Power converter

Abstract

The embodiment of the present application provides a power converter, which comprises a controller, at least one bridge arm, and a first capacitor and a second capacitor connected in series. Each bridge arm comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube, the first switch tube and the fourth switch tube are connected in series and then connected in parallel at two ends of the first capacitor and the second capacitor connected in series, and the connection end is connected with the connection end of the first capacitor and the second capacitor through the second switch tube and the third switch tube connected in reverse series. After the power converter is started, the controller controls the target switch tube in each bridge arm to keep conducting, and the target capacitor starts charging after the target switch tube in each bridge arm conducts, the target capacitor is at least one of the first capacitor and the second capacitor, and the target switch tube is at least one of the switch tubes in each bridge arm. When the voltage at two ends of the target capacitor does not reach a voltage threshold after the target capacitor is charged, the controller outputs information that there is a short circuit fault of the switch tube in each bridge arm.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, and in particular to a power converter. BACKGROUND

[0002] With the gradual increase of the penetration rate of distributed energy such as photovoltaic, wind power and energy storage devices, power converters or converters, as an important component unit of energy exchange, are also more and more widely used in power supply systems. During the working process of the power converter or the converter, the switching tube may fail, such as topology through caused by switching tube short circuit, bus short circuit, switching tube overcurrent damage, etc. In order to start up the power converter or the converter in the abnormal condition without further damage, it is necessary to do some start-up self-checking before starting up the power converter or the converter to ensure the safe operation of the equipment. SUMMARY

[0003] The embodiment of the present application provides a power converter, which can detect short circuit fault of the switching tube before the power converter works, avoid abnormal working conditions such as bus short circuit and short circuit fault diffusion during the working process of the power converter, and improve the reliability of the working process of the power converter.

[0004] In a first aspect, the present application provides a power converter, the power converter comprising a controller, at least one bridge arm, and a first capacitor and a second capacitor connected in series, the first capacitor being connected to a positive direct current bus, and the second capacitor being connected to a negative direct current bus. Each bridge arm in the at least one bridge arm comprises a first switching tube, a second switching tube, a third switching tube and a fourth switching tube, the first switching tube and the fourth switching tube being connected in series and then connected in parallel across the first capacitor and the second capacitor connected in series, and the connection end of the first switching tube and the fourth switching tube being connected to the connection end of the first capacitor and the second capacitor through the second switching tube and the third switching tube connected in reverse series. The controller is configured to, after the power converter is started, control a target switching tube in each bridge arm to be kept on, wherein other switching tubes in each bridge arm except the target switching tube are kept off, and a target capacitor starts to charge after the target switching tube in each bridge arm is turned on, the target capacitor being at least one of the first capacitor and the second capacitor, and the target switching tube being at least one of the first switching tube, the second switching tube, the third switching tube and the fourth switching tube in each bridge arm. The controller is further configured to, when the voltage across the target capacitor after charging does not reach a voltage threshold, output information that there is a switching tube short circuit fault in each bridge arm.

[0005] In the application, the controller in the power converter controls the target switch in each bridge arm to keep conducting after the power converter is powered on and before it formally works. The target capacitor starts charging after the target switch in each bridge arm is turned on. The voltage across the target capacitor is zero, which can be that the target capacitor is not charged and the voltage across it is zero before the power converter is connected to the DC power supply, or the target capacitor can be discharged until the voltage across it is zero. Then, when the voltage across the target capacitor after charging does not reach the voltage threshold, the controller determines that there is a short circuit in the switch in the current power converter, and outputs information that there is a short circuit fault in the switch in each bridge arm. By detecting the faulty switch before the power converter works, the abnormal working conditions such as bus short circuit and short circuit fault propagation during the working process of the power converter are avoided, and the reliability of the working process of the power converter is improved.

