Power conversion device

Abstract

A power conversion device is provided. The control unit (50) executes a first control for controlling the primary-side full-bridge circuit (30) so as to apply a three-level primary-side voltage to the primary-side winding (22), and for controlling the secondary-side full-bridge circuit (40) so as to apply a two-level secondary-side voltage to the series connection body (24) of the secondary-side winding (23) and the reactor (L1). In the first control, the control unit (50) controls the primary-side full-bridge circuit (30) and the secondary-side full-bridge circuit (40) so as to achieve a combination between a first phase difference and a second phase difference that can output the required power and satisfy conditions 1 and 2, thereby outputting the required power.

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] When the output voltage to input voltage ratio is converted to a 1:1 ratio of the transformer winding ratio, the equivalent voltage ratio is close to 1. In this case, there is a situation where soft switching of the primary and secondary switching elements cannot be performed. Summary of the Invention

[0005] The power conversion device disclosed herein includes: a transformer having a primary winding and a secondary winding; a reactor connected to the primary winding, wherein the primary winding and the reactor form a series connection; a primary-side full-bridge circuit connected to the reactor and having a plurality of primary-side switching elements; a secondary-side full-bridge circuit connected to the secondary winding and having a plurality of secondary-side switching elements; and a control unit configured to control the plurality of primary-side switching elements and the plurality of secondary-side switching elements for performing the plurality of primary-side switching elements. The condition for soft-switching operation of the primary-side switching element is condition 1, and the condition for soft-switching operation of the plurality of secondary-side switching elements is condition 2. Condition 1 is that when at least one of the primary-side switching elements switches between on and off, the value of the current flowing in the primary-side winding and in the diode connected in parallel with the primary-side switching element that changes from off to on among the plurality of primary-side switching elements in the forward direction is greater than the absolute value of the primary-side winding current threshold. Condition 2 is that when at least one of the secondary-side switching elements switches between on and off, the value of the current flowing in the primary-side winding in the forward direction at the diode connected in parallel with the primary-side switching element that changes from off to on is greater than the absolute value of the primary-side winding current threshold. The value of the forward-flowing current at the diode connected in parallel with the secondary-side switching elements (which change from open to closed among the aforementioned plurality of secondary-side switching elements) at the secondary-side winding is greater than or equal to the absolute value of the secondary-side winding current threshold. The control unit is configured to perform first control, which controls the primary-side full-bridge circuit by applying a two-level primary-side voltage to the series connector and controlling the secondary-side full-bridge circuit by applying a three-level secondary-side voltage to the secondary-side winding. The primary-side voltage and the secondary-side voltage are in phase, flipping every 180 degrees. For waveforms of the same frequency, the difference between the first moment when the secondary side voltage rises from a low level to a medium level and the second moment when the primary side voltage rises from a low level to a high level is the first phase difference, and the difference between the first moment and the third moment when the secondary side voltage rises from a medium level to a high level is the second phase difference. The control unit is configured to control the primary side full-bridge circuit and the secondary side full-bridge circuit in the first control in a manner that enables the output of the required power and satisfies the combination of the first phase difference and the second phase difference under conditions 1 and 2, thereby outputting the required power.

[0006] For the primary-side switching elements to perform soft-switching, condition 1 must be met. For the secondary-side switching elements to perform soft-switching, condition 2 must be met. When the equivalent input voltage and equivalent output voltage / equivalent input voltage are close to 1 (assuming a 1:1 transformer winding ratio), the voltage applied to the reactor is low. With this low reactor voltage, even controlling the primary-side full-bridge circuit by applying a three-level primary-side voltage to the series connection may result in insufficient soft-switching due to the small change in current. In contrast, when the reactor voltage is low, controlling the secondary-side full-bridge circuit by applying a three-level secondary-side voltage to the secondary windings allows for a larger change in current. This enables soft-switching of both the primary and secondary-side switching elements.

[0007] One aspect of this disclosure relates to a power conversion device comprising: a transformer having a primary winding and a secondary winding; a reactor connected to the secondary winding, wherein the secondary winding and the reactor form a series connection; a primary-side full-bridge circuit connected to the primary winding and having a plurality of primary-side switching elements; a secondary-side full-bridge circuit connected to the reactor and having a plurality of secondary-side switching elements; and a control unit configured to control the plurality of primary-side switching elements and the plurality of secondary-side switching elements for performing the plurality of primary-side switching elements. The condition for the soft-switching operation of the secondary-side switching element is condition 1, and the condition for performing the soft-switching operation of the plurality of secondary-side switching elements is condition 2. Condition 1 is that the current flowing in the primary-side winding when at least one of the primary-side switching elements switches between on and off, and the forward current flowing in the diode connected in parallel with the primary-side switching element that changes from off to on among the plurality of primary-side switching elements, is greater than the absolute value of the primary-side winding current threshold. Condition 2 is that when at least one of the secondary-side switching elements switches between on and off, the current flowing in the secondary-side winding is greater than the absolute value of the primary-side winding current threshold. The value of the forward-flowing current at the diode connected in parallel with the secondary-side switching element (which changes from open to closed among the aforementioned plurality of secondary-side switching elements) in the primary winding is greater than or equal to the absolute value of the secondary winding current threshold. The control unit is configured to execute a first control. This first control controls the primary-side full-bridge circuit by applying a three-level primary-side voltage to the primary winding and a two-level secondary-side voltage to the series connector. The primary-side voltage and the secondary-side voltage are in phase, flipping every 180 degrees. The waveform of the frequency is such that the difference between the first moment when the primary side voltage rises from a low level to a medium level and the second moment when the secondary side voltage rises from a low level to a high level is the first phase difference, and the difference between the first moment and the third moment when the primary side voltage rises from a medium level to a high level is the second phase difference. The control unit is configured such that, in the first control, the primary side full-bridge circuit and the secondary side full-bridge circuit are controlled in a manner that enables the output of the required power and satisfies the combination of the first phase difference and the second phase difference, thereby enabling the output of the required power.

