Power converter and power conversion system

Abstract

This power conversion device according to an aspect of the present invention comprises: a first power terminal that has two connecting terminals; a voltage sensor that is able to detect the voltage between the two connecting terminals; a switching circuit that is connected to the first power terminal; a transformer that has a first winding that is connected to the switching circuit, and a second winding; a rectifying circuit that is connected to the second winding; a smoothing circuit that is connected to the rectifying circuit; a second power terminal that is connected to the smoothing circuit; and a control circuit that is able to control the operations of the switching circuit and the rectifying circuit. The control circuit is able to cause the rectifying circuit to operate so as to supply power from the second power terminal toward the first power terminal in a second period before a first period for supplying power from the first power terminal toward the second power terminal, and is able to detect a short circuit between the two connecting terminals by performing a comparison operation for comparing the voltage detected by the voltage sensor and a predetermined threshold voltage within the period of the second period.

Description

Technical Field

[0001] The present invention relates to a power conversion device and a power conversion system for converting power.

Background Art

[0002] Some power conversion devices detect overcurrent. For example, Patent Document 1 discloses a technique of reducing the duty ratio of a switching operation so as to eliminate the overcurrent when an overcurrent occurs.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] By the way, in a power conversion device that converts the power of a primary battery and supplies it to a secondary battery, before performing a power conversion operation, a so-called precharge operation is performed in which the power of the secondary battery is supplied to a capacitor connected to the primary input terminal via the power conversion device. In this precharge operation, it is desired that when a short circuit occurs in the primary input terminal, this short circuit can be effectively detected.

[0005] It is desirable to provide a power conversion device and a power conversion system that can effectively detect a short circuit in a primary input terminal.

[0006] A power conversion device according to one embodiment of the present invention comprises a first power terminal having two connection terminals, a voltage sensor, a switching circuit, a transformer, a rectifier circuit, a smoothing circuit, a second power terminal, and a control circuit. The voltage sensor is capable of detecting the voltage between the two connection terminals of the first power terminal. The switching circuit is connected to the first power terminal and has one or more switching elements. The transformer has a first winding and a second winding connected to the switching circuit. The rectifier circuit is connected to the second winding and has one or more switching elements. The smoothing circuit is connected to the rectifier circuit and has an inductor and a first capacitor. 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 above control circuit is capable of operating the rectifier circuit to supply power from the second power terminal to the first power terminal during a second period prior to the first period during which power is supplied from the first power terminal to the second power terminal, and during the second period, it is capable of detecting a short circuit between the two connection terminals by performing a comparison operation that compares the voltage detected by the voltage sensor with a predetermined threshold voltage. The second period may include a first sub-period and a second sub-period following the first sub-period, and the control circuit may set the duty cycle of one or more switching elements of the rectifier circuit to a first duty cycle during the first sub-period, and may set the duty cycle of one or more switching elements of the rectifier circuit to a second duty cycle that is greater than the first duty cycle during the second sub-period.

[0007] A power conversion system according to one embodiment of the present invention comprises a first battery, a second 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 second capacitor has a first terminal and a second terminal. The first switch is provided in the path connecting the first terminal of the first battery and the first terminal of the second capacitor. The second switch is provided in the path connecting the second terminal of the first battery and the second terminal of the second capacitor. The power conversion device includes a first power terminal, a voltage sensor, a switching circuit, a transformer, a rectifier circuit, a smoothing circuit, a second power terminal, and a control circuit. The first power terminal has a first connection terminal connected to the first terminal of the second capacitor and a second connection terminal connected to the second terminal of the second capacitor. The voltage sensor is capable of detecting the voltage between the first connection terminal and the second connection terminal. The switching circuit is connected to the first power terminal and has one or more switching elements. The transformer has a first winding and a second winding connected to the switching circuit. The rectifier circuit is connected to the second winding and has one or more switching elements. The smoothing circuit is connected to the rectifier circuit and has an inductor and a first capacitor. The second power terminal is connected to the smoothing circuit and also to a second battery. The control circuit is capable of controlling the operation of the switching circuit and the rectifier circuit. The control circuit is capable of operating the rectifier circuit to supply power from the second power terminal to the first power terminal in a second period prior to a first period of supplying power from the first power terminal to the second power terminal, and is capable of detecting a short circuit between the first and second connection terminals by performing a comparison operation during the second period, comparing the voltage detected by a voltage sensor with a predetermined threshold voltage. The second period may include a first sub-period and a second sub-period following the first sub-period, and the control circuit may set the duty cycle of one or more switching elements of the rectifier circuit to a first duty cycle during the first sub-period, and may set the duty cycle of one or more switching elements of the rectifier circuit to a second duty cycle that is greater than the first duty cycle during the second sub-period.

[0008] According to one embodiment of the present invention, a power conversion device and power conversion system can effectively detect a short circuit at the primary input terminal. [Brief explanation of the drawing]

[0009] [Figure 1] This is a circuit diagram showing one example configuration of a power conversion system according to the first embodiment of the present invention. [Figure 2] Figure 1 is a block diagram showing one example configuration of the control circuit. [Figure 3] This timing diagram shows an example of operation in the power conversion system shown in Figure 1 when no short circuit occurs. [Figure 4] Figure 1 shows a timing waveform diagram illustrating an example of operation in the power conversion system when no short circuit occurs. [Figure 5] This timing diagram shows an example of operation in the power conversion system shown in Figure 1 when a short circuit occurs. [Figure 6] Figure 1 shows a timing waveform diagram illustrating an example of operation in the power conversion system when a short circuit occurs. [Figure 7A] This timing diagram shows an example of operation in a power conversion system according to a modified version of the first embodiment, in the case where a short circuit does not occur. [Figure 7B] This is a timing diagram showing an example of operation in a power conversion system according to a modified version of the first embodiment when a short circuit occurs. [Figure 8A] This timing diagram shows an example of operation in a power conversion system according to another modification of the first embodiment, in the case where a short circuit does not occur. [Figure 8B] This is a timing diagram showing an example of operation in a power conversion system according to another modification of the first embodiment when a short circuit occurs. [Figure 9] This timing diagram shows an example of operation in a power conversion system according to another modification of the first embodiment, in the case where a short circuit does not occur. [Figure 10]It is a block diagram showing a configuration example of a control circuit according to another modification of the first embodiment. [Figure 11] It is a timing diagram showing an example of an operation when no short circuit occurs in a power conversion system having the control circuit shown in FIG. 10. [Figure 12] It is a circuit diagram showing a configuration example of a power conversion system according to another modification of the first embodiment. [Figure 13] It is a circuit diagram showing a configuration example of a power conversion system according to another modification of the first embodiment. [Figure 14] It is a circuit diagram showing a configuration example of a power conversion system according to the second embodiment. [Figure 15] It is a block diagram showing a configuration example of the control circuit shown in FIG. 14. [Figure 16A] It is a timing diagram showing an example of an operation when no short circuit occurs in the power conversion system shown in FIG. 15. [Figure 16B] It is a timing diagram showing an example of an operation when a short circuit occurs in the power conversion system shown in FIG. 15. [Figure 16C] It is a timing diagram showing an example of an operation when a short circuit occurs midway in the power conversion system shown in FIG. 15. [Figure 17A] It is a timing diagram showing an example of an operation when no short circuit occurs in a power conversion system according to a modification of the second embodiment. [Figure 17B] It is a timing diagram showing an example of an operation when a short circuit occurs in a power conversion system according to a modification of the second embodiment. [Figure 17C] It is a timing diagram showing an example of an operation when a short circuit occurs midway in a power conversion system according to a modification of the second embodiment. [Figure 18A] It is a timing diagram showing an example of an operation when a short circuit occurs in a power conversion system according to another modification of the second embodiment. [Figure 18B]A timing diagram showing an example of an operation when a short circuit occurs midway in a power conversion system according to another modification of the second embodiment. [Figure 19A] A timing diagram showing an example of an operation when no short circuit occurs in a power conversion system according to another modification of the second embodiment. [Figure 19B] A timing diagram showing an example of an operation when a short circuit occurs in a power conversion system according to another modification of the second embodiment. [Figure 20] A timing diagram showing an example of an operation when no short circuit occurs in a power conversion system according to another modification of the first embodiment.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The description will be made in the following order. 1. First Embodiment 2. Second Embodiment

[0011] <1. First Embodiment> [Configuration Example] FIG. 1 shows a configuration example 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. This power conversion system 1 is configured to convert the 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 power. The high-voltage battery BH supplies power to the power conversion device 10 via the switches SW1 and SW2.

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

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

[0015] The power converter 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 converter 10 is a so-called center-tap type power converter. The power converter 10 has terminals T11, T12, a voltage sensor 11, a switching circuit 12, a transformer 13, a rectifier circuit 14, a smoothing circuit 15, a voltage sensor 18, a control circuit 19, and terminals T21, T22. The high-voltage battery BH, switches SW1, SW2, capacitor 9, voltage sensor 11, and switching circuit 12 constitute the primary side circuit of the power conversion system 1, while the rectifier circuit 14, smoothing circuit 15, voltage sensor 18, and low-voltage battery BL constitute the secondary side circuit of the power conversion system 1.

[0016] Terminals T11 and T12 are configured to receive voltage from the high-voltage battery BH when switches SW1 and SW2 are turned ON. Within the power converter 10, terminal T11 is connected to voltage line L11, and terminal T12 is connected to reference voltage line L12.

[0017] The voltage sensor 11 is configured to detect the voltage VH on the voltage line L11. One end of the voltage sensor 11 is connected to the voltage line L11, and the other end is connected to the reference voltage line L12. The voltage sensor 11 detects the voltage VH on the voltage line L11 with the voltage on the reference voltage line L12 as the reference. The voltage sensor 11 then supplies the detection result of voltage VH as the detected voltage VH2 to the control circuit 19. In this example, the voltage sensor 11 is supplied with voltage VH as the power supply voltage. The voltage sensor 11 operates by being supplied with voltage VH as the power supply voltage in this way, and is configured to detect the voltage VH on the voltage line L11. In this example, the voltage sensor 11 is supplied with voltage VH directly as the power supply voltage, but this is not limited to this, and for example, a voltage converted from voltage VH by a power converter (not shown) may be supplied. This power converter may be, for example, an isolated type power converter.

[0018] The switching circuit 12 is configured to convert the DC voltage supplied from the high-voltage battery BH into an AC voltage. The switching circuit 12 is a full-bridge type circuit and has transistors S1 to S4. Transistors S1 to S4 are switching elements that perform switching operations based on gate signals GA to GD. Transistors S1 to S4 are constructed using, for example, N-type field-effect transistors (FETs). Transistors S1 to S4 each have body diodes D1 to D4. For example, the anode of body diode D1 is connected to the source of transistor S1, and the cathode is connected to the drain of transistor S1. The same applies to body diodes D2 to D4. In this example, N-type field-effect transistors are used, but any switching element can be used. Also, in this example, transistors with body diodes are used, but transistors without body diodes can be used. In this case, for example, a diode is added instead of a body diode.

