Power conversion device

Abstract

A power conversion device (10) comprises a transformer unit (31), a primary-side full bridge circuit (41), and a secondary-side full bridge circuit (51). The primary-side full bridge circuit (41) comprises a first bidirectional switch (43), a second bidirectional switch (44), a third bidirectional switch (46), and a fourth bidirectional switch (47). The secondary-side full bridge circuit (51) comprises a fifth bidirectional switch (53), a sixth bidirectional switch (54), a seventh bidirectional switch (56), and an eighth bidirectional switch (57).

Description

Power conversion device

[0001] This disclosure relates to a power conversion device.

[0002] The power conversion device disclosed in Patent Document 1 includes an AC / DC conversion unit, a PFC coil, a DAB converter (a DC / DC converter of the dual active bridge type), and a bus capacitor. The AC / DC conversion unit is a full-bridge circuit of four switching elements. The AC / DC conversion unit converts an AC voltage into a DC voltage while improving the power factor. The PFC coil connects an AC power supply and the AC / DC conversion unit. The PFC coil is a coil for improving the power factor. The PFC coil is, for example, a boost coil. The DC voltage output by the AC / DC conversion unit is input to the DAB converter. The bus capacitor is provided between the AC / DC conversion unit and the DAB converter.

[0003] Japanese Patent No. 6710615

[0004] In Patent Document 1, it is necessary to provide a bus capacitor between the AC / DC conversion unit and the DAB converter.

[0005] A power converter according to one aspect of the present disclosure includes a transformer section having a primary winding, a secondary winding, and a reactor connected to at least one of the primary winding and the secondary winding; a first power line connected to the first end of a power supply; a second power line connected to the second end of the power supply; a primary full-bridge circuit connected to the primary winding and having a plurality of primary bidirectional switches; a secondary full-bridge circuit connected to the secondary winding and having a plurality of secondary switching elements; and the plurality of primary bidirectional switches and the plurality The system comprises a control unit configured to control secondary switching elements, each of the plurality of primary bidirectional switches comprising two primary switching elements, the two primary switching elements connected to each primary switching element in parallel with each primary switching element being oriented in opposite directions, and the plurality of primary switching elements comprising the plurality of primary bidirectional switches comprising a first switching element, a second switching element, a third switching element, a fourth switching element, a fifth switching element, The system includes a sixth switching element, a seventh switching element, and an eighth switching element, wherein the first switching element, the second switching element, the third switching element, and the fourth switching element are connected between the first power line and the second power line in this order, and the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element are connected between the first power line and the second power line in this order, and the condition for performing soft switching of the plurality of primary-side switching elements is condition 1, and the condition for performing soft switching of the plurality of secondary-side switching elements is condition 2, wherein the condition 1 is that when at least one of the plurality of primary-side switching elements switches from OFF to ON, the primary-side condition current value, which is the value of the current flowing in the primary-side winding in the forward direction of the diode connected in parallel with the at least one primary-side switching element, is greater than or equal to the absolute value of the primary-side winding current threshold, and the condition 2 is that when at least one of the plurality of secondary-side switching elements switches from OFF to ON,The secondary condition current value, which is the value of the current flowing in the secondary winding in the forward direction of the diode connected in parallel to at least one secondary switching element, is greater than or equal to the absolute value of the secondary winding current threshold, the control unit is configured to control the primary full-bridge circuit and the secondary full-bridge circuit so that one of the primary full-bridge circuit and the secondary full-bridge circuit applies a 2-level voltage to the transformer section, and the other applies a 3-level voltage to the transformer section, the 2-level voltage and the 3-level voltage are waveforms of the same frequency that invert every 180 degrees of phase, the difference between the first time when the 3-level voltage rises from a low level to a middle level and the second time when the 2-level voltage rises from a low level to a high level is the first phase difference, the difference between the first time and the third time when the 3-level voltage rises from a middle level to a high level is the second phase difference, and the control unit The device is configured to output the required power and to satisfy conditions 1 and 2 by controlling at least one of the first phase difference, the second phase difference, and the frequencies of the two-level voltage and the third-level voltage. When the potential at the first end is higher than the potential at the second end, the first, third, fifth, and seventh switching elements are kept ON while the second, fourth, sixth, and eighth switching elements are switched. When the potential at the first end is lower than the potential at the second end, the second, fourth, sixth, and eighth switching elements are kept ON while the second, fourth, sixth, and eighth switching elements are switched.

[0006] The primary-side full-bridge circuit has multiple primary-side bidirectional switches. This allows the voltage applied from the primary-side full-bridge circuit to the transformer section to have the same waveform, regardless of whether the potential at the first terminal is higher or lower than the potential at the second terminal. The elimination of bus capacitors reduces the number of components.

[0007] The power converter described above comprises a first output terminal, a second output terminal, a third power line connected to the first output terminal, and a fourth power line connected to the second output terminal. The secondary full-bridge circuit comprises a plurality of secondary bidirectional switches, each of the plurality of secondary bidirectional switches comprises two secondary switching elements from the plurality of secondary switching elements, and the two secondary switching elements are connected to each other such that the diodes connected in parallel to each of the two secondary switching elements are oriented in opposite directions. The plurality of secondary switching elements in the plurality of secondary bidirectional switches include a ninth switching element, a tenth switching element, an eleventh switching element, a twelfth switching element, a thirteenth switching element, a fourteenth switching element, a fifteenth switching element, and a sixteenth switching element, and the ninth switching element, the tenth switching element, the eleventh switching element, and the twelfth switching element are connected between the third power line and the fourth power line. The switching elements may be connected in this order, with the 13th switching element, the 14th switching element, the 15th switching element, and the 16th switching element connected in this order between the third power line and the fourth power line, and the control unit may be configured to switch the 9th switching element, the 11th switching element, the 13th switching element, and the 15th switching element while keeping the 10th switching element, the 12th switching element, the 14th switching element, and the 16th switching element ON when the potential of the first output terminal is higher than the potential of the second output terminal, and to switch the 10th switching element, the 12th switching element, the 14th switching element, and the 16th switching element while keeping the 9th switching element, the 11th switching element, the 13th switching element, and the 15th switching element ON when the potential of the first output terminal is lower than the potential of the second output terminal.

[0008] Regarding the power converter described above, the power supply is an AC power supply that outputs three phase AC voltages with phases shifted by 120 degrees, the primary full-bridge circuit is one of three primary full-bridge circuits, the secondary full-bridge circuit is one of three secondary full-bridge circuits, and each of the three primary full-bridge circuits is input with an AC voltage of one phase of the three phase AC voltages, and the output currents of the three secondary full-bridge circuits may be merged and output.

[0009] Regarding the power conversion device described above, the power supply is an AC power supply that outputs an AC voltage, and the control unit is configured to put the primary side full bridge circuit into a flat state when the difference between the potential of the first end and the potential of the second end is 0. The flat state may be a state in which the first switching element, the second switching element, the fifth switching element, and the sixth switching element are ON, or a state in which the third switching element, the fourth switching element, the seventh switching element, and the eighth switching element are ON.

[0010] According to the present invention, the number of parts can be reduced.

[0011] Figure 1 is a circuit diagram of a power converter. Figure 2 is a diagram showing the relationship between the equivalent voltage ratio and the load mode. Figure 3 is a diagram showing the primary and secondary voltages in the step-down lagging phase mode, which is one of the load modes in Figure 2. Figure 4 is a diagram showing the primary and secondary voltages in the step-down in-phase mode, which is one of the load modes in Figure 2. Figure 5 is a diagram showing the primary and secondary voltages in the step-down leading phase mode, which is one of the load modes in Figure 2. Figure 6 is a diagram showing the primary and secondary voltages in the step-up lagging phase mode, which is one of the load modes in Figure 2. Figure 7 is a diagram showing the primary and secondary voltages in the step-up in-phase mode, which is one of the load modes in Figure 2. Figure 8 is a diagram showing the primary and secondary voltages in the step-up leading phase mode, which is one of the load modes in Figure 2. Figure 9 is a flowchart showing the output control. Figure 10 is a diagram showing the primary and secondary currents in the step-down lagging phase mode, which is one of the load modes in Figure 2. Figure 11 shows a modified power converter. Figure 12 shows a modified power converter.

[0012] An embodiment of a power converter will be described. As shown in Figure 1, the power converter 10 is installed between the power supply PS and the load 100. The power converter 10 receives the input voltage V from the power supply PS. ｉｎ output voltage V ｏｕｔ It can be converted and output to load 100. The power supply PS may be an AC power supply or a DC power supply. The power supply PS has a first terminal P1 and a second terminal P2. When the power supply PS is an AC power supply, the first terminal P1 or the second terminal P2 switches to being positive depending on the passage of time. When the power supply PS is a DC power supply, the first terminal P1 is the positive terminal and the second terminal P2 is the negative terminal. Figure 1 illustrates an example where the power supply PS is an AC power supply.

[0013] The power converter 10 comprises a conversion circuit 11, an output filter 61, a first output terminal 14, a second output terminal 15, and a control unit 70. The conversion circuit 11 comprises a first input terminal 12, a second input terminal 13, an input filter 21, a first power line L1, a second power line L2, a DAB converter 40, a third power line L3, and a fourth power line L4.

