Power conversion device and power conversion system

Abstract

To obtain an electric power conversion device capable of making voltage ripple smaller.SOLUTION: An electric power conversion device according to an embodiment of the disclosure includes: a first power terminal; a switching circuit having a switching element; a transformer having a first winding connected to the switching circuit and a second winding; a rectifying circuit connected to the second winding and having a switching element; a smoothing circuit; a second power terminal; a control circuit; and a driving circuit. The control circuit is capable of operating a first operation and a second operation alternatively before supplying power from the first power terminal to the second power terminal, and capable of controlling the operation of the switching circuit and the rectifying circuit so as to supplying first power from the second power terminal to the first power terminal in the first operation and supplying second power smaller than the first power from the second power terminal to the first power terminal in the second operation.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a power conversion device and a power conversion system that convert electric power. [Background technology]

[0002] Some power conversion devices that convert the power of a primary battery and supply it to a secondary battery perform a so-called precharge operation, in which the power of the secondary battery is supplied to a primary capacitor via the power conversion device before performing a power conversion operation. For example, Patent Document 1 discloses a technique for alternately providing a period during which a switching operation is performed and a period during which the switching operation is stopped when boosting the voltage of a capacitor by performing a precharge. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-34959 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a power conversion device that performs such a precharge operation, the voltage of the primary-side capacitor is maintained after being boosted. During the period in which this voltage is maintained, it is desirable for the ripple of the voltage of the primary-side capacitor to be small.

[0005] It is desirable to provide a power conversion device and a power conversion system that can reduce voltage ripple. [Means for solving the problem]

[0006] A power conversion device according to an embodiment of the present invention includes a first power terminal, a switching circuit, a transformer, a rectifier circuit, a smoothing circuit, a second power terminal, a control circuit, and a drive circuit. The switching circuit is connected to the first power terminal and has a switching element capable of performing a switching operation based on a first drive signal. The transformer has a first winding connected to the switching circuit and a second winding. The rectifier circuit is connected to the second winding and has a switching element capable of performing a switching operation based on a second drive signal. The smoothing circuit is connected to the rectifier circuit. The second power terminal is connected to the smoothing circuit. The control circuit is capable of controlling the operation of the switching circuit and the rectifier circuit. The drive circuit is capable of generating a first drive signal and a second drive signal based on an instruction from the control circuit. The control circuit is capable of alternately performing a first operation and a second operation before supplying power from the first power terminal to the second power terminal, and is capable of controlling the operation of the switching circuit and the rectifier circuit in the first operation so that a first power is supplied from the second power terminal to the first power terminal to increase the voltage at the first power terminal, and is capable of controlling the operation of the switching circuit and the rectifier circuit in the second operation so that a second power smaller than the first power is supplied from the second power terminal to the first power terminal to decrease the voltage at the first power terminal.

[0007] A power conversion system according to an embodiment of the present invention includes a first battery, a capacitor, a first switch, a second switch, a power conversion device, and a second battery. The first battery has a first terminal and a second terminal. The capacitor has a first terminal and a second terminal. The first switch is provided on a path connecting a first terminal of the first battery and a first terminal of the capacitor. The second switch is provided on a path connecting a second terminal of the first battery and a second terminal of the capacitor. The power conversion device includes a first power terminal, a switching circuit, a transformer, a rectifier circuit, a smoothing circuit, a second power terminal, a control circuit, and a drive circuit. The first power terminal has a first connection terminal connected to the first terminal of the capacitor and a second connection terminal connected to the second terminal of the capacitor. The switching circuit includes a switching element connected to the first power terminal and capable of performing a switching operation based on a first drive signal. The transformer has a first winding connected to the switching circuit and a second winding. The rectifier circuit has a switching element connected to the second winding and capable of performing a switching operation based on a second drive signal. The smoothing circuit is connected to the rectifier circuit. The second power terminal is connected to the smoothing circuit and to a second battery. The control circuit is capable of controlling the operation of the switching circuit and the rectifier circuit. The drive circuit is capable of generating a first drive signal and a second drive signal based on an instruction from the control circuit. The control circuit is capable of alternately performing a first operation and a second operation before supplying power from the first power terminal to the second power terminal, and is capable of controlling the operation of the switching circuit and the rectifier circuit in the first operation so that a first power is supplied from the second power terminal to the first power terminal to increase the voltage at the first power terminal, and is capable of controlling the operation of the switching circuit and the rectifier circuit in the second operation so that a second power smaller than the first power is supplied from the second power terminal to the first power terminal to decrease the voltage at the first power terminal. Effect of the Invention

[0008] According to the power conversion device and the power conversion system according to an embodiment of the present invention, it is possible to reduce the ripple in the voltage of the capacitor. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a circuit diagram showing an example of a configuration of a power conversion system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram illustrating an example of the configuration of the auxiliary power supply circuit shown in FIG. [Diagram 3] FIG. 3 is a block diagram illustrating an example of the configuration of the control circuit illustrated in FIG. [Figure 4] FIG. 4 is an explanatory diagram illustrating an example of an operation of the threshold generating unit illustrated in FIG. [Diagram 5] FIG. 5 is an explanatory diagram illustrating an example of a characteristic of a comparison operation in the comparison section shown in FIG. [Figure 6] FIG. 6 is a timing chart illustrating an example of the operation of the comparison unit illustrated in FIG. [Figure 7] FIG. 7 is a timing chart illustrating an example of a precharge operation in the power conversion system illustrated in FIG. [Figure 8] FIG. 8 is a timing waveform diagram illustrating an example of a gate signal in a precharge period of the power conversion system illustrated in FIG. [Figure 9] FIG. 9 is a timing waveform diagram illustrating an example of a precharge operation in the power conversion system shown in FIG. [Figure 10] FIG. 10 is a timing waveform diagram illustrating an example of a gate signal in a voltage maintenance period of the power conversion system illustrated in FIG. [Figure 11] FIG. 11 is a timing waveform diagram illustrating an example of an operation of the power conversion system shown in FIG. 1 during a voltage maintenance period. [Figure 12] FIG. 12 is a timing waveform diagram illustrating an example of an operation of the power conversion system according to the reference example during a voltage maintenance period. [Figure 13] FIG. 13 is a timing chart illustrating an example of a precharge operation in a power conversion system according to a modification. [Figure 14] FIG. 14 is a timing waveform diagram illustrating an example of a gate signal in a voltage maintenance period in a power conversion system according to another modified example. [Figure 15] FIG. 15 is a timing waveform diagram illustrating an example of a gate signal in a voltage maintenance period in a power conversion system according to another modified example. [Figure 16] FIG. 16 is a circuit diagram illustrating a configuration example of a power conversion system according to another modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0011] <Embodiment Mode> [Configuration example] 1 shows an example of the configuration of a power conversion system 1 including a power conversion device according to an embodiment of the present invention. The power conversion system 1 includes a high-voltage battery BH, switches SW1 and SW2, a capacitor 9, a power conversion device 10, and a low-voltage battery BL. The power conversion system 1 is configured to convert power supplied from the high-voltage battery BH and supply the converted power to the low-voltage battery BL.

[0012] The high-voltage battery BH is configured to store electric power and supplies electric power to the power conversion device 10 via the switches SW1 and SW2.

[0013] The switches SW1 and SW2 are configured to supply power stored in the high-voltage battery BH to the power conversion device 10 when they are turned on. The switches SW1 and SW2 are configured using, for example, relays. When the switch SW1 is turned on, it connects the positive terminal of the high-voltage battery BH to the terminal T11 of the power conversion device 10. When the switch SW2 is turned on, it connects the negative terminal of the high-voltage battery BH to the terminal T12 of the power conversion device 10. The switches SW1 and SW2 are configured to be turned on and off based on instructions from a system control unit (not shown).

[0014] One end of the capacitor 9 is connected to a terminal T11 of the power conversion device 10 and the switch SW1, and the other end is connected to a terminal T12 of the power conversion device 10 and the switch SW2.

[0015] The power conversion device 10 is configured to convert power by stepping down the voltage supplied from the high-voltage battery BH and supply the converted power to the low-voltage battery BL. The power conversion device 10 has terminals T11, T12, a switching circuit 12, a transformer 13, a rectifier circuit 14, a smoothing circuit 15, a voltage sensor 18, an auxiliary power circuit 20, drive circuits 32, 34, a control circuit 40, and terminals T21, T22. The high-voltage battery BH, switches SW1, SW2, capacitor 9, switching circuit 12, and drive circuit 32 constitute a primary circuit of the power conversion system 1, and the rectifier circuit 14, smoothing circuit 15, voltage sensor 18, drive circuit 34, and low-voltage battery BL constitute a secondary circuit of the power conversion system 1.

[0016] Terminals T11 and T12 are configured to receive a voltage from high-voltage battery BH when switches SW1 and SW2 are turned on. In power conversion device 10, terminal T11 is connected to voltage line L11, and terminal T12 is connected to reference voltage line L12. The voltage on voltage line L11 relative to the voltage on reference voltage line L12 is voltage VH.

[0017] The switching circuit 12 is configured to convert a DC voltage supplied from the high-voltage battery BH into an AC voltage. The switching circuit 12 is a full-bridge type circuit and includes transistors S1 to S4. The transistors S1 to S4 are switching elements that perform switching operations based on gate signals GA to GD, respectively. The transistors S1 to S4 are configured using, for example, N-type field effect transistors (FETs). The transistors S1 to S4 include body diodes D1 to D4, respectively. For example, the anode of the body diode D1 is connected to the source of the transistor S1, and the cathode is connected to the drain of the transistor S1. The same is true for the body diodes D2 to D4. Note that the present invention is not limited to this configuration, and for example, a diode element may be externally attached between the drain and source of each of the transistors S1 to S4. In addition, although an N-type field effect transistor is used in this example, any switching element may be used.

[0018] The transistor S1 is provided in a path connecting the voltage line L11 and the node N1, and is configured to connect the node N1 to the voltage line L11 when the transistor S1 is in an on state. The drain of the transistor S1 is connected to the voltage line L11, the gate is supplied with a gate signal GA, and the source is connected to the node N1. The transistor S2 is provided in a path connecting the node N1 and the reference voltage line L12, and is configured to connect the node N1 to the reference voltage line L12 when the transistor S2 is in an on state. The drain of the transistor S2 is connected to the node N1, the gate is supplied with a gate signal GB, and the source is connected to the reference voltage line L12. The node N1 is a connection point between the source of the transistor S1 and the drain of the transistor S2.

