Power conversion device

Abstract

A power conversion device (10) comprises: a rectifier circuit (20) that rectifies an AC voltage inputted from an AC power supply (PS); and a DAB converter (30). The DAB converter (30) comprises: a primary-side full bridge circuit (41) having a plurality of primary-side switching elements (Q1-Q4); a secondary-side full bridge circuit (51) having a plurality of secondary-side switching elements (Q5-Q8); and a control unit (80). The control unit (80) controls the plurality of primary-side switching elements (Q1-4) and the plurality of secondary-side switching elements (Q5-Q8).

Description

Power converter

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

[0002] The power conversion device disclosed in Patent Document 1 comprises an AC / DC conversion unit, a PFC coil, and a DAB converter (dual active bridge type DC / DC converter). The AC / DC conversion unit is a full bridge circuit of four switching elements. The AC / DC conversion unit converts AC voltage to DC voltage while performing power factor correction. The PFC coil connects the AC power supply and the AC / DC conversion unit. The PFC coil is a coil for power factor correction. 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.

[0003] Patent No. 6710615

[0004] In Patent Document 1, the AC / DC conversion unit performs power factor correction. Therefore, the power conversion device needs to be equipped with a large PFC coil.

[0005] A power conversion device according to one aspect of the present disclosure comprises a rectifier circuit configured to rectify an AC voltage input from an AC power source, and a DAB converter connected to the rectifier circuit. The DAB converter comprises a transformer section having a primary winding, a secondary winding, and a reactor connected to at least one of the primary and secondary windings; a circuit connected to the primary winding, comprising a primary full-bridge circuit having a plurality of primary switching elements; a circuit connected to the secondary winding, comprising a secondary full-bridge circuit having a plurality of secondary switching elements; and a control unit configured to control the plurality of primary and secondary switching elements, wherein condition 1 is the condition for performing soft switching of the plurality of primary switching elements, and condition 2 is the condition for performing soft switching of the plurality of secondary switching elements, and condition 1 is that when at least one of the plurality of primary switching elements switches from OFF to ON, the primary condition current value, which is the value of the current flowing through the primary winding in the forward direction of a diode connected in parallel with the at least one primary switching element, is greater than or equal to the absolute value of the primary 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 through the secondary winding in the forward direction 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, and the control unit is configured to control the primary full-bridge circuit and the secondary full-bridge circuit such 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, and 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, and 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 is configured to control at least one of the first phase difference and the second phase difference, and the frequencies of the two-level voltage and the three-level voltage, so that it can output the required power and satisfy conditions 1 and 2.

[0006] 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 the input voltage to the conversion circuit. Figure 12 shows the link voltage. Figure 13 shows the output current of the conversion circuit. Figure 14 shows the output current of the power converter.

[0007] An embodiment of a power converter will be described. As shown in Figure 1, the power supply system 100 includes an AC power supply PS, a load 120, and a power converter 10. The AC power supply PS inputs an AC voltage to the power converter 10. The AC power supply PS is, for example, a grid power supply. The AC power supply PS is a three-phase AC power supply and is shown 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. The three power supplies PS1, PS2, and PS3 each have a first terminal P1 and a second terminal P2. In each power supply PS1, PS2, and PS3, the first terminal P1 becomes positive or the second terminal P2 becomes positive depending on the passage of time. The load 120 is, for example, a secondary battery capable of charging and discharging DC power. The secondary battery is, for example, a lithium-ion battery or a lead-acid battery.

[0008] The power converter 10 is installed between the AC power source PS and the load 120. The power converter 10 can convert the AC power input from the AC power source PS into DC power and output it to the load 120.

[0009] The power converter 10 comprises three conversion circuits 11, an output filter 60, output terminals 63 and 64, and a control unit 80. The three conversion circuits 11 are provided corresponding to the AC voltage of each phase of a three-phase AC. One of three power supplies PS1, PS2, and PS3 is connected to each of the three conversion circuits 11. The three conversion circuits 11 are appropriately designated as the first conversion circuit 11A, the second conversion circuit 11B, and the third conversion circuit 11C. For example, the R-phase power supply PS1 is electrically connected to the first conversion circuit 11A. For example, the S-phase power supply PS2 is electrically connected to the second conversion circuit 11B. For example, the T-phase power supply PS3 is electrically connected to the third conversion circuit 11C. Figure 1 shows the configuration of the first conversion circuit 11A in detail, but the configurations of the three conversion circuits 11 are similar. Hereinafter, the configuration of the first conversion circuit 11A will be described as representative.