[0006] In a possible implementation, the power converter includes a slow start switch and a resistor connected in series to the positive DC bus or the negative DC bus, the target capacitor is a first capacitor and a second capacitor, and the target switch is a first switch in each bridge arm. The target capacitor starts charging after the target switch in each bridge arm is turned on, specifically, after the first switch in each bridge arm is kept conducting, the controller controls the slow start switch to turn on to turn on the connection of the first capacitor and the second capacitor to the DC power supply to start charging the first capacitor and the second capacitor through the DC power supply. The controller is also configured to output information that the third switch is short-circuited when the DC power supply charges the first capacitor and the second capacitor and the voltage across the first capacitor does not reach the voltage threshold, or output information that the fourth switch is short-circuited when the DC power supply charges the first capacitor and the second capacitor and the voltage across the first capacitor and the voltage across the second capacitor do not reach the voltage threshold. Here, if the third switch is short-circuited and the second switch is disconnected, the diode connected in parallel with the second switch can conduct the current flowing from the connection end of the first switch and the fourth switch to the connection end of the first capacitor and the second capacitor, so the third switch and the second switch cannot cut off the current flowing from the connection end of the first switch and the fourth switch to the connection end of the first capacitor and the second capacitor, and the first capacitor is short-circuited and cannot be normally boosted. If the fourth switch is short-circuited, the fourth switch cannot cut off the current flowing from the positive DC bus to the negative DC bus, and the first capacitor and the second capacitor are short-circuited and cannot be normally boosted. Therefore, the voltage change of the first capacitor and the second capacitor after charging can accurately detect the short circuit fault of the switch.

[0007] In a possible implementation, the power converter includes a slow start switch and a resistor connected in series to the positive DC bus or the negative DC bus, the target capacitor is the first capacitor and the second capacitor, and the target switch tube is the fourth switch tube in each bridge arm. After the target switch tube in each bridge arm is turned on, the target capacitor starts to charge. Specifically, after the fourth switch tube in each bridge arm is kept turned on, the controller controls the slow start switch to be turned on, so as to turn on the connection between the first capacitor and the second capacitor and the DC power supply, and start charging the first capacitor and the second capacitor by the DC power supply. The controller is further configured to control the slow start switch to be turned on after the fourth switch tube in each bridge arm is kept turned on, so as to turn on the connection between the first capacitor and the second capacitor and the DC power supply, and charge the first capacitor and the second capacitor by the DC power supply. The controller is further configured to output information that the second switch tube is short-circuited when the DC power supply charges the first capacitor and the second capacitor, and the voltage across the second capacitor does not reach the voltage threshold, or output information that the first switch tube is short-circuited when the DC power supply charges the first capacitor and the second capacitor, and the voltage across the first capacitor and the voltage across the second capacitor do not reach the voltage threshold. Here, when the second switch tube is short-circuited and the third switch tube is turned off, the diode connected in parallel with the third switch tube can be turned on to conduct the current flowing from the connection end of the first capacitor and the second capacitor to the connection end of the first switch tube and the fourth switch tube, so that the second switch tube and the third switch tube cannot cut off the current flowing from the connection end of the first capacitor and the second capacitor to the connection end of the first switch tube and the fourth switch tube, and the second capacitor is short-circuited and cannot be normally boosted. When the first switch tube is short-circuited, the first switch tube cannot cut off the current flowing from the positive DC bus to the negative DC bus, and the first capacitor and the second capacitor are short-circuited and cannot be normally boosted. Therefore, the voltage across the first capacitor and the second capacitor after being charged can be used to accurately detect the short-circuit fault of the switch tube.