[0019] The transistor S3 is provided in a path connecting the voltage line L11 and the node N2, and is configured to connect the node N2 to the voltage line L11 when the transistor S3 is turned on. The drain of the transistor S3 is connected to the voltage line L11, the gate is supplied with a gate signal GC, and the source is connected to the node N2. The transistor S4 is provided in a path connecting the node N2 and the reference voltage line L12, and is configured to connect the node N2 to the reference voltage line L12 when the transistor S4 is turned on. The drain of the transistor S4 is connected to the node N2, the gate is supplied with a gate signal GD, and the source is connected to the reference voltage line L12. The node N2 is a connection point between the source of the transistor S3 and the drain of the transistor S4.

[0020] The transformer 13 is configured to insulate the primary circuit and the secondary circuit from each other in terms of DC current and to connect them in terms of AC current, convert the AC voltage supplied from the primary circuit at a transformation ratio N of the transformer 13, and supply the converted AC voltage to the secondary circuit. The transformer 13 has windings 13A and 13B. The winding 13A is a primary winding, and one end is connected to a node N1 in the switching circuit 12, and the other end is connected to a node N2 in the switching circuit 12. The winding 13B is a secondary winding, and one end is connected to a node N4 (described later) in the rectifier circuit 14, and the other end is connected to a node N5 (described later) in the rectifier circuit 14.

[0021] The rectifier circuit 14 is configured to rectify the AC voltage output from the winding 13B of the transformer 13. The rectifier circuit 14 is a full-bridge circuit and has transistors S5 to S8. The transistors S5 to S8 are configured to perform switching operations based on gate signals GE and GF. The transistors S5 to S8 are configured using, for example, N-type field effect transistors, similar to the transistors S1 to S4 of the switching circuit 12. The transistors S5 to S8 have body diodes D5 to D8, respectively, similar to the transistors S1 to S4.

[0022] The transistor S5 is provided in a path connecting the voltage line L21A and the node N4, and is configured to connect the node N4 to the voltage line L21A when the transistor S5 is turned on. The drain of the transistor S5 is connected to the voltage line L21A, the gate is supplied with a gate signal GF, and the source is connected to the node N4. The transistor S6 is provided in a path connecting the node N4 and the reference voltage line L22, and is configured to connect the node N4 to the reference voltage line L22 when the transistor S6 is turned on. The drain of the transistor S6 is connected to the node N4, the gate is supplied with a gate signal GE, and the source is connected to the reference voltage line L22. The node N4 is a connection point between the source of the transistor S5 and the drain of the transistor S6.

[0023] The transistor S7 is provided in a path connecting the voltage line L21A and the node N5, and is configured to connect the node N5 to the voltage line L21A when the transistor S7 is turned on. The drain of the transistor S7 is connected to the voltage line L21A, the gate is supplied with a gate signal GE, and the source is connected to the node N5. The transistor S8 is provided in a path connecting the node N5 and the reference voltage line L22, and is configured to connect the node N5 to the reference voltage line L22 when the transistor S8 is turned on. The drain of the transistor S8 is connected to the node N5, the gate is supplied with a gate signal GF, and the source is connected to the reference voltage line L22. The node N5 is a connection point between the source of the transistor S7 and the drain of the transistor S8.

[0024] The smoothing circuit 15 is configured to smooth the voltage rectified by the rectifier circuit 14. The smoothing circuit 15 has a choke inductor 16 and a capacitor 17. One end of the choke inductor 16 is connected to the voltage line L21A, and the other end is connected to the voltage line L21B. One end of the capacitor 17 is connected to the voltage line L21B, and the other end is connected to the reference voltage line L22. Note that in this example, the choke inductor 16 is provided on the voltage lines L21A and L21B, but this is not limiting, and instead, for example, the choke inductor 16 may be provided on the reference voltage line L22.

[0025] The voltage sensor 18 is configured to detect the voltage on the voltage line L21B. One end of the voltage sensor 18 is connected to the voltage line L21B, and the other end is connected to the reference voltage line L22. The voltage on the voltage line L21B relative to the voltage on the reference voltage line L22 is a voltage VL. The voltage sensor 18 detects this voltage VL, and supplies a detection voltage VL2 corresponding to this voltage VL to the control circuit 40.

[0026] The auxiliary power supply circuit 20 is configured to generate various power supply voltages used within the power conversion device 10 based on the voltages VH and VL, and to generate a detection voltage VH2 proportional to the voltage VH.

[0027] 2 shows an example of the configuration of the auxiliary power supply circuit 20. The auxiliary power supply circuit 20 has a switching element 21, a switching control circuit 22, a transformer 23, a rectifier circuit 24, a smoothing circuit 25, a rectifier circuit 26, a smoothing circuit 27, a regulator 28, and a peak hold circuit 29.

[0028] One end of the switching element 21 is connected to a winding 23A (described later) of a transformer 23, and the other end is connected to a terminal T12. The switching control circuit 22 is configured to control the operation of the switching element 21.

[0029] The transformer 23 has windings 23A, 23B, 23C, and 23D. The windings 23A and 23B are primary windings, and the windings 23C and 23D are secondary windings. One end of the winding 23A is connected to a terminal T11, and the other end is connected to one end of the switching element 21. Both ends of the winding 23B are connected to a rectifier circuit 24. One end of the winding 23B is connected to a terminal T12. Both ends of the winding 23C are connected to a rectifier circuit 26. Both ends of the winding 23D are connected to a peak hold circuit 29. One end of the winding 23C and one end of the winding 23D are connected to a terminal T22.

[0030] The rectifier circuit 24 is configured to rectify the AC voltage output from the winding 23B of the transformer 23. The auxiliary power supply circuit 20 transmits a pulse voltage generated by the switching operation of the switching element 21 from the winding 23A to the winding 23B. The winding 23B and the rectifier circuit 24 transmit power in a flyback manner. The smoothing circuit 25 is configured to smooth the voltage rectified by the rectifier circuit 24 and output the smoothed DC voltage as a power supply voltage VP. As shown in FIG. 1, the auxiliary power supply circuit 20 supplies this power supply voltage VP to the drive circuit 32.

[0031] Rectifier circuit 26 is configured to rectify the AC voltage output from winding 23C of transformer 23. Auxiliary power supply circuit 20 transmits a pulse voltage generated by switching element 21 performing a switching operation from winding 23A to winding 23C. Winding 23C and rectifier circuit 26 transmit power in a flyback manner. Smoothing circuit 27 is configured to smooth the voltage rectified by rectifier circuit 26 and output the smoothed DC voltage as voltage V1.

[0032] The regulator 28 is configured to generate a power supply voltage VDD based on one of the voltages V1 and VL. Specifically, when the voltage V1 is lower than a desired voltage, the regulator 28 generates the power supply voltage VDD based on the voltage VL, and when the voltage V1 is the desired voltage, the regulator 28 generates the power supply voltage VDD based on the voltage V1. The auxiliary power supply circuit 20 supplies the power supply voltage VDD to the control circuit 40, as shown in FIG. 1.

[0033] The peak hold circuit 29 is configured to perform a peak hold operation based on the AC voltage output from the winding 23D of the transformer 23, thereby generating a detection voltage VH2 corresponding to the peak value of the AC voltage. The auxiliary power supply circuit 20 transmits a pulse voltage generated by the switching operation of the switching element 21 from the winding 23A to the winding 23D. The winding 23D and the peak hold circuit 29 transmit power in a forward manner. That is, the detection voltage VH2 generated by the peak hold circuit 29 is a voltage proportional to the voltage VH. The auxiliary power supply circuit 20 supplies the detection voltage VH2 to the control circuit 40, as shown in FIG. 1.

[0034] The drive circuit 32 is configured to operate based on a power supply voltage VP supplied from the auxiliary power supply circuit 20, and to generate gate signals GA to GD based on gate signals GA1 to GD1 supplied from the control circuit 40, respectively.

[0035] The drive circuit 34 is configured to operate using the voltage VL as a power supply voltage, and to generate the gate signals GE and GF based on the gate signals GE1 and GF1 supplied from the control circuit 40. Note that in this example, the drive circuit 34 is configured to operate using the voltage VL as a power supply voltage, but is not limited to this, and may operate based on the power supply voltage VDD generated by the auxiliary power supply circuit 20.

[0036] The control circuit 40 is configured to control the operation of the power conversion device 10 by controlling the operation of the switching circuit 12 and the rectifier circuit 14 based on the detection voltage VH2 supplied from the auxiliary power circuit 20, the detection voltage VL2 supplied from the voltage sensor 18, and the control data CTL supplied from a system control unit (not shown). Specifically, the control circuit 40 generates gate signals GA1 to GF1 based on the detection voltages VH2 and VL2, and controls the operation of the power conversion device 10 by performing PWM (Pulse Width Modulation) control using the gate signals GA1 to GF1. The control circuit 40 operates based on the power supply voltage VDD supplied from the auxiliary power circuit 20. The control circuit 40 is configured using, for example, a microcontroller. The control circuit 40 performs AD (Analog to Digital) conversion on the supplied detection voltages VH2 and VL2, and performs processing based on the AD-converted digital value. Hereinafter, the detection voltages VH2 and VL2 are appropriately used to represent the AD-converted digital value.

[0037] The terminals T21 and T22 are configured to supply the voltage generated by the power conversion device 10 to the low-voltage battery BL. In the power conversion device 10, the terminal T21 is connected to the voltage line L21B, and the terminal T22 is connected to the reference voltage line L22. In addition, the terminal T21 is connected to the positive terminal of the low-voltage battery BL, and the terminal T22 is connected to the negative terminal of the low-voltage battery BL.

[0038] The low-voltage battery BL is configured to store the power supplied from the power conversion device 10.

[0039] With this configuration, the power conversion system 1 performs a power conversion operation of converting the power supplied from the high-voltage battery BH and supplying the converted power to the low-voltage battery BL.

