Power conversion device

Abstract

A power conversion device is provided. The control unit (50) performs all-element soft switching operation control for outputting required power by controlling the first phase difference and the second phase difference so that all of the plurality of primary-side switching elements (Q1-Q4) and the plurality of secondary-side switching elements (Q5-Q8) are subjected to soft switching operation. The control unit (50) performs soft switching operation control of some of the elements when soft switching operation control of all of the elements cannot be performed. The partial element soft switching operation control outputs the required power by controlling the first phase difference and the second phase difference so that all of the switching elements of one type are subjected to soft switching operation and at least one of the switching elements of the other type is subjected to hard switching operation with respect to the plurality of primary-side switching elements (Q1-Q4) and the plurality of secondary-side switching elements (Q5-Q8).

Description

Technical Field

[0001] This disclosure relates to power conversion devices. Background Technology

[0002] Patent Document 1 discloses a power conversion device comprising a transformer, a primary-side full-bridge circuit, a secondary-side full-bridge circuit, and a control unit. The transformer includes a primary-side winding and a secondary-side winding. The primary-side full-bridge circuit includes multiple primary-side switching elements. The secondary-side full-bridge circuit includes multiple secondary-side switching elements. The control unit controls the primary-side full-bridge circuit by applying a three-level primary-side voltage to the primary-side winding. The control unit controls the secondary-side full-bridge circuit by applying a three-level secondary-side voltage to the secondary-side winding. The control unit achieves soft-switching operation of the primary-side and secondary-side switching elements by controlling the phase difference between the primary-side and secondary-side voltages.

[0003] Patent Document 1: International Publication No. 2020 / 003717

[0004] This power conversion device increases the transmitted power by making the phase of the primary-side voltage earlier than the phase of the secondary-side voltage, i.e., by changing from a lagging phase mode to a leading phase mode. Here, regarding the primary and secondary-side voltages, if one is set to a two-level voltage and the other to a three-level voltage, near the in-phase mode (near the switching between light and heavy load modes), there is a situation where soft-switching of all switching elements cannot be performed. The lagging phase mode is a load mode where, after the three-level voltage rises from a low level to a medium level, the two-level voltage rises from a low level to a high level. The leading phase mode is a load mode where, after the three-level voltage rises from a medium level to a high level, either the two-level voltage rises from a low level to a high level, or vice versa, the three-level voltage rises from a low level to a medium level.

[0005] One consideration is to increase the current flowing through the transformer to enable soft switching for all switching elements. However, using a transformer with a smaller magnetizing inductance than usual to increase the current would actually increase losses other than switching losses, potentially worsening overall efficiency. Summary of the Invention

[0006] The power conversion device according to one aspect of this disclosure includes: a transformer section having a primary winding, a secondary winding, and a reactor connected to at least one of the primary winding or the secondary winding; a primary-side full-bridge circuit, which is a circuit connected to the primary winding and has a plurality of primary-side switching elements; a secondary-side full-bridge circuit, which is a circuit connected to the secondary winding and has a plurality of secondary-side switching elements; and a control section that controls the plurality of primary-side switching elements and the plurality of secondary-side switching elements, wherein the condition for performing soft-switching operation of the plurality of primary-side switching elements is condition 1, and the condition for performing soft-switching operation of the plurality of secondary-side switching elements is condition 1. Condition 2 is the condition where, when at least one of the plurality of primary-side switching elements switches between on and off, the value of the forward-flowing current in the primary-side winding at the diode connected in parallel with the primary-side switching element that switches from off to on is greater than the absolute value of the primary-side winding current threshold. Condition 2 is the condition where, when at least one of the plurality of secondary-side switching elements switches between on and off, the value of the forward-flowing current in the secondary-side winding at the diode connected in parallel with the secondary-side switching element that switches from off to on is greater than the absolute value of the primary-side winding current threshold. The value of the current flowing to the secondary winding is above the absolute value of the secondary winding current threshold. The control unit is configured to control the primary-side full-bridge circuit and the secondary-side full-bridge circuit by applying a two-level voltage to the transformer section on one side and a three-level voltage to the transformer section on the other side. The difference between the first moment when the three-level voltage rises from a low level to a medium level and the second moment when the two-level voltage rises from a low level to a high level is the first phase difference. The difference between the first moment and the third moment when the three-level voltage rises from a medium level to a high level is the second phase difference. The control unit is configured to perform soft switching on all components. The control of soft switching of all the above-mentioned components outputs the required power by controlling the first phase difference and the second phase difference in such a way that all of the above-mentioned primary-side switching components and the above-mentioned secondary-side switching components perform soft switching operation. In the case that it is not possible to perform soft switching operation control of all the above-mentioned components, soft switching operation control of some components is performed. The soft switching operation control of some components outputs the required power by controlling the first phase difference and the second phase difference in such a way that all of the above-mentioned primary-side switching components and the above-mentioned secondary-side switching components perform soft switching operation and at least one of the other switching components performs hard switching operation.

[0007] The control unit performs soft-switching control on a subset of components when it is impossible to perform soft-switching control on all components. This allows for soft-switching of all switching components, including any one of the multiple primary-side and multiple secondary-side switching components. Compared to a situation where none of the switching components can perform soft-switching, this reduces the overall efficiency of the power conversion device.

[0008] The power conversion device described above may also have a light load mode and a heavy load mode in which the maximum output power is greater than that in the light load mode. The control unit is configured to perform soft switching control of some of the components when switching between the light load mode and the heavy load mode. Attached Figure Description

[0009] Figure 1 This is a circuit diagram of the power conversion device according to the first embodiment.

[0010] Figure 2 It is a graph showing the relationship between the equivalent voltage ratio and the load mode.

[0011] Figure 3 This is a diagram showing the primary and secondary voltages in the first buck hysteresis phase mode.

[0012] Figure 4 This is a diagram showing the primary and secondary voltages in the first buck in-phase mode.

[0013] Figure 5 This is a diagram showing the primary and secondary voltages in the first buck lead phase mode.

[0014] Figure 6 This is a diagram showing the primary and secondary currents in the first boost hysteresis phase mode.

[0015] Figure 7 This is a diagram showing the primary and secondary voltages in the first boost in-phase mode.

[0016] Figure 8 This is a diagram showing the primary and secondary voltages in the first boost lead phase mode.

[0017] Figure 9 This is a flowchart showing the soft-switching control of all components.

[0018] Figure 10 This is a diagram showing the primary and secondary currents in the first buck hysteresis phase mode.

[0019] Figure 11 This is a flowchart illustrating the soft-switching control of a portion of the components.