[0008] For the primary-side switching elements to perform soft-switching, condition 1 must be met. For the secondary-side switching elements to perform soft-switching, condition 2 must be met. When the equivalent input voltage and equivalent output voltage / equivalent input voltage are close to 1 (assuming a 1:1 transformer winding ratio), the voltage applied to the reactor is low. With this low reactor voltage, even when controlling the secondary-side full-bridge circuit by applying a three-level secondary-side voltage to the series connection, soft-switching may not be possible due to the small change in current. In contrast, when the reactor voltage is low, controlling the primary-side full-bridge circuit by applying a three-level primary-side voltage to the primary winding allows for a larger change in current. Therefore, both the primary-side and secondary-side switching elements can perform soft-switching. Attached Figure Description

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

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

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

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

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

[0014] Figure 6 This is a flowchart illustrating the switching control performed by the control unit.

[0015] Figure 7 This is a diagram showing the primary side current and secondary side current in the first buck hysteresis phase mode of the first embodiment.

[0016] Figure 8 This is a diagram showing the primary side voltage and secondary side voltage in the first boost hysteresis phase mode of the first embodiment.

[0017] Figure 9 This is a diagram showing the primary side voltage and secondary side voltage in the first boost in-phase mode of the first embodiment.

[0018] Figure 10This is a diagram showing the primary side voltage and secondary side voltage in the first boost lead phase mode of the first embodiment.

[0019] Figure 11 This is a diagram showing the primary side voltage and secondary side voltage in the second buck hysteresis phase mode of the first embodiment.

[0020] Figure 12 This is a diagram showing the primary side voltage and secondary side voltage in the second buck in-phase mode of the first embodiment.

[0021] Figure 13 This is a diagram showing the primary side voltage and secondary side voltage in the second buck lead phase mode of the first embodiment.

[0022] Figure 14 This is a graph showing the relationship between the equivalent voltage ratio and the output current of the power conversion device according to the first embodiment.

[0023] Figure 15 This is a circuit diagram of the power conversion device according to the second embodiment.

[0024] Figure 16 This is a diagram showing the primary side voltage and secondary side voltage in the first buck hysteresis phase mode of the second embodiment.

[0025] Figure 17 This is a diagram showing the primary side voltage and secondary side voltage in the first buck in-phase mode of the second embodiment.

[0026] Figure 18 This is a diagram showing the primary side voltage and secondary side voltage in the first buck lead phase mode of the second embodiment.

[0027] Figure 19 This is a diagram showing the primary side voltage and secondary side voltage in the first boost hysteresis phase mode of the second embodiment.

[0028] Figure 20 This is a diagram showing the primary side voltage and secondary side voltage in the first boost in-phase mode of the second embodiment.

[0029] Figure 21 This is a diagram showing the primary side voltage and secondary side voltage in the first boost lead phase mode of the second embodiment.

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

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

[0032] Figure 24 This is a diagram showing the primary side voltage and secondary side voltage in the second boost lead phase mode of the second embodiment.

[0033] Figure 25 This is a graph showing the relationship between the equivalent voltage ratio and the output current of the power conversion device in the second embodiment. Detailed Implementation

[0034] [First Embodiment]

[0035] The first embodiment of the power conversion device will be described.

[0036] 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.

[0037] <Power Conversion Device>

[0038] 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.

[0039] 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.

[0040] The power conversion device 10 includes a transformer 20. 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 includes a reactor L1. The reactor L1 can be a choke or other similar element, or it can be the leakage inductance of the primary winding 22 and the secondary winding 23. The reactor L1 is connected to the primary winding 22.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] The connection point between the first switching element Q1 and the second switching element Q2 is connected to the primary winding 22 via the reactor L1. The connection point between the third switching element Q3 and the fourth switching element Q4 is also connected to the primary winding 22. Thus, the primary-side full-bridge circuit 30 is connected to the primary winding 22. The primary winding 22 and the reactor L1 form a series connection 24.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The output power of the secondary-side full-bridge circuit 40 is supplied to the load 120.

[0051] 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.

[0052] 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 constructed from hardware circuits such as ASIC (Application Specific Integrated Circuit) or 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 combinations thereof, that operate according to a computer program.

[0053] 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.

[0054] <First Control>

[0055] The control unit 50 performs a first control, which involves three-level control for the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 where excitation current flows, and two-level control for the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 where no excitation current flows. The primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 where excitation current flows are circuits without reactor L1 connected. The primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 where no excitation current flows are circuits with reactor L1 connected. In this embodiment, the primary-side full-bridge circuit 30 is subjected to two-level control, and the secondary-side full-bridge circuit 40 is subjected to three-level control.

[0056] Three-level control switches the voltage applied to the secondary winding 23 to three levels: positive, negative, or 0. Two-level control switches the voltage applied to the primary winding 22 and the series connection 24 of reactor L1 to two levels: positive or negative. Appropriately, in three-level control, a positive voltage applied to the secondary winding 23 is called a high level, a 0 voltage applied to the secondary winding 23 is called a medium level, and a negative voltage applied to the secondary winding 23 is called a low level. In two-level control, a positive voltage applied to the series connection 24 is called a high level, and a negative voltage applied to the series connection 24 is called a low level. The voltage applied to the primary winding 22 and the series connection 24 of reactor L1 is called the primary-side voltage V1, and the voltage applied to the secondary winding 23 is called the 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 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. 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. 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.

[0057] 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 1 and type 2.

[0058] 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.

[0059] The second type is a switching action 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.

[0060] 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 3 to 6.

[0061] The third type is a switching action type that turns on the fifth switching element Q5, turns off the sixth switching element Q6, turns off the seventh switching element Q7, and turns on the eighth switch.

[0062] The fourth type is a switching action type that turns on the fifth switching element Q5, turns off the sixth switching element Q6, turns on the seventh switching element Q7, and turns off the eighth switch.

[0063] Type 5 is a type of switch action that disconnects the 5th switch element Q5, connects the 6th switch element Q6, connects the 7th switch element Q7, and disconnects the 8th switch.

[0064] Type 6 is a type of switch action that disconnects the 5th switch element Q5, connects the 6th switch element Q6, disconnects the 7th switch element Q7, and connects the 8th switch.