[0040] The power conversion system 1 also has a function of performing a so-called precharge operation, which charges the capacitor 9 during a period before starting such a power conversion operation. During this precharge operation, the switches SW1 and SW2 are in an off state, and the control circuit 40 controls the operation of the switching circuit 12 and the rectifier circuit 14, so that the power conversion system 1 supplies power from the low-voltage battery BL to the capacitor 9. This makes it possible for the power conversion device 10 to suppress an inrush current flowing from the high-voltage battery BH to the capacitor 9 when the switches SW1 and SW2 are turned on to perform a power conversion operation.

[0041] 3 shows an example of the configuration of the control circuit 40. The control circuit 40 has a precharge control unit 50, a power conversion control unit 42, and gate signal generation units 43 and 44.

[0042] The precharge control unit 50 is configured to generate duty ratios DP1, DP2 of the switching operation in the switching circuit 12 and duty ratios DS1, DS2 of the switching operation in the rectifier circuit 14 based on a detection voltage VL2 corresponding to the voltage VL. The precharge control unit 50 also has a function of generating a mode signal MODE indicating which of the duty ratios DP1, DS1 and the duty ratios DP2, DS2 should be used based on a detection voltage VH2 corresponding to the voltage VH. The precharge control unit 50 has duty ratio generation units 51 to 54, a threshold generation unit 55, and a comparison unit 56. The precharge control unit 50 performs processing based on the voltage VL estimated based on the detection voltage VL2 and the voltage VH estimated based on the detection voltage VH2.

[0043] The duty ratio generating unit 51 is configured to generate a duty ratio DP1 in the switching circuit 12 based on a detection voltage VL2 corresponding to the voltage VL during the precharge period P1 and the voltage maintenance period P2. Specifically, the duty ratio generating unit 51 generates the duty ratio DP1 in the precharge period P1 such that the duty ratio DP1 decreases as the voltage VL increases. The duty ratio generating unit 51 generates the duty ratio DP1 in the precharge period P1 such that the duty ratio DP1 gradually increases. Moreover, the duty ratio generating unit 51 generates the duty ratio DP1 in the voltage maintenance period P2 such that the duty ratio DP1 decreases as the voltage VL increases.

[0044] The duty ratio generating unit 52 is configured to generate a duty ratio DP2 in the switching circuit 12 based on a detection voltage VL2 corresponding to the voltage VL and a target voltage command value VHtarget of the voltage VH included in the control data CTL during the voltage maintenance period P2. The duty ratio DP2 is smaller than the duty ratio DP1 during the voltage maintenance period P2. The duty ratio generating unit 52 generates the duty ratio DP2 such that the duty ratio DP2 decreases as the voltage VL increases during the voltage maintenance period P2. The duty ratio generating unit 52 also generates the duty ratio DP2 such that the duty ratio DP2 increases as the target voltage command value VHtarget increases during the voltage maintenance period P2. The duty ratio generating unit 52 also maintains the duty ratio DP2 at 0 (zero) during the pre-charge period P1.

[0045] The duty ratio generating unit 53 is configured to generate a duty ratio DS1 in the rectifier circuit 14 based on a detection voltage VL2 corresponding to the voltage VL during the precharge period P1 and the voltage maintenance period P2. The duty ratio DS1 is greater than the duty ratio DP1 during the precharge period P1 and the voltage maintenance period P2. The duty ratio generating unit 53 generates the duty ratio DS1 during the precharge period P1 such that the duty ratio DS1 decreases as the voltage VL increases. The duty ratio generating unit 53 generates the duty ratio DS1 during the precharge period P1 such that the duty ratio DS1 gradually increases. The duty ratio generating unit 53 also generates the duty ratio DS1 during the voltage maintenance period P2 such that the duty ratio DS1 decreases as the voltage VL increases.

[0046] The duty ratio generating unit 54 is configured to generate a duty ratio DS2 in the rectifier circuit 14 based on a detection voltage VL2 corresponding to the voltage VL and a target voltage command value VHtarget of the voltage VH included in the control data CTL during the voltage maintenance period P2. The duty ratio DS2 is smaller than the duty ratio DS1 during the voltage maintenance period P2 and is larger than the duty ratio DP2 during the voltage maintenance period P2. The duty ratio generating unit 54 generates the duty ratio DS2 during the voltage maintenance period P2 such that the duty ratio DS2 decreases as the voltage VL increases. The duty ratio generating unit 54 also generates the duty ratio DS2 during the voltage maintenance period P2 such that the duty ratio DS2 increases as the target voltage command value VHtarget increases. The duty ratio generating unit 54 also maintains the duty ratio DS2 at 0 (zero) during the pre-charge period P1.

[0047] The threshold generator 55 is configured to generate thresholds THtop and THbot based on a target voltage command value VHtarget of the voltage VH included in the control data CTL during the precharge period P1 and the voltage maintenance period P2. The threshold THtop is an upper threshold value of the voltage VH, and the threshold THbot is a lower threshold value of the voltage VH.

[0048] FIG. 4 shows an example of the thresholds THtop and THbot. In this example, the threshold generator 55 linearly increases the threshold THtop as time passes after timing t1 when the precharge period P1 starts, and stops the change of the threshold THtop after timing t3. The value of the threshold THtop after timing t3 is the target voltage command value VHtarget. In this example, the value of the threshold THtop is set to the same value as the target voltage command value VHtarget after timing t3, but is not limited to this, and may be, for example, a value (VHtarget+ΔV) obtained by adding a value ΔV to the target voltage command value VHtarget. Here, ΔV is an arbitrary value according to the target voltage command value VHtarget. In addition, the threshold generator 55 linearly increases the threshold THbot as time passes after timing t2 after timing t1, and stops the change of the threshold THbot after timing t4 after timing t3.

[0049] As described later, the control circuit 40 controls the operation of the power conversion device 10 during the precharge period P1 and the voltage maintenance period P2 so that the voltage VH is within a voltage range between the threshold value THbot and the threshold value THtop. During the precharge period P1, the voltage VH rises toward the target voltage command value VHtarget, and in this example, the voltage VH reaches the target voltage command value VHtarget at timing t5. During the voltage maintenance period P2, the voltage VH is maintained near the target voltage command value VHtarget. After the voltage maintenance period P2, the switches SW1 and SW2 are turned on, thereby connecting the high-voltage battery BH to the capacitor 9. This starts a period during which the power conversion operation is performed (power conversion period).

[0050] The comparator 56 (FIG. 3) is configured to generate the mode signal MODE by comparing the voltage VH with the thresholds THtop and THbot based on a detection voltage VH2 corresponding to the voltage VH during the precharge period P1 and the voltage maintenance period P2.

[0051] 5 shows an example of a characteristic of the comparison operation in the comparison section 56. The comparison characteristic in the comparison section 56 shows a hysteresis characteristic in which the difference between the threshold value THtop and the threshold value THbot is the hysteresis amount HYS.

[0052] When the voltage VH is lower than the threshold THbot, the comparator 56 sets the mode signal MODE to a high level. Then, when the voltage VH gradually increases and meets certain conditions including the voltage VH reaching the threshold THtop, the comparator 56 changes the mode signal MODE from a high level to a low level. In this example, when the voltage VH exceeds the threshold THtop five consecutive times, the comparator 56 changes the mode signal MODE from a high level to a low level.

[0053] On the other hand, when the voltage VH is higher than the threshold THtop, the comparator 56 sets the mode signal MODE to a low level. Then, when the voltage VH gradually decreases and meets certain conditions including the voltage VH reaching the threshold THbot, the comparator 56 changes the mode signal MODE from a low level to a high level. In this example, when the voltage VH falls below the threshold THbot five consecutive times, the comparator 56 changes the mode signal MODE from a low level to a high level.

[0054] FIG. 6 shows an example of an operation of the comparison unit 56. For example, at a timing t11, the mode signal MODE changes from a low level to a high level. As described later, when the mode signal MODE becomes a high level, the control circuit 40 generates the gate signals GA1 to GF1 based on the duty ratios DP1 and DS1. The power conversion device 10 performs a switching operation based on the gate signals GA to GF corresponding to the gate signals GA1 to GF1, and supplies the power of the low-voltage battery BL to the capacitor 9. This causes the voltage VH to increase. Then, at a timing t12 when the voltage VH reaches the threshold THtop and exceeds the threshold THtop five times in succession, the comparison unit 56 changes the mode signal MODE from a high level to a low level. When the mode signal MODE becomes a low level, the control circuit 40 generates the gate signals GA1 to GF1 based on the duty ratios DP2 and DS2. The power conversion device 10 performs a switching operation based on the gate signals GA to GF corresponding to the gate signals GA1 to GF1. This causes the voltage VH to decrease. Then, at a timing t13 when the voltage VH reaches the threshold value THbot and falls below the threshold value THbot five times in succession, the comparator 56 changes the mode signal MODE from low level to high level. The subsequent operations are similar.

[0055] In this manner, the comparator 56 generates the mode signal MODE by comparing the voltage VH with the threshold values ​​THtop, THbot based on the detection voltage VH2 during the precharge period P1 and the voltage maintenance period P2.

[0056] The power conversion control unit 42 (FIG. 3) is configured to generate a duty ratio DP3 of the switching operation in the switching circuit 12 and a duty ratio DS3 of the switching operation in the rectifier circuit 14 during the power conversion period based on the detection voltages VH2, VL2 and control data CTL supplied from a system control unit (not shown).

[0057] The gate signal generating unit 43 is configured to generate gate signals GA1 to GD1 based on the duty ratios DP1 and DP2 generated by the precharge control unit 50, the duty ratio DP3 generated by the power conversion control unit 42, and the mode signal MODE generated by the precharge control unit 50. Specifically, in the precharge period P1 and the voltage maintenance period P2, when the mode signal MODE is at a high level, the gate signal generating unit 43 generates gate signals GC1 and GD1 based on the duty ratio DP1 and maintains the gate signals GA1 and GB1 at a low level. When the mode signal MODE is at a low level, the gate signal generating unit 43 generates gate signals GC1 and GD1 based on the duty ratio DP2 and maintains the gate signals GA1 and GB1 at a low level. In addition, the gate signal generating unit 43 generates the gate signals GA1 to GD1 based on the duty ratio DP3 during the power conversion period.