[0014] The first input terminal 12 is connected to the first terminal P1 of the power supply PS. The second input terminal 13 is connected to the second terminal P2 of the power supply PS. Input voltage V is supplied from the first input terminal 12 and the second input terminal 13 to the conversion circuit 11. ｉｎ The following is entered.

[0015] The first power line L1 is connected to the first terminal P1 of the power supply PS via the first input terminal 12. The second power line L2 is connected to the second terminal P2 of the power supply PS via the second input terminal 13. The input filter 21 suppresses noise from flowing into the power supply PS. The input filter 21 is, for example, an LC filter. The input filter 21 comprises a coil 22 and a capacitor 23. The coil 22 is provided on the first power line L1. The capacitor 23 connects the first power line L1 and the second power line L2 on the DAB converter 40 side of the coil 22.

[0016] The DAB converter 40 is a dual active bridge type DC / DC converter. The DAB converter 40 includes a transformer section 31. The transformer section 31 includes a transformer 32 and reactors 36 and 37. The transformer 32 is an isolated type. The transformer 32 includes a magnetic core 33, a primary winding 34, and a secondary winding 35. The primary winding 34 and the secondary winding 35 are wound around the core 33.

[0017] The transformer 32 is connected to reactors 36 and 37. Reactors 36 and 37 may be elements such as choke coils, or they may be the leakage inductances of the primary winding 34 and the secondary winding 35. Reactor 36 is connected to the primary winding 34. Reactor 37 is connected to the secondary winding 35. Reactor 36 may be referred to as the first reactor 36 and reactor 37 as the second reactor 37 as appropriate. The primary winding 34 and the first reactor 36 constitute a series connection SC1. The secondary winding 35 and the second reactor 37 constitute a series connection SC2.

[0018] The DAB converter 40 includes a primary-side full-bridge circuit 41. The primary-side full-bridge circuit 41 includes a first leg 42 and a second leg 45. The first leg 42 includes a first bidirectional switch 43 and a second bidirectional switch 44. The first bidirectional switch 43 and the second bidirectional switch 44 are connected in series with each other between the first power line L1 and the second power line L2. The second leg 45 includes a third bidirectional switch 46 and a fourth bidirectional switch 47. The third bidirectional switch 46 and the fourth bidirectional switch 47 are connected in series with each other between the first power line L1 and the second power line L2. As a result, the first leg 42 and the second leg 45 are connected in parallel with each other. The first bidirectional switch 43 and the third bidirectional switch 46 constitute the upper arm. The second bidirectional switch 44 and the fourth bidirectional switch 47 constitute the lower arm.

[0019] The first bidirectional switch 43, the second bidirectional switch 44, the third bidirectional switch 46, and the fourth bidirectional switch 47 are multiple primary bidirectional switches 43, 44, 46, and 47. The configurations of the first bidirectional switch 43, the second bidirectional switch 44, the third bidirectional switch 46, and the fourth bidirectional switch 47 are identical.

[0020] Each bidirectional switch 43, 44, 46, 47 comprises two switching elements Q1, Q2, two diodes D1, D2, and two capacitors C1, C2. The switching elements Q1, Q2 are, for example, n-type MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The switching elements Q1, Q2 may also be p-type MOSFETs, IGBTs (Insulated Gate Bipolar Transistors), or GaN-HEMTs.

[0021] Diodes D1 and D2 and capacitors C1 and C2 are connected in parallel to switching elements Q1 and Q2, one each. Diodes D1 and D2 may be parasitic diodes or elements. Capacitors C1 and C2 may be parasitic capacitances, elements, or a combination of parasitic capacitances and elements.

[0022] The two switching elements Q1 and Q2 are connected such that the diodes D1 and D2 are oriented in opposite directions. In other words, the two switching elements Q1 and Q2 are back-to-back connected. If the switching elements Q1 and Q2 are MOSFETs, the sources of the two switching elements Q1 and Q2 are connected to each other. The anodes of the two diodes D1 and D2 are connected to each other.

[0023] One of the two switching elements Q1 and Q2 of the first bidirectional switch 43 is the first switching element Q11, and the other is the second switching element Q12. One of the two switching elements Q1 and Q2 of the second bidirectional switch 44 is the third switching element Q21, and the other is the fourth switching element Q22. One of the two switching elements Q1 and Q2 of the third bidirectional switch 46 is the fifth switching element Q31, and the other is the sixth switching element Q32. One of the two switching elements Q1 and Q2 of the fourth bidirectional switch 47 is the seventh switching element Q41, and the other is the eighth switching element Q42. The first switching elements Q11 to the eighth switching elements Q42 are the multiple primary-side switching elements Q11 to Q42 provided in the multiple primary-side bidirectional switches 43, 44, 46, and 47.

[0024] In the first leg 42, the first switching element Q11 is connected to the first power line L1. The second switching element Q12 and the third switching element Q21 are connected to each other. The fourth switching element Q22 is connected to the second power line L2. Between the first power line L1 and the second power line L2, the first switching element Q11, the second switching element Q12, the third switching element Q21, and the fourth switching element Q22 are connected in this order.

[0025] In the second leg 45, the fifth switching element Q31 is connected to the first power line L1. The sixth switching element Q32 and the seventh switching element Q41 are connected to each other. The eighth switching element Q42 is connected to the second power line L2. Between the first power line L1 and the second power line L2, the fifth switching element Q31, the sixth switching element Q32, the seventh switching element Q41, and the eighth switching element Q42 are connected in this order.

[0026] The connection point between the first bidirectional switch 43 and the second bidirectional switch 44 is connected to one end of the primary winding 34 via the first reactor 36, and the connection point between the third bidirectional switch 46 and the fourth bidirectional switch 47 is directly connected to the other end of the primary winding 34. In other words, the primary full-bridge circuit 41 is connected to the transformer section 31. The connection point between the first bidirectional switch 43 and the second bidirectional switch 44 is the connection point between the second switching element Q12 and the third switching element Q21. The connection point between the third bidirectional switch 46 and the fourth bidirectional switch 47 is the connection point between the sixth switching element Q32 and the seventh switching element Q41.

[0027] The DAB converter 40 includes a secondary full-bridge circuit 51. The secondary full-bridge circuit 51 includes a third leg 52 and a fourth leg 55. The third leg 52 includes a fifth bidirectional switch 53 and a sixth bidirectional switch 54. The fifth bidirectional switch 53 and the sixth bidirectional switch 54 are connected in series with each other between the third power line L3 and the fourth power line L4. The fourth leg 55 includes a seventh bidirectional switch 56 and an eighth bidirectional switch 57. The seventh bidirectional switch 56 and the eighth bidirectional switch 57 are connected in series with each other between the third power line L3 and the fourth power line L4. The fifth bidirectional switch 53 and the seventh bidirectional switch 56 constitute the upper arm. The sixth bidirectional switch 54 and the eighth bidirectional switch 57 constitute the lower arm.

[0028] The fifth bidirectional switch 53, the sixth bidirectional switch 54, the seventh bidirectional switch 56, and the eighth bidirectional switch 57 are multiple secondary bidirectional switches 53, 54, 56, and 57. The fifth bidirectional switch 53, the sixth bidirectional switch 54, the seventh bidirectional switch 56, and the eighth bidirectional switch 57 have the same configuration as the bidirectional switches 43, 44, 46, and 47.

[0029] One of the two switching elements Q1 and Q2 of the fifth bidirectional switch 53 is the ninth switching element Q51, and the other is the tenth switching element Q52. One of the two switching elements Q1 and Q2 of the sixth bidirectional switch 54 is the eleventh switching element Q61, and the other is the twelfth switching element Q62. One of the two switching elements Q1 and Q2 of the seventh bidirectional switch 56 is the thirteenth switching element Q71, and the other is the fourteenth switching element Q72. One of the two switching elements Q1 and Q2 of the eighth bidirectional switch 57 is the fifteenth switching element Q81, and the other is the sixteenth switching element Q82. The ninth to sixteenth switching elements Q51 to Q82 are the multiple secondary switching elements Q51 to Q82 provided by the multiple secondary bidirectional switches 53, 54, 56, and 57.

[0030] In the third leg 52, the ninth switching element Q51 is connected to the third power line L3. The tenth switching element Q52 and the eleventh switching element Q61 are connected to each other. The twelfth switching element Q62 is connected to the fourth power line L4. Between the third power line L3 and the fourth power line L4, the ninth switching element Q51, the tenth switching element Q52, the eleventh switching element Q61, and the twelfth switching element Q62 are connected in this order.

[0031] In the fourth leg 55, the 13th switching element Q71 is connected to the third power line L3. The 14th switching element Q72 and the 15th switching element Q81 are connected to each other. The 16th switching element Q82 is connected to the fourth power line L4. Between the third power line L3 and the fourth power line L4, the 13th switching element Q71, the 14th switching element Q72, the 15th switching element Q81, and the 16th switching element Q82 are connected in this order.

[0032] The connection point between the fifth bidirectional switch 53 and the sixth bidirectional switch 54 is connected to one end of the secondary winding 35 via the second reactor 37, and the connection point between the seventh bidirectional switch 56 and the eighth bidirectional switch 57 is directly connected to the other end of the secondary winding 35. In other words, the secondary full-bridge circuit 51 is connected to the transformer section 31. The connection point between the fifth bidirectional switch 53 and the sixth bidirectional switch 54 is the connection point between the tenth switching element Q52 and the eleventh switching element Q61. The connection point between the seventh bidirectional switch 56 and the eighth bidirectional switch 57 is the connection point between the fourteenth switching element Q72 and the fifteenth switching element Q81.