[0065] 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 and second types of the primary full-bridge circuit 30 and any one of the third to sixth types of the secondary full-bridge circuit 40.

[0066] 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 called 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 the first control mode. The first buck mode is a control mode that makes the equivalent voltage ratio less than 1. The first boost mode is a control mode that makes the equivalent voltage ratio greater than 1.

[0067] 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) is 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 explanation.

[0068] <First Pressure Reduction Mode>

[0069] 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.

[0070] like Figure 3 As shown, the first buck hysteresis phase mode is a 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 first buck hysteresis phase mode is the first buck mode in which a small power output is based on the power demand from load 120.

[0071] In the first buck mode, the difference between the first moment T1 when the secondary side voltage V2 rises from a low level to a medium level and the second moment T2 when the primary side voltage V1 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 secondary side voltage V2 rises from a medium level to a high level is the second phase difference θ2.

[0072] 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 T1, the moment when the primary-side voltage V1 drops from a high level to a low level is also the second moment T2, and the moment when the secondary-side voltage V2 drops from a medium level to a low level is also the third moment T3.

[0073] like Figure 4 As shown, the first buck in-phase mode is a mode in which the action of raising the secondary voltage V2 from a low level to a medium level and the action of raising the primary voltage V1 from a low level to a high level are performed simultaneously, followed by raising the secondary voltage V2 from a medium level to a high level. In this first buck in-phase mode, the first time T1 and the second time T2 are the same. Therefore, the first phase difference θ1 is 0. The first buck in-phase mode is the first buck mode in which the medium power is output according to the power demand from the load 120. The medium power is a power greater than the small power.

[0074] like Figure 5 As shown, the first buck lead phase mode is a 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 first buck lead phase mode is the first buck mode in which a large power output is given based on the power demand from load 120. The large power is a power output greater than the medium power.

[0075] The first buck lag phase mode is an example of a light load mode. The first buck lead phase mode is an example of a heavy load mode. The first buck in-phase mode is the mode used when switching between light load and heavy load modes.

[0076] The switching control performed by the control unit 50 in the first buck mode will be explained. The switching control is achieved by switching the primary-side switching elements Q1 to Q4 and the secondary-side switching elements Q5 to Q8 to output the output voltage Vout.

[0077] like Figure 6 and Figure 7 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.

[0078] The condition for soft-switching operation of multiple primary-side switching elements Q1 to Q4 is that when at least one of the primary-side switching elements Q1 to Q4 switches 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 or equal to the absolute value of the primary-side winding current threshold TI1. Hereinafter, this condition is designated as condition 1. The region satisfying condition 1 is the soft-switching operation region of the primary-side current I1. When at least one of the primary-side switching elements Q1 to Q4 switches between on and off, it is the moment when at least one of the primary-side switching elements Q1 to Q4 changes from on to off or from off to on. In the first control of this embodiment, the moment when at least one of the primary-side switching elements Q1 to Q4 switches between on and off coincides with the second moment T2 when the primary-side voltage V1 rises or falls.

[0079] The condition for soft-switching operation of multiple secondary-side switching elements Q5 to Q8 is that when at least one of the secondary-side switching elements Q5 to Q8 switches 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 to Q8 that changes from off to on is greater than or equal to the absolute value of the secondary-side winding current threshold TI2. Hereinafter, this condition is designated as condition 2. The region that satisfies condition 2 is the soft-switching operation region of the secondary-side current I2. When at least one of the secondary-side switching elements Q5 to Q8 switches between on and off, it is the moment when at least one of the secondary-side switching elements Q5 to Q8 changes from on to off or from off to on. In the first control of this embodiment, when at least one of the secondary-side switching elements Q5 to Q8 switches between on and off, it is the same as the first time T1 or the third time T3. Time 1, T1, is the moment when the secondary voltage V2 rises from a low level to a medium level, or when the secondary voltage V2 falls from a high level to a medium level. Time 3 is the moment when the secondary voltage V2 rises from a medium level to a high level, or when the secondary voltage V2 falls from a medium level to a low level.

[0080] 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.

[0081] Figure 7 As 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 7 In the example shown, at time 1 T1, the switching action type of the secondary-side full-bridge circuit 40 switches from type 5 to type 4. Furthermore, at time 3 T3, the switching action type of the secondary-side full-bridge circuit 40 switches from type 4 to type 3. At times 1 T1 and 3 T3, if condition 2 is satisfied, the soft-switching action of the secondary-side switching elements Q5~Q8 is achieved. At time 2 T2, the switching action type of the primary-side full-bridge circuit 30 switches from type 2 to type 1. At this time, if condition 1 is satisfied, the soft-switching action of the primary-side switching elements Q1~Q4 is achieved.

[0082] The primary winding current threshold TI1 is defined by the following equation (1).

[0083] Mathematical Formula 1

[0084]

[0085] 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.

[0086] 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.

[0087] In this control mode, among the primary-side switching elements Q1~Q4, the switching elements that change from open to closed at time 2 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 the primary-side switching elements that change from open to closed when the switching action type changes from type 2 to type 1.

[0088] To satisfy condition 1, the value of the forward-flowing current at diodes D1 and D4 (connected in parallel with the first and fourth switching elements Q1 and Q4, respectively, which change from off to on at time T2) at the primary side current threshold TI1 must be greater than or equal to the absolute value of the primary side winding current threshold TI1, “|TI1|”. This current value is... Figure 1 The value of "-I1". Additionally, as from... Figure 7 As can be seen, at time 2 T2, the primary side current I1 is negative, therefore, "-I1" becomes positive.

[0089] In this control mode, to satisfy condition 2, the secondary side current I2 at time 1 (T1) and time 3 (T3) is considered. Time 1 is the time in this control mode where the absolute value of the secondary side current is smaller than that at time 1 (T1). Therefore, it is sufficient to consider the secondary side current I2 at time 1 (T1). Therefore, to satisfy condition 2, the value of the forward-flowing current at diode D5, which is the secondary side current I2 at time 1 (T1) and is connected in parallel with the fifth switching element Q5 (which changes from off to on at this time), must be greater than or equal to the absolute value of the secondary winding current threshold TI2, "|TI2|". This current value is... Figure 1The value of "+I2". The fifth switching element Q5 is a secondary-side switching element that changes from open to closed when the switching action type changes from type 5 to type 4. Additionally, as from... Figure 7 As can be seen, at time 1 T1, the secondary current I2 is positive, therefore, "+I2" becomes positive. Furthermore, whether the absolute value of the secondary current becomes smaller at time 1 T1 or time 3 T3 depends on the control mode.