[0058] The gate signal generating unit 44 is configured to generate gate signals GE1, GF1 based on the duty ratios DS1, DS2 generated by the precharge control unit 50, the duty ratio DS3 generated by the power conversion control unit 42, and the mode signal MODE generated by the precharge control unit 50. Specifically, in the precharge period P1 and the voltage maintenance period P2, when the mode signal MODE is at a high level, the gate signal generating unit 44 generates the gate signals GE1, GF1 based on the duty ratio DS1, and when the mode signal MODE is at a low level, the gate signal generating unit 44 generates the gate signals GE1, GF1 based on the duty ratio DS2. In addition, in the power conversion period, the gate signal generating unit 44 generates the gate signals GE1, GF1 based on the duty ratio DS3.

[0059] Here, the terminals T11 and T12 correspond to a specific example of a "first power terminal" in an embodiment of the present disclosure. The terminal T11 corresponds to a specific example of a "first connection terminal" in an embodiment of the present disclosure. The terminal T12 corresponds to a specific example of a "second connection terminal" in an embodiment of the present disclosure. The switching circuit 12 corresponds to a specific example of a "switching circuit" in an embodiment of the present disclosure. The gate signals GA to GD correspond to a specific example of a "first drive signal" in an embodiment of the present disclosure. The transformer 13 corresponds to a specific example of a "transformer" in an embodiment of the present disclosure. The winding 13A corresponds to a specific example of a "first winding" in an embodiment of the present disclosure. The winding 13B corresponds to a specific example of a "second winding" in an embodiment of the present disclosure. The rectifier circuit 14 corresponds to a specific example of a "rectifier circuit" in an embodiment of the present disclosure. The gate signals GE to GF correspond to a specific example of a "second drive signal" in an embodiment of the present disclosure. The smoothing circuit 15 corresponds to a specific example of a "smoothing circuit" in an embodiment of the present disclosure. The driving circuits 32 and 34 correspond to a specific example of a "driving circuit" in an embodiment of the present disclosure. The driving circuit 32 corresponds to a specific example of a "first driving circuit" in an embodiment of the present disclosure. The driving circuit 34 corresponds to a specific example of a "second driving circuit" in an embodiment of the present disclosure. The control circuit 40 corresponds to a specific example of a "control circuit" in an embodiment of the present disclosure. The threshold value THbot corresponds to a specific example of a "first threshold value" in an embodiment of the present disclosure. The threshold value THtop corresponds to a specific example of a "second threshold value" in an embodiment of the present disclosure. The duty ratio DS1 corresponds to a specific example of a "first duty ratio" in an embodiment of the present disclosure. The duty ratio DS2 corresponds to a specific example of a "second duty ratio" in an embodiment of the present disclosure. The duty ratio DP1 corresponds to a specific example of a "third duty ratio" in an embodiment of the present disclosure. The duty ratio DP2 corresponds to a specific example of a "fourth duty ratio" in an embodiment of the present disclosure. The auxiliary power supply circuit 20 corresponds to a specific example of a "power supply circuit" in an embodiment of the present disclosure. The power supply voltage VP corresponds to a specific example of a "power supply voltage" in an embodiment of the present disclosure.The detection voltage VH2 corresponds to a specific example of a "detection voltage" in an embodiment of the present disclosure. The high-voltage battery BH corresponds to a specific example of a "first battery" in an embodiment of the present disclosure. The capacitor 9 corresponds to a specific example of a "capacitor" in an embodiment of the present disclosure. The switch SW1 corresponds to a specific example of a "first switch" in an embodiment of the present disclosure. The switch SW2 corresponds to a specific example of a "second switch" in an embodiment of the present disclosure. The low-voltage battery BL corresponds to a specific example of a "second battery" in an embodiment of the present disclosure.

[0060] [Actions and Actions] Next, the operation and function of the power conversion system 1 of the present embodiment will be described.

[0061] (Overview of overall operation) First, referring to FIG. 1, an overview of the overall operation of the power conversion system 1 will be described. When the power conversion system 1 starts, the switches SW1 and SW2 are in an off state. First, in a precharge period P1 and a voltage maintenance period P2, the control circuit 40 generates gate signals GC1 to GF1 based on a detection voltage VH2 corresponding to the voltage VH, a detection voltage VL2 corresponding to the voltage VL, and control data CTL, and maintains the gate signals GA1 and GB1 at a low level. The power conversion device 10 performs a switching operation based on the gate signals GA to GF corresponding to the gate signals GA1 to GF1, and supplies the power of the low-voltage battery BL to the capacitor 9. As a result, the capacitor 9 is charged, and the voltage VH rises and is maintained near the voltage indicated by the target voltage command value VHtarget. Then, in the power conversion period, the switches SW1 and SW2 are turned on, and the control circuit 40 generates the gate signals GA1 to GF1 based on the detection voltages VH2 and VL2. The power conversion device 10 performs switching operations based on gate signals GA to GF corresponding to gate signals GA1 to GF1, converts the power supplied from the high-voltage battery BH, and supplies the converted power to the low-voltage battery BL.

[0062] (Details of operation) FIG. 7 shows an example of a precharge operation in the power conversion system 1, where (A) shows the waveform of the mode signal MODE, (B) shows the duty ratios DP1 and DS1, (C) shows the duty ratios DP2 and DS2, and (D) shows the waveform of the voltage VH and the thresholds THtop and THbot.

[0063] In this example, the precharge period P1 starts at timing t21. The precharge control unit 50 generates the duty ratios DP1 and DS1 so that the duty ratios DP1 and DS1 gradually increase during this precharge period P1 (FIG. 7(B)). In this example, the precharge control unit 50 generates the duty ratios DP1 and DS1 so that the duty ratio DS1 is 0.5 or less and the duty ratio DP1 is equal to or less than the duty ratio DS1. In addition, the precharge control unit 50 maintains the duty ratios DP2 and DS2 at 0 (zero) (FIG. 7(C)).

[0064] Moreover, the threshold value generating unit 55 of the precharge control unit 50 generates the threshold values ​​THtop, THbot so that the threshold values ​​THtop, THbot gradually increase during the precharge period P1 (FIG. 7(D)). The comparing unit 56 generates the mode signal MODE by comparing the voltage VH with the threshold values ​​THtop, THbot based on the detection voltage VH2 (FIG. 7(A)). The gate signal generating unit 43 generates the gate signals GA1-GD1 based on the duty ratios DP1, DP2 and this mode signal MODE. The gate signal generating unit 44 generates the gate signals GE1-GF1 based on the duty ratios DS1, DS2 and this mode signal MODE.

[0065] FIG. 8 shows an example of the gate signals GA1 to GF1 in the precharge period P1, where (A) shows the waveform of the mode signal MODE, and (B) to (G) show the waveforms of the gate signals GA1 to GF1, respectively.

[0066] When the mode signal MODE is at a high level, the gate signal generating unit 43 generates gate signals GC1 and GD1 including pulses based on a duty ratio DP1 and maintains the gate signals GA1 and GB1 at a low level, and the gate signal generating unit 44 generates gate signals GE1 and GF1 including pulses based on a duty ratio DS1.

[0067] When the mode signal MODE is at a low level, the gate signal generating unit 43 maintains the gate signals GA1 to GD1 at a low level based on the duty ratio DP2. That is, as shown in FIG. 7, since the duty ratio DP2 is 0 (zero), when the mode signal MODE is at a low level, the gate signals GC1 and GD1 are maintained at a low level (FIGS. 8(D) and (E)). The gate signal generating unit 44 maintains the gate signals GE1 and GF1 at a low level based on the duty ratio DS2. That is, as shown in FIG. 7, since the duty ratio DS2 is 0 (zero), when the mode signal MODE is at a low level, the gate signals GE1 and GF1 are maintained at a low level (FIGS. 8(F) and (G)).

[0068] As shown in FIG. 7, at timing t21, the power conversion system 1 starts a precharge operation. At this timing t21, the comparator 56 changes the mode signal MODE from low level to high level (FIG. 7(A)). The gate signal generator 43 generates gate signals GC1, GD1 including pulses based on a duty ratio DP1 (FIG. 7(B)), and the gate signal generator 44 generates gate signals GE1, GF1 including pulses based on a duty ratio DS1 (FIG. 7(B)). The power conversion device 10 performs a switching operation based on gate signals GA-GF corresponding to the gate signals GA1-GF1, and supplies power from the low-voltage battery BL to the capacitor 9. This causes the voltage VH to rise (FIG. 7(D)).

[0069] When the voltage VH reaches the threshold THtop and exceeds the threshold THtop five times in a row at timing t22 (FIG. 7(D)), the comparator 56 changes the mode signal MODE from high to low (FIG. 7(A)). The gate signal generator 43 maintains the gate signals GC1 and GD1 at low levels based on the duty ratio DP2 (FIG. 7(C)), and the gate signal generator 44 maintains the gate signals GE1 and GF1 at low levels based on the duty ratio DS2 (FIG. 7(C)). This causes the power converter 10 to stop switching operation, and the voltage VH drops (FIG. 7(D)).

[0070] When the voltage VH reaches the threshold value THbot and falls below the threshold value THbot five times in a row at timing t23 (FIG. 7(D)), the comparator 56 changes the mode signal MODE from low level to high level (FIG. 7(A)). The gate signal generator 43 generates gate signals GC1, GD1 including pulses based on the duty ratio DP1 (FIG. 7(B)), and the gate signal generator 44 generates gate signals GE1, GF1 including pulses based on the duty ratio DS1 (FIG. 7(B)). The power converter 10 performs switching operation based on the gate signals GA-GF corresponding to the gate signals GA1-GF1, and supplies the power of the low-voltage battery BL to the capacitor 9. This causes the voltage VH to rise (FIG. 7(D)).

[0071] When the voltage VH reaches the threshold value THtop and exceeds the threshold value THtop five times consecutively at timing t24 (FIG. 7(D)), the comparator 56 changes the mode signal MODE from high to low (FIG. 7(A)).

[0072] The power conversion system 1 repeats this operation from timing t22 to t24. The gate signal generating units 43, 44 generate gate signals GC1 to GF1 including pulses during a period when the mode signal MODE is at a high level, and generate gate signals GC1 to GF1 at a low level during a period when the mode signal MODE is at a low level. In this manner, the power conversion system 1 performs intermittent switching operations during the precharge period P1. As a result, the voltage VH is controlled to repeatedly rise and fall in the vicinity of a voltage range between the threshold value THbot and the threshold value THtop. As shown in FIG. 7(D), the threshold values ​​THtop, THbot are each set so as to gradually increase over time during the precharge period P1, so that the voltage VH rises to the threshold values ​​THtop, THbot.