[0019] Transistor S1 is located in the path connecting voltage line L11 and node N1, and is configured to connect node N1 to voltage line L11 when it is turned on. The drain of transistor S1 is connected to voltage line L11, the gate signal GA is supplied to its gate, and its source is connected to node N1. Transistor S2 is located in the path connecting node N1 and reference voltage line L12, and is configured to connect node N1 to reference voltage line L12 when it is turned on. The drain of transistor S2 is connected to node N1, the gate signal GB is supplied to its gate, and its source is connected to reference voltage line L12. Node N1 is the connection point between the source of transistor S1 and the drain of transistor S2.

[0020] Transistor S3 is located in the path connecting voltage line L11 and node N2, and is configured to connect node N2 to voltage line L11 when it is turned on. The drain of transistor S3 is connected to voltage line L11, the gate signal GC is supplied to its gate, and its source is connected to node N2. Transistor S4 is located in the path connecting node N2 and reference voltage line L12, and is configured to connect node N2 to reference voltage line L12 when it is turned on. The drain of transistor S4 is connected to node N2, the gate signal GD is supplied to its gate, and its source is connected to reference voltage line L12. Node N2 is the connection point between the source of transistor S3 and the drain of transistor S4.

[0021] The transformer 13 is configured to DC-isolate the primary and secondary circuits while AC-connecting them, to convert the AC voltage supplied from the primary circuit using the transformation ratio N of the transformer 13, and to supply the converted AC voltage to the secondary circuit. The transformer 13 has windings 13A, 13B, and 13C. One end of winding 13A is connected to node N1 in the switching circuit 12, and the other end is connected to node N2 in the switching circuit 12. One end of winding 13B is connected to node N4 in the rectifier circuit 14, and the other end is connected to one end of winding 13C and voltage line L21A. One end of winding 13C is connected to the other end of winding 13B and voltage line L21A, and the other end is connected to node N3 in the rectifier circuit 14.

[0022] The rectifier circuit 14 is configured to generate a pulsating voltage by rectifying the AC voltage output from the windings 13B and 13C of the transformer 13. The rectifier circuit 14 has transistors S5 and S6. Transistors S5 and S6 are switching elements that perform switching operations based on gate signals GE and GF, respectively. Transistors S5 and S6 are constructed using, for example, N-type field-effect transistors, similar to transistors S1 to S4. Transistors S5 and S6 each have body diodes D5 and D6. In this example, N-type field-effect transistors are used, but any switching element can be used. Also, in this example, transistors with body diodes are used, but transistors without body diodes can also be used. In this case, for example, a diode is added to the transistor instead of a body diode.

[0023] Transistor S5 is located in the path connecting node N3 and reference voltage line L22, and is configured to connect node N3 to reference voltage line L22 when it is turned on. The drain of transistor S5 is connected to node N3, the gate is supplied with the gate signal GE, and the source is connected to reference voltage line L22.

[0024] Transistor S6 is located in the path connecting node N4 and reference voltage line L22, and is configured to connect node N4 to reference voltage line L22 when it is turned on. The drain of transistor S6 is connected to node N4, the gate is supplied with the gate signal GF, and the source is connected to reference voltage line L22.

[0025] The smoothing circuit 15 is configured to smooth the pulsating voltage of the rectifier circuit 14. The smoothing circuit 15 includes a choke inductor 16 and a capacitor 17. One end of the choke inductor 16 is connected to voltage line L21A, and the other end is connected to voltage line L21B. One end of the capacitor 17 is connected to voltage line L21B, and the other end is connected to reference voltage line L22. In this example, the choke inductor 16 is provided between voltage lines L21A and L21B, but it is not limited to this, and may be provided on, for example, the reference voltage line L22 instead.

[0026] The voltage sensor 18 is configured to detect the voltage VL 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 sensor 18 detects the voltage VL on the voltage line L21B with the voltage on the reference voltage line L22 as the reference. The voltage sensor 18 then supplies the detection result of the voltage VL as the detected voltage VL2 to the control circuit 19.

[0027] The control circuit 19 is configured to control the operation of the power converter 10 by controlling the operation of the switching circuit 12 and the rectifier circuit 14 based on the voltage VH (detected voltage VH2) detected by the voltage sensor 11 and the voltage VL (detected voltage VL2) detected by the voltage sensor 18. Specifically, the control circuit 19 generates gate signals GA~GF based on the detected voltages VH2 and VL2, and controls the operation of the power converter 10 by performing PWM (Pulse Width Modulation) control using these gate signals GA~GF. The control circuit 19 is configured, for example, using a microcontroller. Furthermore, as an example, the control circuit 19 converts the analog signals supplied from the voltage sensors 11 and 18 into digital signals by AD conversion at a predetermined sampling period, and controls the operation of the switching circuit 12 and the rectifier circuit 14 based on these digital signals.

[0028] Terminals T21 and T22 are configured to supply the voltage generated by the power converter 10 to the low-voltage battery BL. Within the power converter 10, terminal T21 is connected to voltage line L21B, and terminal T22 is connected to reference voltage line L22. In addition, terminal T21 is connected to the positive terminal of the low-voltage battery BL, and terminal T22 is connected to the negative terminal of the low-voltage battery BL.

[0029] The low-voltage battery BL is configured to store the power supplied from the power converter 10.

[0030] With this configuration, the power conversion system 1 performs a power conversion operation during the period when switches SW1 and SW2 are ON, converting the power supplied from the high-voltage battery BH and supplying the converted power to the low-voltage battery BL.

[0031] Furthermore, the power conversion system 1 also has a function to perform a so-called pre-charge operation, which involves charging the capacitor 9 during a preparation period (pre-charge period P1) before starting such power conversion operations. During this pre-charge operation, switches SW1 and SW2 are in the off state, and the control circuit 19 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. As a result, the power conversion device 10 can suppress the inrush current flowing from the high-voltage battery BH to the capacitor 9 when switches SW1 and SW2 are turned on to perform power conversion operations.

[0032] Figure 2 shows an example configuration of the control circuit 19. The control circuit 19 includes a precharge control unit 21, a power conversion control unit 27, and gate signal generation units 28 and 29.

[0033] The precharge control unit 21 is configured to generate the duty cycle DP of the switching operation in the switching circuit 12 and the duty cycle DS of the switching operation in the rectifier circuit 14 based on the detected voltage VL2 during the precharge period P1 and the period following the precharge period P1 (voltage maintenance period P2). The precharge control unit 21 also has the function of generating a disable signal DSBL based on the detected voltage VH2, indicating whether the control circuit 19 stops outputting the gate signals GA to GF. The precharge control unit 21 includes duty cycle generation units 23 and 24, a threshold value generation unit 25, and a comparison unit 26.

[0034] The duty cycle generation unit 23 is configured to generate the duty cycle DP in the switching circuit 12 based on the detected voltage VL2 during the pre-charge period P1 and the voltage maintenance period P2. Specifically, during the pre-charge period P1, the duty cycle generation unit 23 generates the duty cycle DP such that the duty cycle DP decreases as the detected voltage VL2 increases. During the pre-charge period P1, the duty cycle generation unit 23 generates the duty cycle DP such that, for example, the duty cycle DP increases. This allows the power conversion system 1 to adjust the charging voltage of the capacitor 9. Furthermore, during the voltage maintenance period P2, the duty cycle generation unit 23 generates a duty cycle DP of a predetermined value corresponding to, for example, the detected voltage VL2. However, it is not limited to this, and during the voltage maintenance period P2, the duty cycle generation unit 23 may change the duty cycle DP by performing feedback control based on the detected voltage VL2.

[0035] The duty cycle generation unit 24 is configured to generate the duty cycle DS in the rectifier circuit 14 based on the detected voltage VL2 during the pre-charge period P1 and the voltage maintenance period P2. Specifically, during the pre-charge period P1, the duty cycle generation unit 24 generates the duty cycle DS such that the duty cycle DS decreases as the detected voltage VL2 increases. During the pre-charge period P1, the duty cycle generation unit 24 generates the duty cycle DS such that, for example, the duty cycle DS increases. This allows the power conversion system 1 to adjust the charging voltage of the capacitor 9. Furthermore, during the voltage maintenance period P2, the duty cycle generation unit 24 generates a duty cycle DS of a predetermined value corresponding to, for example, the detected voltage VL2. However, it is not limited to this, and during the voltage maintenance period P2, the duty cycle generation unit 24 may change the duty cycle DS by performing feedback control based on the detected voltage VL2.

[0036] The threshold value generation unit 25 is configured to generate a threshold value TH for the detection voltage VH2 to determine whether terminals T11 and T12 are short-circuited to each other. Terminals T11 and T12 may be short-circuited, for example, when both ends of capacitor 9 are short-circuited.

[0037] The comparison unit 26 is configured to generate a disable signal DSBL by comparing the detected voltage VH2 with the threshold value TH. Specifically, the comparison unit 26 compares the detected voltage VH2 with the threshold value TH multiple times during a period (comparison period PD, described later) from the start of the precharge period P1 until a predetermined time (e.g., 100 msec.) has elapsed. During this comparison period PD, if the detected voltage VH2 is always lower than the threshold value TH, the comparison unit 26 activates the disable signal DSBL (e.g., to a high level) at the end of this comparison period PD. That is, if terminals T11 and T12 are short-circuited, for example, even if the voltage VH is increased by precharge operation, the voltage VH will not increase, and therefore the detected voltage VH2 will not increase either. Thus, during the comparison period PD, if the detected voltage VH2 is always lower than the threshold value TH, the comparison unit 26 determines that terminals T11 and T12 are short-circuited due to some factor and activates the disable signal DSBL. Furthermore, if the detected voltage VH2 becomes higher than the threshold TH before the end of the comparison period PD, the comparison unit 26 deactivates the disable signal DSBL (e.g., to a low level) at the end of the comparison period PD. In other words, if terminals T11 and T12 are not short-circuited, the voltage VH gradually increases due to the pre-charge operation, and the detected voltage VH2 becomes higher than the threshold TH before the end of the comparison period PD. Therefore, if the detected voltage VH2 becomes higher than the threshold TH before the end of the comparison period PD, the comparison unit 26 determines that terminals T11 and T12 are not short-circuited and deactivates the disable signal DSBL (e.g., to a low level).

[0038] The power conversion control unit 27 is configured to generate the duty cycle DP of the switching operation in the switching circuit 12 and the duty cycle DS of the switching operation in the rectifier circuit 14 based on the detected voltages VH2 and VL2 during the period in which the power conversion operation is performed (power conversion period P3).

[0039] The gate signal generation unit 28 is configured to generate gate signals GA to GD based on the duty cycle DP generated by the duty cycle generation unit 23 and the power conversion control unit 27, and the disable signal DSBL. Specifically, during the pre-charge period P1 and the voltage maintenance period P2, if the disable signal DSBL is inactive, the gate signal generation unit 28 generates gate signals GC and GD based on the duty cycle DP generated by the duty cycle generation unit 23, and maintains gate signals GA and GB at a low level. If the disable signal is active, it maintains gate signals GA to GD at a low level. Furthermore, during the power conversion period P3, the gate signal generation unit 28 generates gate signals GA to GD based on the duty cycle DP generated by the power conversion control unit 27.