[0010] The first conversion circuit 11A includes a first input terminal 12, a second input terminal 13, an input filter 14, a rectifier circuit 20, a first positive bus L1, a first negative bus L2, a DC link capacitor 25, a first voltage sensor 71, a DAB converter 30, a second positive bus L3, a second negative bus L4, a secondary capacitor 54, and a second voltage sensor 72. Therefore, the power conversion device 10 includes three rectifier circuits 20 and three DAB converters 30.

[0011] The first input terminal 12 is connected to the first terminal P1 of the power supply PS1. The second input terminal 13 is connected to the second terminal P2 of the power supply PS1. AC voltage is input to the conversion circuit 11 from the first input terminal 12 and the second input terminal 13.

[0012] The input filter 14 suppresses noise from flowing into the AC power supply PS. The input filter 14 is, for example, an LC filter. The input filter 14 comprises a coil 15 and a capacitor 16.

[0013] The rectifier circuit 20 rectifies the AC voltage input to the conversion circuit 11. The rectifier circuit 20 comprises four rectifier elements 21, 22, 23, and 24. The first rectifier element 21 and the second rectifier element 22 are connected in series between the first positive bus L1 and the first negative bus L2. The third rectifier element 23 and the fourth rectifier element 24 are connected in series between the first positive bus L1 and the first negative bus L2. The four rectifier elements 21, 22, 23, and 24 constitute a full-bridge circuit. The rectifier elements 21, 22, 23, and 24 in this embodiment are switching elements.

[0014] The first input terminal 12 is connected to the connection point between the first rectifier element 21 and the second rectifier element 22 via the input filter 14. The second input terminal 13 is connected to the connection point between the third rectifier element 23 and the fourth rectifier element 24 via the input filter 14. More specifically, the first input terminal 12 is connected to the connection point between the first rectifier element 21 and the second rectifier element 22 via the coil 15. The capacitor 16 is provided in parallel with the power supply PS1 between the coil 15 and the rectifier circuit 20. The second input terminal 13 is connected to the connection point between the third rectifier element 23 and the fourth rectifier element 24.

[0015] The DC link capacitor 25 is provided between the rectifier circuit 20 and the DAB converter 30. The DC link capacitor 25 connects the first positive bus bar L1 and the first negative bus bar L2.

[0016] The first voltage sensor 71 is provided in parallel with the DC link capacitor 25. The first voltage sensor 71 detects the link voltage V ｌｉｎｋ which is the voltage across the DC link capacitor 25. The link voltage V ｌｉｎｋ is the output voltage of the rectifier circuit 20.

[0017] The DAB converter 30 is a DC / DC converter of the dual active bridge type. The DAB converter 30 includes a transformer section 31. The transformer section 31 includes a transformer 32 and reactors 36, 37. The transformer 32 is of an isolation 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.

[0018] The transformer 32 is connected to the reactors 36, 37. The reactors 36, 37 may be elements such as choke coils or may be the leakage inductances of the primary winding 34 and the secondary winding 35. The reactor 36 is connected to the primary winding 34. The reactor 37 is connected to the secondary winding 35. Appropriately, the reactor 36 may be referred to as the first reactor 36 and the reactor 37 may be referred to as the second reactor 37. The primary winding 34 and the first reactor 36 constitute a series connection body SC1. The secondary winding 35 and the second reactor 37 constitute a series connection body SC2.

[0019] The DAB converter 30 includes a primary full-bridge circuit 41. The primary full-bridge circuit 41 includes a first leg 42 and a second leg 43. The first leg 42 includes a first switching element Q1, a second switching element Q2, diodes D1 and D2, and capacitors C1 and C2. The first switching element Q1 and the second switching element Q2 are connected in series with each other between a first positive bus bar L1 and a first negative bus bar L2. The second leg 43 includes a third switching element Q3, a fourth switching element Q4, diodes D3 and D4, and capacitors C3 and C4. The third switching element Q3 and the fourth switching element Q4 are connected in series with each other between the first positive bus bar L1 and the first negative bus bar L2. Thereby, the first leg 42 and the second leg 43 are connected in parallel with each other. The first switching element Q1 and the third switching element Q3 constitute an upper arm. The second switching element Q2 and the fourth switching element Q4 constitute a lower arm.