[0008] In a possible implementation, the first capacitor and the second capacitor are connected in parallel with a discharging circuit, and the controller is configured to, after controlling the slow start switch to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, control the first switch tube to be turned off, and control the slow start switch to be turned off to turn off the connection between the first capacitor and the second capacitor and the DC power supply, so that the discharging circuit discharges the first capacitor and the second capacitor, and when the first capacitor and the second capacitor are discharged to zero voltage, control the second switch tube in each bridge arm to be kept turned on, and control the slow start switch to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, and when the second capacitor is charged and the voltage across the second capacitor does not reach the voltage threshold, output information that the fourth switch tube is short-circuited. Here, when the voltages across the first capacitor and the second capacitor are both greater than or equal to the voltage threshold after the first capacitor and the second capacitor are charged, the second short-circuit fault detection of the fourth switch tube is performed, which can avoid that the first switch tube cannot be normally detected whether it is short-circuited in the case that the fourth switch tube is turned off, and improves the accuracy of the switch tube short-circuit fault detection.

[0009] In a possible implementation, the first capacitor and the second capacitor are connected in parallel with a discharging circuit, and the controller is configured to, after controlling the slow start switch to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, control the fourth switch tube to be turned off, and control the slow start switch to be turned off to turn off the connection between the first capacitor and the second capacitor and the DC power supply, so that the discharging circuit discharges the first capacitor and the second capacitor, and when the first capacitor and the second capacitor are discharged to zero voltage, control the third switch tube in each bridge arm to be kept turned on, and control the slow start switch to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, and when the first capacitor is charged and the voltage across the first capacitor does not reach the voltage threshold, output information that the first switch tube is short-circuited. Here, when the voltages across the first capacitor and the second capacitor are both greater than or equal to the voltage threshold after the first capacitor and the second capacitor are charged, the second short-circuit fault detection of the first switch tube is performed, which can avoid that the first switch tube cannot be normally detected whether it is short-circuited in the case that the fourth switch tube is turned off, and improves the accuracy of the switch tube short-circuit fault detection.

[0010] In a possible implementation, the first capacitor and the second capacitor are connected in parallel with a discharging circuit, and the connection end of the first switch tube and the fourth switch tube in each bridge arm is further connected to the connection end of the first capacitor and the second capacitor through a filter capacitor. After the slow-start switch is controlled to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor through the DC power supply, the controller is further configured to: if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to a voltage threshold, control the target switch tube to be turned off, and control the slow-start switch to be turned off to turn off the connection between the first capacitor and the second capacitor and the DC power supply, so that the discharging circuit discharges the first capacitor and the second capacitor, and when the voltage across the first capacitor and the voltage across the second capacitor are both zero, control the slow-start switch to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor through the DC power supply, if the first capacitor and the second capacitor are charged, and the voltage across the first capacitor and the voltage across the second capacitor do not reach the voltage threshold, output information that the first switch tube and the fourth switch tube are short-circuited. Alternatively, the controller is further configured to: if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to a voltage threshold, control the target switch tube to be turned off, and control the slow-start switch to be turned off to turn off the connection between the first capacitor and the second capacitor and the DC power supply, so that the discharging circuit discharges the first capacitor and the second capacitor, and when the voltage across the first capacitor and the voltage across the second capacitor are both zero, control the slow-start switch to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor through the DC power supply, if the first capacitor and the second capacitor are charged, and the voltage across the filter capacitor is equal to the voltage across the first capacitor or the voltage across the second capacitor, output information that the first switch tube or the fourth switch tube is short-circuited. Here, when the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold after the first capacitor and the second capacitor are charged, the second short-circuit fault detection is performed on the first switch tube or the fourth switch tube, which can avoid the situation that the first switch tube cannot be normally detected to be short-circuited when the fourth switch tube is open, and the fourth switch tube cannot be normally detected to be short-circuited when the first switch tube is open, and the accuracy of the switch tube short-circuit fault detection is improved.