[0040] The gate signal generation unit 29 is configured to generate gate signals GE and GF based on the duty cycle DS generated by the duty cycle generation unit 24 and the power conversion control unit 27, and the disable signal DSBL. Specifically, during the pre-charge period P1 and the voltage maintenance period P2, the gate signal generation unit 29 generates gate signals GE and GF based on the duty cycle DS generated by the duty cycle generation unit 24 when the disable signal DSBL is inactive, and maintains gate signals GE and GF at a low level when the disable signal DSBL is active. Furthermore, during the power conversion period P3, the gate signal generation unit 29 generates gate signals GE and GF based on the duty cycle DS generated by the power conversion control unit 27.

[0041] Here, terminals T11 and T12 correspond to a specific example of the "first power terminal" in this disclosure. Terminal T11 corresponds to a specific example of the "first connection terminal" in this disclosure. Terminal T12 corresponds to a specific example of the "second connection terminal" in this disclosure. Voltage sensor 11 corresponds to a specific example of the "voltage sensor" in this disclosure. Switching circuit 12 corresponds to a specific example of the "switching circuit" in this disclosure. Transformer 13 corresponds to a specific example of the "transformer" in this disclosure. Rectifier circuit 14 corresponds to a specific example of the "rectifier circuit" in this disclosure. Smoothing circuit 15 corresponds to a specific example of the "smoothing circuit" in this disclosure. Choke inductor 16 corresponds to a specific example of the "inductor" in this disclosure. Capacitor 17 corresponds to a specific example of the "first capacitor" in this disclosure. Terminals T21 and T22 correspond to a specific example of the "second power terminal" in this disclosure. Control circuit 19 corresponds to a specific example of the "control circuit" in this disclosure. The pre-charge period P1 corresponds to one specific example of the "second period" in this disclosure. The power conversion period P3 corresponds to one specific example of the "first period" in this disclosure. The threshold voltage TH corresponds to one specific example of the "threshold voltage" in this disclosure. The high-voltage battery BH corresponds to one specific example of the "first battery" in this disclosure. The capacitor 9 corresponds to one specific example of the "second capacitor" in this disclosure. The switch SW1 corresponds to one specific example of the "first switch" in this disclosure. The switch SW2 corresponds to one specific example of the "second switch" in this disclosure. The power converter 10 corresponds to one specific example of the "power converter" in this disclosure. The low-voltage battery BL corresponds to one specific example of the "second battery" in this disclosure.

[0042] [Action and function] Next, the operation and function of the power conversion system 1 of this embodiment will be described.

[0043] (Overview of overall operation) First, with reference to Figure 1, the overall operation of the power conversion system 1 will be explained. During the pre-charge period P1, switches SW1 and SW2 are in the off state, and the control circuit 19 generates gate signals GC to GF based on voltages VH and VL, while maintaining gate signals GA and GB at low levels. As a result, the switching circuit 12 and the rectifier circuit 14 operate, and the power converter 10 supplies power from the low-voltage battery BL to the capacitor 9. As a result, the capacitor 9 is charged and the voltage VH rises. When the voltage VH reaches, for example, the target voltage Vtarget, the pre-charge operation ends, and the voltage VH is maintained near this target voltage Vtarget. Then, during the power conversion period P3, switches SW1 and SW2 are turned on, and the control circuit 19 generates gate signals GA to GF based on voltages VH and VL. As a result, the power converter 10 converts the power supplied from the high-voltage battery BH and supplies the converted power to the low-voltage battery BL.

[0044] (Detailed operation) Figure 3 shows an example of pre-charge operation when there is no short circuit between terminals T11 and T12, where (A) shows the duty cycle DS of the switching operation in the rectifier circuit 14, (B) shows the duty cycle DP of the switching operation in the switching circuit 12, (C) shows the waveform of the voltage VH, (D) shows the waveform of the detection result (detected voltage VH2) of the voltage sensor 11, and (E) shows the waveform of the disable signal DSBL.

[0045] In this example, the power conversion system 1 performs a pre-charge operation during the period from timing t1 to t5 (pre-charge period P1).

[0046] First, the duty cycle generation unit 24 of the precharge control unit 21 sets the duty cycle DS to the value DS1 during the timing period t1 to t4 (Figure 3(A)). The duration of this timing period t1 to t4 is, for example, 100 [msec.], and timing t4 is set, for example, based on the timer of the control circuit 19. The gate signal generation unit 29 generates gate signals GE and GF based on the duty cycle DS generated by the precharge control unit 21, and the rectifier circuit 14 performs switching operations based on these gate signals GE and GF. Also, the duty cycle generation unit 23 sets the duty cycle DP to "0" (zero) during the timing period t1 to t4 (Figure 3(B)). The gate signal generation unit 28 maintains the gate signals GA to GD at a low level based on the duty cycle DP generated by the precharge control unit 21, and the switching circuit 12 maintains transistors S1 to S4 in the off state based on these gate signals GA to GD. As the rectifier circuit 14 performs switching operations in this manner, the voltage VH across the capacitor 9 gradually increases (Figure 3(C)).

[0047] The detected voltage VH2 is 0V at timings t1 to t2 (Figure 3(D)). In other words, in this example, the voltage sensor 11 operates when voltage VH is supplied as the power supply voltage, so it cannot operate if voltage VH is sufficiently low. At timing t2, voltage VH becomes high enough for the voltage sensor 11 to operate, and the voltage sensor 11 starts operating at timing t2. As a result, the detected voltage VH2 becomes a voltage corresponding to voltage VH from timing t2 onward.

[0048] In this example, the comparison unit 26 of the precharge control unit 21 compares the detected voltage VH2 with the threshold value TH every 10 msec. during the period t1 to t4 (comparison period PD) (Figure 3(D)). In Figure 3(D), the arrows indicate the comparison timings that the comparison unit 26 compares. In this example, the detected voltage VH2 is below the threshold value TH before timing t3 and above the threshold value TH after timing t3. Therefore, in the two comparison operations after timing t3, the detected voltage VH2 is higher than the threshold value TH. Since the detected voltage VH2 is higher than the threshold value TH by the time the comparison period PD ends, the comparison unit 26 keeps the disable signal DSBL inactive (low level in this example) from timing t4, which is the end timing of the comparison period PD (Figure 3(E)).

[0049] The duty cycle generation unit 24 of the precharge control unit 21 sets the duty cycle DS to a value DS2, which is higher than the value DS1, during the period from timing t4 to t5 (Figure 3(A)). Since the disable signal DSBL is inactive, the gate signal generation unit 29 generates gate signals GE and GF based on the duty cycle DS generated by the precharge control unit 21, and the rectifier circuit 14 performs switching operations based on these gate signals GE and GF. As a result, as shown in Figure 3(A), the duty cycle DS of the switching operation in the rectifier circuit 14 changes from the value DS1 to the value DS2. In addition, the duty cycle generation unit 24 of the precharge control unit 21 generates the duty cycle DP such that the duty cycle DP gradually increases during the period from timing t4 to t5 (Figure 3(B)). Since the disable signal DSBL is inactive, the gate signal generation unit 28 generates gate signals GC and GD based on the duty cycle DP generated by the precharge control unit 21, and maintains gate signals GA and GB at a low level. The switching circuit 12 performs switching operations based on these gate signals GA to GD. As a result, as shown in Figure 3(B), the duty cycle DP of the switching operation in the switching circuit 12 gradually increases during the timing period t4 to t5. As the switching circuit 12 and the rectifier circuit 14 perform switching operations in this way, the voltage VH across the capacitor 9 gradually increases (Figure 3(C)).

[0050] Then, at timing t5, when the detected voltage VH2 reaches the target voltage Vtarget, the power conversion system 1 performs a voltage maintenance operation to maintain the voltage VH near the target voltage Vtarget during the period after timing t5 (voltage maintenance period P2). Specifically, the duty cycle generation unit 24 of the precharge control unit 21 sets the duty cycle DS to a value DS3 that is lower than the value DS2 after timing t5 (Figure 3(A)). The gate signal generation unit 29 generates gate signals GE and GF based on the duty cycle DS generated by the precharge control unit 21, and the rectifier circuit 14 performs switching operations based on these gate signals GE and GF. In addition, the duty cycle generation unit 23 of the precharge control unit 21 sets the duty cycle DP to a value DP3 that is lower than the previous value after timing t5 (Figure 3(B)). The gate signal generation unit 28 generates gate signals GC and GD based on the duty cycle DP generated by the precharge control unit 21, and maintains gate signals GA and GB at a low level. The switching circuit 12 performs switching operations based on these gate signals GA to GD. As the switching circuit 12 and rectifier circuit 14 perform switching operations in this manner, the voltage VH in the capacitor 9 is maintained near the target voltage Vtarget (Figure 3(C)).

[0051] Here, the period from timing t1 to t4 corresponds to one specific example of the "first sub-period" in this disclosure. The duty cycle value DS1 corresponds to one specific example of the "first duty cycle" in this disclosure. For example, the period from timing t4 to t5 corresponds to one specific example of the "second sub-period" in this disclosure. The duty cycle value DS2 corresponds to one specific example of the "second duty cycle" in this disclosure.

[0052] Figure 4 shows an example of a simulated waveform of the operation during the timing period t1 to t4 in Figure 3. (A) shows the waveforms of gate signals GE and GF, (B) shows the waveforms of gate signals GC and GD, (C) shows the waveform of the current flowing into capacitor 9 (charge current ICHG), (D) shows the waveform of the excitation current IM of transformer 13, (E) shows the waveform of the current flowing from voltage line L21B to voltage line L21A in choke inductor 16 (inductor current IL), (F) shows the waveform of the voltage at node N1 with reference to node N2 in winding 13A of transformer 13 (transformer voltage VTR1), and (G) shows the waveform of voltage VH. In Figure 4, Tsw indicates the period of switching operation (switching period).

[0053] The control circuit 19 generates gate signals GC and GD based on the duty cycle DP, and gate signals GE and GF based on the duty cycle DS. The duty cycle DP represents the pulse width of gate signals GC and GD when the switching period Tsw is set to "1", and the duty cycle DS represents the pulse width of gate signals GE and GF when the switching period Tsw is set to "1". Note that during the timing period t1 to t4 in Figure 3, the duty cycle DP is 0 (zero), so the gate signals GC and GD remain at a low level.

[0054] At timing t11, the control circuit 19 changes the gate signal GF from a low level to a high level (Figure 4(A)). This changes the transistor S6 from the off state to the on state. Then, at timing t12, which is after a time corresponding to the duty cycle DS (duty cycle DS × switching period Tsw) has elapsed from timing t11, the control circuit 19 changes the gate signal GF from a high level to a low level. This changes the transistor S6 from the on state to the off state.