[0020] The first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 are a plurality of primary-side switching elements Q1 to Q4. The primary-side switching elements Q1 to Q4 are, for example, n-type MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The primary-side switching elements Q1 to Q4 may be p-type MOSFETs, IGBTs (Insulated Gate Bipolar Transistors), or GaN-HEMTs.

[0021] The diodes D1 to D4 and the capacitors C1 to C4 are connected in parallel to the primary-side switching elements Q1 to Q4, respectively. The diodes D1 to D4 may be parasitic diodes or elements. The capacitors C1 to C4 may be parasitic capacitances, elements, or combinations of parasitic capacitances and elements.

[0022] The connection point between the first switching element Q1 and the second switching element Q2 is connected to one end of the primary winding 34 via the first reactor 36, and the connection point between the third switching element Q3 and the fourth switching element Q4 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.

[0023] The DAB converter 30 includes a secondary full-bridge circuit 51. The secondary full-bridge circuit 51 includes a third leg 52 and a fourth leg 53. The third leg 52 includes a fifth switching element Q5, a sixth switching element Q6, diodes D5 and D6, and capacitors C5 and C6. The fifth switching element Q5 and the sixth switching element Q6 are connected in series with each other between the second positive bus L3 and the second negative bus L4. The fourth leg 53 includes a seventh switching element Q7, an eighth switching element Q8, diodes D7 and D8, and capacitors C7 and C8. The seventh switching element Q7 and the eighth switching element Q8 are connected in series with each other between the second positive bus L3 and the second negative bus L4. The fifth switching element Q5 and the seventh switching element Q7 constitute the upper arm. The sixth switching element Q6 and the eighth switching element Q8 constitute the lower arm.

[0024] The fifth switching element Q5, the sixth switching element Q6, the seventh switching element Q7, and the eighth switching element Q8 are a plurality of secondary switching elements Q5 to Q8. The secondary switching elements Q5 to Q8 are, for example, n-type MOSFETs. The secondary switching elements Q5 to Q8 may also be p-type MOSFETs, IGBTs, or GaN-HEMTs.

[0025] Diodes D5 to D8 and capacitors C5 to C8 are connected in parallel to the secondary switching elements Q5 to Q8, respectively. Diodes D5 to D8 may be parasitic diodes or elements. Capacitors C5 to C8 may be parasitic capacitances, elements, or a combination of parasitic capacitances and elements.

[0026] The connection point between the fifth switching element Q5 and the sixth switching element Q6 is connected to one end of the secondary winding 35 via the second reactor 37, and the connection point between the seventh switching element Q7 and the eighth switching element Q8 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.

[0027] The secondary capacitor 54 is located between the DAB converter 30 and the output filter 60. The second voltage sensor 72 connects the second positive busbar L3 and the second negative busbar L4. The second voltage sensor 72 measures the output voltage V of the DAB converter 30. ｏｕｔ Detects.

[0028] The second positive busbars L3 of the three conversion circuits 11 are connected to each other. The second negative busbars L4 of the three conversion circuits 11 are connected to each other. In the example shown in Figure 1, the second positive busbar L3 of the first conversion circuit 11A is connected to the second positive busbar L3 of the two conversion circuits 11B and 11C. The second negative busbar L4 of the first conversion circuit 11A is connected to the second negative busbar L4 of the two conversion circuits 11B and 11C. As a result, the output current I of the three DAB converters 30 ｏｕｔ They will merge.

[0029] The output filter 60 is, for example, an LC filter. The output filter 60 is provided on the output side of the connection points of the three second positive busbars L3 and the three second negative busbars L4, and on the input side of the two output terminals 63 and 64. The output filter 60 comprises a coil 61 and a capacitor 62. Specifically, the coil 61 is connected between the connection points of the three second positive busbars L3 and the output terminal 63. The connection points of the three second negative busbars L4 are connected to the output terminal 64. The capacitor 62 is provided in parallel with the load 120 on the DAB converter 30 side of the coil 61.