[0033] The third power line L3 is connected to the first output terminal 14. The fourth power line L4 is connected to the second output terminal 15. The output filter 61 is, for example, an LC filter. The output filter 61 is provided between the DAB converter 40 and the two output terminals 14 and 15. The output filter 61 includes a coil 62 and a capacitor 63. The coil 62 is provided on the third power line L3. The capacitor 63 connects the third power line L3 and the fourth power line L4 on the DAB converter 40 side of the coil 62.

[0034] The two output terminals 14 and 15 are connected to the load 100. The output power of the power converter 10 is supplied to the load 100 from the two output terminals 14 and 15. The control unit 70 comprises a processor and a memory unit. The processor is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or a DSP (Digital Signal Processor). The memory unit includes RAM (Random Access Memory) and ROM (Read Only Memory). The memory unit stores program code or instructions configured to cause the processor to perform processing. The memory unit, i.e., the computer-readable medium, includes any available medium that can be accessed by a general-purpose or dedicated computer. The control unit 70 may be composed of hardware circuits such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control unit 70, which is a processing circuit, may include one or more processors that operate according to a computer program, one or more hardware circuits such as an ASIC or FPGA, or a combination thereof.

[0035] The control unit 70 controls the input voltage V by controlling a plurality of primary bidirectional switches 43, 44, 46, 47 and a plurality of secondary bidirectional switches 53, 54, 56, 57. ｉｎ output voltage V ｏｕｔ Convert to.

[0036] The number of turns of the primary winding 34 of transformer 32 is N1, and the number of turns of the secondary winding 35 is N2. The equivalent voltage ratio, which is the equivalent voltage ratio when the turns ratio of transformer 32 is converted to 1:1, is (|V ｏｕｔ | × N1) / ( | V ｉｎ The control unit 70 is configured as follows: (x N2). The control unit 70 includes a step-down mode and a step-up mode as load modes. The step-down mode is a load mode that makes the equivalent voltage ratio less than 1. The step-up mode is a load mode that makes the equivalent voltage ratio greater than 1.

[0037] For example, when the turns ratio of the transformer 32 is 1:2, and the absolute value of the input voltage V ｉｎ |V ｉｎ | = 200 V, and the absolute value of the output voltage V ｏｕｔ |V ｏｕｔ | = 400 V, when the turns ratio is converted to 1:1, the equivalent voltage ratio = (|V ｏｕｔ | × 1) / (|V ｉｎ | × 2) = 1. Therefore, when the turns ratio of the transformer 32 is 1:2 and the absolute value of the output voltage V ｏｕｔ |V ｏｕｔ | = 400 V, if the absolute value of the input voltage V ｉｎ |V ｉｎ | is greater than 200 V, it is in the step - down mode, and if it is less than 200 V, it is in the step - up mode. In the following description, unless otherwise specified, the turns ratio is assumed to be 1:1.

[0038] The control unit 70 performs three - level control on one of the primary - side full - bridge circuit 41 and the secondary - side full - bridge circuit 51, and performs two - level control on the other. Thereby, one of the primary - side full - bridge circuit 41 and the secondary - side full - bridge circuit 51 applies a two - level voltage to the transformer unit 31, and the other applies a three - level voltage to the transformer unit 31.

[0039] In boost mode, the secondary full-bridge circuit 51 is controlled in three levels. In buck mode, the primary full-bridge circuit 41 is controlled in three levels. In boost mode, the primary full-bridge circuit 41 is controlled in two levels. In buck mode, the secondary full-bridge circuit 51 is controlled in two levels. In buck mode, three-level control is a control that switches the voltage applied to the series connection SC1 of the primary winding 34 and the first reactor 36 between positive, negative, or zero. In buck mode, two-level control is a control that switches the voltage applied to the series connection SC2 of the secondary winding 35 and the second reactor 37 between positive or negative. In boost mode, three-level control is a control that switches the voltage applied to the series connection SC2 of the secondary winding 35 and the second reactor 37 between positive, negative, or zero. In boost mode, two-level control is a control method in which the voltage applied to the series connection SC1 of the primary winding 34 and the first reactor 36 is switched between two stages: positive and negative. In three-level control, the case where the voltage applied to the series connection SC1 or SC2 is positive is referred to as high level, the case where the voltage applied to the series connection SC1 or SC2 is zero is referred to as middle level, and the case where the voltage applied to the series connection SC1 or SC2 is negative is referred to as low level. In two-level control, the case where the voltage applied to the series connection SC1 or SC2 is positive is referred to as high level, and the case where the voltage applied to the series connection SC1 or SC2 is negative is referred to as low level. The voltage applied to the series connection SC1 is referred to as the primary voltage V1, and the voltage applied to the series connection SC2 is referred to as the secondary voltage V2. The arrows in Figure 1 are considered positive for the primary voltage V1 and secondary voltage V2. Under normal operation, when the output is not changed, the primary voltage V1 and secondary voltage V2 are waveforms of the same frequency that invert every 180 degrees of phase.

[0040] <Step-Down Mode> The control performed by the control unit 70 when the load mode is step-down mode will be described below. When performing three-level control of the primary side full-bridge circuit 41, the control unit 70 independently controls the first leg 42 and the second leg 45. When the power supply PS is an AC power supply, the control unit 70 controls the input voltage V ｉｎ When it is positive and the input voltage V ｉｎDifferent control is performed depending on whether the value is negative or negative. When the potential of the first terminal P1 is higher than that of the second terminal P2, the input voltage V ｉｎ This is positive. When the potential at the first terminal P1 is lower than that at the second terminal P2, the input voltage V ｉｎ It is negative.

[0041] The control unit 70 receives the input voltage V ｉｎ If the condition is positive, the second switching element Q12, the fourth switching element Q22, the sixth switching element Q32, and the eighth switching element Q42 are kept ON. Then, the control unit 70 switches the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41 in this state. The switching patterns of the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41 include the first to fourth patterns.

[0042] The first pattern is a switching pattern in which the first switching element Q11 is turned ON, the third switching element Q21 is turned OFF, the fifth switching element Q31 is turned OFF, and the seventh switching element Q41 is turned ON.

[0043] The second pattern is a switching pattern in which the first switching element Q11 is turned ON, the third switching element Q21 is turned OFF, the fifth switching element Q31 is turned ON, and the seventh switching element Q41 is turned OFF.

[0044] The third pattern is a switching pattern in which the first switching element Q11 is turned OFF, the third switching element Q21 is turned ON, the fifth switching element Q31 is turned ON, and the seventh switching element Q41 is turned OFF.

[0045] The fourth pattern is a switching pattern in which the first switching element Q11 is turned OFF, the third switching element Q21 is turned ON, the fifth switching element Q31 is turned OFF, and the seventh switching element Q41 is turned ON.

[0046] The control unit 70 receives the input voltage V ｉｎIf the value is negative, the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41 are kept ON. Then, the control unit 70 switches the second switching element Q12, the fourth switching element Q22, the sixth switching element Q32, and the eighth switching element Q42 in this state. The switching patterns of the second switching element Q12, the fourth switching element Q22, the sixth switching element Q32, and the eighth switching element Q42 include patterns 5 to 8.

[0047] The fifth pattern is a switching pattern in which the second switching element Q12 is turned ON, the fourth switching element Q22 is turned OFF, the sixth switching element Q32 is turned OFF, and the eighth switching element Q42 is turned ON.

[0048] The sixth pattern is a switching pattern in which the second switching element Q12 is turned ON, the fourth switching element Q22 is turned OFF, the sixth switching element Q32 is turned ON, and the eighth switching element Q42 is turned OFF.

[0049] The seventh pattern is a switching pattern in which the second switching element Q12 is turned OFF, the fourth switching element Q22 is turned ON, the sixth switching element Q32 is turned ON, and the eighth switching element Q42 is turned OFF.

[0050] The eighth pattern is a switching pattern in which the second switching element Q12 is turned OFF, the fourth switching element Q22 is turned ON, the sixth switching element Q32 is turned OFF, and the eighth switching element Q42 is turned ON.

[0051] Input voltage V ｉｎ A first switching element Q11 is switched when the input voltage V is positive, and ｉｎ This corresponds to the fourth switching element Q22, which is switched when the input voltage V is negative. ｉｎ A third switching element Q21 is switched when the input voltage V is positive, and ｉｎ This corresponds to the second switching element Q12, which is switched when the input voltage V is negative. ｉｎThe fifth switching element Q31 is switched when the input voltage V is positive, and ｉｎ This corresponds to the eighth switching element Q42, which is switched when the input voltage V is negative. ｉｎ The seventh switching element Q41 is switched when the input voltage V is positive, and ｉｎ This corresponds to the sixth switching element Q32, which is switched when the value is negative.

