Power converter

Abstract

To reduce the number of parts. [Solution] The power converter 10 comprises a rectifier circuit 20 that rectifies the AC voltage input from the AC power supply PS, and a DAB converter 30. The DAB converter 30 comprises a primary full-bridge circuit 41 having a plurality of primary switching elements Q1 to Q4, a secondary full-bridge circuit 51 having a plurality of secondary switching elements Q5 to Q8, and a control unit 80. The rectifier circuit 20 rectifies the AC voltage input from the AC power supply PS without performing power factor correction operation, and therefore does not need to have a PFC coil for power factor correction operation, thus reducing the number of parts.

Description

[Technical Field]

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

[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, for example, a boost coil. The DC voltage output by the AC / DC conversion unit is input to the DAB converter. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6710615 [Overview of the Initiative] [Problems that the invention aims to solve]

[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. [Means for solving the problem]

[0005] A power converter that solves the above problems comprises a rectifier circuit that rectifies 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 or 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 that controls the plurality of primary switching elements and the plurality of secondary switching elements, wherein condition 1, which is a condition for performing soft switching of the plurality of primary switching elements, is a primary condition current value which is the current flowing in the primary winding when the primary switching element is turned ON / OFF, and is the forward current value of a diode connected in parallel to the primary switching element that changes from OFF to ON, and is greater than or equal to the absolute value of the primary winding current threshold, and Condition 2 is that when the secondary switching element is switched ON / OFF, the secondary condition current value, which is the current flowing in the secondary winding and is the forward current value of the diode connected in parallel to the secondary switching element when it changes from OFF to ON, is greater than or equal to the absolute value of the secondary winding current threshold, and the control unit applies a voltage of 2 levels to the transformer section with one of the primary full-bridge circuit and the secondary full-bridge circuit with the other applying a voltage of 3 levels to the transformer section. The bridge circuit is controlled such that the voltages of the two levels and the voltage of the third level are waveforms of the same frequency that invert every 180 degrees in phase, the difference between the first time when the voltage of the third level 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, the difference between the first time and the third time when the voltage of the third level rises from a middle level to a high level is the second phase difference, and the control unit can output the required power and satisfies the conditions 1 and 2 by setting the first phase difference and the second phase difference,Control at least one of the frequencies of the two-level voltage and the three-level voltage.

[0006] The rectifier circuit rectifies the AC voltage input from the AC power supply without performing a power factor correction operation. Since the power conversion device may not include a PFC coil for the power factor correction operation, the number of components can be reduced.

[0007] Regarding the above power conversion device, the rectifier circuit may be a full-bridge circuit using switching elements. Regarding the above power conversion device, the AC power supply outputs three-phase AC voltages with phases shifted by 120 degrees each, and the power conversion device includes three of the rectifier circuits and three of the DAB converters. Each of the three rectifier circuits receives an AC voltage corresponding to one phase of the three-phase AC voltage, and the output currents of the three DAB converters may be combined and output.

Advantages of the Invention

[0008] According to the present invention, the number of components can be reduced.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a circuit diagram of a power conversion device. [Figure 2] FIG. 2 is a diagram showing the relationship between the equivalent voltage ratio and the load mode. [Figure 3] FIG. 3 is a diagram showing the primary-side voltage and the secondary-side voltage in the step-down lag phase mode. [Figure 4] FIG. 4 is a diagram showing the primary-side voltage and the secondary-side voltage in the step-down in-phase mode. [Figure 5] FIG. 5 is a diagram showing the primary-side voltage and the secondary-side voltage in the step-down leading phase mode. [Figure 6] FIG. 6 is a diagram showing the primary-side voltage and the secondary-side voltage in the boost lag phase mode. [Figure 7] FIG. 7 is a diagram showing the primary-side voltage and the secondary-side voltage in the boost in-phase mode. [Figure 8] Figure 8 shows the primary and secondary voltages in the boost leading phase mode. [Figure 9] Figure 9 is a flowchart showing the output control. [Figure 10] Figure 10 shows the primary and secondary currents in step-down lag phase mode. [Figure 11] Figure 11 shows the input voltage applied to the conversion circuit. [Figure 12] Figure 12 shows the link voltage. [Figure 13] Figure 13 shows the output current of the conversion circuit. [Figure 14] Figure 14 shows the output current of the power converter. [Modes for carrying out the invention]