[0030] The two output terminals 63 and 64 are connected to the load 120. The output power of the power converter 10 is supplied to the load 120 from the two output terminals 63 and 64. The output current I of the power converter 10 ｔｏｔａｌ The output current I of the three DAB converters 30 ｏｕｔ This is a combination of the two.

[0031] The power converter 10 includes a control unit 80. The control unit 80 includes 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 execute 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 80 may be composed of hardware circuits such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control unit 80, 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.

[0032] The control unit 80 rectifies the AC voltages input from power supplies PS1, PS2, and PS3 by controlling the rectifier circuit 20. When the AC voltage is positive, the control unit 80 turns on the first rectifier element 21 and the fourth rectifier element 24, and turns off the second rectifier element 22 and the third rectifier element 23. When the AC voltage is negative, the control unit 80 turns off the first rectifier element 21 and the fourth rectifier element 24, and turns on the second rectifier element 22 and the third rectifier element 23. As a result, the rectifier circuit 20 outputs a DC voltage obtained by full-wave rectifying the AC voltage. This DC voltage is the link voltage V ｌｉｎｋ Therefore, if the potential at the first terminal P1 is higher than the potential at the second terminal P2, the AC voltage is positive. If the potential at the first terminal P1 is lower than the potential at the second terminal P2, the AC voltage is negative.

[0033] The control unit 80 controls the link voltage V by controlling a plurality of primary-side switching elements Q1 to Q4 and a plurality of secondary-side switching elements Q5 to Q8. ｌｉｎｋ output voltage Vｏｕｔ is converted. At this time, the input current input to the DAB converter 30 is controlled with the same phase as the link voltage V ｌｉｎｋ .

[0034] The number of turns of the primary winding 34 of the 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 turn ratio is converted to 1:1, is (V ｏｕｔ × N1) / (V ｌｉｎｋ × N2). The control unit 80 includes a step-down mode and a boost mode as load modes. The step-down mode is a load mode in which the equivalent voltage ratio is made smaller than 1. The boost mode is a load mode in which the equivalent voltage ratio is made larger than 1.

[0035] For example, when the turn ratio of the transformer 32 is 1:2, the link voltage V ｌｉｎｋ = 200 V, and the output voltage V ｏｕｔ = 400 V, when the turn ratio is converted to 1:1, the equivalent voltage ratio = (V оｕｔ × 1) / (V ｌｉｎｋ × 2) = 1. Therefore, when the turn ratio of the transformer 32 is 1:2 and the output voltage V ｏｕｔ = 400 V, if the link voltage V ｌｉｎｋ is greater than 200 V, it is in the step-down mode, and if it is less than 200 V, it is in the boost mode. In the following description, unless otherwise specified, the turn ratio is assumed to be 1:1.

[0036] The control unit 80 performs three-level control on one of the primary full-bridge circuit 41 and the secondary full-bridge circuit 51, and performs two-level control on the other. As a result, one of the primary full-bridge circuit 41 and the secondary 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.

[0037] 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.

[0038] <Step-Down Mode> The control performed by the control unit 80 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 80 independently controls the first leg 42 and the second leg 43. The switching pattern of the primary side full-bridge circuit 41 includes the first to fourth patterns.

[0039] The first pattern is a switching pattern in which the first switching element Q1 is turned ON, the second switching element Q2 is turned OFF, the third switching element Q3 is turned OFF, and the fourth switching element Q4 is turned ON.

[0040] The second pattern is a switching pattern in which the first switching element Q1 is turned ON, the second switching element Q2 is turned OFF, the third switching element Q3 is turned ON, and the fourth switching element Q4 is turned OFF.

[0041] The third pattern is a switching pattern in which the first switching element Q1 is turned OFF, the second switching element Q2 is turned ON, the third switching element Q3 is turned ON, and the fourth switching element Q4 is turned OFF.

[0042] The fourth pattern is a switching pattern in which the first switching element Q1 is turned OFF, the second switching element Q2 is turned ON, the third switching element Q3 is turned OFF, and the fourth switching element Q4 is turned ON.