[0052] Input voltage V ｉｎ When it is positive and the input voltage V ｉｎ When the value is negative, by similarly controlling the primary switching elements Q11 to Q42 which have the corresponding relationship described above, the primary voltage V1 applied to the series connection SC1 of the primary winding 34 and the first reactor 36 is equal to the input voltage V ｉｎ The waveform is the same regardless of whether it is positive or negative. That is, the input voltage V ｉｎ The waveform of the primary voltage V1 when it is positive, and the input voltage V ｉｎ The waveform of the primary voltage V1 will be the same when it is negative.

[0053] When the power supply PS is a DC power supply, the potential at the first terminal P1 is always higher than the potential at the second terminal P2. Therefore, the input voltage V ｉｎ This is always positive. When the power supply PS is a DC power supply, when the power supply PS is an AC power supply and the input voltage V ｉｎ The control is performed in the same way as when the value is positive. That is, the control unit 70 keeps the second switching element Q12, the fourth switching element Q22, the sixth switching element Q32, and the eighth switching element Q42 ON. Then, in this state, the control unit 70 switches the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41. The switching patterns of the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41 include the first to fourth patterns.

[0054] When performing two-level control of the secondary full-bridge circuit 51, the control unit 70 controls the third leg 52 and the fourth leg 55 in conjunction. Output voltage V ｏｕｔ When the output voltage is an AC voltage, the control unit 70 controls the output voltage Vｏｕｔ When it is positive and the output voltage V ｏｕｔ Different control is performed depending on whether it is negative or negative. When the potential of the first output terminal 14 is higher than that of the second output terminal 15, the output voltage V ｏｕｔ This is positive. When the potential of the first output terminal 14 is lower than that of the second output terminal 15, the output voltage V ｏｕｔ It is negative.

[0055] The control unit 70 controls the output voltage V ｏｕｔ If the condition is positive, the 10th switching element Q52, the 12th switching element Q62, the 14th switching element Q72, and the 16th switching element Q82 are kept ON. Then, in this state, the control unit 70 switches the 9th switching element Q51, the 11th switching element Q61, the 13th switching element Q71, and the 15th switching element Q81. The 9th switching element Q51 and the 15th switching element Q81 are turned ON simultaneously. The 11th switching element Q61 and the 13th switching element Q71 are turned ON simultaneously. The switching patterns of the 9th switching element Q51, the 11th switching element Q61, the 13th switching element Q71, and the 15th switching element Q81 include the 9th pattern and the 10th pattern.

[0056] The ninth pattern is a switching pattern in which the ninth switching element Q51 is turned ON, the eleventh switching element Q61 is turned OFF, the thirteenth switching element Q71 is turned OFF, and the fifteenth switching element Q81 is turned ON.

[0057] The tenth pattern is a switching pattern in which the ninth switching element Q51 is turned OFF, the eleventh switching element Q61 is turned ON, the thirteenth switching element Q71 is turned ON, and the fifteenth switching element Q81 is turned OFF.

[0058] The control unit 70 controls the output voltage V ｏｕｔIf the value is negative, the ninth switching element Q51, the eleventh switching element Q61, the thirteenth switching element Q71, and the fifteenth switching element Q81 are kept ON. Then, in this state, the control unit 70 switches the tenth switching element Q52, the twelfth switching element Q62, the fourteenth switching element Q72, and the sixteenth switching element Q82. The switching patterns of the tenth switching element Q52, the twelfth switching element Q62, the fourteenth switching element Q72, and the sixteenth switching element Q82 include the eleventh pattern and the twelfth pattern.

[0059] The 11th pattern is a switching pattern in which the 10th switching element Q52 is turned OFF, the 12th switching element Q62 is turned ON, the 14th switching element Q72 is turned ON, and the 16th switching element Q82 is turned OFF.

[0060] The 12th pattern is a switching pattern in which the 10th switching element Q52 is turned ON, the 12th switching element Q62 is turned OFF, the 14th switching element Q72 is turned OFF, and the 16th switching element Q82 is turned ON.

[0061] Output voltage V ｏｕｔ The ninth switching element Q51 is switched when the voltage is positive, and the output voltage V ｏｕｔ This corresponds to the 12th switching element Q62, which is switched when the output voltage V is negative. ｏｕｔ The 11th switching element Q61 is switched when the voltage is positive, and the output voltage V ｏｕｔ This corresponds to the tenth switching element Q52, which is switched when the output voltage V is negative. ｏｕｔ The 13th switching element Q71 is switched when the voltage is positive, and the output voltage V ｏｕｔ This corresponds to the 16th switching element Q82, which is switched when the output voltage V is negative. ｏｕｔ The 15th switching element Q81 is switched when the voltage is positive, and the output voltage V ｏｕｔ This corresponds to the 14th switching element Q72, which is switched when the value is negative.

[0062] Output voltage V ｏｕｔWhen it is positive and the output voltage V ｏｕｔ When the value is negative, by similarly controlling the secondary switching elements Q51 to Q82 which have the corresponding relationship described above, the secondary voltage V2 applied to the series connection SC2 of the secondary winding 35 and the second reactor 37 is the output voltage V ｏｕｔ The waveform is the same regardless of whether it is positive or negative. That is, the output voltage V ｏｕｔ The waveform of the secondary voltage V2 and the output voltage V when the value is positive. ｏｕｔ The waveform of the secondary voltage V2 will be the same when it is negative.

[0063] Output voltage V ｏｕｔ When the voltage is set to a DC voltage, the control unit 70 always sets the potential of the first terminal P1 higher than the potential of the second terminal P2. Therefore, the output voltage V ｏｕｔ When this is a DC voltage, the output voltage V ｏｕｔ When the voltage is an AC voltage, the output voltage V ｏｕｔ The control is performed in the same way as when the value is positive. That is, the control unit 70 keeps the 10th switching element Q52, the 12th switching element Q62, the 14th switching element Q72, and the 16th switching element Q82 ON. Then, in this state, the control unit 70 switches the 9th switching element Q51, the 11th switching element Q61, the 13th switching element Q71, and the 15th switching element Q81. The 9th switching element Q51 and the 15th switching element Q81 are turned ON simultaneously. The 11th switching element Q61 and the 13th switching element Q71 are turned ON simultaneously. The switching patterns of the 9th switching element Q51, the 11th switching element Q61, the 13th switching element Q71, and the 15th switching element Q81 include the 9th pattern and the 10th pattern.

[0064] The control unit 70 receives the input voltage V input to the primary full-bridge circuit 41 by a combination of one of the first to eighth patterns of the primary full-bridge circuit 41 and one of the ninth to twelfth patterns of the secondary full-bridge circuit 51. ｉｎ Converts the output voltage V from the secondary side full bridge circuit 51. ｏｕｔ It outputs the input voltage V. ｉｎ The current can be either DC or AC, and the output voltage is Vｏｕｔ It can be either direct current or alternating current.

[0065] As shown in Figure 2, the step-down modes include a step-down lag phase mode, a step-down in-phase mode, and a step-down leading phase mode. As shown in Figure 3, the step-down lag phase mode is a step-down mode in which the primary voltage V1 is raised from a low level to a middle level, then the secondary voltage V2 is raised from a low level to a high level, and then the primary voltage V1 is raised from a middle level to a high level. The step-down lag phase mode is a step-down mode used when outputting a small amount of power in response to the power demand from the load 100.

[0066] The difference between the first time T1 when the 3-level voltage rises from low to middle level and the second time T2 when the 2-level voltage rises from low to high level is the first phase difference θ1. The difference between the first time and the third time T3 when the 3-level voltage rises from middle to high level is the second phase difference θ2.

[0067] In step-down mode, the first phase difference θ1 is the difference between the first time T1 when the primary voltage V1 rises from a low level to a middle level and the second time T2 when the secondary voltage V2 rises from a low level to a high level. The second phase difference θ2 is the difference between the first time T1 and the third time T3 when the primary voltage V1 rises from a middle level to a high level.

[0068] The primary voltage V1 and secondary voltage V2 are waveforms of the same frequency that invert every 180 degrees in phase during normal operation without changing the output. Therefore, the time when the 3-level voltage falls from high level to middle level is the first time T1. The time when the 2-level voltage falls from high level to low level is the second time T2. The time when the 3-level voltage falls from middle level to low level is the third time T3.

[0069] As shown in Figure 4, the step-down in-phase mode is a step-down mode in which the primary voltage V1 is raised from a low level to a middle level, and then the primary voltage V1 is raised from a middle level to a high level and the secondary voltage V2 is raised from a low level to a high level simultaneously. In the step-down in-phase mode, the second time T2 and the third time T3 are the same time. Therefore, the first phase difference θ1 and the second phase difference θ2 are the same value. That is, the difference between the first phase difference θ1 and the second phase difference θ2 is 0. The step-down in-phase mode is a step-down mode used when outputting medium power in response to the power demanded from the load 100. Medium power is an output power with a larger maximum value than low power.

[0070] As shown in Figure 5, the step-back leading-phase mode is a step-back mode in which the primary voltage V1 is raised from a low level to a middle level, then raised from a middle level to a high level, and then the secondary voltage V2 is raised from a low level to a high level. The step-back leading-phase mode is a step-back mode used when outputting high power in response to the power demand from the load 100. High power is output power with a maximum value greater than medium power.

[0071] In step-down mode, the step-down lag phase mode and step-down lead phase mode switch when the difference between the first phase difference θ1 and the second phase difference θ2 is zero. <Step-up mode> The control performed by the control unit 70 when the load mode is step-up mode will be described below.