[0010] One embodiment of a power conversion device 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 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. The three power supplies PS1, PS2, and PS3 each have a first terminal P1 and a second terminal P2. The power supplies PS1, PS2, and PS3 switch between having a positive first terminal P1 or a positive second terminal P2 depending on the passage of time. The load 120 is, for example, a secondary battery capable of charging and discharging DC power. These are secondary batteries, such as lithium-ion batteries or lead-acid batteries.

[0011] The power converter 10 is installed between the AC power supply PS and the load 120. The power converter 10 can convert the AC power input from the AC power supply PS into DC power and output it to the load 120.

[0012] 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. The configuration of the three conversion circuits 11 is similar.

[0013] The conversion circuit 11 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.

[0014] The first input terminal 12 is connected to the first terminal P1 of power supplies PS1, PS2, and PS3. The second input terminal 13 is connected to the second terminal P2 of power supplies PS1, PS2, and PS3. AC voltage is input to the conversion circuit 11 from the first input terminal 12 and the second input terminal 13.

[0015] 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.

[0016] 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.

[0017] 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. 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 supplies PS1, PS2, and PS3 on the rectifier circuit 20 side of the coil 15. The second input terminal 13 is connected to the connection point between the third rectifier element 23 and the fourth rectifier element 24.

[0018] The DC link capacitor 25 is located between the rectifier circuit 20 and the DAB converter 30. The DC link capacitor 25 connects the first positive busbar L1 and the first negative busbar L2.

[0019] The first voltage sensor 71 is connected in parallel with the DC link capacitor 25. The first voltage sensor 71 measures the link voltage V, which is the voltage across the DC link capacitor 25. link Detects the link voltage V. link This is the output voltage of the rectifier circuit 20.

[0020] The DAB converter 30 is a dual active bridge type DC / DC converter. The DAB converter 30 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.

[0021] 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.

[0022] The DAB converter 30 includes a primary-side full-bridge circuit 41. The primary-side 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 the first positive bus L1 and the first negative bus 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 L1 and the first negative bus L2. As a result, 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 the upper arm. The second switching element Q2 and the fourth switching element Q4 constitute the lower arm.

[0023] 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 also be p-type MOSFETs, IGBTs (Insulated Gate Bipolar Transistors), or GaN-HEMTs.

[0024] Diodes D1-D4 and capacitors C1-C4 are connected in parallel to the primary switching elements Q1-Q4, respectively. Diodes D1-D4 may be parasitic diodes or elements. Capacitors C1-C4 may be parasitic capacitances, elements, or a combination of parasitic capacitances and elements.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Diodes D5-D8 and capacitors C5-C8 are connected in parallel to the secondary switching elements Q5-Q8, respectively. Diodes D5-D8 may be parasitic diodes or elements. Capacitors C5-C8 may be parasitic capacitances, elements, or a combination of parasitic capacitances and elements.

[0029] 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.

[0030] 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 receives the output voltage V of the DAB converter 30. out It detects.

[0031] The second positive buses L3 of the three conversion circuits 11 are connected to each other. The second negative buses L4 of the three conversion circuits 11 are connected to each other. In the example shown in Figure 1, the second positive bus L3 of the first conversion circuit 11A is connected to the second positive buses L3 of the two conversion circuits 11B and 11C. The second negative bus L4 of the first conversion circuit 11A is connected to the second negative buses 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.

[0032] The output filter 60 is, for example, an LC filter. The output filter 60 is provided between the connection points of the three second positive buses L3 and the connection points of the three second negative buses L4 and 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 buses L3 and the output terminal 63. The connection points of the three second negative buses 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.