[0043] When performing two-level control of the secondary full-bridge circuit 51, the control unit 80 controls the third leg 52 and the fourth leg 53 in conjunction. The control unit 80 simultaneously turns on the fifth switching element Q5 and the eighth switching element Q8. The control unit 80 simultaneously turns on the sixth switching element Q6 and the seventh switching element Q7. The switching pattern of the secondary full-bridge circuit 51 includes the fifth pattern and the sixth pattern.

[0044] The fifth pattern is a switching pattern in which the fifth switching element Q5 is turned ON, the sixth switching element Q6 is turned OFF, the seventh switching element Q7 is turned OFF, and the eighth switching element Q8 is turned ON.

[0045] The sixth pattern is a switching pattern in which the fifth switching element Q5 is turned OFF, the sixth switching element Q6 is turned ON, the seventh switching element Q7 is turned ON, and the eighth switching element Q8 is turned OFF.

[0046] The control unit 80 generates an output voltage V from the secondary full-bridge circuit 51 by combining one of the first to fourth patterns of the primary full-bridge circuit 41 with one of the fifth or sixth patterns of the secondary full-bridge circuit 51. ｏｕｔ Outputs.

[0047] As shown in Figure 2, the step-down modes include a step-down lagging phase mode, a step-down in-phase mode, and a step-down leading phase mode. As shown in Figure 3, the step-down lagging 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 lagging phase mode is a step-down mode used when outputting low power in response to the power demand from the load 120.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 according to the power demanded from the load 120. Medium power is an output power with a larger maximum value than low power.

[0052] 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 120. High power is output power with a maximum value greater than medium power.

[0053] 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 80 when the load mode is step-up mode will be described below.

[0054] When performing two-level control of the primary full-bridge circuit 41, the control unit 80 controls the first leg 42 and the second leg 43 in conjunction. The control unit 80 simultaneously turns on the first switching element Q1 and the fourth switching element Q4. The control unit 80 simultaneously turns on the second switching element Q2 and the third switching element Q3. The switching patterns of the primary full-bridge circuit 41 include the seventh and eighth patterns.

[0055] The seventh pattern is a switching pattern in which the first switching element Q1 is turned ON, the second switching element Q2 is turned OFF, the third switching element Q3 is turned OFF, and the fourth switching element Q4 is turned ON.

[0056] The eighth pattern is a switching pattern in which the first switching element Q1 is turned OFF, the second switching element Q2 is turned ON, the third switching element Q3 is turned ON, and the fourth switching element Q4 is turned OFF.

[0057] When performing three-level control of the secondary full-bridge circuit 51, the control unit 80 independently controls the third leg 52 and the fourth leg 53. The switching patterns of the secondary full-bridge circuit 51 include patterns 9 to 12.

[0058] The ninth pattern is a switching pattern in which the fifth switching element Q5 is turned ON, the sixth switching element Q6 is turned OFF, the seventh switching element Q7 is turned OFF, and the eighth switching element Q8 is turned ON.

[0059] The tenth pattern is a switching pattern in which the fifth switching element Q5 is turned ON, the sixth switching element Q6 is turned OFF, the seventh switching element Q7 is turned ON, and the eighth switching element Q8 is turned OFF.

[0060] The 11th pattern is a switching pattern in which the 5th switching element Q5 is turned OFF, the 6th switching element Q6 is turned ON, the 7th switching element Q7 is turned ON, and the 8th switching element Q8 is turned OFF.

[0061] The twelfth pattern is a switching pattern in which the fifth switching element Q5 is turned OFF, the sixth switching element Q6 is turned ON, the seventh switching element Q7 is turned OFF, and the eighth switching element Q8 is turned ON.

[0062] The control unit 80 generates an output voltage V from the secondary full-bridge circuit 51 by combining either the 7th or 8th pattern of the primary full-bridge circuit 41 with any of the 9th to 12th patterns of the secondary full-bridge circuit 51. ｏｕｔ Outputs.

[0063] 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 120.

[0064] 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.

[0065] 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 demand from the load 120.

[0066] 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 120.

[0067] In boost mode, the boost lag phase mode and boost lead phase mode switch when the first phase difference θ11 is 0. <Output Control> The control unit 80 performs output control. Output control is a control that outputs the required power by controlling the DAB converter 30. The control unit 80 outputs the required power by controlling the first phase differences θ1, θ11, the second phase differences 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 explanation, the frequency of the primary voltage V1 and the frequency of the secondary voltage V2 may be referred to as frequency.