[0072] When performing two-level control of the primary side full-bridge circuit 41, the control unit 70 controls the first leg 42 and the second leg 45 in conjunction. When the power supply PS is an AC power supply, the control unit 70 controls the input voltage V ｉｎ When it is positive and the input voltage V ｉｎ Different control methods are used depending on whether the value is negative or negative.

[0073] The control unit 70 receives the input voltage V ｉｎIf the condition is positive, the second switching element Q12, the fourth switching element Q22, the sixth switching element Q32, and the eighth switching element Q42 are kept ON. Then, the control unit 70 switches the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41 in this state. The first switching element Q11 and the seventh switching element Q41 are turned ON simultaneously. The third switching element Q21 and the fifth switching element Q31 are turned ON simultaneously. The switching patterns of the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41 include the thirteenth and fourteenth patterns.

[0074] The 13th pattern is a switching pattern in which the first switching element Q11 is turned ON, the third switching element Q21 is turned OFF, the fifth switching element Q31 is turned OFF, and the seventh switching element Q41 is turned ON.

[0075] The 14th pattern is a switching pattern in which the first switching element Q11 is turned OFF, the third switching element Q21 is turned ON, the fifth switching element Q31 is turned ON, and the seventh switching element Q41 is turned OFF.

[0076] The control unit 70 receives the input voltage V ｉｎ If the value is negative, the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41 are kept ON. Then, the control unit 70 switches the second switching element Q12, the fourth switching element Q22, the sixth switching element Q32, and the eighth switching element Q42 in this state. The second switching element Q12 and the eighth switching element Q42 are turned ON simultaneously. The fourth switching element Q22 and the sixth switching element Q32 are turned ON simultaneously. The switching patterns of the second switching element Q12, the fourth switching element Q22, the sixth switching element Q32, and the eighth switching element Q42 include the 15th pattern and the 16th pattern.

[0077] The 15th pattern is a switching pattern in which the second switching element Q12 is turned OFF, the fourth switching element Q22 is turned ON, the sixth switching element Q32 is turned ON, and the eighth switching element Q42 is turned OFF.

[0078] The 16th pattern is a switching pattern in which the second switching element Q12 is turned ON, the fourth switching element Q22 is turned OFF, the sixth switching element Q32 is turned OFF, and the eighth switching element Q42 is turned ON.

[0079] The control unit 70 is configured such that when the power supply PS is a DC power supply, and when the power supply PS is an AC power supply, the input voltage V ｉｎ The control is performed in the same way as when the value is positive. That is, the control unit 70 keeps the second switching element Q12, the fourth switching element Q22, the sixth switching element Q32, and the eighth switching element Q42 ON. Then, in this state, the control unit 70 switches the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41. The switching patterns of the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41 include the thirteenth and fourteenth patterns.

[0080] When performing three-level control of the secondary full-bridge circuit 51, the control unit 70 independently controls the third leg 52 and the fourth leg 55. Output voltage V ｏｕｔ When the output voltage is an AC voltage, the control unit 70 controls the output voltage V ｏｕｔ When it is positive and the output voltage V ｏｕｔ Different control methods are used depending on whether the value is negative or negative.

[0081] The control unit 70 controls the output voltage V ｏｕｔIf the condition is positive, the 10th switching element Q52, the 12th switching element Q62, the 14th switching element Q72, and the 16th switching element Q82 are kept ON. Then, in this state, the control unit 70 switches the 9th switching element Q51, the 11th switching element Q61, the 13th switching element Q71, and the 15th switching element Q81. The switching patterns of the 9th switching element Q51, the 11th switching element Q61, the 13th switching element Q71, and the 15th switching element Q81 include patterns 17 to 20.

[0082] The 17th pattern is a switching pattern in which the 9th switching element Q51 is turned ON, the 11th switching element Q61 is turned OFF, the 13th switching element Q71 is turned OFF, and the 15th switching element Q81 is turned ON.

[0083] The 18th pattern is a switching pattern in which the 9th switching element Q51 is turned ON, the 11th switching element Q61 is turned OFF, the 13th switching element Q71 is turned ON, and the 15th switching element Q81 is turned OFF.

[0084] The 19th pattern is a switching pattern in which the 9th switching element Q51 is turned OFF, the 11th switching element Q61 is turned ON, the 13th switching element Q71 is turned ON, and the 15th switching element Q81 is turned OFF.

[0085] The 20th pattern is a switching pattern in which the 9th switching element Q51 is turned OFF, the 11th switching element Q61 is turned ON, the 13th switching element Q71 is turned OFF, and the 15th switching element Q81 is turned ON.

[0086] The control unit 70 controls the output voltage V ｏｕｔIf the value is negative, the ninth switching element Q51, the eleventh switching element Q61, the thirteenth switching element Q71, and the fifteenth switching element Q81 are kept ON. Then, in this state, the control unit 70 switches the tenth switching element Q52, the twelfth switching element Q62, the fourteenth switching element Q72, and the sixteenth switching element Q82. The switching patterns of the tenth switching element Q52, the twelfth switching element Q62, the fourteenth switching element Q72, and the sixteenth switching element Q82 include patterns 21 to 24.

[0087] The 21st pattern is a switching pattern in which the 10th switching element Q52 is turned ON, the 12th switching element Q62 is turned OFF, the 14th switching element Q72 is turned OFF, and the 16th switching element Q82 is turned ON.

[0088] The 22nd pattern is a switching pattern in which the 10th switching element Q52 is turned ON, the 12th switching element Q62 is turned OFF, the 14th switching element Q72 is turned ON, and the 16th switching element Q82 is turned OFF.

[0089] The 23rd pattern is a switching pattern in which the 10th switching element Q52 is turned OFF, the 12th switching element Q62 is turned ON, the 14th switching element Q72 is turned ON, and the 16th switching element Q82 is turned OFF.

[0090] The 24th pattern is a switching pattern in which the 10th switching element Q52 is turned OFF, the 12th switching element Q62 is turned ON, the 14th switching element Q72 is turned OFF, and the 16th switching element Q82 is turned ON.

[0091] Output voltage V ｏｕｔ When the output voltage is set to a DC voltage, the control unit 70 controls the output voltage V ｏｕｔ When the voltage is an AC voltage, the output voltage V ｏｕｔThe control is performed in the same way as when the value is positive. That is, the control unit 70 keeps the 10th switching element Q52, the 12th switching element Q62, the 14th switching element Q72, and the 16th switching element Q82 ON. Then, in this state, the control unit 70 switches the 9th switching element Q51, the 11th switching element Q61, the 13th switching element Q71, and the 15th switching element Q81. The switching patterns of the 9th switching element Q51, the 11th switching element Q61, the 13th switching element Q71, and the 15th switching element Q81 include patterns 17 to 20.

[0092] The control unit 70 outputs the output voltage V from the secondary full-bridge circuit 51 by combining one of the 13th to 16th patterns of the primary full-bridge circuit 41 with one of the 17th to 24th patterns of the secondary full-bridge circuit 51. ｏｕｔ Outputs.

[0093] As shown in Figure 2, the boost mode includes a boost lag phase mode, a boost in phase mode, and a boost leading phase mode. As shown in Figure 6, the boost lag phase mode is a boost mode in which the secondary voltage V2 is raised from a low level to a middle level, then the primary voltage V1 is raised from a low level to a high level, and then the secondary voltage V2 is raised from a middle level to a high level. The boost lag phase mode is a boost mode used when outputting a small amount of power in response to the power demand from the load 100.

[0094] In boost mode, the first phase difference θ11 is the difference between the first time T11 when the secondary voltage V2 rises from a low level to a middle level and the second time T12 when the primary voltage V1 rises from a low level to a high level. The second phase difference θ12 is the difference between the first time T11 and the third time T13 when the secondary voltage V2 rises from a middle level to a high level.

[0095] As shown in Figure 7, the boost in-phase mode is a boost mode in which the primary voltage V1 is raised from a low level to a high level and the secondary voltage V2 is raised from a low level to a medium level simultaneously, and then the secondary voltage V2 is raised from a medium level to a high level. In the 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 boost in-phase mode is a boost mode used when outputting medium power in response to the power demanded from the load 100.

[0096] As shown in Figure 8, the boost leading phase mode is a boost mode in which the primary voltage V1 is raised from a low level to a high level, then the secondary voltage V2 is raised from a low level to a middle level, and then the secondary voltage V2 is raised from a middle level to a high level. The boost leading phase mode is a boost mode used when outputting a large amount of power in response to the power demand from the load 100.

[0097] In boost mode, the boost lag phase mode and boost lead phase mode are switched when the first phase difference θ11 is 0. <Flat state> In at least one load mode among the buck mode and boost mode, the control unit 70 may put the primary side full bridge circuit 41 into a flat state when the difference between the potential of the first terminal P1 and the potential of the second terminal P2 is 0. When the difference between the potential of the first terminal P1 and the potential of the second terminal P2 is 0, the input voltage V ｉｎ The value is 0. The flat state is when the first switching element Q11, the second switching element Q12, the fifth switching element Q31, and the sixth switching element Q32 are ON. The flat state may also be when the third switching element Q21, the fourth switching element Q22, the seventh switching element Q41, and the eighth switching element Q42 are ON.