[0020] Figure 12 This is a diagram showing the primary and secondary currents when some components are controlled by soft switching.

[0021] Figure 13 This is a diagram showing the primary and secondary currents when some components are controlled by soft switching.

[0022] Figure 14 This is a diagram showing the primary and secondary currents when some components are controlled by soft switching.

[0023] Figure 15 This is a diagram showing the primary and secondary currents when some components are controlled by soft switching.

[0024] Figure 16 This is a diagram showing the primary and secondary currents when some components are controlled by soft switching.

[0025] Figure 17 This is a diagram showing the primary and secondary currents when some components are controlled by soft switching.

[0026] Figure 18 This is a circuit diagram of the power conversion device according to the second embodiment.

[0027] Figure 19 This is a diagram showing the primary and secondary voltages in the second buck hysteresis phase mode.

[0028] Figure 20 This is a diagram showing the primary and secondary voltages in the second buck in-phase mode.

[0029] Figure 21 This is a diagram showing the primary and secondary voltages in the second buck lead phase mode.

[0030] Figure 22 This is a diagram showing the primary and secondary voltages in the second boost hysteresis phase mode.

[0031] Figure 23 This is a diagram showing the primary and secondary voltages in the second boost in-phase mode.

[0032] Figure 24 This is a diagram showing the primary and secondary voltages in the second boost lead phase mode. Detailed Implementation

[0033] [First Embodiment]

[0034] The first embodiment of the power conversion device will be described.

[0035] like Figure 1 As shown, the power system 100 includes a DC power supply 110, a load 120, and a power conversion device 10. The DC power supply 110 inputs DC power to the power conversion device 10. The DC power supply 110 is, for example, a battery or a power circuit. The power circuit is, for example, an AC / DC converter that converts AC power to DC power and outputs it. The load 120 is, for example, a secondary battery capable of charging and discharging DC power. The secondary battery is, for example, a lithium-ion battery or a lead-acid battery.

[0036] <Power Conversion Device>

[0037] 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 converts the DC power input from the DC power supply 110 and outputs it to the load 120. The power conversion device 10 also converts the DC power input from the load 120 and outputs it to the DC power supply 110. In the following description, the primary side is treated as the input and the secondary side as the output. That is, the power conversion device 10 converts the DC voltage input from the DC power supply 110 and outputs it to the load 120.

[0038] The power conversion device 10 has two primary side terminals 11 and 12 and two secondary side terminals 13 and 14. A DC power supply 110 is electrically connected to the primary side terminals 11 and 12. A load 120 is electrically connected to the secondary side terminals 13 and 14.

[0039] The power conversion device 10 includes a transformer section TS. The transformer section TS includes a transformer 20 and a reactor L1. The transformer 20 is an insulated type. The transformer 20 includes 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 is connected to the reactor L1. The reactor L1 may be a choke or other similar element, or it may be the leakage inductance of the primary winding 22 and the secondary winding 23. In this embodiment, the reactor L1 is connected to the primary winding 22. The reactor L1 and the primary winding 22 form a series connection 24.

[0040] The power conversion device 10 includes a primary-side full-bridge circuit 30. The primary-side full-bridge circuit 30 includes a first bridge arm 31 and a second bridge arm 32. The first bridge arm 31 and the second bridge arm 32 are connected in parallel to primary-side terminals 11 and 12. Thus, the primary-side full-bridge circuit 30 is electrically connected to a DC power supply 110 via the primary-side terminals 11 and 12. The first bridge arm 31 includes 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 bridge arm 32 includes 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. The first switching element Q1 and the third switching element Q3 constitute the upper arm. The second switching element Q2 and the fourth switching element Q4 constitute the lower arm.

[0041] Switching elements Q1, Q2, Q3, and Q4 are multiple primary-side switching elements Q1 to Q4. These primary-side switching elements Q1 to Q4 are, for example, n-type MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). Alternatively, they can be p-type MOSFETs, IGBTs (Insulated Gate Bipolar Transistors), or GaN-HEMTs.

[0042] Diodes D1-D4 and capacitors C1-C4 are connected in parallel with primary-side switching elements Q1-Q4, respectively. Diodes D1-D4 can be parasitic diodes or components. Capacitors C1-C4 can be parasitic capacitances, components, or a combination of parasitic capacitances and components.

[0043] The connection points between the first switching element Q1 and the second switching element Q2, and between the third switching element Q3 and the fourth switching element Q4, are respectively connected to the primary winding 22. Thus, the primary-side full-bridge circuit 30 is connected to the primary winding 22. Furthermore, the primary-side full-bridge circuit 30 is connected to the reactor L1.

[0044] The power conversion device 10 includes a primary-side voltage sensor 37. The primary-side voltage sensor 37 detects the input voltage Vin from the DC power supply 110 to the primary-side full-bridge circuit 30.

[0045] The power conversion device 10 includes a secondary-side full-bridge circuit 40. The secondary-side full-bridge circuit 40 includes a third bridge arm 41 and a fourth bridge arm 42. The third bridge arm 41 and the fourth bridge arm 42 are connected in parallel to the secondary-side terminals 13 and 14. Thus, the secondary-side full-bridge circuit 40 is electrically connected to the load 120. The third bridge arm 41 includes 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 bridge arm 42 includes 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 the upper arm. The sixth switching element Q6 and the eighth switching element Q8 form the lower arm.

[0046] Switching elements Q5 (5th), Q6 (6th), Q7 (7th), and Q8 (8th) are multiple secondary-side switching elements Q5-Q8. These secondary-side switching elements Q5-Q8 are, for example, n-type MOSFETs. Alternatively, they can be p-type MOSFETs, IGBTs, or GaN-HEMTs.

[0047] Diodes D5-D8 and capacitors C5-C8 are connected in parallel with secondary-side switching elements Q5-Q8, respectively. Diodes D5-D8 can be parasitic diodes or components. Capacitors C5-C8 can be parasitic capacitances, components, or a combination of parasitic capacitances and components.

[0048] The connection points between the fifth switching element Q5 and the sixth switching element Q6, and between the seventh switching element Q7 and the eighth switching element Q8, are respectively connected to the secondary winding 23. Thus, the secondary full-bridge circuit 40 is connected to the secondary winding 23.

[0049] The output power of the secondary-side full-bridge circuit 40 is supplied to the load 120.

[0050] The power conversion device 10 includes a secondary-side voltage sensor 47. The secondary-side voltage sensor 47 detects the output voltage Vout of the power conversion device 10.