[0068] As shown in Figure 9, in step S1, the control unit 80 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 current flows from the connection point between the first switching element Q1 and the second switching element Q2 towards the connection point between the third switching element Q3 and the fourth switching element Q4. The positive direction for the secondary current I2 is the direction in which current flows from the connection point between the seventh switching element Q7 and the eighth switching element Q8 towards the connection point between the fifth switching element Q5 and the sixth switching element Q6.

[0069] The condition for soft switching of multiple primary-side switching elements Q1 to Q4 is that when primary-side switching elements Q1 to Q4 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 of the diode connected in parallel to the switching element among the primary-side switching elements Q1 to Q4 that changes from OFF to ON, is greater than or equal to the absolute value of the primary-side winding current threshold TI1. 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. When primary-side switching elements Q1 to Q4 switch between ON and OFF, it is the time when at least one of the primary-side switching elements Q1 to Q4 switches 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.

[0070] The condition for soft switching of multiple secondary switching elements Q5 to Q8 is that when the secondary switching elements Q5 to Q8 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 of the diode connected in parallel to the switching element among the secondary switching elements Q5 to Q8 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. When the secondary switching elements Q5 to Q8 switch between ON and OFF, it is the time when at least one of the secondary switching elements Q5 to Q8 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 T11 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.

[0071] As described above, the primary voltage V1 and the secondary voltage V2 are waveforms of the same frequency, inverting every 180 degrees of phase. Since only the sign is reversed during the rising and falling edges of the primary and secondary voltages V1 and V2, we only need to consider one or the other. The following explanation will focus only on the rising edge.

[0072] 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. 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. If condition 1 is met at the first time T1 and the third time T3, soft switching of the primary switching elements Q1 to Q4 is achieved. At the second time T2, the switching pattern of the secondary full-bridge circuit 51 is switched from the sixth pattern to the fifth pattern. At this time, if condition 2 is met, soft switching of the secondary switching elements Q5 to Q8 is achieved.

[0073] The primary winding current threshold TI1 is defined by the following equation (1).

[0074] TI1: Primary winding current threshold, k1: coefficient, V1: Primary voltage, L: Inductance of the first reactor 36, C01: Capacitance corresponding to one switching element relative to the combined capacitance of all capacitors C1 to C4 arranged in parallel with switching elements Q1 to Q4 of the primary full-bridge circuit 41. If the capacitance of capacitor C1 is C11, the capacitance of capacitor C2 is C12, the capacitance of capacitor C3 is C13, and the capacitance of capacitor C4 is C14, then C01 = (C11 + C12 + C13 + C14) / 4 may also be used. If Cx is the largest capacitance among C11 to C14, then C01 = Cx may also be used. The secondary winding current threshold TI2 is similarly defined by substituting each value with the secondary values. In this way, the soft switching region is derived.

[0075] Next, in step S2, the control unit 80 calculates the target current. The target current is a current value that can output the required power from the load 120 and satisfies conditions 1 and 2. The required power is expressed as the effective value of the power.

[0076] 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 Q1 to Q4, the fourth switching element Q4 is the one that changes from OFF to ON at the third time T3. The fourth switching element Q4 is a primary switching element that changes from OFF to ON when the switching pattern changes from the second pattern to the first pattern.

[0077] To satisfy condition 1, the primary current I1 at the third time T3, which flows in the forward direction through the diode D4 connected in parallel to the fourth switching element Q4 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.

[0078] 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 diodes D5 and D8 connected in parallel to the fifth switching element Q5 and the eighth switching element Q8 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|". This value of the secondary current I2 is the value of "I2" in Figure 1. The fifth switching element Q5 and the eighth switching element Q8 are secondary switching elements that change from OFF to ON when the switching pattern changes from the sixth pattern to the fifth pattern. Note that at the second time T2, the secondary current I2 is a positive value, so "I2" is a positive value.

[0079] 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.

[0080] In this way, it is possible to calculate a combination of target currents that can output the required power from load 120 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.