[0098] The control unit 70 receives the input voltage V ｉｎ If the input voltage V is within a predetermined range including 0, the primary side full bridge circuit 41 may be set to a flat state. The predetermined range can be set arbitrarily. In one example, the input voltage V ｉｎ If the voltage fluctuates between -400[V] and +400[V], the specified range is -30[V] to +30[V].

[0099] Input voltage V ｉｎ When the input voltage V changes around 0, the control unit 70 changes the state of the primary side full bridge circuit 41, with the state of the flat state in between. This is the case in step-down mode when the input voltage V ｉｎ The input voltage V is negative. ｉｎ When this becomes a positive state, the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41 change from a state where they are kept ON to a flat state. Then, from the flat state, the second switching element Q12, the fourth switching element Q22, the sixth switching element Q32, and the eighth switching element Q42 change to a state where they are kept ON.

[0100] When the primary full-bridge circuit 41 is in a flat state, the control unit 70 may switch switching elements other than the primary switching elements Q11 to Q42 that are kept ON in the flat state. For example, the control unit 70 may output a voltage by switching the secondary switching elements Q51 to Q82. When the first switching element Q11, the second switching element Q12, the fifth switching element Q31, and the sixth switching element Q32 are kept ON in the flat state, the control unit 70 may switch the third switching element Q21, the fourth switching element Q22, the seventh switching element Q41, and the eighth switching element Q42.

[0101] <Output Control> The control unit 70 performs output control. Output control is a control that outputs the required power by controlling the DAB converter 40. The control unit 70 outputs the required power by controlling the first phase difference θ1, θ11, the second phase difference θ2, θ12, the frequency of the primary voltage V1, and the frequency of the secondary voltage V2. The frequency of the primary voltage V1 and the frequency of the secondary voltage V2 are the same value. In the following description, the frequency of the primary voltage V1 and the frequency of the secondary voltage V2 may be referred to as frequency. Furthermore, output control controls the DAB converter 40 to at least the input voltage V ｉｎ Or output voltage V ｏｕｔExcept for the timing when the polarity changes in the case of AC, soft switching control is performed.

[0102] As shown in Figure 9, in step S1, the control unit 70 derives a soft switching region. The soft switching region is set for the primary current I1 and the secondary current I2, respectively. The primary current I1 is the current flowing through the primary winding 34. The secondary current I2 is the current flowing through the secondary winding 35. In Figure 1, the direction of the arrows is the positive direction for the primary current I1 and the secondary current I2. The positive direction for the primary current I1 is the direction in which the current flows from the connection point between the first bidirectional switch 43 and the second bidirectional switch 44 towards the connection point between the third bidirectional switch 46 and the fourth bidirectional switch 47. The positive direction for the secondary current I2 is the direction in which the current flows from the connection point between the seventh bidirectional switch 56 and the eighth bidirectional switch 57 towards the connection point between the fifth bidirectional switch 53 and the sixth bidirectional switch 54.

[0103] The condition for soft switching of multiple primary-side switching elements Q11 to Q42 is that when the primary-side switching elements Q11 to Q42 switch between ON and OFF, the primary-side condition current value, which is the value of the primary-side current I1 flowing in the forward direction through diodes D1 and D2 connected in parallel to the switching element among the primary-side switching elements Q11 to Q42 that changes from OFF to ON, is greater than or equal to the absolute value of the primary-side winding current threshold TI1. Hereafter, this condition will be referred to as condition 1. The region that satisfies this condition is the soft-switching region of the primary-side current I1.

[0104] When the primary switching elements Q11 to Q42 switch between ON and OFF, it is the time when at least one of the primary switching elements Q11 to Q42 that is being switched changes from ON to OFF, or from OFF to ON. This time is the same as the first time T1 or the third time T3 in step-down mode, and the same as the second time T12 in step-up mode. In step-down mode, the first time T1 is the time when the primary voltage V1 rises from a low level to a middle level, or when the primary voltage V1 falls from a high level to a middle level. In step-down mode, the third time T3 is the time when the primary voltage V1 rises from a middle level to a high level, or when the primary voltage V1 falls from a middle level to a low level. In step-up mode, the second time T12 is the time when the primary voltage V1 rises from a low level to a high level, or when the primary voltage V1 falls from a high level to a low level. The primary-side switching elements Q11 to Q42 that are switched are those primary-side switching elements Q11 to Q42 that are not kept ON.

[0105] The condition for soft switching of multiple secondary switching elements Q51 to Q82 is that when the secondary switching elements Q51 to Q82 switch between ON and OFF, the value of the secondary condition current, which is the value of the secondary current I2 flowing in the forward direction through diodes D1 and D2 connected in parallel to the switching element among the secondary switching elements Q51 to Q82 that changes from OFF to ON, is greater than or equal to the absolute value of the secondary winding current threshold TI2. Hereafter, this condition will be referred to as condition 2. The region that satisfies this condition is the soft switching region of the secondary current I2.

[0106] When the secondary switching elements Q51 to Q82 switch between ON and OFF, it is the time when at least one of the switching elements Q51 to Q82 switches from ON to OFF, or from OFF to ON. This time is the same as the second time T2 in step-down mode, and the same as the first time T11 or the third time T13 in step-up mode. In step-down mode, the second time T2 is the time when the secondary voltage V2 rises from a low level to a high level, or when the secondary voltage V2 falls from a high level to a low level. In step-up mode, the first time is the time when the secondary voltage V2 rises from a low level to a middle level, or when the secondary voltage V2 falls from a high level to a middle level. In step-up mode, the third time T13 is the time when the secondary voltage V2 rises from a middle level to a high level, or when the secondary voltage V2 falls from a middle level to a low level. The secondary switching elements Q51 to Q82 that are switched are those Q51 to Q82 that are not kept ON.

[0107] As described above, the primary voltage V1 and secondary voltage V2 are waveforms of the same frequency, inverting every 180 degrees of phase. Since only the positive and negative signs are reversed during the rising and falling edges, we only need to consider one or the other. The following explanation will focus only on the rising edge.

[0108] Let's explain using the step-down lag phase mode as an example. As shown in Figure 10, at the first time T1, the switching pattern of the primary full-bridge circuit 41 is switched from the third pattern to the second pattern, or from the fifth pattern to the eighth pattern. At the third time T3, the switching pattern of the primary full-bridge circuit 41 is switched from the second pattern to the first pattern, or from the eighth pattern to the seventh pattern. If condition 1 is met at the first time T1 and the third time T3, soft switching of the primary switching elements Q11 to Q42 is achieved. At the second time T2, the switching pattern of the secondary full-bridge circuit 51 is switched from the tenth pattern to the ninth pattern, or from the twelfth pattern to the eleventh pattern. At this time, if condition 2 is met, soft switching of the secondary switching elements Q51 to Q82 is achieved.

[0109] The primary winding current threshold TI1 is defined by the following equation (1).

[0110] TI1: Primary winding current threshold, k1: coefficient, V1: Primary voltage, L: Inductance of the first reactor 36, C01: Capacitance corresponding to one primary switching element Q11 to Q42, relative to the combined capacitance of capacitors C1 and C2 arranged in parallel with the primary switching elements Q11 to Q42 that are switched. The capacitance of capacitor C1 connected in parallel with the first switching element Q11 is C11, the capacitance of capacitor C1 connected in parallel with the third switching element Q21 is C13, the capacitance of capacitor C1 connected in parallel with the fifth switching element Q31 is C15, and the capacitance of capacitor C1 connected in parallel with the seventh switching element Q41 is C17. For example, input voltage V ｉｎ If the condition is positive, when switching the first switching element Q11, the third switching element Q21, the fifth switching element Q31, and the seventh switching element Q41, C01 may also be = (C11 + C13 + C15 + C17) / 4. If Cx1 is the largest capacitance among C11, C13, C15, and C17, then C01 may also be = Cx1.

[0111] Let the capacitance of the capacitor C2 connected in parallel with the second switching element Q12 be C12, the capacitance of the capacitor C2 connected in parallel with the fourth switching element Q22 be C14, the capacitance of the capacitor C2 connected in parallel with the sixth switching element Q32 be C16, and the capacitance of the capacitor C2 connected in parallel with the eighth switching element Q42 be C18. For example, when the input voltage V ｉｎ is negative, when switching the second switching element Q12, the fourth switching element Q22, the sixth switching element Q32, and the eighth switching element Q42, C01 = (C12 + C14 + C16 + C18) / 4 may be used. When Cx2 is the largest capacitance among C12, C14, C16, and C18, C01 = Cx2 may also be used.

[0112] Regarding the secondary side winding current threshold TI2, each value is similarly defined by replacing it with the value on the secondary side. Thus, the soft switching region is derived. Next, in step S2, the control unit 70 calculates the target current. The target current is a current value that can output the required power from the load 100 and satisfies condition 1 and condition 2.