[0051] The power conversion device 10 includes a control unit 50. The control unit 50 includes a processor and a storage unit. The processor may be, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or a DSP (Digital Signal Processor). The storage unit includes RAM (Random Access Memory) and ROM (Read Only Memory). The storage unit stores program code or instructions configured to cause the processor to perform processing. The storage unit, i.e., computer-readable medium, includes all usable media accessible by a general-purpose or special-purpose computer. The control unit 50 may also be a hardware circuit structure such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control unit 50, as a processing circuit, may include one or more hardware circuits such as a processor, ASIC, or FPGA, or a combination thereof, that operate according to a computer program.

[0052] The control unit 50 converts the input voltage Vin into the output voltage Vout by controlling multiple primary-side switching elements Q1 to Q4 and multiple secondary-side switching elements Q5 to Q8.

[0053] In this embodiment, the control unit 50 performs three-level control on the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40, and performs two-level control on the secondary-side full-bridge circuit 40.

[0054] Three-level control refers to the control that switches the voltage applied to the primary winding 22 and the series connection 24 of the transformer section TS to three levels: positive, negative, or 0. Two-level control refers to the control that switches the voltage applied to the secondary winding 23 of the transformer section TS to two levels: positive or negative. Appropriately, in three-level control, the case where the voltage applied to the series connection 24 is positive is called high level, the case where the voltage applied to the series connection 24 is 0 is called medium level, and the case where the voltage applied to the series connection 24 is negative is called low level. In two-level control, the case where the voltage applied to the secondary winding 23 is positive is called high level, and the case where the voltage applied to the secondary winding 23 is negative is called low level. The voltage applied to the series connection 24 is called primary side voltage V1, and the voltage applied to the secondary winding 23 is called secondary side voltage V2. The primary-side voltage V1 is the potential difference between the connection points of the first switching element Q1 and the second switching element Q2, and between the connection points of the third switching element Q3 and the fourth switching element Q4. The secondary-side voltage V2 is the potential difference between the connection points of the fifth switching element Q5 and the sixth switching element Q6, and between the seventh switching element Q7 and the eighth switching element Q8. In the first embodiment, the primary-side voltage V1 is a three-level voltage. The secondary-side voltage V2 is a two-level voltage. Figure 1 The direction of the arrow is set as the positive direction of the primary side voltage V1 and the secondary side voltage V2. When the normal operation of the output is not changed, the primary side voltage V1 and the secondary side voltage V2 are waveforms with the same frequency whose phase flips every 180 degrees.

[0055] When performing three-level control of the primary-side full-bridge circuit 30, the control unit 50 controls the first bridge arm 31 and the second bridge arm 32 independently. The switching operation types of the primary-side full-bridge circuit 30 include type 1 to type 4.

[0056] The first type is a switching action that turns on the first switching element Q1, turns off the second switching element Q2, turns off the third switching element Q3, and turns on the fourth switching element Q4.

[0057] The second type is a switching action type that turns on the first switching element Q1, turns off the second switching element Q2, turns on the third switching element Q3, and turns off the fourth switching element Q4.

[0058] The third type is a switching action type that disconnects the first switching element Q1, connects the second switching element Q2, connects the third switching element Q3, and disconnects the fourth switching element Q4.

[0059] The fourth type is a switching action type that disconnects the first switching element Q1, connects the second switching element Q2, disconnects the third switching element Q3, and connects the fourth switching element Q4.

[0060] When performing two-level control of the secondary-side full-bridge circuit 40, the control unit 50 controls the third bridge arm 41 and the fourth bridge arm 42 in a coordinated manner. The control unit 50 simultaneously turns on the fifth switching element Q5 and the eighth switching element Q8. The control unit 50 simultaneously turns on the sixth switching element Q6 and the seventh switching element Q7. The switching operation types of the secondary-side full-bridge circuit 40 include type 5 and type 6.

[0061] Type 5 is a switching action type that turns on the 5th switching element Q5, turns off the 6th switching element Q6, turns off the 7th switching element Q7, and turns on the 8th switching element Q8.

[0062] Type 6 is a switching action type that disconnects the 5th switching element Q5, connects the 6th switching element Q6, connects the 7th switching element Q7, and disconnects the 8th switching element Q8.

[0063] The control unit 50 outputs the output voltage Vout from the secondary full-bridge circuit 40 through a combination of any one of the first to fourth types of the primary full-bridge circuit 30 and any one of the fifth and sixth types of the secondary full-bridge circuit 40.

[0064] Here, the number of turns in the primary winding 22 of transformer 20 is N1, and the number of turns in the secondary winding 23 is N2. The ratio of the input voltage Vin to the primary full-bridge circuit 30 to the output voltage Vout from the secondary full-bridge circuit 40 is the voltage ratio. The equivalent voltage ratio when the turns ratio of transformer 20 is converted to 1:1 is (Vout×N1) / (Vin×N2). Vin×N2 is the equivalent input voltage when the transformer winding ratio is converted to 1:1. Vout×N1 is the equivalent output voltage when the transformer winding ratio is converted to 1:1. The control unit 50 has a first buck mode and a first boost mode as load modes. The first buck mode is a load mode that makes the equivalent voltage ratio less than 1. The first boost mode is a load mode that makes the equivalent voltage ratio greater than 1.

[0065] For example, with a winding ratio of 1:2 for transformer 20 and an input voltage Vin = 200V and an output voltage Vout = 400V, if the winding ratio is converted to 1:1, the equivalent voltage ratio = (Vout × 1) / (Vin × 2) = 1. Therefore, with a winding ratio of 1:2 for transformer 20 and an input voltage Vin = 200V, if the output voltage Vout is less than 400V, it is in buck mode; if it is greater than 400V, it is in boost mode. Furthermore, unless otherwise stated, the winding ratio will be described as 1:1 in the following description.

[0066] <First Pressure Reduction Mode>

[0067] like Figure 2 As shown, the first buck mode includes a first buck lag phase mode, a first buck in-phase mode, and a first buck lead phase mode.

[0068] like Figure 3 As shown, the first buck-hysteresis phase mode is a buck-hysteresis mode in which the primary side voltage V1 rises from a low level to a medium level, then the secondary side voltage V2 rises from a low level to a high level, and then the primary side voltage V1 rises from a medium level to a high level. The first buck-hysteresis phase mode is the first buck mode in which a small amount of power is output based on the power demand from load 120. The first buck-hysteresis phase mode is an example of a hysteresis phase mode. A hysteresis phase mode is a load mode in which the three-level voltage rises from a low level to a medium level, and then the two-level voltage rises from a low level to a high level.