[0055] During the period t11-t12 when transistor S6 is ON, current flows in the following order: choke inductor 16, winding 13B of transformer 13, and transistor S6. The inductor current IL gradually increases during this period t11-t12 (Figure 4(E)). Then, at timing t12 when transistor S6 changes from the ON state to the OFF state, the inductor current IL decreases toward 0 (zero) and then remains at 0 (zero).

[0056] The excitation current IM increases during the timing period t11-t12 and decreases during the timing period t12-t13 (Figure 4(D)). Accordingly, the charge current ICHG also increases during the timing period t11-t12 and decreases during the timing period t12-t13 (Figure 4(C)).

[0057] Next, at timing t13, the control circuit 19 changes the gate signal GE from a low level to a high level (Figure 4(A)). This changes the transistor S5 from the off state to the on state. Then, at timing t14, which is after a time corresponding to the duty cycle DS (duty cycle DS × switching period Tsw) has elapsed from timing t13, the control circuit 19 changes the gate signal GE from a high level to a low level. This changes the transistor S5 from the on state to the off state.

[0058] During the timing t13-t14 when transistor S5 is turned on, current flows in the following order: choke inductor 16, winding 13C of transformer 13, and transistor S5. The inductor current IL gradually increases during this timing t13-t14 (Figure 4(E)). Then, at timing t14 when transistor S5 changes from the on state to the off state, the inductor current IL decreases toward 0 (zero) and then remains at 0 (zero).

[0059] The excitation current IM decreases during the timing period t13-t14 and increases during the timing period t14-t15 (Figure 4(D)). Accordingly, the charge current ICHG increases during the timing period t13-t14 and decreases during the timing period t14-t15 (Figure 4(C)).

[0060] Thus, a charge current ICHG flows at timings t11 to t15. As this charge current ICHG flows through capacitor 9, capacitor 9 is charged, and the voltage VH gradually increases.

[0061] In Figure 4, the operation during the timing period t1 to t4 in Figure 3 is shown, but the operation during the timing period t4 to t5 is similar, with the voltage VH gradually increasing due to the charge current ICHG. During this timing period t4 to t5, the switching circuit 12 performs switching operations based on the gate signals GC and GD. During this timing period t4 to t5, the inductor current IL also gradually increases for a certain period, then decreases toward 0 (zero), and then remains at 0 (zero), as shown in Figure 4(E). ) .

[0062] Figure 5 shows an example of pre-charge operation when a short circuit occurs between terminals T11 and T12. In Figure 5, the dotted waveform shows the waveform when there is no short circuit between terminals T11 and T12 (Figure 3). Timings t21 and t24 correspond to timings t1 and t4 in the example in Figure 3, respectively.

[0063] During the period of timing t21 to t24, the power conversion system 1 sets the duty cycle DS to value DS1 and the duty cycle DP to "0" (zero), similar to the period of timing t1 to t4 shown in Figure 3 (Figures 5(A), (B)). In this example, a short circuit occurs between terminals T11 and T12, so the voltage VH across capacitor 9 does not rise and is maintained at 0V (Figure 5(C)). Since the voltage VH is maintained at 0V in this way, the voltage sensor 11 cannot operate, and the detected voltage VH2 also remains at 0V (Figure 5(D)).

[0064] The comparison unit 26 of the precharge control unit 21 compares the detected voltage VH2 with the threshold value TH every 10 msec. during the period t21 to t24 (comparison period PD) (Figure 5(D)). In this example, a short circuit occurs between terminals T11 and T12, so the detected voltage VH2 is below the threshold value TH for the entire period t21 to t24. As a result, the comparison unit 26 activates the disable signal DSBL (to a high level in this example) at timing t24, which is the end timing of the comparison period PD. In this way, the control circuit 19 detects the short circuit between terminals T11 and T12.

[0065] Since the disable signal DSBL is active, the gate signal generation unit 29 generates gate signals GE and GF that are maintained at a low level regardless of the duty cycle DS generated by the precharge control unit 21, and the rectifier circuit 14 stops switching operation based on these gate signals GE and GF. As a result, as shown in Figure 5(A), the duty cycle DS of the switching operation in the rectifier circuit 14 becomes 0 (zero). Similarly, since the disable signal DSBL is active, the gate signal generation unit 28 generates gate signals GA to GD that are maintained at a low level regardless of the duty cycle DP generated by the precharge control unit 21, and the switching circuit 12 maintains the stop of switching operation based on these gate signals GA to GD. As a result, as shown in Figure 5(B), the duty cycle DP of the switching operation in the switching circuit 12 becomes 0 (zero). In this way, the power conversion system 1 temporarily stops the precharge operation.

[0066] Subsequently, the power conversion system 1, for example, after a predetermined time has elapsed, starts the pre-charge operation again and checks whether a short circuit has occurred between terminals T11 and T12. If the power conversion system 1 starts the pre-charge operation multiple times and a short circuit continues to occur between terminals T11 and T12, it completely stops the operation. The power conversion system 1 then notifies an external device, for example, that a short circuit has occurred between terminals T11 and T12.

[0067] Figure 6 shows an example of a simulated waveform of the operation during the timing period t21 to t24 in Figure 5. The vertical axis scale of each waveform in Figure 6 is the same as the vertical axis scale of each waveform in Figure 4.

[0068] At timing t31, the control circuit 19 changes the gate signal GF from a low level to a high level (Figure 6(A)). This changes the transistor S6 from the off state to the on state. Then, at timing t32, which is after a time corresponding to the duty cycle DS (duty cycle DS × switching period Tsw) has elapsed from timing t31, the control circuit 19 changes the gate signal GF from a high level to a low level. This changes the transistor S6 from the on state to the off state.

[0069] During the period t31-t32 when transistor S6 is ON, current flows in the following order: choke inductor 16, winding 13B of transformer 13, and transistor S6. The inductor current IL gradually increases during this period t31-t32 (Figure 6(E)). This inductor current IL is greater than the inductor current IL when there is no short circuit between terminals T11 and T12 (Figure 4(E)). At timing t32 when transistor S6 changes from the ON state to the OFF state, the inductor current IL decreases toward 0 (zero) and then remains at 0 (zero).

[0070] In this example, a short circuit occurs between terminals T11 and T12, so the excitation current IM hardly flows (Figure 6(D)). The charge current ICHG gradually increases in accordance with the inductor current IL during the period from timing t31 to t32, and decreases toward 0 (zero) at timing t32 when transistor S6 changes from the ON state to the OFF state (Figure 6(C)).

[0071] Next, at timing t33, the control circuit 19 changes the gate signal GE from a low level to a high level (Figure 6(A)). This changes the transistor S5 from the off state to the on state. Then, at timing t34, which is after a time corresponding to the duty cycle DS (duty cycle DS × switching period Tsw) has elapsed from timing t33, the control circuit 19 changes the gate signal GE from a high level to a low level. This changes the transistor S5 from the on state to the off state.

[0072] During the timing t33-t34 when transistor S5 is turned on, current flows in the following order: choke inductor 16, winding 13C of transformer 13, and transistor S5. The inductor current IL gradually increases during this timing t33-t34 (Figure 6(E)). Then, at timing t34 when transistor S5 changes from the on state to the off state, the inductor current IL decreases toward 0 (zero) and then remains at 0 (zero).

[0073] In this example, a short circuit occurs between terminals T11 and T12, so the excitation current IM hardly flows (Figure 6(D)). The charge current ICHG gradually increases during the period from timing t33 ​​to t34 in accordance with the inductor current IL, and decreases toward 0 (zero) at timing t34 (Figure 6(C)).

[0074] Thus, a charge current ICHG flows at timings t31 to t35. However, in this example, a short circuit occurs between terminals T11 and T12, so capacitor 9 is not charged, and the voltage VH does not rise.

[0075] As shown in Figures 4(E) and 6(E), the period corresponding to the switching period Tsw includes the period when the inductor current IL is 0 (zero). The inductor current IL rises from 0 (zero), reaches a peak value Ipeak, and then becomes 0 (zero) again. Thus, the power conversion system 1 operates in a so-called discontinuous region during pre-charge operation. The peak value Ipeak of the inductor current IL when a short circuit occurs between terminals T11 and T12 (Figure 6(E)) is greater than the peak value Ipeak of the inductor current IL when there is no short circuit between terminals T11 and T12 (Figure 4(E)). The peak value Ipeak of the inductor current IL when a short circuit occurs between terminals T11 and T12 can be expressed by the following formula. Ipeak = VL / Lch × DS × Tsw …(EQ1) Here, Lch is the inductance of the choke inductor 16. For the power conversion system 1 to operate in such a discontinuous region, the duty cycle DS must satisfy the following equation. DS < (Vclmp - VL) / Vclmp …(EQ2) Here, Vclmp is the clamp voltage of transistors S5 and S6, and if transistors S5 and S6 are operating in the avalanche region, this clamp voltage is the breakdown voltage.

[0076] When transistors S5 and S6 are operated in the avalanche region, losses occur in transistors S5 and S6 during the period Tav (Figure 6(E)) in which the inductor current IL decreases. The loss Ploss in each of transistors S5 and S6 can be expressed by the following equation. Ploss = 1 / 2 × Ipeak × Vclmp × Tav / Tsw …(EQ3) If a short circuit occurs between terminals T11 and T12, the peak value Ipeak will increase, and therefore the loss Ploss will also increase. Therefore, in order to prevent transistors S5 and S6 from failing due to this loss Ploss, it is necessary to lower the loss Ploss. As shown in equation EQ1, the peak value Ipeak is proportional to the duty cycle DS. Therefore, by limiting the duty cycle DS, for example, the peak value Ipeak can be limited, and the loss Ploss in each of transistors S5 and S6 can be suppressed. As a result, transistors S5 and S6 can be prevented from failing.

[0077] Thus, in the power conversion system 1, the control circuit 19 operates the rectifier circuit 14 to supply power from terminals T21 and T22 to terminals T11 and T12 during the pre-charge period P1 before the power conversion period P3 in which power is supplied from terminals T11 and T12 to terminals T21 and T22. During the pre-charge period P1, the control circuit 19 performs a comparison operation to compare the voltage between terminals T11 and T12 detected by the voltage sensor 11 with a threshold value TH, thereby detecting a short circuit between terminals T11 and T12. This allows for effective detection of a short circuit between terminals T11 and T12.

[0078] In other words, for example, one method is to install a current sensor on the voltage line L21B of the secondary circuit and use this current sensor to detect a short circuit between terminals T11 and T12. However, generally, the current sensor on the voltage line L21B is installed for the purpose of detecting the load current, so in order to detect a short circuit between terminals T11 and T12, the circuit of the current sensor would need to be modified. Also, in power conversion operation, a lot of load current can flow through the voltage line L21B, so this current sensor may cause a voltage drop. In addition, installing a current sensor increases costs. On the other hand, in power conversion system 1, a short circuit between terminals T11 and T12 is detected by performing a comparison operation that compares the voltage between terminals T11 and T12 detected by the voltage sensor 11 with a threshold value TH, so a short circuit between terminals T11 and T12 can be detected without installing such a current sensor. In this way, it is not necessary to install a current sensor, so for example, there is no possibility of a voltage drop caused by the current sensor, and costs can be reduced.