[0090] From a practical standpoint, for example, regarding condition 2, it can also be satisfied by comparing TI2', obtained by converting the secondary winding current threshold TI2 to the primary side, with the primary side current I1 at time 1 T1, and vice versa. In this case, either the primary side current I1 or the secondary side current I2 can be considered. Alternatively, the inductance L of reactor L1 can be pre-set in such a way that if one of conditions 1 and 2 is satisfied, the other one will naturally be satisfied.

[0091] 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 combination of target currents that can output the required power and satisfy conditions 1 and 2 exists, it means that soft-switching operation cannot be achieved in this power demand and control mode.

[0092] Next, in step S3, the control unit 50 derives the combination between the first phase difference θ1 and the second phase difference θ2 based on the calculated target current. Here, the combination between the first phase difference θ1 and the second phase difference θ2 is derived by following the calculated target current at the first time T1 and the target current at the second time T2. That is, the combination between 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.

[0093] 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.

[0094] 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.

[0095] <First Boost Mode>

[0096] 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.

[0097] like Figure 8As shown, the first boost hysteresis phase mode is a 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 first boost hysteresis phase mode is the first boost mode in which a small power output is based on 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.

[0098] In the first boost mode, 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.

[0099] 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.

[0100] like Figure 9 As shown, the first boost in-phase mode is a 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 this case of the first 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 first boost in-phase mode is the first boost mode that outputs medium power 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.

[0101] like Figure 10As 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 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 first boost lead phase mode is the first boost mode in the case of outputting large power according to the power demand 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.

[0102] The first boost phase lag mode is an example of a light load mode. The first boost phase lead mode is an example of a heavy load mode. The first boost phase in-phase mode is the mode used when switching between light and heavy load modes.

[0103] In the case of the first boost mode, the switching control performed by the control unit 50 is the same as in the first buck mode. That is, the control unit 50 derives a combination between the first phase difference θ11 and the second phase difference θ12 that can output the required power. This combination satisfies conditions 1 and 2. Furthermore, the control unit 50 outputs the required power by controlling the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 in a manner that realizes the derived first phase difference θ11 and second phase difference θ12.

[0104] <Second Control>

[0105] The control unit 50 can also perform the second control. In the second control, the control unit 50 controls the primary-side full-bridge circuit 30 by applying a three-level primary-side voltage V1 to the series connector 24, and controls the secondary-side full-bridge circuit 40 by applying a two-level secondary-side voltage V2 to the secondary-side winding 23.

[0106] In the first embodiment, when the second control is executed, if the equivalent voltage ratio is less than a predetermined threshold of less than 1, the control unit 50 executes the second control. If the equivalent voltage ratio is above the predetermined threshold, the control unit 50 executes the first control.

[0107] 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 types 7 to 10.

[0108] 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.

[0109] Type 8 is a type of switching action 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.

[0110] Type 9 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.

[0111] Type 10 is a type of switching action 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.

[0112] 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 11 and type 12.

[0113] Type 11 is a type of switching action 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.

[0114] Type 12 is a type of switch action that disconnects the 5th switch element Q5, connects the 6th switch element Q6, connects the 7th switch element Q7, and disconnects the 8th switch element Q8.

[0115] 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 to 10th types of the primary full-bridge circuit 30 and any one of the 11th and 12th types of the secondary full-bridge circuit 40.

[0116] <Second Blood Pressure Reduction Mode>

[0117] The control unit 50 has a second buck mode as a control mode for the second control. The second buck mode is the control mode when the equivalent voltage ratio is less than 1. The second buck mode has a second buck lag phase mode, a second buck in-phase mode, and a second buck lead phase mode.

[0118] like Figure 11As shown, the second buck hysteresis phase mode is a second buck 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 second buck hysteresis phase mode is the second buck mode in the case of outputting small power according to the power demand from the load 120.

[0119] In the second control, the difference between the first moment T21 when the primary side voltage V1 rises from a low level to a medium level and the second moment T22 when the secondary side voltage V2 rises from a low level to a high level is the first phase difference θ21. The difference between the first moment T21 and the third moment T23 when the primary side voltage V1 rises from a medium level to a high level is the second phase difference θ22.

[0120] 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 T21, the moment when the secondary-side voltage V2 drops from a high level to a low level is also the second moment T22, and the moment when the primary-side voltage V1 drops from a medium level to a low level is also the third moment T23.

[0121] like Figure 12 As shown, the second buck in-phase mode is a second buck mode in which the action of raising the secondary voltage V2 from low level to high level and the action of raising the primary voltage V1 from medium level to high level are performed simultaneously after the primary voltage V1 rises from low level to medium level. In this case of the second buck in-phase mode, the first time T21 and the second time T22 are the same time. Therefore, the first phase difference θ21 and the second phase difference θ22 are the same value. The second buck in-phase mode is the second buck mode in which the power output is moderate according to the power demand from the load 120.

[0122] like Figure 13 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 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 second buck lead phase mode is the second buck mode in which a large power output is given based on the power demand from load 120. The large power is a power output greater than the medium power.

[0123] 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 mode used when switching between light load and heavy load modes.

[0124] In the second buck mode, the switching control performed by the control unit 50 is achieved by controlling the first phase difference θ21 and the second phase difference θ22. The control unit 50 derives a combination between the first phase difference θ21 and the second phase difference θ22 that can output the required power. This combination satisfies the same condition as condition 1 of the first control for soft switching operation of the primary side switching elements Q1 to Q4, and satisfies the same condition as condition 2 of the first control for soft switching operation of the secondary side switching elements Q5 to Q8.