[0069] In the load mode of the first embodiment, the difference between the first moment T1 when the primary side voltage V1 rises from a low level to a medium level and the second moment T2 when the secondary side voltage V2 rises from a low level to a high level is the first phase difference θ1. The difference between the first moment T1 and the third moment T3 when the primary side voltage V1 rises from a medium level to a high level is the second phase difference θ2.

[0070] Furthermore, as described above, when the normal operation of the output is not altered, the primary-side voltage V1 and the secondary-side voltage V2 are waveforms with the same frequency whose phase flips every 180 degrees. Therefore, the moment when the primary-side voltage V1 drops from a high level to a medium level is also the first moment T1, the moment when the secondary-side voltage V2 drops from a high level to a low level is also the second moment T2, and the moment when the primary-side voltage V1 drops from a medium level to a low level is also the third moment T3.

[0071] like Figure 4 As shown, the first buck in-phase mode is a mode in which the primary-side voltage V1 rises from a low level to a medium level while simultaneously rising the secondary-side voltage V2 from a low level to a high level and rising the primary-side voltage V1 from a medium level to a high level. In the case of the first buck in-phase mode, time T2 and time T3 are the same. Therefore, the first phase difference θ1 and the second phase difference θ2 are the same. The first buck in-phase mode is the first buck mode in which a medium power is output according to the power demand from load 120. Medium power is power greater than small power.

[0072] like Figure 5As shown, the first buck-lead phase mode is a buck-lead phase mode in which the primary side voltage V1 rises from a low level to a medium level, then rises from a medium level to a high level, and then the secondary side voltage V2 rises from a low level to a high level. The first buck-lead phase mode is the first buck mode in which a large power output is performed based on the power demand from the load 120. Large power is power greater than medium power. The first buck-lead phase mode is an example of a lead phase mode. In this embodiment, the lead phase mode is a load mode in which the three-level voltage rises from a medium level to a high level, and then the two-level voltage rises from a low level to a high level.

[0073] The first buck lagging phase mode is an example of a light load mode. The first buck leading phase mode is an example of a heavy load mode. Compared to the light load mode, the heavy load mode has a larger maximum output power. The first buck in-phase mode is the load mode used when switching between the light load mode and the heavy load mode. The first buck mode switches between the first buck lagging phase mode and the first buck leading phase mode when the first phase difference θ1 and the second phase difference θ2 are the same.

[0074] <First Boost Mode>

[0075] like Figure 2 As shown, the first boost mode includes a first boost lagging phase mode, a first boost in-phase mode, and a first boost leading phase mode.

[0076] like Figure 6 As shown, the first boost hysteresis phase mode is a boost mode in which the primary side voltage V1 rises from a low level to a medium level, then the secondary side voltage V2 rises from a low level to a high level, and then the primary side voltage V1 rises from a medium level to a high level. The first boost hysteresis phase mode is used when the power output is small according to the power demand from the load 120. The first boost hysteresis phase mode differs from the first buck hysteresis phase mode in that the high level of the secondary side voltage V2 is higher than the high level of the primary side voltage V1. Furthermore, it differs from the first buck hysteresis phase mode in that the low level of the secondary side voltage V2 is lower than the low level of the primary side voltage V1. The first boost hysteresis phase mode is an example of a hysteresis phase mode.

[0077] like Figure 7As shown, the first boost in-phase mode is a mode in which the primary-side voltage V1 rises from a low level to a medium level, and simultaneously the secondary-side voltage V2 rises from a low level to a high level, and the primary-side voltage V1 rises from a medium level to a high level. In the first boost in-phase mode, time T2 and time T3 are the same. Therefore, the first phase difference θ1 and the second phase difference θ2 are the same. The first boost in-phase mode is the first boost mode used when the power output is medium according to the power demand from the load 120. Medium power is power greater than small power. For the first boost in-phase mode, it differs from the first buck in-phase mode in that the high level of the secondary-side voltage V2 is higher than the high level of the primary-side voltage V1. Furthermore, it differs from the first buck in-phase mode in that the low level of the secondary-side voltage V2 is lower than the low level of the primary-side voltage V1.

[0078] like Figure 8 As shown, the first boost lead phase mode is a boost mode in which the primary side voltage V1 rises from a low level to a medium level, then rises from a medium level to a high level, and then the secondary side voltage V2 rises from a low level to a high level. The first boost lead phase mode is used when a large power output is required from the load 120. The first boost lead phase mode differs from the first buck lead phase mode in that the high level of the secondary side voltage V2 is higher than the high level of the primary side voltage V1. Furthermore, it differs from the first buck lead phase mode in that the low level of the secondary side voltage V2 is lower than the low level of the primary side voltage V1. The first boost lead phase mode is an example of a lead phase mode.

[0079] The first boost lagging phase mode is an example of a light load mode. The first boost leading phase mode is an example of a heavy load mode. The first boost in-phase mode is used when switching between light load and heavy load modes. The first boost mode switches between the first boost lagging phase mode and the first boost leading phase mode when the first phase difference θ1 and the second phase difference θ2 are the same.

[0080] <Soft switching control of all components>

[0081] The control unit 50 performs soft-switching control of all components. This soft-switching control is achieved by controlling the first phase difference θ1 and the second phase difference θ2 to output the required power, thereby causing all primary-side switching components Q1-Q4 and all secondary-side switching components Q5-Q8 to perform soft-switching operations. The soft-switching control of all components will be explained below.

[0082] like Figure 9 and Figure 10 As shown, in step S1, the control unit 50 derives the soft-switching operation region. The soft-switching operation region is set for the primary side current I1 and the secondary side current I2 respectively. The primary side current I1 is the current flowing in the primary side winding 22. The secondary side current I2 is the current flowing in the secondary side winding 23. Figure 1 The direction of the middle arrow is set as the positive direction of the primary side current I1 and the secondary side current I2.

[0083] The condition for soft-switching operation of multiple primary-side switching elements Q1 to Q4 is that when the primary-side switching elements Q1 to Q4 switch between on and off, the value of the forward-flowing current at the diode connected in parallel with the primary-side switching element Q1 to Q4 that changes from off to on is greater than the absolute value of the primary-side winding current threshold TI1. Hereinafter, this condition is designated as condition 1. The region satisfying this condition is the soft-switching operation region of the primary-side current I1. When the primary-side switching elements Q1 to Q4 switch between on and off, it is the time point at which at least one of the primary-side switching elements Q1 to Q4 changes from on to off or from off to on. This is the same as time point T1 (first time) or time point T3 (third time). Time point T1 is the moment when the primary-side voltage V1 rises from a low level to a medium level or when the primary-side voltage V1 decreases from a high level to a medium level. The third moment T3 is the moment when the primary side voltage V1 rises from the intermediate level to the high level or when the primary side voltage V1 drops from the intermediate level to the low level.