[0081] Next, in step S3, the control unit 80 derives a combination of the first phase difference θ1, θ11, the second phase difference θ2, θ12, and frequency from the calculated target current. Here, the combination of the first phase difference θ1, θ11, the second phase difference θ2, θ12, and frequency is derived so as to follow the calculated target current at the third time T3 and the target current at the second time T2. If the first phase difference θ1, θ11 and the second phase difference 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 secondary voltage V2 become shorter, so the greater the required power, the longer the period of the primary voltage V1 and the secondary voltage V2 should be. As the period becomes longer, the primary current I1 and the secondary current I2 become larger. The control unit 80 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 120 and satisfy conditions 1 and 2.

[0082] The control unit 80 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.

[0083] In step S4, the control unit 80 controls the primary full-bridge circuit 41 and the secondary full-bridge circuit 51 so that the first phase difference θ1, θ11, the second phase difference θ2, θ12, and the frequency are as derived in step S3.

[0084] 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. [Operation of this embodiment] As shown in Figure 11, a sinusoidal AC voltage is input to the conversion circuit 11A from the power supply PS1 as the input voltage V. The input voltage V is expressed by the following equation (2). The input current I input from the power supply PS1 is expressed by the following equation (3). The power P input from the power supply PS1 is the value obtained by multiplying the input voltage V and the input current I, and is expressed by the following equation (4).

[0085] V ｒｍｓ This is the RMS value of the input voltage V. ｒｍｓ This is the effective value of the input current I. ｒｍｓ P is the effective value of power P, ｒｍｓ = V ｒｍｓ ×I ｒｍｓ Furthermore, power supply PS2 receives input voltage and input current that are 120 degrees out of phase with power supply PS1, and power supply PS3 receives input voltage and input current that are 240 degrees out of phase with power supply PS1.

[0086] As shown in Figure 12, the input voltage V is full-wave rectified by the rectifier circuit 20. The link voltage V output by the rectifier circuit 20 ｌｉｎｋ This becomes a DC voltage that fluctuates between 0 and Vmax. Link voltage V ｌｉｎｋ This is expressed by the following equation (5). In the DAB converter 30, the link voltage V ｌｉｎｋ The input current to the DAB converter 30 is controlled in the same phase as the link voltage V. ｌｉｎｋ This results in a sine wave in the same phase.

[0087] The link voltage V is the voltage input to the DAB converter 30.ｌｉｎｋ V is a DC voltage that fluctuates between 0 and Vmax, but the DAB converter 30 has a link voltage V ｌｉｎｋ A constant output voltage V ｏｕｔ It is controlled to convert to the output current I ｏｕｔ is I ｏｕｔ = P / V ｏｕｔ Therefore, as shown in Figure 13, the output current I output from each conversion circuit 11 ｏｕｔ This can be expressed by equation (6) below.

[0088] As shown in Figure 14, each conversion circuit 11 outputs an output current I that is 120 degrees out of phase with respect to the others. ｏｕｔ It outputs the output current of the first conversion circuit 11A to I ｏｕｔ１ , the output current of the second conversion circuit 11B is I ｏｕｔ２ , the output current of the third conversion circuit 11C is I ｏｕｔ３ Let's assume that in this case, the output current I ｏｕｔ１ , I ｏｕｔ２ , I ｏｕｔ３ The output current I is expressed by the following equations (7) to (9). ｏｕｔ１ This is shown by a solid line in Figure 14. Output current I ｏｕｔ２ This is shown by a dashed line in Figure 14. Output current I ｏｕｔ３ This is shown by a dashed line in Figure 14.

[0089] The output current of the power converter 10 is equal to the output current I of the three conversion circuits 11. ｏｕｔ This is a combination of the two. Therefore, the output current I of the power converter 10 ｔｏｔａｌ This can be expressed by equation (10) below.

[0090] As can be seen from equation (10), the output current I of the three conversion circuits 11 ｏｕｔ By summing them up, the respective output currents I ｏｕｔ The pulsating components contained in it cancel each other out. That is, the output current I for one phase ｏｕｔ This includes ripple, but the output current I for all three phases ｏｕｔ By merging them, the ripples cancel each other out.

[0091] [Effects of the Embodiment] (1) The power converter 10 is equipped with a rectifier circuit 20. The rectifier circuit 20 rectifies the AC voltage input from the AC power supply PS without performing power factor correction operation. Since the power converter 10 does not need to be equipped with a PFC coil for power factor correction operation, the number of parts can be reduced.