[0125] In the second control scenario, when at least one of the primary-side switching elements Q1 to Q4 switches between on and off, the moment when at least one of the primary-side switching elements Q1 to Q4 changes from on to off or from off to on is the same as the first moment T21 or the third moment T23. The first moment T21 is the moment when the primary-side voltage V1 rises from a low level to a medium level or falls from a high level to a medium level. The third moment T23 is the moment when the primary-side voltage V1 rises from a medium level to a high level or falls from a medium level to a low level. Furthermore, in the second control scenario, when at least one of the secondary-side switching elements Q5 to Q8 switches between on and off, the moment when at least one of the secondary-side switching elements Q5 to Q8 changes from on to off or from off to on is the same as the moment when at least one of the secondary-side switching elements Q5 to Q8 changes from on to off or from off to on. This moment is the same as the moment when the secondary voltage V2 rises from low level to high level or when the secondary voltage V2 falls from high level to low level, which is also the second moment T22.

[0126] 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 derived first phase difference θ21 and second phase difference θ22, thereby outputting the required power.

[0127] [Effect of the first embodiment]

[0128] Figure 14 This shows the relationship between the equivalent voltage ratio and the output current. Line L12 is the dividing line between heavy load mode and light load mode when the second control is in effect. Region A2 indicates the operating area where soft switching cannot be achieved when the second control is in effect. (The last sentence appears to be incomplete and possibly refers to a different topic.) Figure 14 As we have determined, region A2 includes cases where the equivalent voltage ratio is 1. Therefore, in the second control, soft switching cannot be performed even in heavy load mode within region A2, which includes cases where the equivalent voltage ratio is 1.

[0129] In the second buck mode, the primary-side full-bridge circuit 30 is controlled by applying a three-level primary-side voltage V1 to the series connector 24. The voltage applied to the reactor L1 is the value obtained by subtracting the voltage applied to the primary-side winding 22 from the primary-side voltage V1. If the equivalent voltage ratio is close to 1, the voltage applied to the reactor L1 becomes lower. When the voltage applied to the reactor L1 is low, even if the primary-side full-bridge circuit 30 is controlled by applying a three-level primary-side voltage V1 to the series connector 24, the change in current is small, so soft-switching operation may not be achieved. That is, the primary-side current I1 and the secondary-side current I2 may not be able to change to values ​​within the soft-switching operation region.

[0130] When the voltage applied to reactor L1 is low, the change in current can be increased by controlling the secondary full-bridge circuit 40 by applying a three-level secondary voltage V2 to the secondary winding 23. This enables soft-switching of the primary-side switching elements Q1-Q4 and the secondary-side switching elements Q5-Q8.

[0131] Figure 14 Line L11 is the dividing line for switching between heavy load and light load modes under the first control. Region A1 shows the operating area where soft switching cannot be performed under the first control. Thus, the area where soft switching cannot be performed is region A2 under the second control, but changes to region A1 under the first control. Region A1, where soft switching cannot be performed under the first control, does not overlap with region A2, where soft switching cannot be performed under the second control. Therefore, even in region A2, where soft switching cannot be performed under the second control, soft switching can still be performed by performing the first control.

[0132] As described above, when the equivalent voltage ratio is less than a predetermined threshold of less than 1, the control unit 50 performs the second control. This threshold only needs to be, for example, a value that is less than the lower limit of the equivalent voltage ratio represented in region A2 and greater than the upper limit of the equivalent voltage ratio represented in region A1. That is, the threshold can be set in such a way that the second control is performed in region A1 and the first control is performed in region A2.

[0133] [Effects of the first embodiment]

[0134] (1-1) When the equivalent voltage ratio is close to 1, the voltage applied to reactor L1 is low. When the voltage applied to reactor L1 is low, even if the primary-side full-bridge circuit 30 is controlled by applying a three-level primary-side voltage V1 to the series connector 24, soft-switching operation cannot be performed due to the small change in current (area A2). When the voltage applied to reactor L1 is low, controlling the secondary-side full-bridge circuit 40 by applying a three-level secondary-side voltage V2 to the secondary-side winding 23 increases the change in current. Therefore, even when the equivalent voltage ratio is close to 1, soft-switching operation can be performed on the primary-side switching elements Q1~Q4 and the secondary-side switching elements Q5~Q8.

[0135] (1-2) When the equivalent voltage ratio is less than the threshold, the control unit 50 executes the second control; when the equivalent voltage ratio is above the threshold, it executes the first control. When the equivalent voltage ratio is less than the threshold, there is a situation where soft-switching cannot be performed under the first control (area A1). In this case, by executing the second control, soft-switching can be performed even when soft-switching cannot be performed under the first control. When the equivalent voltage ratio is above the threshold, there is a situation where soft-switching cannot be performed under the second control (area A2). In this case, by executing the first control, soft-switching can be performed even when soft-switching cannot be performed under the second control.

[0136] [Second Embodiment]

[0137] A second embodiment of the power conversion device will be described.

[0138] like Figure 15 As shown, in the second embodiment, the primary and secondary sides are reversed in the case where the reactor L2 is connected to the secondary winding 23 instead of the primary winding 22, and three-level and two-level control are performed. The secondary winding 23 and the reactor L2 form a series connection 25.

[0139] <First Control>

[0140] The first control in the second embodiment is to perform three-level control on the primary side full-bridge circuit 30 and two-level control on the secondary side full-bridge circuit 40.

[0141] Three-level control involves switching the voltage applied to the primary winding 22 to three levels: positive, negative, or 0. Two-level control involves switching the voltage applied to the series connection 25 between the reactor L2 and the secondary winding 23 to two levels: positive or negative. Appropriately, in three-level control, a positive voltage applied to the primary winding 22 is called a high level, a 0 voltage applied to the primary winding 22 is called a medium level, and a negative voltage applied to the primary winding 22 is called a low level. In two-level control, a positive voltage applied to the series connection 25 is called a high level, and a negative voltage applied to the series connection 25 is called a low level.

[0142] The control unit 50 outputs the output voltage Vout from the primary-side full-bridge circuit 30 through a combination of any one of the 7th to 10th types of the primary-side full-bridge circuit 30 and any one of the 11th and 12th types of the secondary-side full-bridge circuit 40.