[0073] 9 shows an example of simulated waveforms of the precharge operation during the precharge period P1 when the mode signal MODE is at a high level, where (A) shows the waveforms of the gate signals GE1 and GF1, (B) shows the waveforms of the gate signals GC1 and GD1, (C) shows the waveform of the current (charge current ICHG) flowing into the capacitor 9, (D) shows the waveform of the excitation current IM of the transformer 13, (E) shows the waveform of the current (inductor current IL) flowing from the voltage line L21B to the voltage line L21A in the choke inductor 16, (F) shows the waveform of the voltage (transformer voltage VTR2) at the node N4 with respect to the node N5 in the winding 13B of the transformer 13, and (G) shows the waveform of the voltage VH. In FIG. 9, T indicates the period of the switching operation.

[0074] In the precharge operation, the control circuit 40 generates gate signals GC1 and GD1 based on a duty ratio DP1, and generates gate signals GE1 and GF1 based on a duty ratio DS1. The duty ratio DP1 indicates the pulse width of each of the gate signals GC1 and GD1 when the period T (the time length from timings t41 to t43) is set to "1", and the duty ratio DS1 indicates the pulse width of each of the gate signals GE1 and GF1 when the period T is set to "1". As shown in Figures 9(A) and (B), the control circuit 40 changes the gate signals GC1 and GF1 from a low level to a high level at timing t41. Then, the control circuit 40 changes the gate signal GC1 from high level to low level at the timing when the time corresponding to the duty ratio DP1 (duty ratio DP1 × cycle T) has elapsed from this timing t41, and changes the gate signal GF1 from high level to low level at the timing when the time corresponding to the duty ratio DS1 (duty ratio DS1 × cycle T) has elapsed from this timing t41. Next, the control circuit 40 changes the gate signals GD1 and GE1 from low level to high level at timing t42. Then, the control circuit 40 changes the gate signal GD1 from high level to low level at the timing when the time corresponding to the duty ratio DP1 (duty ratio DP1 × cycle T) has elapsed from this timing t42, and changes the gate signal GE1 from high level to low level at the timing when the time corresponding to the duty ratio DS1 (duty ratio DS1 × cycle T) has elapsed from this timing t42. Although not shown, the control circuit 40 maintains the gate signals GA1 and GB1 at low level. As a result, the charge current ICHG as shown in FIG. 9(C) flows into the capacitor 9, and the voltage VH gradually increases (FIG. 9(G)).

[0075] In the example of Fig. 7, after timing t25, threshold generator 55 sets threshold THtop to a value indicated by target voltage command value VHtarget, and sets threshold THbot to a value corresponding to target voltage command value VHtarget (Fig. 7(D)). Then, at timing t26, voltage VH exceeds threshold THtop, which is target voltage command value VHtarget, five times in a row (Fig. 7(D)). This ends pre-charge period P1 and starts voltage maintenance period P2.

[0076] In the voltage maintenance period P2, the precharge control unit 50 sets the duty ratios DP1, DS1, DP2, and DS2 to values ​​corresponding to the voltage VL (FIGS. 7(B) and (C)). In this example, the precharge control unit 50 sets the duty ratio DP1 to a value slightly lower than the value immediately before timing t26, and sets the duty ratio DS1 to a value slightly lower than the value immediately before timing t26. In addition, the precharge control unit 50 sets the duty ratio DP2 to a value smaller than the duty ratio DP1, and sets the duty ratio DS2 to a value smaller than the duty ratio DS1.

[0077] FIG. 10 shows an example of the gate signals GA1 to GF1 in the voltage maintenance period P2, where (A) shows the waveform of the mode signal MODE, and (B) to (G) show the waveforms of the gate signals GA1 to GF1, respectively.

[0078] When the mode signal MODE is at a high level, the gate signal generating unit 43 generates gate signals GC1 and GD1 including pulses based on a duty ratio DP1 and maintains the gate signals GA1 and GB1 at a low level, and the gate signal generating unit 44 generates gate signals GE1 and GF1 including pulses based on a duty ratio DS1.

[0079] When the mode signal MODE is at a low level, the gate signal generating unit 43 generates gate signals GC1 and GD1 including a pulse based on a duty ratio DP2 and maintains the gate signals GA1 and GB1 at a low level. As shown in FIG. 7, the duty ratio DP2 is lower than the duty ratio DP1, so the gate signal generating unit 43 narrows the pulse width of the gate signals GC1 and GD1 when the mode signal MODE is at a low level compared to the pulse width of the gate signals GC1 and GD1 when the mode signal MODE is at a high level (FIGS. 10(D), (E)). The gate signal generating unit 44 generates gate signals GE1 and GF1 including a pulse based on a duty ratio DS2. As shown in FIG. 7, the duty ratio DS2 is lower than the duty ratio DS1, so the gate signal generating unit 44 narrows the pulse width of the gate signals GE1 and GF1 when the mode signal MODE is at a low level compared to the pulse width of the gate signals GE1 and GF1 when the mode signal MODE is at a high level (FIGS. 10(F), (G)).

[0080] As shown in FIG. 7, when the voltage VH exceeds the threshold value THtop five times in succession at timing t26 (FIG. 7(D)), the comparator 56 changes the mode signal MODE from high level to low level (FIG. 7(A)). The gate signal generator 43 generates gate signals GC1, GD1 including pulses based on a duty ratio DP2 (FIG. 7(C)), and the gate signal generator 44 generates gate signals GE1, GF1 including pulses based on a duty ratio DS2 (FIG. 7(C)). The power converter 10 performs switching operations based on gate signals GA-GF corresponding to these gate signals GA1-GF1. The duty ratios DP2, DS2 are low, and the power transmitted from the secondary side circuit to the primary side circuit is small, so that the voltage VH drops (FIG. 7(D)). That is, during the period from timing t26 to t27, the power transmitted from the secondary side circuit to the primary side circuit is smaller than the power consumption of the circuits (switching circuit 12 and auxiliary power circuit 20) that operate by receiving power supply from terminals T11 and T12. Therefore, voltage VH decreases.

[0081] When the voltage VH reaches the threshold THbot and falls below the threshold THbot five times in a row at timing t27 (FIG. 7(D)), the comparator 56 changes the mode signal MODE from low level to high level (FIG. 7(A)). The gate signal generator 43 generates gate signals GC1, GD1 including pulses based on the duty ratio DP1 (FIG. 7(B)), and the gate signal generator 44 generates gate signals GE1, GF1 including pulses based on the duty ratio DS1 (FIG. 7(B)). The power converter 10 performs switching operation based on the gate signals GA-GF corresponding to the gate signals GA1-GF1, supplies the power of the low-voltage battery BL to the capacitor 9, and the voltage VH rises (FIG. 7(D)). That is, during the period from timing t27 to t28, the power transmitted from the secondary side circuit to the primary side circuit is greater than the power consumption of the circuit that operates by receiving power supply from the terminals T11, T12. Therefore, the voltage VH rises.

[0082] When the voltage VH reaches the threshold value THtop and exceeds the threshold value THtop five times consecutively at timing t28 (FIG. 7(D)), the comparator 56 changes the mode signal MODE from high to low (FIG. 7(A)).

[0083] The power conversion system 1 repeats the operation from timing t26 to t28. The control circuit 40 generates gate signals GC1 to GF1 including pulses with a wide pulse width during a period when the mode signal MODE is at a high level. As a result, the power transmitted from the secondary circuit to the primary circuit becomes larger than the power consumption of the circuit that operates by receiving power from the terminals T11 and T12, so the voltage VH rises. The control circuit 40 then generates gate signals GC1 to GF1 including pulses with a narrow pulse width during a period when the mode signal MODE is at a low level. As a result, the power transmitted from the secondary circuit to the primary circuit becomes smaller than the power consumption of the circuit that operates by receiving power from the terminals T11 and T12, so the voltage VH falls. As a result, the voltage VH is controlled to repeatedly rise and fall in the vicinity of a voltage range between the threshold value THbot and the threshold value THtop. Since thresholds THtop and THbot are set to values ​​corresponding to target voltage command value VHtarget in voltage maintenance period P2, voltage VH is maintained near the voltage indicated by target voltage command value VHtarget.

[0084] Next, the operation during the voltage maintenance period P2 will be described in more detail.

[0085] FIG. 11 shows an example of an operation of the power conversion system 1 in the voltage maintenance period P2, in which (A) shows the waveform of the voltage VH, (B) shows the waveform of the voltage VH (estimated voltage VHe) estimated based on the detected voltage VH2, (C) shows the waveform of the mode signal MODE, and (D) shows the duty ratio DP of the switching circuit 12 and the duty ratio DS of the rectifier circuit 14. For convenience of explanation, thresholds THtop and THbot are also illustrated in FIG. 11(A) and (B). The duty ratio DP includes a duty ratio DP1 when the mode signal MODE is at a high level and a duty ratio DP2 when the mode signal MODE is at a low level. The duty ratio DS includes a duty ratio DS1 when the mode signal MODE is at a high level and a duty ratio DS2 when the mode signal MODE is at a low level.

[0086] In this example, before timing t51, the mode signal MODE is at a high level and the voltage VH is rising (FIGS. 11A and 11C). The auxiliary power supply circuit 20 generates a detection voltage VH2 based on this voltage VH, so the waveform of the estimated voltage VHe lags behind the waveform of the voltage VH by the delay time (time td) of the auxiliary power supply circuit 20 (FIGS. 11A and 11B). For example, if the voltage VH exceeds the threshold value THtop at timing t51, the estimated voltage VHe exceeds the threshold value THtop at timing t52, which is delayed by time td from timing t51.

[0087] For example, when the estimated voltage VHe exceeds the threshold value THtop five times in succession at timing t53 (FIG. 11(B)), the control circuit 40 changes the mode signal MODE from high level to low level at this timing t53 (FIG. 11(C)). In response to this, the control circuit 40 changes the duty ratio DP from the duty ratio DP1 to the duty ratio DP2 lower than this duty ratio DP1, and changes the duty ratio DS from the duty ratio DS1 to the duty ratio DS2 lower than this duty ratio DS1. Since both the duty ratios DP and DS become lower and the power transmitted from the secondary side circuit to the primary side circuit becomes smaller, the voltage VH starts to decrease at this timing t53 (FIG. 11(A)). Then, at timing t54, which is delayed by the time td from the timing t53, the estimated voltage VHe starts to decrease. Then, the voltage VH and the estimated voltage VHe gradually decrease.