[0079] Furthermore, in the power conversion system 1, during the pre-charge period P1, each period corresponding to the switching period Tsw of the rectifier circuit 14 includes a period during which no current flows through the choke inductor 16. As a result, the inductor current IL increases from 0 (zero), and by limiting the duty cycle DS, the peak value Ipeak can be limited, thereby suppressing the loss Ploss in transistors S5 and S6. Consequently, even if a short circuit occurs between terminals T11 and T12, for example, failure of transistors S5 and S6 can be prevented.

[0080] Furthermore, in the power conversion system 1, the control circuit 19 sets the duty cycle DS of transistors S5 and S6 of the rectifier circuit 14 to value DS1 during the period t1 to t4 in timing 3, for example, and sets the duty cycle DS of transistors S5 and S6 of the rectifier circuit 14 to value DS2, which is greater than value DS1, during the period t4 to t5 in timing 3. In this way, by limiting the duty cycle DS to value DS1 during the period t1 to t4, even if a short circuit occurs between terminals T11 and T12, transistors S5 and S6 will not fail. That is, immediately after the start of the pre-charge operation, the voltage VH is sufficiently low that it is not possible to detect whether a short circuit has occurred between terminals T11 and T12, and therefore the pre-charge operation continues. Therefore, if a short circuit occurs between terminals T11 and T12, losses will occur in each of transistors S5 and S6. In power conversion system 1, the duty cycle DS is limited to value DS1 immediately after the start of pre-charge operation. This suppresses the loss Ploss in transistors S5 and S6 even when a short circuit occurs between terminals T11 and T12. As a result, transistors S5 and S6 can be prevented from failing even when a short circuit occurs between terminals T11 and T12.

[0081] Furthermore, in the power conversion system 1, the control circuit 19 performs multiple comparison operations during the period of timing t1 to t4 in Figure 3, and detects a short circuit between terminals T11 and T12 based on the comparison results of these multiple comparison operations, thereby preventing false detections. That is, for example, if the control circuit 19 performs a comparison operation only once at timing t4 and detects a short circuit between terminals T11 and T12 based on this comparison result, the desired operation may not be performed. For example, if the detected voltage VH2 is slightly higher than the threshold TH, but due to noise the control circuit 19 determines that the detected voltage VH2 is lower than the threshold TH, the control circuit 19 will stop the pre-charge operation. In the power conversion system 1, the control circuit 19 performs multiple comparison operations during the period of timing t1 to t4, and detects a short circuit between terminals T11 and T12 based on the comparison results of these multiple comparison operations. As a result, the control circuit 19 can more reliably determine that the detected voltage VH2 is higher than the threshold TH, thereby preventing false detections when detecting a short circuit between terminals T11 and T12.

[0082] Furthermore, in the power conversion system 1, the control circuit 19 is configured to stop the operation of the switching circuit 12 and the rectifier circuit 14 when it detects a short circuit between terminals T11 and T12, as shown in Figure 5, thereby enhancing safety.

[0083] [effect] As described above, in this embodiment, the control circuit operates the rectifier circuit to supply power from terminals T21 and T22 to terminals T11 and T12 during the pre-charge period before the power conversion period in which power is supplied from terminals T11 and T12 to terminals T21 and T22. During the pre-charge period, a comparison operation is performed to compare the voltage between terminals T11 and T12 detected by the voltage sensor 11 with a threshold value TH, thereby detecting a short circuit between terminals T11 and T12. Thus, a short circuit between terminals T11 and T12 can be effectively detected.

[0084] In this embodiment, during the pre-charge period, each period corresponding to the switching period of the rectifier circuit includes a period during which no current flows through the choke inductor. Therefore, even if a short circuit occurs between terminals T11 and T12, transistors S5 and S6 will not fail, for example.

[0085] In this embodiment, the control circuit sets the duty cycle DS of transistors S5 and S6 of the rectifier circuit to value DS1 during the timing period t1 to t4 in Figure 3, and sets the duty cycle DS of transistors S5 and S6 of the rectifier circuit to a value DS2, which is greater than value DS1, during the timing period t4 to t5 in Figure 3. Therefore, even if a short circuit occurs between terminals T11 and T12, transistors S5 and S6 can be prevented from failing.

[0086] In this embodiment, the control circuit performs multiple comparison operations during the timing period t1 to t4 in Figure 3, for example, and detects a short circuit between terminals T11 and T12 based on the comparison results of these multiple comparison operations, thereby preventing false detections.

[0087] In this embodiment, the control circuit is configured to stop the operation of the switching circuit and the rectifier circuit when a short circuit is detected between terminals T11 and T12, thereby enhancing safety.

[0088] [Variation 1-1] In the above embodiment, the voltage sensor 11 is configured not to operate immediately after the start of the pre-charge operation, but this is not the only configuration. Alternatively, for example, the voltage sensor 11 may be configured to operate immediately after the start of the pre-charge operation by operating based on a power supply voltage supplied from another circuit, as shown in Figures 7A and 7B. Specifically, for example, the voltage sensor 11 may be supplied with a power supply voltage converted from voltage VL by an isolated power converter (not shown). This allows the voltage sensor 11 to operate immediately after the start of the pre-charge operation. Figures 7A and 7B correspond to Figures 3 and 5 of the above embodiment, respectively.

[0089] In the example shown in Figure 7A, since there is no short circuit between terminals T11 and T12, the detected voltage VH2 gradually rises from 0V, unlike in the above embodiment (Figures 3 and 5). That is, the voltage sensor 11 according to this modified example can operate based on the power supply voltage supplied from other circuits, even when the voltage VH is sufficiently low. Therefore, the detected voltage VH2 is a voltage corresponding to the voltage VH throughout the entire period. By the time the comparison period PD ends, the detected voltage VH2 becomes higher than the threshold TH (Figure 7A(D)). The comparison unit 26 maintains the disable signal DSBL inactive (low level in this example) from timing t4, which is the end timing of this comparison period PD, onwards (Figure 7A(E)).

[0090] In the example in Figure 7B, a short circuit occurs between terminals T11 and T12, so the detected voltage VH2 is below the threshold TH for the entire period from timing t21 to t24 (Figure 7B(D)). At timing t24, which is the end timing of this comparison period PD, the comparison unit 26 activates the disable signal DSBL (high level in this example) (Figure 7B(E)). In this way, the control circuit 19 detects the short circuit between terminals T11 and T12.

[0091] [Variation 1-2] In the above embodiment, as shown in Figures 3 and 5, the comparison period PD is started at the start timing of the precharge period P1, but it is not limited to this. Alternatively, for example, the comparison period PD may be started at a timing after a predetermined time has elapsed from the start timing of the precharge period P1, as shown in Figures 8A and 8B. Figures 8A and 8B correspond to Figures 3 and 5 of the above embodiment, respectively.

[0092] In the example in Figure 8A, the comparison period PD starts at timing t6. In this example, since there is no short circuit between terminals T11 and T12, the detected voltage VH2 becomes higher than the threshold TH by the time the comparison period PD ends (Figure 8A(D)). The comparison unit 26 keeps the disable signal DSBL inactive (low level in this example) from timing t4 onward, which is the end timing of this comparison period PD (Figure 8A(E)).

[0093] In the example in Figure 8B, the comparison period PD starts at timing t26. In this example, a short circuit occurs between terminals T11 and T12, so the detected voltage VH2 is below the threshold TH for the entire period from timing t26 to t24 (Figure 8B(E)). At timing t24, which is the end timing of this comparison period PD, the comparison unit 26 activates the disable signal DSBL (high level in this example) (Figure 8B(E)). In this way, the control circuit 19 detects the short circuit between terminals T11 and T12.

[0094] [Modification 1-3] In the above embodiment, as shown in Figure 3, the threshold value TH was set higher than the voltage immediately after the detection voltage VH2 rose at timing t2. However, the embodiment is not limited to this, and instead, for example, as shown in Figure 9, the threshold value TH may be set lower than the voltage immediately after the detection voltage VH2 rose at timing t2.

[0095] [Modifications 1-4] In the above embodiment, the comparison unit 26 sets the disable signal DSBL at the end of the comparison period PD, but it is not limited to this, and instead, for example, the disable signal DSBL may be set before the end of the comparison period PD. This modified example will be described in detail below.

[0096] Figure 10 shows a specific example of the control circuit 19D according to this modified example. The control circuit 19D has a precharge control unit 21D. The precharge control unit 21D has duty cycle generation units 23D and 24D and a comparison unit 26D.

[0097] The duty cycle generation unit 23D is configured to generate the duty cycle DP in the switching circuit 12 based on the detected voltage VL2 during the pre-charge period P1 and the voltage maintenance period P2, similar to the duty cycle generation unit 23 in the above embodiment. The duty cycle generation unit 23D starts changing the duty cycle DP from the timing indicated by the control signal CTL supplied from the comparison unit 26D.

[0098] The duty cycle generation unit 24D is configured to generate the duty cycle DS in the rectifier circuit 14 based on the detected voltage VL2 during the pre-charge period P1 and the voltage maintenance period P2, similar to the duty cycle generation unit 24 in the above embodiment. The duty cycle generation unit 24D starts changing the duty cycle DS from the timing indicated by the control signal CTL supplied from the comparison unit 26D.

[0099] The comparison unit 26D is configured to generate a disable signal DSBL by comparing the detected voltage VH2 with the threshold value TH, similar to the comparison unit 26 in the above embodiment. The comparison unit 26D also has the function of generating a control signal CTL that transitions when the detected voltage VH2 exceeds the threshold value TH.

[0100] Figure 11 shows an example of pre-charge operation when there is no short circuit between terminals T11 and T12. This Figure 11 corresponds to Figure 3 in the above embodiment. In this example, the comparison unit 26D of the pre-charge control unit 21D compares the detected voltage VH2 with the threshold value TH every 10 msec. during the period of timings t1 to t4 (Figure 11(D)). In this example, the detected voltage VH2 is below the threshold value TH before timing t3, and above the threshold value TH after timing t3. That is, at timing t7, which is the comparison timing immediately following timing t3, the detected voltage VH2 exceeds the threshold value TH. The comparison unit 26D transitions the control signal CTL at this timing t7.

[0101] The duty cycle generation unit 24D of the precharge control unit 21D starts changing the duty cycle DS at timing t7 based on the control signal CTL. Since the disable signal DSBL is inactive, the gate signal generation unit 29 generates gate signals GE and GF based on the duty cycle DS generated by the precharge control unit 21D, and the rectifier circuit 14 performs switching operations based on these gate signals GE and GF. As a result, as shown in Figure 11(A), the duty cycle DS of the switching operation in the rectifier circuit 14 changes from value DS1 to value DS2 after timing t7.