[0011] In a possible implementation, the power converter further comprises an electric energy transfer unit, and the controller is configured to, after controlling the slow start switch to be turned on to turn on the connection of the first capacitor and the second capacitor to the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, and if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, control the first switch tube to be turned off, and control the electric energy transfer unit to discharge the first capacitor by the electric energy transfer unit. The controller is further configured to, when the first capacitor is discharged to zero by the electric energy transfer unit, control the third switch tube in each bridge arm to be kept turned on, and control the electric energy transfer unit to charge the first capacitor by the electric energy transfer unit. The controller is further configured to, if the voltage across the first capacitor does not reach the voltage threshold after the first capacitor is charged by the electric energy transfer unit, output information that the first switch tube is short-circuited. Here, if the first switch tube is short-circuited, the first switch tube cannot cut off the current flowing from the positive DC bus to the negative DC bus, and the first capacitor is short-circuited and cannot be normally boosted, and therefore, the voltage change across the first capacitor after the first capacitor is charged can be used to accurately detect the short-circuit fault of the switch tube.

[0012] In a possible implementation, the power converter further comprises an electric energy transfer unit, and the controller is configured to, after controlling the slow start switch to be turned on to turn on the connection of the first capacitor and the second capacitor to the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, and if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, control the first switch tube to be turned off, and control the electric energy transfer unit to discharge the first capacitor by the electric energy transfer unit. The controller is further configured to, when the first capacitor is discharged to zero by the electric energy transfer unit, control the third switch tube in each bridge arm to be kept turned on, and control the electric energy transfer unit to charge the first capacitor by the electric energy transfer unit. The controller is further configured to, if the voltage across the first capacitor does not reach the voltage threshold after the first capacitor is charged by the electric energy transfer unit, output information that the first switch tube is short-circuited. Here, if the first switch tube is short-circuited, the first switch tube cannot cut off the current flowing from the positive DC bus to the negative DC bus, and the first capacitor is short-circuited and cannot be normally boosted, and therefore, the voltage change across the first capacitor after the first capacitor is charged can be used to accurately detect the short-circuit fault of the switch tube.

[0013] In a possible implementation, the power converter further comprises an electric energy transfer unit; the controller is configured to, after controlling the slow start switch to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, control the fourth switch tube to be turned off, and control the electric energy transfer unit to discharge the first capacitor by the electric energy transfer unit. The controller is further configured to, when the first capacitor is discharged to zero voltage by the electric energy transfer unit, control the first switch tube in each bridge arm to remain turned on, and control the electric energy transfer unit to charge the first capacitor by the electric energy transfer unit. The controller is further configured to, if the voltage across the first capacitor does not reach the voltage threshold after the first capacitor is charged by the electric energy transfer unit, output information that the third switch tube is short-circuited. Here, if the third switch tube is short-circuited and the second switch tube is turned off, the diode connected in parallel with the second switch tube can conduct the current flowing from the connection end of the first switch tube and the fourth switch tube to the connection end of the first capacitor and the second capacitor, so that the third switch tube and the second switch tube cannot cut off the current flowing from the connection end of the first switch tube and the fourth switch tube to the connection end of the first capacitor and the second capacitor, and the first capacitor is short-circuited and cannot be normally boosted. The voltage change across the first capacitor after the first capacitor is charged can be used to accurately detect the short-circuit fault of the switch tube.

[0014] In a possible implementation, the power converter further comprises an electric energy transfer unit; the controller is configured to, after controlling the slow start switch to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, control the fourth switch tube to be turned off, and control the electric energy transfer unit to discharge the first capacitor by the electric energy transfer unit. The controller is further configured to, when the first capacitor is discharged to zero voltage by the electric energy transfer unit, control the first switch tube in each bridge arm to remain turned on, and control the electric energy transfer unit to charge the first capacitor by the electric energy transfer unit. The controller is further configured to, if the voltage across the first capacitor does not reach the voltage threshold after the first capacitor is charged by the electric energy transfer unit, output information that the third switch tube is short-circuited. Here, if the third switch tube is short-circuited and the second switch tube is turned off, the diode connected in parallel with the second switch tube can conduct the current flowing from the connection end of the first switch tube and the fourth switch tube to the connection end of the first capacitor and the second capacitor, so that the third switch tube and the second switch tube cannot cut off the current flowing from the connection end of the first switch tube and the fourth switch tube to the connection end of the first capacitor and the second capacitor, and the first capacitor is short-circuited and cannot be normally boosted. The voltage change across the first capacitor after the first capacitor is charged can be used to accurately detect the short-circuit fault of the switch tube.