[0033] 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.

[0034] 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 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 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.

[0035] 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 terminal P1 is higher than the potential at terminal P2, the AC voltage is positive. If the potential at terminal P1 is lower than the potential at terminal P2, the AC voltage is negative.

[0036] 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 Convert it to. At this time, the input current input to the DAB converter 30 is controlled with the same phase as the link voltage V link When 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 turns ratio is converted to 1:1, is (V

[0037] × N1) / (V out × N2). The control unit 80 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. link For example, when the turns ratio of the transformer 32 is 1:2, the link voltage V

[0038] = 200V, and the output voltage V link = 400V, when the turns ratio is converted to 1:1, the equivalent voltage ratio = (V out × 1) / (V оut × 2) = 1. Therefore, when the turns ratio of the transformer 32 is 1:2 and the output voltage V link = 400V, if the link voltage V out is greater than 200V, it is in the step - down mode, and if it is less than 200V, it is in the step - up mode. In the following description, unless otherwise specified, the turns ratio is assumed to be 1:1 for explanation. link The control unit 80 controls one of the primary - side full - bridge circuit 41 and the secondary - side full - bridge circuit 51 at three levels and the other at two levels. 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] The control unit 80 controls one of the primary - side full - bridge circuit 41 and the secondary - side full - bridge circuit 51 at three levels and the other at two levels. 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.

[0040] In boost mode, the secondary full-bridge circuit 51 is controlled in three levels, and 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, and 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, 2-level control is a control method in which the voltage applied to the series connection SC1 between the primary winding 34 and the first reactor 36 is switched between positive and negative. In 3-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 2-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 direction of the arrows in Figure 1 is considered positive for each. During normal operation without changing the output, the primary voltage V1 and secondary voltage V2 are waveforms of the same frequency, inverting every 180 degrees of phase.

[0041] <Step-down mode> The control performed by the control unit 80 when the load mode is the 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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 patterns of the secondary full-bridge circuit 51 include the fifth pattern and the sixth pattern.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] As shown in Figure 2, the buck mode includes a buck lag phase mode, a buck in phase mode, and a buck lead 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 low power in response to the power demand from load 120.

[0051] Let the first phase difference θ1 be 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. Let the second phase difference θ2 be the difference between the first time and the third time T3 when the 3-level voltage rises from middle to high level.

[0052] 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.

[0053] During normal operation without changing the output, the primary voltage V1 and secondary voltage V2 are waveforms of the same frequency that invert every 180 degrees of phase. Therefore, the time when the 3-level voltage falls from high to middle level can be called the first time T1, the time when the 2-level voltage falls from high to low level can be called the second time T2, and the time when the 3-level voltage falls from middle to low level can be called the third time T3.

[0054] 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 point T2 and the third time point 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 demand from load 120. Medium power is an output power with a larger maximum value than low power.

[0055] 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.

[0056] In step-down mode, the system switches between step-down lagging phase mode and step-down leading phase mode when the difference between the first phase difference θ1 and the second phase difference θ2 is zero. <Boost Mode> The control performed by the control unit 80 when the load mode is boost mode will be described below.

[0057] When performing two-level control of the primary-side 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-side full-bridge circuit 41 include the seventh and eighth patterns.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] The 10th pattern is a switching pattern in which the 5th switching element Q5 is turned ON, the 6th switching element Q6 is turned OFF, the 7th switching element Q7 is turned ON, and the 8th switching element Q8 is turned OFF.

[0063] 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.

[0064] The 12th 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 OFF, and the 8th switching element Q8 is turned ON.

[0065] 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.

[0066] As shown in Figure 2, the boost mode includes a boost lag phase mode, a boost in phase mode, and a boost lead 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 low power in response to the power demand from load 120.

[0067] 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.

[0068] 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.

[0069] 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 high power in response to the power demand from the load 120.

[0070] In boost mode, the system switches between boost lag phase mode and boost lead phase mode 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 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.