[0088] After that, at time t55, when the estimated voltage VHe falls below the threshold value THbot five times in a row (FIG. 11(B)), the control circuit 40 changes the mode signal MODE from low level to high level at this time t55 (FIG. 11(C)). In response to this, the control circuit 40 changes the duty ratio DP from the duty ratio DP2 to the duty ratio DP1, and changes the duty ratio DS from the duty ratio DS2 to the duty ratio DS1. Since both the duty ratios DP and DS become high and the power transmitted from the secondary side circuit to the primary side circuit increases, the voltage VH starts to rise at this time t55 (FIG. 11(A)). Then, at time t56, which is delayed by a time td from the time t55, the estimated voltage VHe starts to rise.

[0089] In this manner, in the power conversion system 1, during the voltage maintenance period P2, the switching circuit 12 and the rectifier circuit 14 continue to perform the switching operation even when the mode signal MODE is set to a low level as shown in Fig. 10. As a result, in the power conversion system 1, it is possible to reduce the ripple of the voltage VH, as will be described below in comparison with a reference example.

[0090] (Reference example) Next, a power conversion system according to a reference example will be described. In this reference example, the switching operation during the voltage maintenance period P2 is different from that of the present embodiment. That is, in this embodiment, as shown in Fig. 10, the switching circuit 12 and the rectifier circuit 14 continue to perform the switching operation during the period when the mode signal MODE is at a low level, but in this reference example, the switching circuit 12 and the rectifier circuit 14 stop the switching operation during the period when the mode signal MODE is at a low level, as in the case of the precharge period P1 (Fig. 8).

[0091] Fig. 12 shows an example of operation of the power conversion system according to this reference example, where (A) shows the waveform of the voltage VH, (B) shows the waveform of the voltage VH estimated based on the detected voltage VH2 (estimated voltage VHe), (C) shows the waveform of the mode signal MODE, and (D) shows the duty ratio DP of the switching circuit 12 and the duty ratio DS of the rectifier circuit 14. Fig. 12 corresponds to Fig. 11 according to the present embodiment.

[0092] In this example, before timing t61, the mode signal MODE is at a high level and the voltage VH is rising (FIGS. 12(A) and (C)). The auxiliary power supply circuit 20 generates a detection voltage VH2 based on this voltage VH, so the waveform of the estimated voltage VHe lags behind the waveform of the voltage VH by the delay time (time td) of the auxiliary power supply circuit 20 (FIGS. 12(A) and (B)). For example, if the voltage VH exceeds the threshold value THtop at timing t61, then the estimated voltage VHe exceeds the threshold value THtop at timing t52, which is delayed by time td from timing t61.

[0093] For example, when the estimated voltage VHe exceeds the threshold THtop five times in succession at timing t63 (FIG. 12(B)), the control circuit 40 changes the mode signal MODE from high level to low level at this timing t63 (FIG. 12(C)). In response to this, the control circuit 40 changes the duty ratio DP from the duty ratio DP1 to 0 (zero) and changes the duty ratio DS from the duty ratio DS1 to 0 (zero). As a result, the switching circuit 12 and the rectifier circuit 14 stop switching operations, so that the power transmission from the secondary side circuit to the primary side circuit is stopped, and at this timing t63, the voltage VH starts to decrease (FIG. 12(A)). The gradient at which the voltage VH decreases is larger than that in the case of this embodiment (FIG. 11). That is, in this reference example, the power transmission from the secondary side circuit to the primary side circuit is stopped, so that the voltage VH decreases more rapidly than that in the case of this embodiment (FIG. 11). Then, at timing t64, which is delayed by a time td from timing t63, estimated voltage VHe begins to decrease.

[0094] Thereafter, at time t65, when the estimated voltage VHe falls below the threshold value THbot five consecutive times (FIG. 12(B)), the control circuit 40 changes the mode signal MODE from low level to high level at this time t65 (FIG. 12(C)). In response to this, the control circuit 40 changes the duty ratio DP from 0 (zero) to duty ratio DP1, and changes the duty ratio DS from 0 (zero) to duty ratio DS1. This causes the switching circuit 12 and the rectifier circuit 14 to start switching operations, and at this time t65, the voltage VH begins to rise (FIG. 12(A)).

[0095] In this manner, at timing t65, the switching circuit 12 starts a switching operation. The drive circuit 32 drives the switching circuit 12. The auxiliary power circuit 20 supplies the power supply voltage VP to the drive circuit 32. Therefore, when the switching circuit 12 starts a switching operation at timing t65, the load on the auxiliary power supply circuit 20 becomes heavy at this timing t65. As a result, at this timing t65, for example, the power supply voltages VP and VDD drop transiently, and the detection voltage VH2 also drops transiently. Due to this transient drop in the detection voltage VH2, the estimated voltage VHe also drops transiently (FIG. 12(B)). Then, in this example, at timing t66, the estimated voltage VEe starts to rise.

[0096] In this way, in the power conversion system according to the reference example, the switching circuit 12 and the rectifier circuit 14 stop switching operations during the period when the mode signal MODE is at a low level. Therefore, the gradient when the voltage VH drops is large. Therefore, for example, the voltage width ΔV1 when the voltage VH falls below the threshold THbot is large (FIG. 12(A)), so the ripple of the voltage VH becomes larger than the ripple assumed by the thresholds THtop and THbot. In addition, at timing t65, the estimated voltage VHe drops transiently, so the voltage width ΔV2 up to the threshold THtop where the estimated voltage VHe should rise becomes large (FIG. 12(B)). In this case, the time when the mode signal MODE is at a high level becomes longer, so the fluctuation width of the voltage VH becomes larger. As a result, the ripple of the voltage VH becomes larger than the ripple assumed by the thresholds THtop and THbot.

[0097] On the other hand, in the power conversion system 1 according to the present embodiment, as shown in FIG. 10, the switching circuit 12 and the rectifier circuit 14 continue to perform switching operations during the period when the mode signal MODE is at a low level and during the period when the mode signal MODE is at a high level. The control circuit 40 sets the duty ratio DP to a duty ratio DP2 lower than the duty ratio DP1 and sets the duty ratio DS to a duty ratio DS2 lower than the duty ratio DS1 during the period when the mode signal MODE is at a low level. As a result, the power conversion system 1 does not stop the power transmission from the secondary side circuit to the primary side circuit, so that the gradient when the voltage VH drops can be reduced. As a result, in the power conversion system 1, for example, the voltage width ΔV1 (FIG. 11(A)) when the voltage VH falls below the threshold value THbot can be reduced, and the ripple of the voltage VH can be reduced.

[0098] In the power conversion system 1, the switching circuit 12 and the rectifier circuit 14 continue to perform switching operations while the mode signal MODE is at a low level and while the mode signal MODE is at a high level. At that time, the switching frequency does not change, so the load on the auxiliary power supply circuit 20 does not change. Therefore, unlike the reference example, the estimated voltage VHe does not drop transiently. As a result, the power conversion system 1 can suppress the fluctuation range of the voltage VH, and therefore the ripple of the voltage VH can be reduced.

[0099] In this manner, the power conversion system 1 includes a first power terminal (terminals T11, T12), a switching circuit 12 having a switching element connected to the first power terminal (terminals T11, T12) and capable of performing a switching operation based on a first drive signal (gate signals GA to GD), a transformer 13 having a first winding (winding 13A) and a second winding (winding 13B) connected to the switching circuit 12, a rectifier circuit 14 having a switching element connected to the second winding (winding 13B) and capable of performing a switching operation based on a second drive signal (gate signals GE, GF), a smoothing circuit 15 connected to the rectifier circuit 14, a second power terminal (terminals T21, T22) connected to the smoothing circuit 15, a control circuit 40 capable of controlling the operation of the switching circuit 12 and the rectifier circuit 14, and drive circuits 32, 34 capable of generating a first drive signal and a second drive signal based on an instruction from the control circuit 40. The control circuit 40 is capable of alternately performing a first operation and a second operation before supplying power from the first power terminal (terminals T11, T12) to the second power terminal (terminals T21, T22). In the first operation, the control circuit 40 is capable of controlling the operation of the switching circuit 12 and the rectifier circuit 14 so that a first power is supplied from the second power terminal (terminals T21, T22) to the first power terminal (terminals T11, T12) to increase the voltage VH at the first power terminal (terminals T11, T12). In the second operation, the control circuit 40 is capable of controlling the operation of the switching circuit 12 and the rectifier circuit 14 so that a second power smaller than the first power is supplied from the second power terminal (terminals T21, T22) to the first power terminal (terminals T11, T12) to decrease the voltage VH at the first power terminal (terminals T11, T12). In this way, for example, in the power conversion system 1, a first power can be supplied from the terminals T21, T22 to the terminals T11, T12 during a period in which the mode signal MODE is at a high level, and a second power smaller than the first power can be supplied from the terminals T21, T22 to the terminals T11, T12 during a period in which the mode signal MODE is at a low level. This allows the power conversion system 1 to reduce the ripple of the voltage VH during the voltage maintenance period P2.

[0100] In the power conversion system 1, the control circuit 40 can start the first operation when a predetermined condition including that the voltage value of the voltage VH at the first power terminal (terminals T11, T12) is smaller than a first threshold (threshold THbot) is satisfied, and can start the second operation when a predetermined condition including that the voltage value of the voltage VH at the first power terminal (terminals T11, T12) is larger than a second threshold (threshold THtop) is satisfied. Specifically, the control circuit 40 starts the first operation when the voltage VH falls below the threshold THbot five consecutive times, and starts the second operation when the voltage VH exceeds the threshold THtop five consecutive times. As a result, the voltage VH is controlled to repeatedly rise and fall in the vicinity of the voltage range between the threshold THbot and the threshold THtop. As a result, in the power conversion system 1, the voltage VH can be maintained and the ripple of the voltage VH can be reduced.

