power by controlling the primary full bridge circuit 30 and the secondary full bridge circuit 40 in such a way that the specific first phase difference θ51 and the specific second phase difference θ52 are achieved. [Operation according to the second embodiment]

[0133] Fig. Figure 25 shows a relationship between the equivalent voltage ratio and the output current. Line L22 is a boundary line where the heavy-duty and light-duty modes are switched when the second control is performed. Region A12 is an area where soft switching cannot be performed when the second control is executed. As shown in Fig. As shown in Figure 25, region A12 has the equivalent voltage ratio of 1. Therefore, soft switching in the heavy-duty mode of region A12, which has the equivalent voltage ratio of 1, cannot be performed in the second controller.

[0134] In the second boost mode, the secondary full-bridge circuit 40 is controlled such that the secondary voltage V2 is applied to the series core 25 at three levels. The voltage applied to the inductor L2 is a value obtained by subtracting the voltage applied to the secondary winding 23 from the secondary voltage V2. If the value of the equivalent voltage ratio is close to 1, the voltage applied to the inductor L2 is low. When the voltage applied to the inductor L2 is low, even if the secondary full-bridge circuit 40 is controlled to apply the secondary voltage V2 at three levels to the series core 25, soft switching may not be possible because the change in current magnitude is small.

[0135] When the voltage applied to the choke coil L2 is low, the rate of change in the current can be increased by controlling the primary full-bridge circuit 30 such that the primary voltage V1 is applied to the primary winding 22 at three levels. This allows for soft switching at the primary switching elements Q1 to Q4 and the secondary switching elements Q5 to Q8.

[0136] A line L21 in Fig. 25 is a boundary line where the heavy-duty and light-duty modes are switched when the first control is executed. Region A11 is an area where soft shifting cannot be performed when the first control is executed. In this way, the region where soft shifting cannot be performed shifts from region A12 under the second control to region A11 under the first control. Region A11, where soft shifting cannot be performed under the first control, does not overlap with region A12, which cannot perform soft shifting under the second control. Thus, even if soft shifting cannot be performed under the first control, soft shifting can still be performed in region A11 under the second control.

[0137] As described above, the control device 50 performs the second control when the equivalent voltage ratio is greater than the predetermined threshold, which is greater than 1. For example, the threshold can be a value greater than an upper limit of the equivalent voltage ratio represented by region A12 and less than a lower limit of the equivalent voltage ratio represented by region A11. In other words, the threshold can be set such that the second control is performed in region A11 and the first control is performed in region A12. [Advantages according to the second embodiment] (2-1) If the voltage applied to the inductor L2 is low, even if the secondary full-bridge circuit 40 is controlled such that the secondary voltage V2 is applied to the series body 25 at three levels, soft switching may not be possible because the change in the magnitude of the current is small (region A12). If the voltage applied to the inductor L2 is low, the change in the current can be increased by controlling the primary full-bridge circuit 30 such that the primary voltage V1 is applied to the primary winding 22 at three levels. Accordingly, even if the value of the equivalent voltage ratio is close to 1, soft switching can be performed at the primary switching elements Q1 to Q4 and the secondary switching elements Q5 to Q8. (2-2) The control unit 50 performs the second control when the equivalent voltage ratio is greater than the threshold, and performs the first control when the equivalent voltage ratio is equal to or less than the threshold. When the equivalent voltage ratio is greater than the threshold, there are cases in which soft switching cannot be performed using the first control (region A11). In such a case, the execution of the second control allows soft switching to be performed, even if soft switching cannot be performed using the first control. When the equivalent voltage ratio is equal to or less than the threshold, there are cases in which soft switching cannot be performed using the second control (region A12).In such a case, the execution of the first control allows for soft switching, even if soft switching cannot be performed with the second control. REFERENCE MARK LIST L1, L2 choke coil; Q1 to Q4 primary switching element; Q5 to Q8 secondary switching element; 10 Power conversion device; 20 Transformer; 22 Primary winding; 23 Secondary winding; 24, 25 series circuit bodies; 30 primary full bridge circuits; 40 secondary full bridge circuits; 50 Control unit.< / leistungsumwandlungsvorrichtung>