[0102] Furthermore, the duty cycle generation unit 23D of the precharge control unit 21D starts outputting the duty cycle DP at timing t7 based on this control signal CTL. Since the disable signal DSBL is inactive, the gate signal generation unit 28 generates gate signals GC and GD based on the duty cycle DP generated by the precharge control unit 21 and maintains gate signals GA and GB at a low level, and the switching circuit 12 performs switching operations based on these gate signals GA to GD. As a result, as shown in Figure 11(B), the duty cycle DP of the switching operation in the switching circuit 12 gradually increases after timing t7.

[0103] Here, for example, the period from timing t1 to t7 corresponds to one specific example of the "first sub-period" in this disclosure. For example, the period from timing t7 to t5 corresponds to one specific example of the "second sub-period" in this disclosure.

[0104] Thus, in the power conversion system 1 according to this modified example, at timing t7, when it is detected that the detected voltage VH2 has exceeded the threshold TH, the duty cycle DS is changed from value DS1 to value DS2 and the duty cycle DP is increased. Therefore, in this example, the period from timing t1 to t7 is the comparison period PD. This allows the pre-charge operation to be performed in a shorter time.

[0105] [Variations 1-5] In the above embodiment, this technology was applied to a center-tapped power conversion circuit, but it is not limited to this. Several examples of this modification will be given below to explain the modifications in detail.

[0106] (Circuit example E1) Figure 12 shows an example configuration of the power conversion system 1E according to this modified example. The power conversion system 1E includes a power conversion device 30. The power conversion device 30 includes a transformer 33, a rectifier circuit 34, and a control circuit 39.

[0107] The transformer 33 has windings 33A and 33B. One end of winding 33A is connected to node N1 in the switching circuit 12, and the other end is connected to node N2 in the switching circuit 12. One end of winding 33B is connected to node N4 in the rectifier circuit 34, and the other end is connected to node N5 in the rectifier circuit 34.

[0108] The rectifier circuit 34 is a full-bridge type circuit and has transistors S5 to S8. Transistors S5 to S8 are constructed using, for example, N-type field-effect transistors. Transistors S5 to S8 each have body diodes D5 to D8, similar to transistors S1 to S4. In this example, N-type field-effect transistors are used, but any switching element can be used. In this example, transistors with body diodes are used, but transistors without body diodes can also be used. In this case, for example, a diode is added to the transistor instead of a body diode. The drain of transistor S5 is connected to voltage line L21A, the gate signal GF is supplied to the gate, and the source is connected to node N4. The drain of transistor S6 is connected to node N4, the gate signal GE is supplied to the gate, and the source is connected to reference voltage line L22. Node N4 is the connection point between the source of transistor S5 and the drain of transistor S6. The drain of transistor S7 is connected to voltage line L21A, the gate signal GE is supplied to the gate, and the source is connected to node N5. The drain of transistor S8 is connected to node N5, the gate is supplied with the gate signal GF, and the source is connected to the reference voltage line L22. Node N5 is the connection point between the source of transistor S7 and the drain of transistor S8.

[0109] The control circuit 39, similar to the control circuit 19 in the above embodiment, is configured to control the operation of the power converter 30 by controlling the operation of the switching circuit 12 and the rectifier circuit 34 based on the voltage VH detected by the voltage sensor 11 and the voltage VL detected by the voltage sensor 18. Specifically, the control circuit 39 generates gate signals GA~GF based on the voltages VH and VL, and controls the operation of the power converter 30 by performing PWM control using these gate signals GA~GF.

[0110] In this power conversion system 1E, similar to the embodiment described above, the control circuit 39 operates the rectifier circuit 34 to supply power from terminals T21 and T22 to terminals T11 and T12 during the pre-charge period P1, and during the pre-charge period P1, it performs a comparison operation to compare the voltage between terminals T11 and T12 detected by the voltage sensor 11 with a threshold value TH, thereby detecting a short circuit between terminals T11 and T12.

[0111] (Circuit example E2) Figure 13 shows an example configuration of another power conversion system 1F according to this modified example. The power conversion system 1F includes a power conversion device 40. The power conversion device 40 is a so-called forward converter. The power conversion device 40 includes a switching circuit 42, a transformer 43, a rectifier circuit 44, and a control circuit 49.

[0112] The switching circuit 42 has a transistor S11. Each transistor S11 is a switching element that performs switching operation based on a gate signal G11. Like the transistors S1 to S4 in the above embodiment, transistor S11 has a body diode D11. The drain of transistor S11 is connected to the winding 43A (described later) of the transformer 43, the gate signal G11 is supplied to the gate, and the source is connected to the reference voltage line L12.

[0113] Transformer 43 has windings 43A and 43B. One end of winding 43A is connected to voltage line L11, and the other end is connected to the drain of transistor S11 in switching circuit 42. One end of winding 43B is connected to voltage line L21A, and the other end is connected to the drain of transistor S12 (described later) in rectifier circuit 44.

[0114] The rectifier circuit 44 has transistors S12 and S13. Transistors S12 and S13 are constructed using, for example, N-type field-effect transistors. Transistors S12 and S13 each have body diodes D12 and D13, similar to transistors S1 to S4. In this example, N-type field-effect transistors are used, but any switching element can be used. In this example, transistors with body diodes are used, but transistors without body diodes can also be used. In this case, for example, a diode is added to the transistor instead of the body diode. The drain of transistor S12 is connected to the other end of winding 43B, the gate signal GE is supplied to the gate, and the source is connected to the reference voltage line L22. The drain of transistor S13 is connected to the voltage line L21A, the gate signal GF is supplied to the gate, and the source is connected to the reference voltage line L22.

[0115] The control circuit 49, similar to the control circuit 19 in the above embodiment, is configured to control the operation of the power converter 40 by controlling the operation of the switching circuit 42 and the rectifier circuit 44 based on the voltage VH (detected voltage VH2) detected by the voltage sensor 11 and the voltage VL (detected voltage VL2) detected by the voltage sensor 18. Specifically, the control circuit 49 generates gate signals G11, G12, and G13 based on the voltages VH and VL, and controls the operation of the power converter 40 by performing PWM control using these gate signals G11, G12, and G13. For example, the control circuit 49 may generate both gate signals G12 and G13 during the pre-charge period P1, or it may generate gate signal G12 while maintaining gate signal G13 at a low level. For example, the control circuit 49 may maintain gate signal G11 at a low level during the pre-charge period P1. In this case, the body diode D11 of transistor S11 performs diode rectification.

[0116] In this power conversion system 1F, similar to the embodiment described above, the control circuit 49 operates the rectifier circuit 44 to supply power from terminals T21 and T22 to terminals T11 and T12 during the pre-charge period P1, and detects a short circuit between terminals T11 and T12 by performing a comparison operation that compares the voltage between terminals T11 and T12 detected by the voltage sensor 11 with a threshold value TH during the pre-charge period P1.

[0117] Thus, this technology can be applied to various power conversion devices.

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

[0119] <2. Second Embodiment> Next, a power conversion system 2 according to a second embodiment will be described. In this embodiment, the comparison period PD for comparing the detected voltage VH2 and the threshold value TH differs from that of the first embodiment. Components that are substantially the same as those in the power conversion system 2 according to the first embodiment are denoted by the same reference numerals, and their descriptions are omitted as appropriate.

[0120] Figure 14 shows an example configuration of the power conversion system 2. The power conversion system 2 includes a power conversion device 50. The power conversion device 50 has a control circuit 59. The control circuit 59 is configured to control the operation of the power conversion device 50 by controlling the operation of the switching circuit 12 and the rectifier circuit 14 based on the voltage VH (detected voltage VH2) detected by the voltage sensor 11 and the voltage VL (detected voltage VL2) detected by the voltage sensor 18.

[0121] Figure 15 shows an example configuration of the control circuit 59. The control circuit 59 has a precharge control unit 61. The precharge control unit 61 has a comparison unit 66. The comparison unit 66 is configured to generate a disable signal DSBL by comparing a detected voltage VH2 with a threshold value TH. Specifically, the comparison unit 66 compares the detected voltage VH2 with the threshold value TH at least once during a period (comparison period PD, described later) after a predetermined time (e.g., 100 msec.) has elapsed since the start of the precharge period P1. Specifically, the comparison unit 66 compares the detected voltage VH2 with the threshold value TH, and if the detected voltage VH2 is higher than the threshold value TH, it deactivates the disable signal DSBL (e.g., to a low level). Also, the comparison unit 66 compares the detected voltage VH2 with the threshold value TH, and if the detected voltage VH2 is lower than the threshold value TH, it activates the disable signal DSBL (e.g., to a high level) and does not perform any further comparison operations.

[0122] Figure 16A shows an example of pre-charge operation when there is no short circuit between terminals T11 and T12, where (A) shows the duty cycle DS of the switching operation in the rectifier circuit 14, (B) shows the duty cycle DP of the switching operation in the switching circuit 12, (C) shows the waveform of the voltage VH, (D) shows the waveform of the detection result (detected voltage VH2) of the voltage sensor 11, and (E) shows the waveform of the disable signal DSBL.

[0123] First, the duty cycle generation unit 24 of the precharge control unit 61 sets the duty cycle DS to the value DS1 during the period t51 to t54 (Figure 16A(A)). The duration of this timing t51 to t54 is, for example, 100 [msec.], and the timing t54 is set, for example, based on the timer of the control circuit 59. The gate signal generation unit 29 generates gate signals GE and GF based on the duty cycle DS generated by the precharge control unit 61, and the rectifier circuit 14 performs switching operations based on these gate signals GE and GF. Also, the duty cycle generation unit 23 sets the duty cycle DP to "0" (zero) during the period t51 to t54 (Figure 16A(B)). The gate signal generation unit 28 maintains the gate signals GA to GD at a low level based on the duty cycle DP generated by the precharge control unit 61, and the switching circuit 12 maintains transistors S1 to S4 in the off state based on these gate signals GA to GD. As the rectifier circuit 14 performs switching operations in this manner, the voltage VH across the capacitor 9 gradually increases (Figure 16A(C)).

[0124] The detected voltage VH2 is 0V at timings t51 to t52 (Figure 16A(D)). At timing t52, the voltage VH becomes sufficient for the voltage sensor 11 to operate, and the voltage sensor 11 starts operating at timing t52. As a result, the detected voltage VH2 becomes a voltage corresponding to the voltage VH from timing t52 onward.

[0125] The comparison unit 66 of the precharge control unit 61 compares the detected voltage VH2 with the threshold TH every 10 msec., for example, during the period from timing t54 until the start of power conversion operation (comparison period PD) (Figure 16A(D)). In Figure 16A(D), the arrows indicate the comparison timings that the comparison unit 66 compares. In this example, since there is no short circuit between terminals T11 and T12, the detected voltage VH2 exceeds the threshold TH at timing t53. For example, at timing t54, the detected voltage VH2 is higher than the threshold TH, so the comparison unit 66 deactivates the disable signal DSBL (low level in this example). The comparison unit 66 sets the disable signal DSBL each time it compares the detected voltage VH2 with the threshold TH. In this example, the detected voltage VH2 is higher than the threshold TH throughout the entire comparison period PD from timing t54 onwards. Therefore, the comparison unit 66 maintains the disabled signal DSBL inactive (at a low level in this example) during this comparison period PD (Figure 16A(E)).