[0084] The condition for soft-switching operation of multiple secondary-side switching elements Q5~Q8 is that when the secondary-side switching elements Q5~Q8 switch between on and off, the value of the forward-flowing current at the diode connected in parallel with the switching element of the secondary-side switching elements Q5~Q8 that changes from off to on is greater than the absolute value of the secondary-side winding current threshold TI2. Hereinafter, this condition is set as condition 2. The region that satisfies this condition is the soft-switching operation region of the secondary-side current I2. The switching of secondary-side switching elements Q5~Q8 between on and off is the time point at which at least one of the secondary-side switching elements Q5~Q8 changes from on to off or from off to on. This is the same as the time point at which the secondary-side voltage V2 rises from low level to high level or decreases from high level to low level, i.e., the second time point T2.

[0085] As described above, the primary voltage V1 and the secondary voltage V2 are waveforms with the same frequency whose phase flips every 180 degrees. Therefore, they only flip in opposite directions during the rising and falling phases, so only one of them needs to be considered. The following explanation focuses only on the rising phase.

[0086] Figure 10As an example, the primary-side current I1 and secondary-side current I2 are shown in the first buck hysteresis phase mode. (As with...) Figure 3 As can be seen from the comparison of voltage waveforms, in Figure 10 In the example shown, at time 1 T1, the switching action type of the primary-side full-bridge circuit 30 switches from type 3 to type 2. Furthermore, at time 3 T3, the switching action type of the primary-side full-bridge circuit 30 switches from type 2 to type 1. At these times, if condition 1 is satisfied, the soft-switching action of the primary-side switching elements Q1~Q4 is achieved. At time 2 T2, the switching action type of the secondary-side full-bridge circuit 40 switches from type 6 to type 5. At this time, if condition 2 is satisfied, the soft-switching action of the secondary-side switching elements Q5~Q8 is achieved.

[0087] The primary winding current threshold TI1 is defined by the following equation (1).

[0088] Mathematical Formula 1

[0089]

[0090] TI1 is the primary winding current threshold, k1 is a coefficient, V1 is the primary side voltage, L is the inductance of reactor L1, and C01 is the capacitance corresponding to one switching element for the combined capacitance of all capacitors C1 to C4 connected in parallel with the switching elements Q1 to Q4 of the primary side full-bridge circuit 30. Alternatively, 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. Alternatively, if Cx is set to the maximum capacitance among C11 to C14, then C01 = Cx. Furthermore, the secondary winding current threshold TI2 is also defined similarly by replacing each value with a secondary side value. This derives the soft-switching operation region.

[0091] Next, in step S2, the control unit 50 calculates the target current. The target current is the current value that can output the required power from the load 120 and satisfy conditions 1 and 2.

[0092] Among the primary-side switching elements Q1~Q4, the switching element that changes from open to closed at time 3 T3 is the fourth switching element Q4. The fourth switching element Q4 is the primary-side switching element that changes from open to closed when the switching action type changes from type 2 to type 1.

[0093] To satisfy condition 1, consider the primary-side current I1 at time 1 (T1) and time 3 (T3). However, it is sufficient to consider the primary-side current I1 at time 3 (T3), which is the time when the absolute value of the current under this load mode is smaller. Therefore, to satisfy condition 1, the forward-flowing current at diode D4, which is the primary-side current I1 at time 3 (T3) and is connected in parallel with the fourth switching element Q4 (which changes from off to on at this time), must be greater than or equal to the absolute value of the primary-side winding current threshold TI1, "|TI1|". The value of this current is... Figure 1 The value of "-I1". Additionally, as from... Figure 10 As can be seen, at time 3 T3, the primary side current I1 is negative, therefore, "-I1" is positive. Furthermore, whether the absolute value decreases at time 1 T1 or time 3 T3 depends on the load mode.

[0094] In this load mode, to satisfy condition 2, the forward-flowing current at diodes D5 and D8 (connected in parallel with the fifth and eighth switching elements Q5 and Q8, which change from off to on at time T2) of the secondary side current I2 at time T2 must be greater than or equal to the absolute value of the secondary winding current threshold TI2, “|TI2|”. This current value is... Figure 1 The value of "I2". Switching element Q5 (5th) and switching element Q8 (8th) are secondary-side switching elements that change from open to closed when the switching action type changes from type 6 to type 5. Additionally, as from... Figure 10 As can be seen, at the second moment T2, the secondary side current I2 is positive, therefore, "I2" is positive.

[0095] In practical terms, for example, for condition 1, it can also be satisfied by comparing TI1', obtained by converting the primary winding current threshold TI1 to the secondary winding, with the secondary winding current I2 at time 1 T1, and vice versa. In this case, it is sufficient to consider either the primary winding current I1 or the secondary winding current I2. Alternatively, the inductance L of reactor L1 can be pre-set in such a way that if either condition 1 or condition 2 is satisfied, the other one will naturally be satisfied.

[0096] In this way, the combination of target currents that can output the required power from load 120 and satisfy conditions 1 and 2 can be calculated. Furthermore, if no such combination of target currents exists that can output the required power and satisfy conditions 1 and 2, it means that soft-switching operation cannot be achieved under this power demand and load mode.

[0097] Next, in step S3, the control unit 50 derives a combination of the first phase difference θ1 and the second phase difference θ2 based on the calculated target current. Here, the combination of the first phase difference θ1 and the second phase difference θ2 is derived by following the calculated target current at time 1 T1 and time 2 T2. That is, the combination of the first phase difference θ1 and the second phase difference θ2 is a combination that can output the required power of the load 120 and satisfy conditions 1 and 2.

[0098] In step S4, the control unit 50 controls the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 in a manner that realizes the first phase difference θ1 and the second phase difference θ2 derived in step S3.

[0099] The required power and the first phase difference θ1 and the second phase difference θ2 can be calculated each time, or they can be calculated in advance and stored in a mapping table, etc.

[0100] <Soft switching control of some components>

[0101] The control unit 50 performs partial soft-switching control on some components. This partial soft-switching control is performed when it is impossible to perform soft-switching control on all components. Alternatively, it may be performed when performing soft-switching control on all components fails to derive the combination of the first phase difference θ1 and the second phase difference θ2. Or, it may be performed when determining whether soft-switching control on all components is possible based on demand power, the first phase difference θ1, and the second phase difference θ2, and determining that it is impossible to perform soft-switching control on all components.