[0071] 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 considered positive. For the primary current I1, the positive direction is when it 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. For the secondary current I2, the positive direction is when it 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.

[0072] The condition for soft switching of multiple primary-side switching elements Q1 to Q4 is that, when primary-side switching elements Q1 to Q4 are switched ON / OFF, the primary-side current I1, which is the forward current value 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 are switched ON / OFF, it is the point in time when at least one of the primary-side switching elements Q1 to Q4 changes from ON to OFF, or from OFF to ON. In step-down mode, this point in time is the same as the first time T1 and third time T3 when the primary-side voltage V1 rises from a low or middle level, or falls from a high or middle level. In boost mode, the second time T12 is the same as when the primary voltage V1 rises from a low level to a high level, or falls from a high level to a low level.

[0073] The condition for soft switching of multiple secondary switching elements Q5 to Q8 is that, when the secondary switching elements Q5 to Q8 are switched ON / OFF, the secondary current I2, which is the forward current value 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 are switched ON / OFF, it is the point in time when at least one of the secondary switching elements Q5 to Q8 changes from ON to OFF, or from OFF to ON. In step-down mode, this point in time is the same as the second time T2, which is the point in time when the secondary voltage V2 rises from a low level or falls from a high level. In boost mode, the first time point T11 and the third time point T13 are the same when the secondary voltage V2 rises from a low or middle level, or falls from a high or middle level.

[0074] As mentioned above, the primary voltage V1 and secondary voltage V2 are waveforms of the same frequency that invert every 180 degrees of phase. Therefore, only the positive and negative signs are reversed during the rising and falling edges, so we only need to consider one or the other. From here on, we will only explain the rising edge.

[0075] 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 both 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. If condition 2 is met at this time, soft switching of the secondary switching elements Q5 to Q8 is achieved.

[0076] The primary winding current threshold TI1 is defined by equation (1) below.

[0077]

number

[0078] 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.

[0079] To satisfy condition 1, the primary current I1 at the first time T1 and the third time T3 must be considered. However, since the primary current I1 at the third time T3 is the one with the smaller absolute value of the current in this load mode, it is sufficient to consider the primary current I1 at the third time T3. Therefore, to satisfy condition 1, the primary current I1 at the third time T3 must be greater than or equal to the absolute value of the primary winding current threshold TI1 "|TI1|", and the forward current flowing through the diode D4 connected in parallel with the fourth switching element Q4, which changes from OFF to ON at this time (i.e., changes from OFF to ON when the switching pattern changes from the second pattern to the first pattern), must be greater than or equal to the absolute value of the primary winding current threshold TI1 "|TI1|". Note that at the third time T3, the primary current I1 is a negative value, so "-I1" will be a positive value. Also, which of the first time T1 and the third time T3 has a smaller absolute value depends on the load mode.

[0080] In this load mode, for condition 2 to be satisfied, the secondary current I2 at the second time T2 must be greater than or equal to the absolute value of the secondary winding current threshold TI2 "|TI2|", which is the forward current flowing through diodes D5 and D8 connected in parallel to the fifth switching element Q5 and the eighth switching element Q8, which change from OFF to ON at this time (i.e., 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.

[0081] In practical terms, for example, for condition 1, one can satisfy condition 1 by comparing TI1', which is the primary winding current threshold TI1 converted to the secondary side, with the secondary current I2 at the third time point 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.

[0082] 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 / load mode.

[0083] 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 track 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 required power of the load 120 and satisfy conditions 1 and 2.

[0084] 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.

[0085] 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.

[0086] The required power, the first phase difference θ1, θ11, the second phase difference θ2, θ12, and the frequency may be calculated each time, or they may be calculated in advance and stored in a map or similar. [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 equation (2) below. The input current I input from the power supply PS1 is expressed by equation (3) below. The power P input from the power supply PS1 is the product of the input voltage V and the input current I, and is expressed by equation (4).