[0015] In a possible implementation, the electric energy transfer unit includes an inductor, a fifth switch tube and a sixth switch tube connected in series, the fifth switch tube is connected with the positive DC bus, the sixth switch tube is connected with the negative DC bus, and a connection end of the fifth switch tube and the sixth switch tube is connected with connection ends of the first capacitor and the second capacitor through the inductor. The electric energy transfer unit is controlled to discharge the first capacitor or the second capacitor, specifically, the fifth switch tube and the sixth switch tube are controlled to operate to transfer electric energy of the first capacitor to the second capacitor through the inductor to discharge the first capacitor, or transfer electric energy of the second capacitor to the first capacitor through the inductor to discharge the second capacitor. The electric energy transfer unit is controlled to charge the first capacitor or the second capacitor, specifically, the fifth switch tube and the sixth switch tube are controlled to operate to transfer electric energy of the second capacitor to the first capacitor through the inductor to charge the first capacitor, or transfer electric energy of the first capacitor to the second capacitor through the inductor to charge the second capacitor.

[0016] In a possible implementation, during the target capacitor charging process, a voltage change rate of the target capacitor is less than a set threshold. Here, since the resistor is included in the slow start circuit, the resistor can limit the inrush current when the power converter is powered on, so that the voltage change rate of the first capacitor and the second capacitor is less than the set threshold during the charging process, to avoid the voltage of the first capacitor and the second capacitor jumping instantaneously, and in addition, to prevent a larger current from being accessed when a short-circuit switch tube exists in the bridge arm, causing some switch tubes to be damaged by overcurrent. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is an application scenario schematic diagram of the power supply system provided by the present application;

[0018] Figure 2 is another application scenario schematic diagram of the power supply system provided by the present application;

[0019] Figure 3 is a structure schematic diagram of the power converter provided by the present application;

[0020] Figure 4 is another structure schematic diagram of the power converter provided by the present application;

[0021] Figure 5 is another structure schematic diagram of the power converter provided by the present application;

[0022] Figure 6 is another structure schematic diagram of the power converter provided by the present application;

[0023] Figure 7 is another structure schematic diagram of the power converter provided by the present application;

[0024] Figure 8is a schematic diagram of short circuit of a switch tube of a power converter provided in the present application;

[0025] Figure 9 is another schematic diagram of short circuit of a switch tube of a power converter provided in the present application;

[0026] Figure 10 is another schematic diagram of short circuit of a switch tube of a power converter provided in the present application;

[0027] Figure 11 is another schematic diagram of structure of a power converter provided in the present application. DETAILED DESCRIPTION

[0028] Referring to Figure 1 , Figure 1 is a schematic diagram of an application scenario of a power supply system provided in the present application. The power supply system provided in the present application can include a direct current power supply and at least one power converter, wherein the direct current power supply is a photovoltaic assembly. Taking the power supply system including multiple power converters as an example, the direct current end of the power converter is used to connect the photovoltaic assembly, and the alternating current end of the power converter is used to connect the power grid or load in parallel. The power converter can perform inversion conversion on the direct current power supplied by the battery, and output the alternating current obtained after inversion conversion to the power grid or load for power supply.