[0102] Partial soft-switching control is a control that outputs the required power by controlling the first phase difference θ1 and the second phase difference θ2 by causing all of one type of primary-side switching elements Q1-Q4 and the other type of secondary-side switching elements Q5-Q8 to perform soft-switching operations, while at least one of the other type of switching elements performs hard-switching operations. In other words, it is a control that prioritizes soft-switching operations for any one of the primary-side switching elements Q1-Q4 and the secondary-side switching elements Q5-Q8. First, the case where all of the primary-side switching elements Q1-Q4 perform soft-switching operations and a portion of the secondary-side switching elements Q5-Q8 perform hard-switching operations will be explained.

[0103] like Figure 11As shown, in step S11, the control unit 50 derives a combination of a first phase difference θ1 and a second phase difference θ2 that can output the required power to the load 120 and satisfy condition 1. That is, it is sufficient to derive a first phase difference θ1 and a second phase difference θ2 such that only the primary side switching elements Q1~Q4 and the secondary side switching elements Q5~Q8 can perform soft switching operation.

[0104] Next, in step S12, the control unit 50 controls the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 in a manner that enables the combination of the first phase difference θ1 and the second phase difference θ2 derived in step S11. Since soft-switching control of some components cannot be performed when soft-switching control of all components is not possible, even if control is performed in a manner that achieves the first phase difference θ1 and the second phase difference θ2 derived in step S11, it is impossible to cause all switching elements Q1 to Q8 to perform soft-switching operations. Therefore, condition 2 is not satisfied, and as a result, at least one secondary-side switching element Q5 to Q8 performs hard-switching operation.

[0105] Soft-switching control of some components is performed, for example, when the equivalent voltage ratio is close to 1. That is, soft-switching control of some components is performed when switching from a light load mode to a heavy load mode or from a heavy load mode to a light load mode.

[0106] Figures 12-14 The diagram illustrates the primary-side current I1 and secondary-side current I2 during the switching from the first buck lag phase mode to the first buck lead phase mode, where partial element soft-switching is performed to prioritize the soft-switching of primary-side switching elements Q1~Q4. There are cases where condition 1 is satisfied, but condition 2 is not. Figures 12-14 In the example shown, at the second moment T2 when the secondary side voltage V2 rises from low level to high level or falls from high level to low level, two secondary side switching elements, or in other words, four secondary side switching elements Q5~Q8 perform hard switching operations in one cycle.

[0107] Next, we will explain the case where all secondary-side switching elements Q5-Q8 are soft-switched and some of the primary-side switching elements Q1-Q4 are hard-switched. In this case, the control unit 50 derives a combination of the first phase difference θ1 and the second phase difference θ2 that enables the output of the required power to the load 120 and satisfies condition 2. That is, it is sufficient to derive the first phase difference θ1 and the second phase difference θ2 such that only the secondary-side switching elements Q5-Q8 among the primary-side switching elements Q1-Q4 and the secondary-side switching elements Q5-Q8 can perform soft-switching operations.

[0108] Figures 15-17 The diagram illustrates the primary-side current I1 and secondary-side current I2 during the switch from the first buck lag phase mode to the first buck lead phase mode, where partial soft-switching of secondary-side switching elements Q5-Q8 is prioritized. However, there are cases where condition 2 is satisfied, but condition 1 is not. Figures 15-17 In the example shown, at the third moment T3 when the primary side voltage V1 rises from the medium level to the high level or decreases from the medium level to the low level, there is one primary side switching element, or in other words, two primary side switching elements Q1~Q4 perform hard switching in one cycle.

[0109] [Effects of the first embodiment]

[0110] (1-1) When it is impossible to perform soft-switching control on all components, the control unit 50 performs soft-switching control on a subset of components. Therefore, soft-switching can be performed on all of the primary-side switching components Q1-Q4 and the secondary-side switching components Q5-Q8. Compared to the case where soft-switching cannot be performed on all switching components Q1-Q8, the overall efficiency reduction of the power conversion device 10 can be suppressed.

[0111] [Second Embodiment]

[0112] A second embodiment of the power conversion device will be described. The differences from the first embodiment will be explained.

[0113] like Figure 18 As shown, the second embodiment differs from the first embodiment in that the connection between the primary and secondary sides is reversed, instead of the primary winding 22, and the reactor L2 is connected to the secondary winding 23, and three-level control and two-level control are performed. The transformer section TS includes a transformer 20 and a reactor L2. The secondary winding 23 and the reactor L2 form a series connection body 25.

[0114] In the second embodiment, the control unit 50 performs two-level control on the primary side full-bridge circuit 30 and three-level control on the secondary side full-bridge circuit 40.

[0115] Three-level control controls the voltage applied to the transformer section TS (i.e., the voltage applied to the series connection 25 between the secondary winding 23 and the reactor L2) at three levels: positive, negative, or 0. Two-level control controls the voltage applied to the transformer section TS (i.e., the voltage applied to the primary winding 22) at two levels: positive or negative. Appropriately, in three-level control, a positive voltage applied to the series connection 25 is called a high level, a 0 voltage applied to the series connection 25 is called a medium level, and a negative voltage applied to the series connection 25 is called a low level. In two-level control, a positive voltage applied to the primary winding 22 is called a high level, and a negative voltage applied to the primary winding 22 is called a low level. The voltage applied to the primary winding 22 is designated as the primary-side voltage V1. The voltage applied to the series connection 25 is designated as the secondary-side voltage V2. The primary-side voltage V1 is a two-level voltage. The secondary-side voltage V2 is a three-level voltage. Figure 18 The direction of the arrow is set as the positive direction of the primary side voltage V1 and the secondary side voltage V2. Under normal operation without changing the output, the primary side voltage V1 and the secondary side voltage V2 are waveforms with the same frequency whose phase flips every 180 degrees.

[0116] When performing two-level control of the primary-side full-bridge circuit 30, the control unit 50 controls the first bridge arm 31 and the second bridge arm 32 in a linked manner. The control unit 50 simultaneously turns on the first switching element Q1 and the fourth switching element Q4. The control unit 50 simultaneously turns on the second switching element Q2 and the third switching element Q3. The switching operation types of the primary-side full-bridge circuit 30 include type 7 and type 8.

[0117] Type 7 is a switching action type that turns on the first switching element Q1, turns off the second switching element Q2, turns off the third switching element Q3, and turns on the fourth switching element Q4.

[0118] Type 8 is a switching action type that disconnects the first switching element Q1, connects the second switching element Q2, connects the third switching element Q3, and disconnects the fourth switching element Q4.