[0113] To satisfy condition 1, the primary current I1 at the first time T1 and the third time T3 should be considered, but it is sufficient to consider the primary current I1 at the third time T3, which is the time when the absolute value of the current is smaller in this load mode. Of the primary switching elements Q11 to Q42, the one that changes from OFF to ON at the third time T3 is the seventh switching element Q41 or the sixth switching element Q32. The seventh switching element Q41 is a primary switching element that changes from OFF to ON when the switching pattern changes from the second pattern to the first pattern. The sixth switching element Q32 is a primary switching element that changes from OFF to ON when the switching pattern changes from the eighth pattern to the seventh pattern. Therefore, to satisfy condition 1, the primary current I1 at the third time T3, which flows in the forward direction through diodes D1 and D2 connected in parallel to the seventh switching element Q41 or the sixth switching element Q32 that changes from OFF to ON at this time, must be greater than or equal to the absolute value of the primary winding current threshold TI1 "|TI1|". This value of primary current I1 is the value of "-I1" in Figure 1. Note that at the third time T3, the primary current I1 is a negative value, so "-I1" becomes a positive value. Also, whether the absolute value is smaller at the first time T1 or the third time T3 depends on the load mode.

[0114] In this load mode, for condition 2 to be satisfied, the value of the secondary current I2 at the second time T2, which flows in the forward direction through diode D1 connected in parallel to each of the ninth switching element Q51 and the fifteenth switching element Q81 that change 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|". Also, for condition 2 to be satisfied, the value of the secondary current I2 at the second time T2, which flows in the forward direction through diode D2 connected in parallel to each of the twelfth switching element Q62 and the fourteenth switching element Q72 that change 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|". These values ​​of secondary current I2 are the values ​​of "I2" in Figure 1. The ninth switching element Q51 and the fifteenth switching element Q81 are secondary-side switching elements that switch from OFF to ON when the switching pattern changes from the tenth pattern to the ninth pattern. The twelfth switching element Q62 and the fourteenth switching element Q72 are secondary-side switching elements that switch from OFF to ON when the switching pattern changes from the twelfth pattern to the eleventh pattern. Note that at the second time T2, the secondary-side current I2 is a positive value, so "I2" will be a positive value.

[0115] In practical terms, for example, for condition 1, one can satisfy condition 1 by comparing the primary winding current threshold TI1 with the secondary current I2 at the third time T3, or vice versa. In this case, it is sufficient to consider either the primary current I1 or the secondary current I2. Alternatively, the inductance L of the first reactor 36 can be set in advance such that satisfying one of condition 1 or condition 2 will automatically satisfy the other.

[0116] In this way, it is possible to calculate a combination of target currents that can output the required power from load 100 and satisfy conditions 1 and 2. If there is no combination of target currents that can output the required power and satisfy conditions 1 and 2, it means that soft switching is not possible for that required power and load mode.

[0117] Next, in step S3, the control unit 70 derives a combination of the first phase differences θ1, θ11, the second phase differences θ2, θ12, and the frequency from the calculated target current. Here, the combination of the first phase differences θ1, θ11, the second phase differences θ2, θ12, and the frequency is derived so as to follow the calculated target current at the first time T1 and the target current at the second time T2. If the first phase differences θ1, θ11 and the second phase differences θ2, θ12 are constant, the lower the frequency, the greater the output power. As the frequency increases, the period of the primary voltage V1 and the period of the secondary voltage V2 become shorter, so the greater the required power, the longer the period of the primary voltage V1 and the period of the secondary voltage V2 are made. As the period becomes longer, the primary current I1 and the secondary current I2 become larger. The control unit 70 derives combinations of first phase differences θ1, θ11, second phase differences θ2, θ12, and frequency from these correlations so as to satisfy conditions 1 and 2. That is, the combinations of first phase differences θ1, θ11, second phase differences θ2, θ12, and frequency are combinations that can output the power required by the load 100 and satisfy conditions 1 and 2.

[0118] The control unit 70 derives a combination of first phase differences θ1, θ11, second phase differences θ2, θ12, and frequency that minimizes the difference between the primary current I1 and the primary winding current threshold TI1, and minimizes the difference between the secondary current I2 and the secondary winding current threshold TI2.

[0119] In step S4, the control unit 70 controls the primary full-bridge circuit 41 and the secondary full-bridge circuit 51 so that the first phase differences θ1, θ11, the second phase differences θ2, θ12, and the frequency are as derived in step S3.

[0120] The required power, the first phase differences θ1, θ11, the second phase differences θ2, θ12, and the frequency may be calculated each time, or they may be calculated in advance and stored in a map or the like. [Effects of the embodiment] (1) The primary side full bridge circuit 41 is equipped with a plurality of primary side bidirectional switches 43, 44, 46, 47. As a result, the input voltage V at the first terminal P1 is higher than the potential at the second terminal P2. ｉｎ Even if the value is positive, the input voltage V at the first terminal P1 is lower than the potential at the second terminal P2. ｉｎEven if the value is negative, the primary voltage V1 applied from the primary full-bridge circuit 41 to the transformer section 31 can be made to have the same waveform. In other words, the power converter 10 does not need to have a rectifier circuit, and a bus capacitor connected to the rectifier circuit becomes unnecessary. Therefore, the number of components can be reduced.

[0121] (2) The power converter 10 uses a bidirectional switch equipped with two switching elements Q1 and Q2. Therefore, the number of elements can be reduced compared to the case where separate elements are used as switching elements Q1 and Q2.

[0122] (3) The primary side full bridge circuit 41 is equipped with a plurality of primary side bidirectional switches 43, 44, 46, and 47. This allows power conversion to be performed whether the power supply PS is an AC power supply or a DC power supply.

[0123] (4) The secondary full-bridge circuit 51 is equipped with a plurality of secondary bidirectional switches 53, 54, 56, and 57. This allows the secondary full-bridge circuit 51 to output either AC voltage or DC voltage.

[0124] (5) The primary full-bridge circuit 41 does not perform conventional power factor correction operations, but instead corrects the power factor through the control of the DAB converter 40. Therefore, soft switching is easier. In addition, the power converter 10 does not need to be equipped with a PFC coil for conventional power factor correction operations, thus reducing the number of components.

[0125] (6) When the difference between the potential at the first terminal P1 and the potential at the second terminal P2 is 0, the control unit 70 sets the primary side full bridge circuit 41 to a flat state. ｉｎ When it is positive and the input voltage V ｉｎ When the value is negative, it is necessary to switch the primary-side switching elements Q11 to Q42 that are kept ON. If this switching is delayed, a short-circuit current will occur, so the primary-side switching elements Q11 to Q42 that are kept ON are switched while a flat state is interposed.

[0126] If all primary-side switching elements Q11 to Q42 are in the OFF state (flat state), current cannot flow from the primary-side winding 34, which may cause surge voltage to occur.

[0127] In contrast, by setting the flat state as in the embodiment, the primary switching elements Q11 to Q42, which are turned ON, create a path for the current from the primary winding 34 to flow back. This suppresses the generation of surge voltage.

[0128] [Examples of Modifications] The embodiment can be implemented with the following modifications. The embodiment and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically.

[0129] ○As shown in Figure 11, the power supply PS may be a three-phase AC power supply. The power supply PS is illustrated as three power supplies PS1, PS2, and PS3. The three power supplies PS1, PS2, and PS3 are, for example, an R-phase power supply PS1, an S-phase power supply PS2, and a T-phase power supply PS3. The three power supplies PS1, PS2, and PS3 output three-phase AC voltages that are 120 degrees out of phase with each other. Each of the three power supplies PS1, PS2, and PS3 has a first terminal P1 and a second terminal P2. The power supplies PS1, PS2, and PS3 switch between having the first terminal P1 positive or the second terminal P2 positive over time.

[0130] The power converter 10 includes three conversion circuits 11 corresponding to the AC voltage of each phase of a three-phase AC. Therefore, the power converter 10 includes three primary-side full-bridge circuits 41 and three secondary-side full-bridge circuits 51. Each of the three primary-side full-bridge circuits 41 is input with the AC voltage of one phase of the three-phase AC voltage. The third power lines L3 of the three conversion circuits 11 are connected to each other. The fourth power lines L4 of the three conversion circuits 11 are connected to each other.

[0131] Each conversion circuit 11 converts the input AC voltage into a DC voltage and outputs it. Because the third power lines L3 and the fourth power lines L4 of the three conversion circuits 11 are connected to each other, the output currents of the three secondary full-bridge circuits 51 merge. When the output voltages of the three conversion circuits 11 are set to the same constant value, each output current contains ripple. By merging the output currents of the three conversion circuits 11, the ripple contained in the output currents can be canceled out.

[0132] ○As shown in Figure 12, the secondary full-bridge circuit 51 may include switching elements Q101 to Q104 that are different from the bidirectional switches 53, 54, 56, and 57. The secondary full-bridge circuit 51 includes a ninth switching element Q101 in place of the fifth bidirectional switch 53. The secondary full-bridge circuit 51 includes a tenth switching element Q102 in place of the sixth bidirectional switch 54. The secondary full-bridge circuit 51 includes an eleventh switching element Q103 in place of the seventh bidirectional switch 56. The secondary full-bridge circuit 51 includes a twelfth switching element Q104 in place of the eighth bidirectional switch 57. The ninth to twelfth switching elements Q101 to Q104 are a plurality of secondary switching elements Q101 to Q104. Diodes D10, D20, D30, and D40 and capacitors C10, C20, C30, and C40 are connected in parallel to the ninth switching element Q101 to the twelfth switching element Q104, respectively.