[0029] In some feasible embodiments, the direct current power supply is an energy storage battery, and the direct current end of each power converter can be used to connect the energy storage battery, please refer to Figure 2 , Figure 2 is another schematic diagram of an application scenario of a power supply system provided in the present application. In the multiple power converters of the power supply system, the direct current end of part of the power converters is used to connect the energy storage battery, and the alternating current end of the multiple power converters is used to connect the power grid or load in parallel. Each power converter can perform inversion conversion on the direct current power supplied by the photovoltaic assembly or the energy storage battery, and output the alternating current obtained after inversion conversion to the power grid or load for power supply. Here, the power converter connected to the photovoltaic assembly in the power supply system can be an inverter, and the power converter connected to the energy storage battery in the power supply system can be a converter.

[0030] In Figure 1 or Figure 2 application scenario of the power supply system, during the working process of the power converter, the switch tube may fail, such as topology through caused by short circuit of the switch tube, bus short circuit, switch tube overcurrent damage, etc. In order to start up in the case of abnormality of the power converter or the converter without further damage, it is necessary to set up a start-up self-check before the power converter starts working, that is, before the power converter accesses the load or the power grid and performs inversion conversion, to ensure the safe working of the equipment.

[0031] Referring to Figure 3 ,Figure 3 This is a schematic diagram of the power converter provided in this application. Figure 3 As shown, Figure 3 The power converter in the circuit may include a first capacitor C1 and a second capacitor C2 connected in series, and a bridge arm. The bridge arm may include a first switch Q11 and a fourth switch Q14 connected in series, with the first switch Q11 and the fourth switch Q14 connected in parallel across the first capacitor C1 and the second capacitor C2. The connection terminals of the first switch Q11 and the fourth switch Q14 are connected to the connection terminals of the first capacitor C1 and the second capacitor C2 through a second switch Q12 and a third switch Q13 connected in reverse series. The connection terminals of the first switch Q11 and the fourth switch Q14 can be used to lead to an output port. Here, the reverse series connection of the second switch Q12 and the third switch Q13 can be achieved by the diodes connected in parallel on the second switch Q12 and the third switch Q13 having opposite directions of current conduction. These diodes can be body diodes included in the second switch Q12 and the third switch Q13. For example, the diode connected in parallel with the second switch Q12 can conduct current flowing from the connection terminal of the first switch Q11 and the fourth switch Q14 to the connection terminal of the first capacitor C1 and the second capacitor C2, while the diode connected in parallel with the third switch Q13 can conduct current flowing from the connection terminal of the first capacitor C1 and the second capacitor C2 to the connection terminal of the first switch Q11 and the fourth switch Q14. Here, in the above-mentioned reverse series connection of the second switch Q12 and the third switch Q13, the third switch Q13 can be connected to the connection terminal of the first capacitor C1 and the second capacitor C2, or the second switch Q12 can be connected to the connection terminal of the first capacitor C1 and the second capacitor C2. In this embodiment, the connection terminal of the third switch Q13 to the connection terminal of the first capacitor C1 and the second capacitor C2 is used as an example, and will not be described in detail below.