[0119] When performing three-level control of the secondary-side full-bridge circuit 40, the control unit 50 independently controls the third bridge arm 41 and the fourth bridge arm 42. The switching operation types of the secondary-side full-bridge circuit 40 include types 9 to 12.

[0120] Type 9 is a switching action type that turns on the 5th switching element Q5, turns off the 6th switching element Q6, turns off the 7th switching element Q7, and turns on the 8th switching element Q8.

[0121] Type 10 is a switching action type that turns on the 5th switching element Q5, turns off the 6th switching element Q6, turns on the 7th switching element Q7, and turns off the 8th switching element Q8.

[0122] Type 11 is a switching action type that disconnects the 5th switching element Q5, connects the 6th switching element Q6, connects the 7th switching element Q7, and disconnects the 8th switching element Q8.

[0123] Type 12 is a switching action type that disconnects the 5th switching element Q5, connects the 6th switching element Q6, disconnects the 7th switching element Q7, and connects the 8th switching element Q8.

[0124] The control unit 50 outputs the output voltage Vout from the secondary full-bridge circuit 40 through a combination of any one of the 7th and 8th types of the primary full-bridge circuit 30 and any one of the 9th to 12th types of the secondary full-bridge circuit 40.

[0125] In the second embodiment, the control unit 50 has a second buck mode and a second boost mode as a load mode.

[0126] <Second Blood Pressure Reduction Mode>

[0127] The second buck mode includes a second buck hysteresis mode, a second buck in-phase mode, and a second buck hysteresis mode.

[0128] like Figure 19 As shown, the second buck hysteresis phase mode is a second buck mode in which the secondary side voltage V2 rises from a low level to a medium level, then the primary side voltage V1 rises from a low level to a high level, and then the secondary side voltage V2 rises from a medium level to a high level. The second buck hysteresis phase mode is the second buck mode in which a small power output is based on the power demand from load 120. The second buck hysteresis phase mode is an example of a hysteresis phase mode.

[0129] In the load mode of the second embodiment, the difference between the first moment T11 when the secondary side voltage V2 rises from a low level to a medium level and the second moment T12 when the primary side voltage V1 rises from a low level to a high level is the first phase difference θ11. The difference between the first moment T11 and the third moment T13 when the secondary side voltage V2 rises from a medium level to a high level is the second phase difference θ12.

[0130] Furthermore, as described above, when the normal operation of the output is not altered, the primary-side voltage V1 and the secondary-side voltage V2 are waveforms with the same frequency whose phase flips every 180 degrees. Therefore, the moment when the secondary-side voltage V2 drops from a high level to a medium level is also the first moment T11, the moment when the primary-side voltage V1 drops from a high level to a low level is also the second moment T12, and the moment when the secondary-side voltage V2 drops from a medium level to a low level is also the third moment T13.

[0131] like Figure 20 As shown, the second buck in-phase mode is a second buck mode that simultaneously performs the actions of raising the secondary side voltage V2 from a low level to a medium level and raising the primary side voltage V1 from a low level to a high level, and then raises the secondary side voltage V2 from a medium level to a high level. In the case of the second buck in-phase mode, the first time T11 and the second time T12 are the same time. Therefore, the first phase difference θ11 is 0. The second buck in-phase mode is the second buck mode in the case of outputting medium power according to the power demand from the load 120.

[0132] like Figure 21 As shown, the second buck lead phase mode is a second buck mode in which the primary side voltage V1 rises from a low level to a high level, then the secondary side voltage V2 rises from a low level to a medium level, and then the secondary side voltage V2 rises from a medium level to a high level. The second buck lead phase mode is the second buck mode in the case of outputting large power according to the power demand from load 120. The second buck lead phase mode is an example of a lead phase mode. The lead phase mode in this embodiment is a load mode in which two-level voltages rise from a low level to a high level, and then three-level voltages rise from a low level to a medium level.

[0133] The second buck lag phase mode is an example of a light load mode. The second buck lead phase mode is an example of a heavy load mode. The second buck in-phase mode is the load mode used when switching between light load and heavy load modes. In the second buck mode, the second buck lag phase mode and the second buck lead phase mode switch when the first phase difference θ11 is 0.

[0134] <Second Boost Mode>

[0135] The second boost mode includes a second boost phase lag mode, a second boost phase in-phase mode, and a second boost phase lag mode.

[0136] like Figure 22As shown, the second boost hysteresis phase mode is a second boost mode in which the secondary side voltage V2 rises from a low level to a medium level, then the primary side voltage V1 rises from a low level to a high level, and then the secondary side voltage V2 rises from a medium level to a high level. The second boost hysteresis phase mode is the second boost mode in which a small power output is based on the power demand from the load 120. The second boost hysteresis phase mode differs from the second buck hysteresis phase mode in that the high level of the secondary side voltage V2 is higher than the high level of the primary side voltage V1. Furthermore, it differs from the second buck hysteresis phase mode in that the low level of the secondary side voltage V2 is lower than the low level of the primary side voltage V1. The second boost hysteresis phase mode is an example of a hysteresis phase mode.

[0137] like Figure 23 As shown, the second boost in-phase mode is a second boost mode that simultaneously performs the actions of raising the secondary-side voltage V2 from a low level to a medium level and raising the primary-side voltage V1 from a low level to a high level, and then raises the secondary-side voltage V2 from a medium level to a high level. In the case of the second boost in-phase mode, the first time T11 and the second time T12 are the same time. Therefore, the first phase difference θ11 is 0. The second boost in-phase mode is the second boost mode when the power output is moderate according to the power demand from the load 120. For the second boost in-phase mode, it differs from the second buck in-phase mode in that the high level of the secondary-side voltage V2 is higher than the high level of the primary-side voltage V1. Furthermore, it differs from the second buck in-phase mode in that the low level of the secondary-side voltage V2 is lower than the low level of the primary-side voltage V1.

[0138] like Figure 24 As shown, the second boost lead phase mode is a second boost mode in which the primary side voltage V1 rises from a low level to a high level, then the secondary side voltage V2 rises from a low level to a medium level, and then the secondary side voltage V2 rises from a medium level to a high level. The second boost lead phase mode is the second boost mode in which a large power output is performed based on the power demand from the load 120. The second boost lead phase mode differs from the second buck lead phase mode in that the high level of the secondary side voltage V2 is higher than the high level of the primary side voltage V1. Furthermore, it differs from the second buck lead phase mode in that the low level of the secondary side voltage V2 is lower than the low level of the primary side voltage V1. The second boost lead phase mode is an example of a lead phase mode.