[0101] In the power conversion system 1, the control circuit 40 can set the duty ratio DS of the second drive signal (gate signals GE, GF) to a first duty ratio (duty ratio DS1) in the first operation, and can set the duty ratio DS of the second drive signal (gate signals GE, GF) to a second duty ratio (duty ratio DS2) smaller than the first duty ratio (duty ratio DS1) in the second operation. In addition, the control circuit 40 can set the duty ratio DP of the first drive signal (gate signals GC, GD) to a third duty ratio (duty ratio DP1) smaller than the first duty ratio (duty ratio DS1) in the first operation, and can set the duty ratio of the first drive signal (gate signals GC, GD) to a fourth duty ratio (duty ratio DP2) smaller than the second duty ratio (duty ratio DS2) and the third duty ratio (duty ratio DP1) in the second operation. As a result, in the power conversion system 1, in the first operation, a first power is supplied from the second power terminal (terminals T21, T22) to the first power terminal (terminals T11, T12), and in the second operation, a second power smaller than the first power is supplied from the second power terminal (terminals T21, T22) to the first power terminal (terminals T11, T12). As a result, in the power conversion system 1, the ripple of the voltage VH can be reduced in the voltage maintenance period P2.

[0102] [effect] As described above, this embodiment includes a first power terminal, a switching circuit having a switching element connected to the first power terminal and capable of performing a switching operation based on a first drive signal, a transformer having a first winding and a second winding connected to the switching circuit, a rectifier circuit having a switching element connected to the second winding and capable of performing a switching operation based on a second drive signal, a smoothing circuit connected to the rectifier circuit, a second power terminal connected to the smoothing circuit, a control circuit capable of controlling the operation of the switching circuit and the rectifier circuit, and a drive circuit capable of generating a first drive signal and a second drive signal based on instructions from the control circuit. The control circuit is capable of alternately performing a first operation and a second operation before supplying power from the first power terminal to the second power terminal, and is capable of controlling the operation of the switching circuit and the rectifier circuit in the first operation so that a first power is supplied from the second power terminal to the first power terminal to increase the voltage at the first power terminal, and is capable of controlling the operation of the switching circuit and the rectifier circuit in the second operation so that a second power smaller than the first power is supplied from the second power terminal to the first power terminal to decrease the voltage at the first power terminal, thereby reducing the ripple in the voltage at the first power terminal.

[0103] In this embodiment, the control circuit is capable of starting a first operation when predetermined conditions are satisfied, including the voltage value of the voltage at the first power terminal being smaller than a first threshold value, and is capable of starting a second operation when predetermined conditions are satisfied, including the voltage value of the voltage at the first power terminal being greater than a second threshold value, so that the voltage at the first power terminal can be maintained while reducing the ripple of this voltage.

[0104] In this embodiment, the control circuit can set the duty ratio of the second drive signal to a first duty ratio in the first operation, and can set the duty ratio of the second drive signal to a second duty ratio smaller than the first duty ratio in the second operation. Also, the control circuit can set the duty ratio of the first drive signal to a third duty ratio smaller than the first duty ratio in the first operation, and can set the duty ratio of the first drive signal to a fourth duty ratio smaller than the second duty ratio and the third duty ratio in the second operation, so that the ripple of the voltage at the first power terminal can be reduced.

[0105] [Variation 1] In the above embodiment, as shown in Fig. 7, the switching circuit 12 performs the switching operation based on the duty ratios DP1 and DP2 during the precharge period P1 and the voltage maintenance period P2, but the present invention is not limited to this. Instead of this, for example, as shown in Fig. 13, the duty ratios DP1 and DP2 may be maintained at 0 (zero) during the precharge period P1 and the voltage maintenance period P2, and the switching circuit 12 may not perform the switching operation. For example, when the voltage of the high-voltage battery BH is not higher than the voltage obtained by the transformation ratio of the low-voltage battery BL and the transformer 13, the switching circuit 12 may not perform the switching operation in this manner during the precharge period P1 and the voltage maintenance period P2.

[0106] [Variation 2] In the above embodiment, in the voltage maintenance period P2, as shown in Fig. 10, the switching frequency of the gate signals GC1 to GF1 during the period when the mode signal MODE is at a low level is equal to the switching frequency of the gate signals GC1 to GF1 during the period when the mode signal MODE is at a high level, but this is not limited to this. Instead of this, for example, the switching frequency of the gate signals GC1 to GF1 during the period when the mode signal MODE is at a low level may be lower than the switching frequency of the gate signals GC1 to GF1 during the period when the mode signal MODE is at a high level.

[0107] 14 shows an example of the gate signals GA1 to GF1 according to this modification, where (A) shows the waveform of the mode signal MODE, and (B) to (G) show the waveforms of the gate signals GA1 to GF1, respectively. This Fig. 14 corresponds to Fig. 10 according to the above embodiment.

[0108] In this example, the switching frequency of the gate signals GC1 to GF1 during the period when the mode signal MODE is at a low level is set lower than the switching frequency of the gate signals GC1 to GF1 during the period when the mode signal MODE is at a high level. In this example, the pulse width of the gate signals GC1 to GF1 is almost constant. Therefore, the duty ratios DP, DS when the mode signal MODE is at a low level are lower than the duty ratios DP, DS when the mode signal MODE is at a high level. In this case, the transistors S1 to S4 of the switching circuit 12 and the transistors S5 to S8 of the rectifier circuit 14 are turned on less frequently, so that the power transmitted from the secondary side circuit to the primary side circuit can be reduced. As a result, in the power conversion system according to this modification, the gradient at which the voltage VH decreases can be reduced, so that the ripple of the voltage VH can be reduced.

[0109] [Variation 3] In the above embodiment, in the voltage maintenance period P2, as shown in Figures 10 and 11, the duty ratios DP, DS during the period when the mode signal MODE is at a low level are lower than the duty ratios DP, DS during the period when the mode signal MODE is at a high level, but this is not limited to this. Instead, for example, the switching frequency during the period when the mode signal MODE is at a low level may be higher than the switching frequency during the period when the mode signal MODE is at a high level. This modification will be described in detail below.

[0110] 15 shows an example of gate signals GA1 to GF1 according to this modification, where (A) shows the waveform of the mode signal MODE, and (B) to (G) show the waveforms of the gate signals GA1 to GF1, respectively. This Fig. 15 corresponds to Fig. 10 according to the above embodiment.

[0111] In this example, when the mode signal MODE is at a low level, the control circuit 40 according to this modification makes the switching frequency of the gate signals GC1 to GF1 higher than the switching frequency when the mode signal MODE is at a low level. The duty ratios DP, DS when the mode signal MODE is at a low level may be the same as or different from the duty ratios DP, DS when the mode signal MODE is at a high level. In this way, by making the switching frequency higher than the switching frequency during the period when the mode signal MODE is at a low level, it is possible to reduce the transmission power from the secondary side circuit to the primary side circuit. As a result, in the power conversion system according to this modification, the gradient at which the voltage VH decreases can be reduced, and therefore the ripple of the voltage VH can be reduced.

[0112] [Variation 4] In the above embodiment, as shown in Fig. 1, the rectifier circuit 14 is configured using a full-bridge type circuit, but the present invention is not limited to this and various circuits can be applied. For example, a so-called center tap type power conversion system may be used. This modification will be described in detail below.

[0113] 16 illustrates an example of a power conversion system 2 according to this modification. The power conversion system 2 includes a power conversion device 60. The power conversion device 60 includes a transformer 63, a rectifier circuit 64, and a control circuit 70.

[0114] The transformer 63 has windings 63A, 63B, and 63C. The winding 63A is a primary winding, one end of which is connected to a node N1 in the switching circuit 12, and the other end of which is connected to a node N2 in the switching circuit 12. The winding 63B is a secondary winding, one end of which is connected to a node N6 in the rectifier circuit 64, and the other end of which is connected to one end of the winding 63C and the voltage line L21A. The winding 63C is a secondary winding, one end of which is connected to the other end of the winding 63B and the voltage line L21A, and the other end of which is connected to a node N7 in the rectifier circuit 64.

[0115] The rectifier circuit 64 includes transistors S9 and S10. The transistors S9 and S10 are configured using, for example, N-type field effect transistors. The transistors S9 and S10 include body diodes D9 and D10, respectively. The transistor S9 is provided in a path connecting the node N6 and the reference voltage line L22, and is configured to connect the node N6 to the reference voltage line L22 when the transistor S9 is turned on. The drain of the transistor S9 is connected to the node N6, the gate of which is supplied with a gate signal GF, and the source of which is connected to the reference voltage line L22. The transistor S10 is provided in a path connecting the node N7 and the reference voltage line L22, and is configured to connect the node N7 to the reference voltage line L22 when the transistor S10 is turned on. The drain of the transistor S10 is connected to the node N7, the gate of which is supplied with a gate signal GE, and the source of which is connected to the reference voltage line L22.

[0116] The control circuit 70 is configured to control the operation of the power conversion device 60 by controlling the operation of the switching circuit 12 and the rectifier circuit 14 based on the detected voltage VH2 supplied from the auxiliary power circuit 20, the detected voltage VL2 supplied from the voltage sensor 18, and control data CTL supplied from a system control unit (not shown). Specifically, the control circuit 70 generates gate signals GA1-GF1 based on the detected voltages VH2, VL2, and controls the operation of the power conversion device 60 by performing PWM control using the gate signals GA1-GF1.

[0117] Similarly, in the above embodiment, as shown in FIG. 1, the switching circuit 12 is configured using a full-bridge type circuit, but the present invention is not limited to this and various circuits can be applied.

[0118] [Other variations] Also, two or more of these variations may be combined.

[0119] Although the present invention has been described above by way of the embodiments and modifications, the present invention is not limited to these embodiments and can be modified in various ways.

[0120] For example, in the above embodiment, a step-down operation is performed in the power conversion operation, but this is not limiting, and a step-up operation may also be performed.

[0121] The effects described in this specification are merely examples, and the effects of the present disclosure are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present disclosure.

[0122] Furthermore, the present disclosure may take the following aspects.