[0143] In the second embodiment, the control unit 50 has a first buck mode and a first boost mode as a control mode for the first control.

[0144] <First Pressure Reduction Mode>

[0145] The first buck mode includes the first buck hysteresis mode, the first buck in-phase mode, and the first buck hysteresis mode.

[0146] like Figure 16 As shown, the first buck hysteresis phase mode is a buck 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 also a buck mode in which a small power output is based on the power demand from load 120.

[0147] The difference between the first moment T31 when the primary side voltage V1 rises from a low level to a medium level and the second moment T32 when the secondary side voltage V2 rises from a low level to a high level is the first phase difference θ31. The difference between the first moment T31 and the third moment T33 when the primary side voltage V1 rises from a medium level to a high level is the second phase difference θ32.

[0148] Furthermore, without altering the normal operation of the output, the primary-side voltage V1 and the secondary-side voltage V2 are controlled to have the same phase, flipping at the same frequency 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 T31, the moment when the secondary-side voltage V2 drops from a high level to a low level is also the second moment T32, and the moment when the primary-side voltage V1 drops from a medium level to a low level is also the third moment T33.

[0149] like Figure 17 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, and then simultaneously rises the primary-side voltage V1 from a medium level to a high level and the secondary-side voltage V2 rises from a low level to a high level. In this first buck in-phase mode, time T32 and time T33 are the same. Therefore, the first phase difference θ31 and the second phase difference θ32 are the same value. The first buck in-phase mode is the first buck mode in which the power output is moderate according to the power demand from the load 120.

[0150] like Figure 18 As shown, the first buck lead phase mode is a buck 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 the case of outputting large power according to the power demand from load 120.

[0151] In the first buck mode, the switching control performed by the control unit 50 is the same as in the first embodiment, achieved by controlling the first phase difference θ31 and the second phase difference θ32. The control unit 50 derives a combination between the first phase difference θ31 and the second phase difference θ32 that enables the output of the required power. This combination is a condition identical to condition 1 of the first control, which is used for the soft-switching operation of the primary-side switching elements Q1 to Q4, and a condition identical to condition 2 of the first control, which is used for the soft-switching operation of the secondary-side switching elements Q5 to Q8.

[0152] In the first control case of this embodiment, when at least one of the primary-side switching elements Q1 to Q4 switches between on and off, it is the moment when at least one of the primary-side switching elements Q1 to Q4 changes from on to off or from off to on. This moment is the same as the first moment T31 or the third moment T33. The first moment T31 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 falls from a high level to a medium level. The third moment T33 is the moment when the primary-side voltage V1 rises from a medium level to a high level or when the primary-side voltage V1 falls from a medium level to a low level. Furthermore, in the first control case of this embodiment, when at least one of the secondary-side switching elements Q5 to Q8 switches between on and off, it is the moment when at least one of the secondary-side switching elements Q5 to Q8 changes from on to off or from off to on. This moment is the same as the moment when the secondary voltage V2 rises from low level to high level or when the secondary voltage V2 falls from high level to low level, which is also the second moment T32.

[0153] 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 derived first phase difference θ31 and second phase difference θ32, thereby outputting the required power.

[0154] <First Boost Mode>

[0155] The first boost mode of the second embodiment includes a first boost lag phase mode, a first boost in-phase mode, and a first boost lag phase mode.

[0156] like Figure 19 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 the first boost mode in which a small power output is based on 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.

[0157] The difference between the first moment T41 when the primary side voltage V1 rises from a low level to a medium level and the second moment T42 when the secondary side voltage V2 rises from a low level to a high level is the first phase difference θ41. The difference between the first moment T41 and the third moment T43 when the primary side voltage V1 rises from a medium level to a high level is the second phase difference θ42.

[0158] 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 T41, the moment when the secondary-side voltage V2 drops from a high level to a low level is also the second moment T42, and the moment when the primary-side voltage V1 drops from a medium level to a low level is also the third moment T43.

[0159] like Figure 20 As shown, the first boost in-phase mode is a boost mode in which the primary side voltage V1 rises from a low level to a medium level, and then simultaneously rises the primary side voltage V1 from a medium level to a high level and the secondary side voltage V2 rises from a low level to a high level. In this case of the first boost in-phase mode, the second time T42 and the third time T43 are the same time. Therefore, the first phase difference θ41 and the second phase difference θ42 are the same value. The first boost in-phase mode is the first boost mode in which the power output is moderate according to the power demand from the load 120. The first boost in-phase mode 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.

[0160] like Figure 21 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 the first boost mode in which a large power output is performed based on the power demand 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.

[0161] For the switching control performed by the control unit 50 in the first boost mode, the process is the same as in the first buck mode. That is, the control unit 50 derives a combination between the first phase difference θ41 and the second phase difference θ42 that can output the required power. This combination satisfies conditions 1 and 2. Furthermore, the control unit 50 outputs the required power by controlling the primary-side full-bridge circuit 30 and the secondary-side full-bridge circuit 40 in a manner that realizes the derived first phase difference θ41 and second phase difference θ42.

[0162] <Second Control>

[0163] The control unit 50 can also perform the second control. In the second embodiment, the second control controls the primary-side full-bridge circuit 30 by applying a two-level primary-side voltage V1 to the primary-side winding 22, and controls the secondary-side full-bridge circuit 40 by applying a three-level secondary-side voltage V2 to the series connector 25. In the second embodiment, when the second control is performed, the control unit 50 performs the second control if the equivalent voltage ratio is greater than a predetermined threshold greater than 1. The control unit 50 performs the first control if the equivalent voltage ratio is less than or equal to the predetermined threshold.

[0164] 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 and second types of the primary full-bridge circuit 30 and any one of the third to sixth types of the secondary full-bridge circuit 40.

[0165] <Second Boost Mode>

[0166] The control unit 50 has a second boost mode as a control mode for the second control. The second boost mode is a control mode when the equivalent voltage ratio is greater than 1. The second boost mode has a second boost leading phase mode, a second boost in-phase mode, and a second boost lagging phase mode.

[0167] like Figure 22 As 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.