Claims

[1] Power conversion device with: a transformer that has a primary winding and a secondary winding, a choke coil connected to the primary winding, wherein the choke coil and the primary winding form a series circuit body, a primary full bridge circuit connected to the choke coil and featuring primary switching elements, a secondary full bridge circuit connected to the secondary winding and having secondary switching elements, and a control device configured to control the primary switching elements and the secondary switching elements, wherein a soft switching operation is performed on the primary switching elements under a condition defined as condition 1, and a soft switching operation is performed on the secondary switching elements under a condition defined as condition 2, Condition 1 is that, when at least one of the primary switching elements is switched between ON and OFF, a value of a current flowing through the primary winding in a forward direction of diodes connected in parallel to one or more of the primary switching elements being switched from OFF to ON is equal to or greater than an absolute value of a primary winding current threshold. Condition 2 is that, when at least one of the secondary switching elements is switched between ON and OFF, a value of a current flowing through the secondary winding in a forward direction of diodes connected in parallel to one or more of the secondary switching elements, switching from OFF to ON, is equal to or greater than an absolute value of a secondary winding current threshold value. the control device is configured to perform a first control operation that controls the primary full bridge circuit such that a primary voltage in two levels is applied to the series circuit body, and controls the secondary full bridge circuit such that a secondary voltage in three levels is applied to the secondary winding, the primary voltage and the secondary voltage exhibit waveforms of the same frequency, each inverted by a phase of 180 degrees, a difference between a first time at which the secondary voltage rises from a low level to a medium level, and a second time at which the primary voltage rises from a low level to a high level, is defined as a first phase difference, and a difference between the first time and a third time at which the secondary voltage rises from a medium level to a high level is defined as a second phase difference, and The control device is configured to output the required power in the first control by controlling the primary full bridge circuit and the secondary full bridge circuit in such a way as to achieve a combination of the first phase difference and the second phase difference that allows the output of the required power while satisfying condition 1 and condition 2. [2] Power conversion device according to claim 1, wherein, where a number of turns of the primary winding of the transformer is represented by N1, a number of turns of the secondary winding is represented by N2, an input voltage fed into the primary full bridge circuit is represented by Vin, an output voltage output from the secondary full bridge circuit is represented by Vout, an equivalent voltage ratio when the number of turns of the transformer is converted to a 1:1 ratio is expressed as (Vout×N1) / (Vin×N2); the control unit is configured, If the equivalent voltage ratio is less than a predetermined threshold of less than 1, a second control is to be executed to control the primary full-bridge circuit such that the primary voltage is applied to the series-connected body at three levels, and to control the secondary full-bridge circuit such that the secondary voltage is applied to the secondary winding at two levels, and If the equivalent voltage ratio is equal to or greater than the predetermined threshold, execute the first control. [3] Power conversion device with: a transformer that has a primary winding and a secondary winding, a choke coil connected to the secondary winding, wherein the choke coil and the secondary winding form a series circuit body, a primary full bridge circuit that is connected to the primary winding and has primary switching elements, a secondary full bridge circuit connected to the choke coil and featuring secondary switching elements, and a control device configured to control the primary switching elements and the secondary switching elements, wherein a soft switching operation is performed on the primary switching elements under a condition defined as condition 1, and a soft switching operation is performed on the secondary switching elements under a condition defined as condition 2, Condition 1 is that, when at least one of the primary switching elements is switched between ON and OFF, a value of a current flowing through the primary winding in a forward direction of diodes connected in parallel to one or more of the primary switching elements being switched from OFF to ON is equal to or greater than an absolute value of a primary winding current threshold. Condition 2 is that, when at least one of the secondary switching elements is switched between ON and OFF, a value of a current flowing through the secondary winding in a forward direction of diodes connected in parallel to one or more of the secondary switching elements, switching from OFF to ON, is equal to or greater than an absolute value of a secondary winding current threshold value. the control device is configured to perform a first control operation that controls the primary full bridge circuit such that a primary voltage in three levels is applied to the primary winding, and controls the secondary full bridge circuit such that a secondary voltage in two levels is applied to the series circuit body, the primary voltage and the secondary voltage exhibit waveforms of the same frequency, each inverted by a phase of 180 degrees, a difference between a first time at which the primary voltage rises from a low level to a medium level, and a second time at which the secondary voltage rises from a low level to a high level, is defined as a first phase difference, and a difference between the first time and a third time at which the primary voltage rises from a medium level to a high level is defined as a second phase difference, and The control device is configured to output the required power in the first control by controlling the primary full bridge circuit and the secondary full bridge circuit in such a way as to achieve a combination of the first phase difference and the second phase difference that allows the output of the required power while satisfying condition 1 and condition 2. [4] Power conversion device according to claim 3, wherein, where a number of turns of the primary winding of the transformer is represented by N1, a number of turns of the secondary winding is represented by N2, an input voltage fed into the primary full bridge circuit is represented by Vin, an output voltage output from the secondary full bridge circuit is represented by Vout, an equivalent voltage ratio when the number of turns of the transformer is converted to a 1:1 ratio is expressed as (Vout×N1) / (Vin×N2); the control unit is configured, If the equivalent voltage ratio is greater than a predetermined threshold greater than 1, a second control is to be executed to control the primary full-bridge circuit such that the primary voltage is applied to the primary winding at two levels, and to control the secondary full-bridge circuit such that the secondary voltage is applied to the series-connected bodies at three levels, and If the equivalent voltage ratio is equal to or less than the predetermined threshold, execute the first control.

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