[0123] (1) A first power terminal; a switching circuit connected to the first power terminal and having a switching element capable of performing a switching operation based on a first drive signal; a transformer having a first winding and a second winding connected to the switching circuit; a rectifier circuit having a switching element connected to the second winding and capable of performing a switching operation based on a second drive signal; a smoothing circuit connected to the rectifier circuit; a second power terminal connected to the smoothing circuit; a control circuit capable of controlling operations of the switching circuit and the rectifier circuit; a drive circuit capable of generating the first drive signal and the second drive signal based on an instruction from the control circuit; Equipped with The control circuit includes: A first operation and a second operation may be alternately performed before supplying power from the first power terminal to the second power terminal; In the first operation, the operation of the switching circuit and the rectifier circuit can be controlled so that a first power is supplied from the second power terminal to the first power terminal to increase a voltage at the first power terminal; In the second operation, the operation of the switching circuit and the rectifier circuit can be controlled so that a second power smaller than the first power is supplied from the second power terminal to the first power terminal, thereby causing a voltage at the first power terminal to drop. Power conversion equipment. (2) The control circuit includes: The first operation can be started when a predetermined condition is satisfied, the predetermined condition including a voltage value of the voltage at the first power terminal being smaller than a first threshold value; The second operation can be started when a predetermined condition is satisfied, including a voltage value of the voltage at the first power terminal being greater than a second threshold value. The power conversion device according to (1) above. (3) The control circuit includes: In the first operation, a duty ratio of the second drive signal can be set to a first duty ratio; In the second operation, a duty ratio of the second drive signal can be set to a second duty ratio that is smaller than the first duty ratio. The power conversion device according to (1) or (2). (4) The control circuit includes: In the first operation, a duty ratio of the first drive signal can be set to a third duty ratio that is smaller than the first duty ratio; In the second operation, a duty ratio of the first drive signal can be set to a fourth duty ratio that is smaller than the second duty ratio and the third duty ratio. The power conversion device according to (3) above. (5) The control circuit includes: In the first operation, a switching frequency of the first drive signal and the second drive signal can be set to a first switching frequency; In the second operation, a switching frequency of the first drive signal and the second drive signal can be set to a second switching frequency lower than the first switching frequency. The power conversion device according to (4) above. (6) The control circuit includes: In the first operation, a switching frequency of the first drive signal and the second drive signal can be set to a first switching frequency; In the second operation, a switching frequency of the first drive signal and the second drive signal can be set to a second switching frequency higher than the first switching frequency. The power conversion device according to (1) or (2). (7) The control circuit includes: In the first operation, a duty ratio of the second drive signal can be set to a first duty ratio; In the second operation, a duty ratio of the second drive signal can be set to a second duty ratio that is smaller than the first duty ratio. The power conversion device according to (6) above. (8) a power supply circuit capable of generating a power supply voltage based on a voltage at the first power terminal and generating a detection voltage corresponding to the voltage at the first power terminal; the control circuit is capable of performing one of the first operation and the second operation based on the detected voltage; The drive circuit includes: a first drive circuit capable of generating the first drive signal and operating based on the power supply voltage; a second drive circuit capable of generating the second drive signal; have The power conversion device according to any one of (1) to (7). (9) a first battery having a first terminal and a second terminal; a capacitor having a first terminal and a second terminal; a first switch provided in a path connecting the first terminal of the first battery and the first terminal of the capacitor; a second switch provided in a path connecting the second terminal of the first battery and the second terminal of the capacitor; A power conversion device; Second battery and Equipped with The power conversion device is a first power terminal having a first connection terminal connected to the first terminal of the capacitor and a second connection terminal connected to the second terminal of the capacitor; a switching circuit connected to the first power terminal and having a switching element capable of performing a switching operation based on a first drive signal; a transformer having a first winding and a second winding connected to the switching circuit; a rectifier circuit having a switching element connected to the second winding and capable of performing a switching operation based on a second drive signal; a smoothing circuit connected to the rectifier circuit; a second power terminal connected to the smoothing circuit and to the second battery; a control circuit capable of controlling operations of the switching circuit and the rectifier circuit; a drive circuit capable of generating the first drive signal and the second drive signal based on an instruction from the control circuit; having The control circuit includes: A first operation and a second operation may be alternately performed before supplying power from the first power terminal to the second power terminal; In the first operation, the operation of the switching circuit and the rectifier circuit can be controlled so that a first power is supplied from the second power terminal to the first power terminal to increase a voltage at the first power terminal; In the second operation, the operation of the switching circuit and the rectifier circuit can be controlled so that a second power smaller than the first power is supplied from the second power terminal to the first power terminal, thereby causing a voltage at the first power terminal to drop. Power conversion systems. [Explanation of symbols]

[0124] 1,2...power conversion system, 9...capacitor, 10,60...power conversion device, 12...switching circuit, 13,63...transformer, 13A,13B,63A to 63C...windings, 14,64...rectifier circuit, 15...smoothing circuit, 16...choke inductor, 17...capacitor, 18...voltage sensor, 20...auxiliary power supply circuit, 21...switching element, 22...switching control circuit, 23...transformer, 23A to 23D...windings, 24...rectifier circuit, 25...smoothing circuit, 26...rectifier circuit, 27...smoothing circuit, 28...regulator, 29...peak hold circuit, 32,34...drive circuit, 40,70...control circuit, 42...power conversion control unit, 43,44...gate signal generation unit, 50...precharge control unit, 51 to 54...duty ratio generation unit, 55...threshold generation unit generation unit, 56...comparison unit, BH...high-voltage battery, BL...low-voltage battery, CTL...control data, DP, DP1 to DP3, DS, DS1 to DS3...duty ratio, D1 to D10...body diodes, GA to GF, GA1 to GF1...gate signals, HYS...hysteresis amount, L11, L21A, L21B...voltage lines, L12, L22...reference voltage lines, MODE...mode signal, N1, N2, N4 to N7...nodes, P1...precharge period, P2...voltage maintenance period, SW1, SW2...switches, S1 to S10...transistors, THtop, THbot...threshold value, T11, T12, T21, T22...terminals, VDD, VP...power supply voltage, VH, VL...voltage, VHe...estimated voltage, VH2, VL2...detected voltage, VHtarget...target voltage command value.

Claims

1. A first power terminal; a switching circuit connected to the first power terminal and having a switching element capable of performing a switching operation based on a first drive signal; a transformer having a first winding and a second winding connected to the switching circuit; a rectifier circuit having a switching element connected to the second winding and capable of performing a switching operation based on a second drive signal; a smoothing circuit connected to the rectifier circuit; a second power terminal connected to the smoothing circuit; a control circuit capable of controlling operations of the switching circuit and the rectifier circuit; a drive circuit capable of generating the first drive signal and the second drive signal based on an instruction from the control circuit; Equipped with The control circuit includes: A first operation and a second operation may be alternately performed before supplying power from the first power terminal to the second power terminal; In the first operation, the operation of the switching circuit and the rectifier circuit can be controlled so that a first power is supplied from the second power terminal to the first power terminal to increase a voltage at the first power terminal; In the second operation, the operation of the switching circuit and the rectifier circuit can be controlled so that a second power smaller than the first power is supplied from the second power terminal to the first power terminal, thereby causing a voltage at the first power terminal to drop. Power conversion equipment.

2. The control circuit includes: The first operation can be started when a predetermined condition is satisfied, the predetermined condition including a voltage value of a voltage at the first power terminal being smaller than a first threshold value; The second operation can be started when a predetermined condition is satisfied, including a voltage value of the voltage at the first power terminal being greater than a second threshold value. The power conversion device according to claim 1 .

3. The control circuit includes: In the first operation, a duty ratio of the second drive signal can be set to a first duty ratio; In the second operation, a duty ratio of the second drive signal can be set to a second duty ratio that is smaller than the first duty ratio. The power conversion device according to claim 1 .

4. The control circuit includes: In the first operation, a duty ratio of the first drive signal can be set to a third duty ratio that is smaller than the first duty ratio; In the second operation, a duty ratio of the first drive signal can be set to a fourth duty ratio that is smaller than the second duty ratio and the third duty ratio. The power conversion device according to claim 3 .

5. The control circuit includes: In the first operation, a switching frequency of the first drive signal and the second drive signal can be set to a first switching frequency; In the second operation, a switching frequency of the first drive signal and the second drive signal can be set to a second switching frequency lower than the first switching frequency. The power conversion device according to claim 4.

6. The control circuit includes: In the first operation, a switching frequency of the first drive signal and the second drive signal can be set to a first switching frequency; In the second operation, a switching frequency of the first drive signal and the second drive signal can be set to a second switching frequency higher than the first switching frequency. The power conversion device according to claim 1 .

7. The control circuit includes: In the first operation, a duty ratio of the second drive signal can be set to a first duty ratio; In the second operation, a duty ratio of the second drive signal can be set to a second duty ratio that is smaller than the first duty ratio. The power converter according to claim 6.

8. a power supply circuit capable of generating a power supply voltage based on a voltage at the first power terminal and generating a detection voltage corresponding to the voltage at the first power terminal; the control circuit is capable of performing one of the first operation and the second operation based on the detected voltage; The drive circuit includes: a first drive circuit capable of generating the first drive signal and operating based on the power supply voltage; a second drive circuit capable of generating the second drive signal; have The power conversion device according to claim 1 .

9. a first battery having a first terminal and a second terminal; a capacitor having a first terminal and a second terminal; a first switch provided in a path connecting the first terminal of the first battery and the first terminal of the capacitor; a second switch provided in a path connecting the second terminal of the first battery and the second terminal of the capacitor; A power conversion device; A second battery; Equipped with The power conversion device is a first power terminal having a first connection terminal connected to the first terminal of the capacitor and a second connection terminal connected to the second terminal of the capacitor; a switching circuit connected to the first power terminal and having a switching element capable of performing a switching operation based on a first drive signal; a transformer having a first winding and a second winding connected to the switching circuit; a rectifier circuit having a switching element connected to the second winding and capable of performing a switching operation based on a second drive signal; a smoothing circuit connected to the rectifier circuit; a second power terminal connected to the smoothing circuit and to the second battery; a control circuit capable of controlling operations of the switching circuit and the rectifier circuit; a drive circuit capable of generating the first drive signal and the second drive signal based on an instruction from the control circuit; having The control circuit includes: A first operation and a second operation may be alternately performed before supplying power from the first power terminal to the second power terminal; In the first operation, the operation of the switching circuit and the rectifier circuit can be controlled so that a first power is supplied from the second power terminal to the first power terminal to increase a voltage at the first power terminal; In the second operation, the operation of the switching circuit and the rectifier circuit can be controlled so that a second power smaller than the first power is supplied from the second power terminal to the first power terminal, thereby causing a voltage at the first power terminal to drop. Power conversion systems.

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