[0133] When two-level control of the secondary full-bridge circuit 51 is performed, the switching patterns of the secondary full-bridge circuit 51 include the 25th pattern and the 26th pattern. The 25th pattern is a switching pattern in which the 9th switching element Q101 is turned ON, the 10th switching element Q102 is turned OFF, the 11th switching element Q103 is turned OFF, and the 12th switching element Q104 is turned ON.

[0134] The 26th pattern is a switching pattern in which the 9th switching element Q101 is turned OFF, the 10th switching element Q102 is turned ON, the 11th switching element Q103 is turned ON, and the 12th switching element Q104 is turned OFF.

[0135] When performing three-level control of the secondary full-bridge circuit 51, the switching patterns of the secondary full-bridge circuit 51 include patterns 27 to 30. Pattern 27 is a switching pattern in which the ninth switching element Q101 is turned ON, the tenth switching element Q102 is turned OFF, the eleventh switching element Q103 is turned OFF, and the twelfth switching element Q104 is turned ON.

[0136] The 28th pattern is a switching pattern in which the 9th switching element Q101 is turned ON, the 10th switching element Q102 is turned OFF, the 11th switching element Q103 is turned ON, and the 12th switching element Q104 is turned OFF.

[0137] The 29th pattern is a switching pattern in which the 9th switching element Q101 is turned OFF, the 10th switching element Q102 is turned ON, the 11th switching element Q103 is turned ON, and the 12th switching element Q104 is turned OFF.

[0138] The 30th pattern is a switching pattern in which the 9th switching element Q101 is turned OFF, the 10th switching element Q102 is turned ON, the 11th switching element Q103 is turned OFF, and the 12th switching element Q104 is turned ON.

[0139] ○The transformer section 31 may include either a first reactor 36 connected to the primary winding 34, or a second reactor 37 connected to the secondary winding 35. If the transformer section 31 includes only the first reactor 36, the secondary voltage V2 is the voltage applied to the secondary winding 35. If the transformer section 31 includes only the second reactor 37, the primary voltage V1 is the voltage applied to the primary winding 34.

[0140] ○The control unit 70 may fix the circuits among the primary full-bridge circuit 41 and secondary full-bridge circuit 51 that are controlled at 3 levels and the circuits that are controlled at 2 levels. That is, the control unit 70 may control the primary full-bridge circuit 41 at 3 levels and the secondary full-bridge circuit 51 at 2 levels regardless of the load mode. The control unit 70 may control the primary full-bridge circuit 41 at 2 levels and the secondary full-bridge circuit 51 at 3 levels regardless of the load mode.

[0141] The control unit 70 can output the required power by controlling one of the first phase differences θ1, θ11 and the second phase differences θ2, θ12 and the frequency, and may also control the primary full-bridge circuit 41 and the secondary full-bridge circuit 51 to satisfy conditions 1 and 2.

[0142] ○Instead of a flat state, input voltage V ｉｎ The primary switching elements Q11 to Q42 may be turned ON when the value is positive. Alternatively, instead of a flat state, the primary switching elements Q11 to Q42 may be turned OFF when the current flowing through the primary winding 34 is 0.

[0143] [Definition] As used herein, the expression "at least one" means "one or more" of the desired options. For example, as used herein, "at least one" means "only one option" or "both of the two options" if there are two options. As another example, as used herein, "at least one" means "only one option" or "a combination of two or more any options" if there are three or more options.

[0144] L1...First power line, L2...Second power line, L3...Third power line, L4...Fourth power line, P1...First terminal, P2...Second terminal, PS...Power supply, Q11-Q42...Primary switching elements, Q51-Q82...Secondary switching elements, 10...Power converter, 12...First input terminal, 13...Second input terminal, 14...First output terminal, 15...Second output terminal, 31...Transformer section, 34...Primary winding, 35...Secondary winding, 36, 37...Reactor, 41...Primary full bridge circuit, 43, 44, 46, 47...Primary bidirectional switch, 51...Secondary full bridge circuit, 53, 54, 56, 57...Secondary bidirectional switch, 70...Control unit.

Claims

1. A transformer section having a primary winding, a secondary winding, and a reactor connected to at least one of the primary winding and the secondary winding; a first power line connected to the first end of a power supply; a second power line connected to the second end of the power supply; a primary full-bridge circuit connected to the primary winding and having a plurality of primary bidirectional switches; a secondary full-bridge circuit connected to the secondary winding and having a plurality of secondary switching elements; and a control unit configured to control the plurality of primary bidirectional switches and the plurality of secondary switching elements, wherein each of the plurality of primary bidirectional switches comprises two primary switching elements, and the two primary switching elements are connected to each other such that the diodes connected in parallel to each of the two primary switching elements are oriented in opposite directions. The plurality of primary-side switching elements provided by the plurality of primary-side bidirectional switches include a first switching element, a second switching element, a third switching element, a fourth switching element, a fifth switching element, a sixth switching element, a seventh switching element, and an eighth switching element, wherein the first switching element, the second switching element, the third switching element, and the fourth switching element are connected between the first power line and the second power line in this order, and the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element are connected between the first power line and the second power line in this order, and the condition for performing soft switching of the plurality of primary-side switching elements is condition 1, and the condition for performing soft switching of the plurality of secondary-side switching elements is condition 2. Condition 1 is that when at least one of the plurality of primary-side switching elements switches from OFF to ON, the primary-side condition current value, which is the value of the current flowing in the primary-side winding in the forward direction of the diode connected in parallel with the at least one primary-side switching element, 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 switching elements switches from OFF to ON, the value of the secondary condition current, which is the value of the current flowing in the forward direction of the secondary winding of the diode connected in parallel with the at least one secondary switching element, is greater than or equal to the absolute value of the secondary winding current threshold, The control unit is configured to control the primary full-bridge circuit and the secondary full-bridge circuit so that one of the primary full-bridge circuit and the secondary full-bridge circuit applies a 2-level voltage to the transformer section, and the other applies a 3-level voltage to the transformer section, The 2-level voltage and the 3-level voltage are waveforms of the same frequency that invert every 180 degrees of phase, The difference between the first time when the 3-level voltage rises from a low level to a middle level and the second time when the 2-level voltage rises from a low level to a high level is the first phase difference, The difference between the first time and the third time when the 3-level voltage rises from a middle level to a high level is the second phase difference, The control unit, A power converter configured to output the required power and satisfy conditions 1 and 2 by controlling at least one of the first phase difference and the second phase difference, and the frequencies of the two-level voltage and the third-level voltage, and to perform switching of the first switching element, the third switching element, the fifth switching element and the seventh switching element while keeping the second switching element, the fourth switching element, the sixth switching element and the eighth switching element ON when the potential of the first end is higher than the potential of the second end, and to perform switching of the second switching element, the fourth switching element, the sixth switching element and the eighth switching element while keeping the first switching element, the third switching element, the fifth switching element and the seventh switching element ON when the potential of the first end is lower than the potential of the second end.

2. The secondary full-bridge circuit comprises a first output terminal, a second output terminal, a third power line connected to the first output terminal, and a fourth power line connected to the second output terminal, wherein the secondary full-bridge circuit comprises a plurality of secondary bidirectional switches, each of the plurality of secondary bidirectional switches comprises two secondary switching elements from the plurality of secondary switching elements, the two secondary switching elements are connected to each other such that the diodes connected in parallel to each of the two secondary switching elements are oriented in opposite directions, the plurality of secondary switching elements comprising the plurality of secondary bidirectional switches include a ninth switching element, a tenth switching element, an eleventh switching element, a twelfth switching element, a thirteenth switching element, a fourteenth switching element, a fifteenth switching element, and a sixteenth switching element, the ninth switching element, the tenth switching element, the eleventh switching element, and the twelfth switching element are connected between the third power line and the fourth power line in this order, The power converter according to claim 1, wherein the 13th switching element, the 14th switching element, the 15th switching element, and the 16th switching element are connected in this order between the third power line and the fourth power line, and the control unit is configured to switch the 9th switching element, the 11th switching element, the 13th switching element, and the 15th switching element while keeping the 10th switching element, the 12th switching element, the 14th switching element, and the 16th switching element ON when the potential of the first output terminal is higher than the potential of the second output terminal, and to switch the 10th switching element, the 12th switching element, the 14th switching element, and the 16th switching element while keeping the 9th switching element, the 11th switching element, the 13th switching element, and the 15th switching element ON when the potential of the first output terminal is lower than the potential of the second output terminal.

3. The power supply is an AC power supply that outputs three phase AC voltages with phases shifted by 120 degrees, the primary full-bridge circuit is one of three primary full-bridge circuits, the secondary full-bridge circuit is one of three secondary full-bridge circuits, each of the three primary full-bridge circuits is input to an AC voltage of one phase of the three phase AC voltages, and the output currents of the three secondary full-bridge circuits are combined and output, as described in claim 1.

4. The power supply is an AC power supply that outputs an AC voltage, the control unit is configured to put the primary side full bridge circuit into a flat state when the difference between the potential of the first end and the potential of the second end is 0, and the flat state is a state in which the first switching element, the second switching element, the fifth switching element, and the sixth switching element are ON, or the third switching element, the fourth switching element, the seventh switching element, and the eighth switching element are ON, the power conversion device according to claim 1.

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