[0126] The duty cycle generation unit 24 of the precharge control unit 61 sets the duty cycle DS to a value DS2, which is higher than the value DS1, during the period from timing t54 to t55 (Figure 16A(A)). Since the disable signal DSBL is inactive, the gate signal generation unit 29 generates gate signals GE and GF based on the duty cycle DS generated by the precharge control unit 61, and the rectifier circuit 14 performs switching operations based on these gate signals GE and GF. As a result, as shown in Figure 16A(A), the duty cycle DS of the switching operation in the rectifier circuit 14 changes from the value DS1 to the value DS2. In addition, the duty cycle generation unit 24 of the precharge control unit 61 generates the duty cycle DP such that the duty cycle DP gradually increases during the period from timing t54 to t55 (Figure 16A(B)). Since the disable signal DSBL is inactive, the gate signal generation unit 28 generates gate signals GC and GD based on the duty cycle DP generated by the precharge control unit 61, and maintains gate signals GA and GB at a low level. The switching circuit 12 performs switching operations based on these gate signals GA to GD. As a result, as shown in Figure 16A(B), the duty cycle DP of the switching operation in the switching circuit 12 gradually increases during the timing period t54 to t55. As the switching circuit 12 and the rectifier circuit 14 perform switching operations in this way, the voltage VH across the capacitor 9 gradually increases (Figure 16A(C)).

[0127] Then, at timing t55, when the detected voltage VH2 reaches the target voltage Vtarget, the power conversion system 2 performs a voltage maintenance operation to maintain the voltage VH near the target voltage Vtarget during the period after timing t55 (voltage maintenance period P2). This operation is the same as in the first embodiment described above. The comparison unit 66 of the precharge control unit 61 continues to repeat the comparison operation during this voltage maintenance period P2. In this example, since there is no short circuit between terminals T11 and T12, the comparison unit 66 maintains the disable signal DSBL inactive (low level in this example) (Figure 16A(E)).

[0128] Here, for example, the period from timing t51 to t54 corresponds to one specific example of the “first sub-period” in this disclosure. The period from timing t54 to t55 corresponds to one specific example of the “second sub-period” in this disclosure.

[0129] The operating waveform during the timing period t51 to t54 is the same as in the first embodiment described above (Figure 4).

[0130] Figure 16B shows an example of pre-charge operation when a short circuit has already occurred between terminals T11 and T12. Timings t61 and t64 correspond to timings t51 and t54 in the example in Figure 16A, respectively.

[0131] During the period from timing t61 to t64, the power conversion system 2 sets the duty cycle DS to value DS1 and the duty cycle DP to "0" (zero), similar to the period from timing t51 to t54 shown in Figure 16A (Figures 16B(A), (B)). In this example, a short circuit occurs between terminals T11 and T12, so the voltage VH across capacitor 9 does not rise and remains at 0V (Figure 16B(C)). Since the voltage VH is maintained at 0V in this way, the voltage sensor 11 cannot operate, and the detected voltage VH2 also remains at 0V (Figure 16B(D)).

[0132] The comparison unit 66 of the precharge control unit 61 compares the detected voltage VH2 with the threshold value TH at timing t64 (Figure 16B(D)). In this example, a short circuit occurs between terminals T11 and T12, so the detected voltage VH2 is lower than the threshold value TH. Therefore, the comparison unit 66 activates the disable signal DSBL (high level in this example). In this way, the control circuit 59 detects the short circuit between terminals T11 and T12. The comparison unit 66 then does not perform any further comparison operations.

[0133] Since the disable signal DSBL is active, the gate signal generation unit 29 generates gate signals GE and GF that are maintained at a low level regardless of the duty cycle DS generated by the precharge control unit 61, and the rectifier circuit 14 stops switching operation based on these gate signals GE and GF. As a result, as shown in Figure 16B(A), the duty cycle DS of the switching operation in the rectifier circuit 14 becomes 0 (zero). Similarly, since the disable signal DSBL is active, the gate signal generation unit 28 generates gate signals GA to GD that are maintained at a low level regardless of the duty cycle DP generated by the precharge control unit 61, and the switching circuit 12 stops switching operation based on these gate signals GA to GD. As a result, as shown in Figure 16B(B), the duty cycle DP of the switching operation in the switching circuit 12 becomes 0 (zero). In this way, the power conversion system 2 temporarily stops the precharge operation.

[0134] Subsequently, the power conversion system 2, for example, after a predetermined time has elapsed, restarts the pre-charge operation and checks whether a short circuit has occurred between terminals T11 and T12. If the power conversion system 2 restarts the pre-charge operation multiple times and a short circuit continues to occur between terminals T11 and T12, it completely stops its operation. The power conversion system 2 then notifies an external device, for example, that a short circuit has occurred between terminals T11 and T12.

[0135] The operating waveform during the timing period t61 to t64 is the same as in the first embodiment described above (Figure 6).

[0136] Figure 16C shows an example of a pre-charge operation when a short circuit occurs between terminals T11 and T12 during the pre-charge operation. Timings t71 to t74 correspond to timings t51 to t54 in the example in Figure 16A, respectively. In this example, a short circuit occurs between terminals T11 and T12 at timing t75.

[0137] During the period from timing t71 to t74, the power conversion system 2 sets the duty cycle DS to value DS1 and the duty cycle DP to "0" (zero), similar to the period from timing t51 to t54 shown in Figure 16A (Figures 16C(A), (B)). In this example, since a short circuit has not yet occurred between terminals T11 and T12 during the period from timing t71 to t74, the voltage VH in the capacitor 9 rises due to the pre-charge operation (Figure 16C(C)). At timing t72, the voltage VH becomes high enough for the voltage sensor 11 to operate, and the voltage sensor 11 starts operating at timing t72. As a result, the detected voltage VH2 becomes a voltage corresponding to the voltage VH from timing t72 onward (Figure 16C(D)).

[0138] The comparison unit 66 of the precharge control unit 61 compares the detected voltage VH2 with the threshold TH every 10 msec. during the comparison period PD, which begins at timing t74 (Figure 16C(D)). For example, at timing t74, the detected voltage VH2 is higher than the threshold TH, so the comparison unit 66 deactivates the disable signal DSBL (low level in this example). The comparison unit 66 sets the disable signal DSBL each time it compares the voltage VH with the threshold TH. In this example, during the period from timing t74 to t75, the detected voltage VH2 is higher than the threshold TH. Therefore, the comparison unit 66 maintains the disable signal DSBL inactive (low level in this example) during the period from timing t74 to t75 (Figure 15C(E)).

[0139] During the period from timing t74 to t76, the disable signal DSBL is inactive, so the power conversion system 2 sets the duty cycle DS to value DS2 and gradually increases the duty cycle DP, as in the case of Figure 16A (Figures 16C(A), (B)).

[0140] In this example, at timing t75, a short circuit occurs between terminals T11 and T12, causing the voltage VH to become 0V (Figure 16C(C)). As a result, the detected voltage VH2 also becomes 0V, and the detected voltage VH2 falls below the threshold TH (Figure 16C(D)). Therefore, at the subsequent comparison timing t76, since the detected voltage VH2 is lower than the threshold TH, the comparison unit 66 activates the disable signal DSBL (high level in this example) (Figure 16C(E)). In this way, the control circuit 59 detects the short circuit between terminals T11 and T12. The comparison unit 66 then does not perform any further comparison operations. Therefore, the comparison period PD ends at timing t76.

[0141] During the period after timing t76, the disable signal DSBL is active, so the gate signal generation unit 29 generates gate signals GE and GF that are maintained at a low level regardless of the duty cycle DS generated by the precharge control unit 61, and the rectifier circuit 14 stops switching operation based on these gate signals GE and GF. As a result, as shown in Figure 16C(A), the duty cycle DS of the switching operation in the rectifier circuit 14 becomes 0 (zero). Similarly, since the disable signal DSBL is active, the gate signal generation unit 28 generates gate signals GA to GD that are maintained at a low level regardless of the duty cycle DP generated by the precharge control unit 61, and the switching circuit 12 stops switching operation based on these gate signals GA to GD. As a result, as shown in Figure 16C(B), the duty cycle DP of the switching operation in the switching circuit 12 becomes 0 (zero). In this way, the power conversion system 2 temporarily stops the precharge operation.

[0142] Subsequently, the power conversion system 2, for example, after a predetermined time has elapsed, restarts the pre-charge operation and checks whether a short circuit has occurred between terminals T11 and T12. If the power conversion system 2 restarts the pre-charge operation multiple times and a short circuit continues to occur between terminals T11 and T12, it completely stops its operation. The power conversion system 2 then notifies an external device, for example, that a short circuit has occurred between terminals T11 and T12.

[0143] Thus, in the power conversion system 2, the control circuit 59 performs multiple comparison operations during the period from timing t54 to t55 in Figure 16A, and detects a short circuit between terminals T11 and T12 based on the comparison results of each of the multiple comparison operations. As a result, even if a short circuit occurs between terminals T11 and T12 during the pre-charge operation, for example as shown in Figure 16C, the short circuit between terminals T11 and T12 can be detected, thus effectively detecting the short circuit between terminals T11 and T12.

[0144] As described above, in this embodiment, the control circuit performs multiple comparison operations during the period from timing t54 to t55 in Figure 16A, and detects a short circuit between terminals T11 and T12 based on the comparison results of these multiple comparison operations. Therefore, a short circuit between terminals T11 and T12 can be effectively detected. Other effects are the same as in the first embodiment described above.

[0145] [Variation 2-1] In the above embodiment, the voltage sensor 11 is not configured to operate immediately after the start of the pre-charge operation, but this is not the only configuration. Alternatively, for example, the voltage sensor 11 may be configured to operate even immediately after the start of the pre-charge operation by operating based on a power supply voltage supplied from another circuit, as shown in Figures 17A to 17C. Figures 17A to 17C correspond to Figures 16A to 16C of the above embodiment, respectively. In this modified configuration, the detected voltage VH2 gradually rises from 0V, unlike in the above embodiment (Figures 16A to 16C). That is, the voltage sensor 11 in this modified configuration can operate based on a power supply voltage supplied from another circuit, even when the voltage VH is sufficiently low. Therefore, the detected voltage VH2 is a voltage corresponding to the voltage VH throughout the entire period. Even in this case, the power conversion system 2 can detect a short circuit between terminals T11 and T12.

[0146] [Modification 2-2] In the above embodiment, as shown in Figures 16B and 16C, the comparison unit 66 compares the detected voltage VH2 with the threshold value TH and activates the disable signal DSBL (e.g., to a high level) when it detects once that the detected voltage VH2 is lower than the threshold value VTH. However, it is not limited to this. Alternatively, for example, as shown in Figures 18A and 18B, the comparison unit 66 may activate the disable signal DSBL (e.g., to a high level) when it detects a predetermined number of consecutive times (3 times in this example) that the detected voltage VH2 is lower than the threshold value VTH. Figures 18A and 18B correspond to Figures 16B and 16C of the above embodiment, respectively.