[0087]

number

[0088] 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 linkThis becomes a DC voltage that fluctuates between 0 and Vmax. Link voltage V link This is expressed by equation (5) below. In the DAB converter 30, the link voltage V link This controls the input current to the DAB converter 30 in the same phase as the link voltage V. link This results in a sine wave in phase with the same wave.

[0089]

number

[0090]

number

[0091]

number

[0092]

number

[0093] [Effects of the Embodiment] (1) The power converter 10 includes 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 have a PFC coil for power factor correction operation, the number of parts can be reduced.

[0094] (2) Since the rectifier circuit 20 does not perform power factor correction, 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.

[0095] (3) When the rectifier circuit 20 performs power factor correction, the switching frequencies of the rectifier elements 21, 22, 23, and 24 need to be set to several tens of kHz. In contrast, when power factor correction is not performed, the switching frequencies of the rectifier elements 21, 22, 23, and 24 can be set to around 100 Hz. Therefore, the number of switching cycles can be reduced, and 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.

[0096] (4) Switching elements are used as rectifier elements 21, 22, 23, and 24. If 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.

[0097] (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. Output current I of the three DAB converters 30 out By combining and outputting the signals, ripples can be canceled out.

[0098] [Example of changes] The embodiment can be implemented with the following modifications. The embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0099] ○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.

[0100] ○The rectifier elements 21-24 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.

[0101] ○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.

[0102] The control unit 80 can output the required power by controlling one of the first phase difference θ1, θ11 and the second phase difference θ2, θ12, and the frequency, and may also control the primary side full bridge circuit 41 and the secondary side full bridge circuit 51 to satisfy conditions 1 and 2.

[0103] [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. [Explanation of Symbols]

[0104] PS...AC power supply, Q1~Q4...Primary switching elements, Q5~Q8...Secondary switching elements, 10...Power converter, 11...Conversion circuit, 20...Rectifier circuit, 30...DAB converter, 31...Transformer section, 32...Transformer, 34...Primary winding, 35...Secondary winding, 36,37...Reactor, 41...Primary full bridge circuit, 51...Secondary full bridge circuit, 80...Control unit.

Claims

1. A rectifier circuit that rectifies the AC voltage input from an AC power source, The rectifier circuit is connected to a DAB converter, The aforementioned DAB converter is A transformer section having a primary winding, a secondary winding, and a reactor connected to at least one of the primary winding or the secondary winding, A 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, The system comprises a plurality of primary-side switching elements and a control unit that controls the plurality of secondary-side switching elements, Condition 1, which is a condition for performing soft switching of the plurality of primary-side switching elements, is that when the primary-side switching elements are turned ON / OFF, the primary-side condition current value, which is the current flowing through the primary-side winding and is the forward current value of the diode connected in parallel to the primary-side switching element that changes from OFF to ON, is greater than or equal to the absolute value of the primary-side winding current threshold. Condition 2, which is a condition for performing soft switching of the plurality of secondary switching elements, is that when the secondary switching elements are turned ON / OFF, the secondary condition current value, which is the current flowing through the secondary winding and is the forward current value of the diode connected in parallel to the secondary switching element when it changes from OFF to ON, is greater than or equal to the absolute value of the secondary winding current threshold. The control unit controls the primary full-bridge circuit and the secondary full-bridge circuit so that one of them applies a voltage of level 2 to the transformer section, and the other applies a voltage of level 3 to the transformer section. The voltages of the two levels and the voltages of the three levels are waveforms of the same frequency that are inverted every 180 degrees of phase. The difference between the first time when the three voltage levels rise from a low level to a middle level and the second time when the two voltage levels rise 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 three voltage levels rise from the middle level to the high level is the second phase difference. The control unit controls 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 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 aforementioned AC power supply outputs three phase AC voltages with phases shifted by 120 degrees each. The aforementioned power converter is The three aforementioned rectifier circuits, The system comprises three of the aforementioned DAB converters, Each of the three rectifier circuits is input to an AC voltage representing one phase of the three-phase AC voltage. The power conversion device according to claim 1, which combines and outputs the output currents of the three DAB converters.

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