[0092] (2) Since the rectifier circuit 20 does not perform power factor correction operation, the DC link capacitor 25 does not need to have an energy buffer function. For this reason, the capacitance of the DC link capacitor 25 can be reduced.

[0093] (3) When the rectifier circuit 20 performs power factor correction, the switching frequency of the rectifier elements 21, 22, 23, and 24 needs to be set to several tens of kHz. In contrast, when power factor correction is not performed, the switching frequency of the rectifier elements 21, 22, 23, and 24 can be set to about 100 Hz. Therefore, the number of switching cycles can be reduced. Also, since switching occurs when the voltage applied to the switching elements used as rectifier elements 21, 22, 23, and 24 is near zero, switching losses can be reduced.

[0094] (4) Switching elements are used as rectifier elements 21, 22, 23, and 24. When diodes are used as rectifier elements 21, 22, 23, and 24, the direction of current flow is restricted, which may prevent soft switching of primary-side switching elements Q1 to Q4. In contrast, by using switching elements as rectifier elements 21, 22, 23, and 24, the direction of current flow is not restricted, making it easier to perform soft switching of primary-side switching elements Q1 to Q4.

[0095] (5) The power converter 10 comprises three rectifier circuits 20 and three DAB converters 30. Each of the three rectifier circuits 20 is input with the AC voltage of one phase of the three-phase AC voltage. The output current I of the three DAB converters 30 ｏｕｔ Each of these contains ripple. The output current I of the three DAB converters 30 ｏｕｔ By combining and outputting the signals, ripples can be canceled out.

[0096] [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.

[0097] ○The power converter 10 may be one that receives a single-phase AC voltage input. In this case, the second conversion circuit 11B and the third conversion circuit 11C can be removed from the power converter 10 of the embodiment.

[0098] ○The rectifier elements 21 to 24 may be diodes. ○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.

[0099] ○The control unit 80 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 80 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 80 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.

[0100] The control unit 80 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.

[0101] [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.

Claims

1. A rectifier circuit configured to rectify an AC voltage input from an AC power source, and a DAB converter connected to the rectifier circuit, wherein the DAB converter comprises: 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 primary full-bridge circuit connected to the primary winding having a plurality of primary switching elements; a secondary full-bridge circuit connected to the secondary winding having a plurality of secondary switching elements; and a control unit configured to control the plurality of primary switching elements and the plurality of secondary switching elements, wherein the condition for performing soft switching of the plurality of primary switching elements is condition 1, and the condition for performing soft switching of the plurality of secondary 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 forward direction of the primary-side winding 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-side switching elements switches from OFF to ON, the secondary-side condition current value, which is the value of the current flowing in the forward direction of the secondary-side winding of the diode connected in parallel with the at least one secondary-side switching element, is greater than or equal to the absolute value of the secondary-side winding current threshold; The control unit is configured to control the primary-side full-bridge circuit and the secondary-side full-bridge circuit such that one of the primary-side full-bridge circuit and the secondary-side full-bridge circuit applies a voltage of 2 levels to the transformer section, and the other applies a voltage of 3 levels to the transformer section. The voltages of the two levels and the voltages of the three levels are waveforms of the same frequency that invert every 180 degrees of phase, and the difference between the first time when the voltage of the three levels rises from a low level to a middle level and the second time when the voltage of the two levels rises from a low level to a high level is the first phase difference.A power converter wherein the difference between the first time and the third time when the voltage of the three levels rises from a middle level to a high level is a second phase difference, and the control unit is configured to control at least one of the first phase difference and the second phase difference, and the frequencies of the voltage of the two levels and the voltage of the three level, so as to be able to output the required power and satisfy the conditions 1 and 2.

2. The power conversion device according to claim 1, wherein the rectifier circuit is a full-bridge circuit using switching elements.

3. The power converter according to claim 1, wherein the AC power supply is configured to output three phase AC voltages with phases shifted by 120 degrees, the rectifier circuit is one of three rectifier circuits, the DAB converter is one of three DAB converters, each of the three rectifier circuits is input with an AC voltage of one phase of the three phase AC voltages, and the power converter is configured to combine and output the output currents of the three DAB converters.

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