[0168] In the second control, the difference between the first moment T51 when the secondary side voltage V2 rises from a low level to a medium level and the second moment T52 when the primary side voltage V1 rises from a low level to a high level is the first phase difference θ51. The difference between the first moment T51 and the third moment T53 when the secondary side voltage V2 rises from a medium level to a high level is the second phase difference θ52.

[0169] 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 T51, the moment when the primary-side voltage V1 drops from a high level to a low level is also the second moment T52, and the moment when the secondary-side voltage V2 drops from a medium level to a low level is also the third moment T53.

[0170] like Figure 23As 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 this second boost in-phase mode, time 1 T51 and time 2 T52 are the same. Therefore, the first phase difference θ51 is 0. The second boost in-phase mode is the second boost mode in which the power output is moderate according to the power demand from the load 120.

[0171] 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 the case of outputting large power according to the power demand from the load 120.

[0172] 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 mode used when switching between light load and heavy load modes.

[0173] In the second boost mode, the switching control performed by the control unit 50 is achieved by controlling the first phase difference θ51 and the second phase difference θ52. The control unit 50 derives a combination between the first phase difference θ51 and the second phase difference θ52 that enables the output of the required power. This combination satisfies the same condition 1 as the condition for soft switching operation of the primary-side switching elements Q1 to Q4, and also satisfies the same condition 2 as the condition for soft switching operation of the secondary-side switching elements Q5 to Q8.

[0174] In the second control scenario, when at least one of the primary-side switching elements Q1 to Q4 switches between on and off, the moment when at least one of the primary-side switching elements Q1 to Q4 changes from on to off or from off to on is the same as the moment when the primary-side voltage V1 rises from a low level to a high level or falls from a high level to a low level, i.e., the second moment T52. Furthermore, in the second control scenario, when at least one of the secondary-side switching elements Q5 to Q8 switches between on and off, the moment when at least one of the secondary-side switching elements Q5 to Q8 changes from on to off or from off to on is the same as the first moment T51 or the third moment T53. The first moment T51 is the moment when the secondary-side voltage V2 rises from a low level to a medium level or falls from a high level to a medium level. The third moment, T53, is the moment when the secondary voltage V2 rises from the intermediate level to the high level or when the secondary voltage V2 falls from the intermediate level to the low level.

[0175] 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 derived first phase difference θ51 and second phase difference θ52, thereby outputting the required power.

[0176] [Effect of the second embodiment]

[0177] Figure 25 This shows the relationship between the equivalent voltage ratio and the output current. Line L22 is the dividing line between heavy load and light load modes when the second control is in effect. Region A12 shows the area where soft switching cannot be achieved when the second control is in effect. (The last sentence appears to be incomplete and possibly refers to a different topic.) Figure 25 As can be determined, region A12 contains an equivalent voltage ratio of 1. Thus, in the second control, soft switching operation cannot be performed in region A12, which contains an equivalent voltage ratio of 1, even under heavy load mode.

[0178] In the second boost mode, the secondary-side full-bridge circuit 40 is controlled by applying a three-level secondary-side voltage V2 to the series connector 25. The voltage applied to the reactor L2 is the value obtained by subtracting the voltage applied to the secondary-side winding 23 from the secondary-side voltage V2. If the equivalent voltage ratio is close to 1, the voltage applied to the reactor L2 becomes lower. When the voltage applied to the reactor L2 is low, even if the secondary-side full-bridge circuit 40 is controlled by applying a three-level secondary-side voltage V2 to the series connector 25, there is a possibility that soft-switching operation cannot be performed due to the small change in current.

[0179] When the voltage applied to reactor L2 is low, the primary-side full-bridge circuit 30 can be controlled by applying a three-level primary-side voltage V1 to the primary-side winding 22, thereby increasing the change in current. This enables soft-switching operation of the primary-side switching elements Q1-Q4 and the secondary-side switching elements Q5-Q8.

[0180] Figure 25 Line L21 is the dividing line between heavy load mode and light load mode when the first control is applied. Region A11 shows the area where soft switching cannot be performed when the first control is applied. Thus, the area where soft switching cannot be performed is region A12 under the second control, but the area where soft switching cannot be performed under the first control changes to A11. Region A11 where soft switching cannot be performed under the first control does not overlap with region A12 where soft switching cannot be performed under the second control. Therefore, even if it is region A11 where soft switching cannot be performed under the first control, soft switching can still be performed by performing the second control.

[0181] As described above, when the second control is executed, the control unit 50 executes the second control if the equivalent voltage ratio is greater than a predetermined threshold greater than 1. This threshold can be, for example, a value greater than the upper limit of the equivalent voltage ratio represented in region A12 and less than the lower limit of the equivalent voltage ratio represented in region A11. That is, the threshold can be set such that the second control is performed in region A11 and the first control is performed in region A12.

[0182] [Effects of the second embodiment]

[0183] (2-1) When the voltage applied to reactor L2 is low, even if the secondary full-bridge circuit 40 is controlled by applying a three-level secondary side voltage V2 to the series connector 25, the current change is small, and therefore soft-switching operation cannot be performed (region A12). In contrast, when the voltage applied to reactor L2 is low, controlling the primary full-bridge circuit 30 by applying a three-level primary side voltage V1 to the primary winding 22 can increase the current change. Therefore, even when the equivalent voltage ratio is close to 1, soft-switching operation can be performed on the primary side switching elements Q1~Q4 and the secondary side switching elements Q5~Q8.

[0184] (2-2) When the equivalent voltage ratio is greater than a threshold, the control unit 50 executes the second control; when the equivalent voltage ratio is less than the threshold, it executes the first control. When the equivalent voltage ratio is greater than the threshold, there is a situation where soft-switching cannot be performed under the first control (area A11). In this case, by executing the second control, soft-switching can be performed even if soft-switching cannot be performed under the first control. When the equivalent voltage ratio is less than the threshold, there is a situation where soft-switching cannot be performed under the second control (area A12). In this case, by executing the first control, soft-switching can be performed even if soft-switching cannot be performed under the second control.

[0185] Explanation of reference numerals in the attached figures

[0186] L1, L2... Reactors; Q1~Q4... Primary-side switching elements; Q5~Q8... Secondary-side switching elements; 10... Power conversion device; 20... Transformer; 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 unit.