[0147] In the example shown in Figure 18A, a short circuit occurs between terminals T11 and T12. Therefore, the comparison unit 66 detects that the detected voltage VH2 is lower than the threshold TH at three comparison timings during the period from timing t64 to t66. In this example, the comparison unit 66 detects that the detected voltage VH2 is lower than the threshold TH three times in a row. Therefore, at the third comparison timing, timing t66, the disable signal DSBL is activated (e.g., to a high level). In this way, the control circuit 59 detects the short circuit between terminals T11 and T12.

[0148] In the example shown in Figure 18B, a short circuit occurred between terminals T11 and T12 at timing t75. Therefore, the comparison unit 66 detects that the detected voltage VH2 is lower than the threshold TH at three comparison timings during the period from timing t76 to t77. In this example, the comparison unit 66 detected that the detected voltage VH2 was lower than the threshold TH three times in a row. Therefore, at the third comparison timing, timing t77, the disable signal DSBL is activated (e.g., to a high level). In this way, the control circuit 59 detects the short circuit between terminals T11 and T12.

[0149] In this example, the comparison unit 66 activated the disable signal DSBL (e.g., to a high level) when it detected that the detected voltage VH2 was lower than the threshold VTH three times in a row, but it is not limited to this. Alternatively, the comparison unit 66 may activate the disable signal DSBL when it detects that the detected voltage VH2 is lower than the threshold VTH two times in a row, or when it detects that the detected voltage VH2 is lower than the threshold VTH four or more times in a row.

[0150] [Modification 2-3] In the above embodiment, as shown in Figures 16A to 16C, the comparison unit 66 performs the comparison operation one or more times. However, it is not limited to this, and instead, for example, as shown in Figures 19A and 19B, the comparison operation may be performed only once. Figures 19A and 19B correspond to Figures 16A and 16B of the above embodiment, respectively.

[0151] In the example in Figure 19A, at timing t54, the comparison unit 66 compares the detected voltage VH2 with the threshold value TH. In this example, since there is no short circuit between terminals T11 and T12, the detected voltage VH2 is higher than the threshold value TH. Therefore, the comparison unit 66 keeps the disable signal DSBL inactive (low level in this example) from timing t54 onward (Figure 19A(E)).

[0152] In the example in Figure 19B, at timing t64, the comparison unit 66 compares the detected voltage VH2 with the threshold value TH. In this example, a short circuit occurs between terminals T11 and T12, so the detected voltage VH2 is lower than the threshold value TH. Therefore, at timing t64, the comparison unit 66 activates the disable signal DSBL (to a high level in this example) (Figure 19B(E)).

[0153] [Other variations] Furthermore, two or more of these variations may be combined.

[0154] Although the present invention has been described above with reference to embodiments and modifications, the present invention is not limited to these embodiments and various modifications are possible.

[0155] For example, in the first embodiment described above, as shown in Figure 3(A), the duty cycle generation unit 24 of the precharge control unit 21 sets the duty cycle DS to value DS1 during the period t1 to t4, and sets the duty cycle DS to a value DS2 that is higher than value DS1 during the period t4 to t5. When setting the duty cycle DS to value DS1 during the period t1 to t4, the duty cycle generation unit 24 may gradually increase the duty cycle DS so that the duty cycle DS ultimately becomes value DS1, for example, as shown in Figure 20. Similarly, when setting the duty cycle DS to value DS2 during the period t4 to t5, the duty cycle generation unit 24 may gradually increase the duty cycle DS so that the duty cycle DS ultimately becomes value DS2, for example, as shown in Figure 20. The same applies to the second embodiment described above.

[0156] For example, in the first embodiment described above, as shown in Figure 3(D), the comparison unit 26 compared the detected voltage VH2 with the threshold value TH at multiple discrete timings, but it is not limited to this. Alternatively, for example, the comparison unit may be configured as an analog circuit, and the comparison unit may continuously compare the detected voltage VH2 with the threshold value TH during the comparison period PD. If the detected voltage VH2 is always lower than the threshold value TH during the comparison period PD, the comparison unit determines that the terminals T11 and T12 are short-circuited due to some factor and activates the disable signal DSBL. Furthermore, if the detected voltage VH2 becomes higher than the threshold value TH before the end of the comparison period PD, the comparison unit deactivates the disable signal DSBL (for example, to a low level) at the end of the comparison period PD. The same applies to the second embodiment described above.

[0157] For example, in the above embodiment, a step-down operation is performed in the power conversion operation, but it is not limited to this, and a step-up operation may also be performed.

[0158] For example, in the above embodiment, the power conversion operation is performed in a unidirectional manner, supplying power from the high-voltage battery BH to the low-voltage battery BL, but it is not limited to this. For example, the power conversion operation may be performed in a bidirectional manner by providing a mode in which power is supplied from the high-voltage battery BH to the low-voltage battery BL and a mode in which power is supplied from the low-voltage battery BL to the high-voltage battery BH. Even in this case, the capacitor 9 can be charged based on the power supplied from the low-voltage battery BL during the preparation period before performing the power conversion operation in the mode in which power is supplied from the high-voltage battery BH to the low-voltage battery BL.

[0159] For example, in the above embodiment, a short circuit between terminals T11 and T12 was detected based on the detection result of the voltage sensor 11, but the system is not limited to this, and a short circuit between terminals T11 and T12 may also be detected based on the detection result of other sensors, such as a current sensor. When a current sensor is used, this current sensor can be installed, for example, on the voltage line L21B or the voltage line L11. This power conversion system can stop the pre-charge operation when, for example, a short circuit between terminals T11 and T12 is detected based on the detection result of the voltage sensor 11 and the current sensor, and a short circuit between terminals T11 and T12 is detected based on the detection result of the current sensor.

[0160] For example, the circuit configuration of the switching circuit, the circuit configuration of the rectifier circuit, and the operating waveform of the gate signal in the above embodiments are examples and may be changed as appropriate.

Claims

1. A first power terminal having two connection terminals, A voltage sensor capable of detecting the voltage between the two connection terminals at the first power terminal, A switching circuit connected to the first power terminal and having one or more switching elements, A transformer having a first winding and a second winding connected to the switching circuit, A rectifier circuit having one or more switching elements is connected to the second winding, A smoothing circuit connected to the rectifier circuit, having an inductor and a first capacitor, 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 Equipped with, The control circuit is capable of operating the rectifier circuit to supply power from the second power terminal to the first power terminal during a second period prior to a first period in which power is supplied from the first power terminal to the second power terminal, and during the second period, it is capable of detecting a short circuit between the two connection terminals by performing a comparison operation that compares the voltage detected by the voltage sensor with a predetermined threshold voltage. The second period may include a first sub-period and a second sub-period following the first sub-period. The aforementioned control circuit is During the first sub-period, the duty cycle of the one or more switching elements of the rectifier circuit can be set to a first duty cycle. During the second sub-period, the duty cycle of the one or more switching elements of the rectifier circuit can be set to a second duty cycle that is greater than the first duty cycle. Power converter.

2. In the second period, each period corresponding to the switching period of the rectifier circuit includes a period during which no current flows through the inductor. The power conversion device according to claim 1.

3. The control circuit can perform the comparison operation multiple times during the first sub-period and detect a short circuit between the two connection terminals based on the comparison results of the multiple comparison operations. A power conversion device according to claim 1 or claim 2.

4. The first sub-period is a period of a predetermined length. The control circuit can determine that a short circuit has occurred between the two connection terminals if, in all of the comparison results of the multiple comparison operations during the first sub-period, the voltage detected by the voltage sensor is lower than the threshold voltage. The power conversion device according to claim 3.

5. The first sub-period is a period of a predetermined length. The control circuit initiates the second sub-period if, in one or more of the comparison results of the multiple comparison operations during the first sub-period, the voltage detected by the voltage sensor is higher than the threshold voltage. The power conversion device according to claim 3.

6. The control circuit initiates the second sub-period if, in the comparison result of the most recent of the multiple comparison operations during the first sub-period, the voltage detected by the voltage sensor is higher than the threshold voltage. The power conversion device according to claim 3.

7. The control circuit can perform the comparison operation once or more times during the second sub-period, and detect a short circuit of the first power terminal based on the comparison result of the one or more comparison operations. A power conversion device according to claim 1 or claim 2.

8. The control circuit can determine that a short circuit has occurred between the two connection terminals if, in the comparison result of the most recent of the one or more comparison operations during the second sub-period, the voltage detected by the voltage sensor is lower than the threshold voltage. The power conversion device according to claim 7.

9. The control circuit performs the comparison operation multiple times during the second sub-period, and if, in all of the comparison results of the two or more most recent predetermined number of comparison operations, the voltage detected by the voltage sensor is lower than the threshold voltage, it can determine that a short circuit has occurred between the two connection terminals. The power conversion device according to claim 7.

10. The control circuit can perform the comparison operation once during the second sub-period and detect a short circuit between the two connection terminals based on the comparison result of the comparison operation. The power conversion device according to claim 7.

11. The voltage sensor is capable of stopping operation for at least a portion of the first sub-period and is capable of operating for at least a portion of the first sub-period and the second sub-period. A power conversion device according to claim 1 or claim 2.

12. The control circuit can stop the operation of the switching circuit and the rectifier circuit if it detects a short circuit at the first power terminal. A power conversion device according to claim 1 or claim 2.

13. A first battery having a first terminal and a second terminal, A second capacitor having a first terminal and a second terminal, A first switch is provided in the path connecting the first terminal of the first battery and the first terminal of the second capacitor, A second switch is provided in the path connecting the second terminal of the first battery and the second terminal of the second capacitor, Power converter and The second battery and Equipped with, The aforementioned power converter is A first power terminal having a first connection terminal connected to the first terminal of the second capacitor, and a second connection terminal connected to the second terminal of the second capacitor, A voltage sensor capable of detecting the voltage between the first connection terminal and the second connection terminal, A switching circuit connected to the first power terminal and having one or more switching elements, A transformer having a first winding and a second winding connected to the switching circuit, A rectifier circuit having one or more switching elements is connected to the second winding, A smoothing circuit connected to the rectifier circuit, having an inductor and a first capacitor, A second power terminal connected to the smoothing circuit and the second battery, A control circuit capable of controlling the operation of the switching circuit and the rectifier circuit It has, The control circuit is capable of operating the rectifier circuit to supply power from the second power terminal to the first power terminal during a second period prior to a first period in which power is supplied from the first power terminal to the second power terminal, and during the second period, it is capable of detecting a short circuit between the first connection terminal and the second connection terminal by performing a comparison operation that compares the voltage detected by the voltage sensor with a predetermined threshold voltage. The second period may include a first sub-period and a second sub-period following the first sub-period. The aforementioned control circuit is During the first sub-period, the duty cycle of the one or more switching elements of the rectifier circuit can be set to a first duty cycle. During the second sub-period, the duty cycle of the one or more switching elements of the rectifier circuit can be set to a second duty cycle that is greater than the first duty cycle. Power conversion system.

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