[0139] The second boost lagging phase mode is an example of a light load mode. The second boost leading phase mode is an example of a heavy load mode. The second boost in-phase mode is the load mode used when switching between light load and heavy load modes. In the second boost mode, the second boost lagging phase mode and the second boost leading phase mode switch when the first phase difference θ11 is 0.

[0140] <Control of the Second Embodiment>

[0141] In the second embodiment, the soft-switching control of all components and the soft-switching control of a portion of components performed by the control unit 50 are the same as in the first embodiment. The control unit 50 performs soft-switching control of all components by controlling the first phase difference θ11 and the second phase difference θ12 to output the required power, thereby causing all primary-side switching elements Q1-Q4 and all secondary-side switching elements Q5-Q8 to perform soft-switching operations. When it is not possible to perform soft-switching control of all components, the control unit 50 performs soft-switching control of a portion of components. This partial soft-switching control outputs the required power by controlling the first phase difference θ11 and the second phase difference θ12 to perform soft-switching operations on all primary-side switching elements Q1-Q4 and all secondary-side switching elements Q5-Q8, and hard-switching operations on at least one of the other switching elements.

[0142] [Effects of the second embodiment]

[0143] Even if (2-1) is a circuit structure in which reactor L2 is connected at the secondary winding 23, the same effect as (1-1) can be obtained.

[0144] [Example of Change]

[0145] The implementation method can be modified as follows. The implementation method and the following modifications can be combined with each other to the extent that they are not technically contradictory.

[0146] △In the first embodiment, the control unit 50 may also control the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 by applying a two-level voltage to the series connector 24 and a three-level voltage to the secondary-side winding 23 in the first buck mode. Alternatively, the control unit 50 may control the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 by applying a two-level voltage to the series connector 24 and a three-level voltage to the secondary-side winding 23 in the first boost mode.

[0147] △In the second embodiment, the control unit 50 may also control the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 by applying a three-level voltage to the primary-side winding 22 and a two-level voltage to the series connector 25 in the second buck mode. Alternatively, the control unit 50 may control the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 by applying a three-level voltage to the primary-side winding 22 and a two-level voltage to the series connector 25 in the second boost mode.

[0148] △In various embodiments, the power conversion device 10 may also include a reactor L1 connected to the primary winding 22 and a reactor L2 connected to the secondary winding 23. The reactor L1 connected to the primary winding 22 is designated as the first reactor L1, and the reactor L2 connected to the secondary winding 23 is designated as the second reactor L2. In this case, the voltage applied to the series connection 24 of the primary winding 22 and the first reactor L1 is the primary side voltage V1. The voltage applied to the series connection 25 of the secondary winding 23 and the second reactor L2 is the secondary side voltage V2. The control performed by the control unit 50 is the same as in each embodiment.

[0149] In this case, for the series connection 24 of the primary winding 22 and the first reactor L1, and the series connection 25 of the secondary winding 23 and the second reactor L2, a three-level voltage is applied to one and a two-level voltage is applied to the other. Alternatively, in each of the first buck mode, the first boost mode, the second buck mode, and the second boost mode, the series connections 24 and 25 to which the three-level voltage is applied and the series connections 24 and 25 to which the two-level voltage is applied are fixed.

[0150] Alternatively, in the first buck mode, the control unit 50 controls the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 by applying a two-level voltage to the series connector 24 and a three-level voltage to the series connector 25. Furthermore, in the first boost mode, the control unit 50 controls the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 by applying a two-level voltage to the series connector 24 and a three-level voltage to the series connector 25.

[0151] Alternatively, in the second buck mode, the control unit 50 controls the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 by applying a three-level voltage to the series connector 24 and a two-level voltage to the series connector 25. Furthermore, in the second boost mode, the control unit 50 controls the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 by applying a three-level voltage to the series connector 24 and a two-level voltage to the series connector 25.

[0152] Explanation of reference numerals in the attached figures

[0153] L1, L2... Reactors; Q1~Q4... Primary-side switching elements; Q5~Q8... Secondary-side switching elements; TS... Transformer section; 10... Power conversion device; 22... Primary-side winding; 23... Secondary-side winding; 24, 25... Series connection; 30... Primary-side full-bridge circuit; 40... Secondary-side full-bridge circuit; 50... Control section.

Claims

1. A power conversion device, characterized in that, have: A transformer section having a primary winding, a secondary winding, and a reactor connected to at least one of the primary winding or the secondary winding; A primary-side full-bridge circuit, which is a circuit connected to the primary-side winding and has multiple primary-side switching elements; The secondary-side full-bridge circuit is a circuit connected to the secondary-side winding and has multiple secondary-side switching elements. as well as The control unit controls the plurality of primary-side switching elements and the plurality of secondary-side switching elements. Condition 1 is the condition for performing soft switching operation on the plurality of primary-side switching elements, and condition 2 is the condition for performing soft switching operation on the plurality of secondary-side switching elements. Condition 1 is that when at least one of the plurality of primary-side switching elements switches between on and off, the value of the current flowing in the primary-side winding at the diode connected in parallel with the primary-side switching element that switches from off to on among the plurality of primary-side switching elements is greater than or equal to the absolute value of the primary-side winding current threshold. Condition 2 is that when at least one of the plurality of secondary-side switching elements switches between on and off, the value of the current flowing in the secondary winding at the diode connected in the forward direction in parallel with the secondary-side switching element that changes from off to on among the plurality of secondary-side switching elements is greater than or equal to the absolute value of the secondary winding current threshold. The control unit is configured to control the primary-side full-bridge circuit and the secondary-side full-bridge circuit in such a way that one of them applies a two-level voltage to the transformer section and the other applies a three-level voltage to the transformer section. The difference between the first moment when the three-level voltage rises from low to medium level and the second moment when the two-level voltage rises from low to high level is the first phase difference; the difference between the first moment and the third moment when the three-level voltage rises from medium to high level is the second phase difference. The control unit is configured such that, All components are subjected to soft-switching control. This soft-switching control is achieved by controlling the first phase difference and the second phase difference to output the required power by causing all primary-side and secondary-side switching components to perform soft-switching operations. In the event that it is not possible to perform soft switching control on all the components, soft switching control on a subset of the components is performed. This subset of the components is controlled by controlling the first phase difference and the second phase difference in such a way that all of the primary-side switching components and the secondary-side switching components are soft-switched and at least one of the other switching components is hard-switched, thereby outputting the required power.

2. The power conversion device according to claim 1, characterized in that, The control unit has a light load mode and a heavy load mode in which the maximum output power is greater than that of the light load mode. The control unit is configured to perform soft-switching control of a portion of the components when switching between the light load mode and the heavy load mode.

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