Claims

1. A power conversion device, characterized by, Possessing: a transformer having a primary side winding and a secondary side winding; a reactor which is a reactor connected to the primary side winding, and the primary side winding and the reactor form a series connection body; a primary side full bridge circuit which is a circuit connected to the reactor, and has a plurality of primary side switching elements; a secondary side full bridge circuit which is a circuit connected to the secondary side winding, and has a plurality of secondary side switching elements; and a control unit configured to control the plurality of primary side switching elements and the plurality of secondary side switching elements, a condition for performing soft switching operation of the plurality of primary side switching elements is condition 1, and a condition for performing soft switching operation of the plurality of secondary side switching elements is condition 2, the condition 1 is that, as a current flowing at the primary side winding when at least one of the primary side switching elements is switched between on and off, a value of a forward direction current at a diode connected in parallel to the primary side switching element among the plurality of primary side switching elements which changes from off to on, is an absolute value of a primary side winding current threshold value or more, the condition 2 is that, as a current flowing at the secondary side winding when at least one of the secondary side switching elements is switched between on and off, a value of a forward direction current at a diode connected in parallel to the secondary side switching element among the plurality of secondary side switching elements which changes from off to on, is an absolute value of a secondary side winding current threshold value or more, the control unit is configured to execute a first control which controls the primary side full bridge circuit in a manner that a two-level primary side voltage is applied to the series connection body, and controls the secondary side full bridge circuit in a manner that a three-level secondary side voltage is applied to the secondary side winding, the primary side voltage and the secondary side voltage are waveforms of the same frequency whose phases flip every 180 degrees, a difference between a first timing at which the secondary side voltage rises from a low level to an intermediate level and a second timing at which the primary side voltage rises from a low level to a high level is a first phase difference, and a difference between the first timing and a third timing at which the secondary side voltage rises from an intermediate level to a high level is a second phase difference, the control unit is configured to, in the first control, control the primary side full bridge circuit and the secondary side full bridge circuit in a manner that the first phase difference and the second phase difference which enable output of a demand power and satisfy the condition 1 and the condition 2 are combined, and thereby output the demand power.

2. The power conversion device according to claim 1, wherein a number of turns of the primary side winding of the transformer is N1, a number of turns of the secondary side winding is N2, an input voltage input to the primary side full bridge circuit is Vin, an output voltage output from the secondary side full bridge circuit is Vout, and an equivalent voltage ratio when a turns ratio of the transformer is converted to 1:1, that is, an equivalent voltage ratio is (Vout x N1) / (Vin x N2), the control unit is configured to ​ In a case where the equivalent voltage ratio is less than a prescribed threshold value of less than 1, a second control is executed, which controls the primary-side full-bridge circuit in a manner to apply a three-level primary-side voltage to the series connection, and controls the secondary-side full-bridge circuit in a manner to apply a two-level secondary-side voltage to the secondary-side winding, In a case where the equivalent voltage ratio is equal to or more than the prescribed threshold value, the first control is executed.

3. A power conversion device, characterized by, Possessing: a transformer having a primary-side winding and a secondary-side winding; a reactor which is a reactor connected to the secondary-side winding, and the secondary-side winding and the reactor form a series connection; a primary-side full-bridge circuit which is a circuit connected to the primary-side winding, and has a plurality of primary-side switching elements; a secondary-side full-bridge circuit which is a circuit connected to the reactor, and has a plurality of secondary-side switching elements; and a control unit configured to control the plurality of primary-side switching elements and the plurality of secondary-side switching elements, a condition for performing soft switching operation of the plurality of primary-side switching elements is a condition 1, and a condition for performing soft switching operation of the plurality of secondary-side switching elements is a condition 2, the condition 1 is that a value of a forward current at a diode connected in parallel to the primary-side switching element of the plurality of primary-side switching elements which changes from off to on, of a current flowing at the primary-side winding when at least one of the primary-side switching elements switches between on and off, is equal to or more than an absolute value of a primary-side winding current threshold value, the condition 2 is that a value of a forward current at a diode connected in parallel to the secondary-side switching element of the plurality of secondary-side switching elements which changes from off to on, of a current flowing at the secondary-side winding when at least one of the secondary-side switching elements switches between on and off, is equal to or more than an absolute value of a secondary-side winding current threshold value, the control unit is configured to execute a first control which controls the primary-side full-bridge circuit in a manner to apply a three-level primary-side voltage to the primary-side winding, and controls the secondary-side full-bridge circuit in a manner to apply a two-level secondary-side voltage to the series connection, the primary-side voltage and the secondary-side voltage are waveforms of the same frequency whose phases flip every 180 degrees, a difference between a first timing at which the primary-side voltage rises from a low level to an intermediate level and a second timing at which the secondary-side voltage rises from a low level to a high level is a first phase difference, and a difference between the first timing and a third timing at which the primary-side voltage rises from the intermediate level to a high level is a second phase difference, the control unit is configured to, in the first control, control the primary-side full-bridge circuit and the secondary-side full-bridge circuit in a manner to realize a combination between the first phase difference and the second phase difference which can output a demand power and satisfy the condition 1 and the condition 2, and thereby output the demand power.

4. The power conversion device according to claim 3, characterized in that, ​ The number of turns of the primary side winding of the transformer is N1, the number of turns of the secondary side winding is N2, an input voltage input to the primary side full-bridge circuit is Vin, an output voltage output from the secondary side full-bridge circuit is Vout, and an equivalent voltage ratio when the turns ratio of the transformer is converted to 1:1, that is, an equivalent voltage ratio is (Vout x N1) / (Vin x N2), The control section is configured to, In a case where the equivalent voltage ratio is greater than a prescribed threshold value that is greater than 1, a second control is executed, the second control controls the primary side full-bridge circuit in a manner that applies a two-level primary side voltage to the primary side winding, and controls the secondary side full-bridge circuit in a manner that applies a three-level secondary side voltage to the series connection body, In a case where the equivalent voltage ratio is equal to or less than the prescribed threshold value, the first control is executed.

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