[0032] Understandably, the above Figure 3 The power converter shown is a single-arm converter. The power converter provided in this application can also be a multi-arm converter; for details, please refer to [link to relevant documentation]. Figure 4 , Figure 4 This is another structural schematic diagram of the power converter provided in this application. For example... Figure 4 As shown, Figure 4The power converter in the circuit may include a first capacitor C1 and a second capacitor C2 connected in series, as well as phase A, phase B, and phase C bridge arms, which correspond to the phase A, phase B, and phase C outputs of the power converter, respectively. The first capacitor C1 is connected to the positive DC bus BUS+, and the second capacitor C2 is connected to the negative DC bus BUS-. The phase A bridge arm may include a first switch Q11, a second switch Q12, a third switch Q13, and a fourth switch Q14. The phase B bridge arm may include a first switch Q21, a second switch Q22, a third switch Q23, and a fourth switch Q24. The phase C bridge arm may include a first switch Q31, a second switch Q32, a third switch Q33, and a fourth switch Q34. It is understood that... Figure 4 In the power converter shown, the circuit structures of phase A, phase B, and phase C bridge arms are the same as those described above. Figure 3 The bridge arms in the power converter shown are the same, and will not be described again here. Optionally, the power converter described above may also include N-phase bridge arms. See [link to relevant documentation]. Figure 5 , Figure 5 This is another structural schematic diagram of the power converter provided in this application. For example... Figure 5 As shown, Figure 5 The power converter in the circuit may include a first capacitor C1 and a second capacitor C2 connected in series, as well as phase A, phase B, phase C, and phase N bridge arms. The structures of the phase A, phase B, and phase C bridge arms are as described above. Figure 4 The power converter shown above has an N-phase bridge arm leading to its N-phase output. The N-phase bridge arm may include a first switch Q41 and a fourth switch Q44 connected in series. These two switches are connected in parallel across a first capacitor C1 and a second capacitor C2. The connection terminals of the first and fourth switches Q41 and Q44 are connected to the connection terminals of the first and second capacitors C1 and C2 via a second switch Q42 and a third switch Q43 connected in reverse series. The connection terminals of the first and fourth switches Q41 and Q44 can lead to the N-phase output.

[0033] exist Figures 3 to 5 In the power converter shown, short circuits may occur in the switching transistors of each bridge arm, for example, in... Figure 3Taking phase A of the power converter as an example, when the first switch Q11 is short-circuited, if the second switch Q12 is turned on and the DC bus is powered normally, the positive DC bus BUS+ will be short-circuited. The first capacitor C1 will not charge properly, and the second switch Q12 will experience excessive short-circuit current, affecting the normal operation of the power converter. Alternatively, when the first switch Q11 is short-circuited, if the fourth switch Q14 is turned on and the DC bus is powered normally, the positive DC bus BUS+ and the negative DC bus BUS- will be short-circuited. The first capacitor C1 and the second capacitor C2 will not charge properly, and the fourth switch Q14 will experience excessive short-circuit current, affecting the normal operation of the power converter.

[0034] In addition, the above Figures 3 to 5 In the power converter shown, the connection terminals of the first and fourth switching transistors of each bridge arm are also connected to the connection terminals of the first and second capacitors through a filter capacitor and a filter inductor. For example, with Figure 5 For example, see the power converter shown below. Figure 6 , Figure 6 This is another structural schematic diagram of the power converter provided in this application. For example... Figure 6 As shown, Figure 6 In the power converter, the connection terminals of the first switch Q11 and the fourth switch Q14 in the A-phase bridge arm are connected to the connection terminals of the first capacitor C1 and the second capacitor C2 through the filter inductor L1 and the filter capacitor C10. The connection terminals of the first switch Q21 and the fourth switch Q24 in the B-phase bridge arm are connected to the connection terminals of the first capacitor C1 and the second capacitor C2 through the filter inductor L2 and the filter capacitor C20. The connection terminals of the first switch Q31 and the fourth switch Q34 in the C-phase bridge arm are connected to the connection terminals of the first capacitor C1 and the second capacitor C2 through the filter inductor L3 and the filter capacitor C30. The connection terminals of the first switch Q41 and the fourth switch Q44 in the N-phase bridge arm are connected to the connection terminals of the first capacitor C1 and the second capacitor C2 through the filter inductor L4 and the filter capacitor C40.

[0035] As described in the foregoing embodiments and combinations Figures 3-5 The technical solution provided in this application is applicable to detecting faulty switching transistors in a power converter after power-on but before formal operation. Specifically, the power converter provided in this application includes a controller (…). Figures 3 to 5(Not shown in the diagram) At least one bridge arm and a first capacitor and a second capacitor connected in series. The first capacitor is connected to the positive DC bus, and the second capacitor is connected to the negative DC bus. Before the power converter is powered on, the DC side of the power converter is not connected to the DC power supply, and the AC side of the power converter is not connected to the load or the power grid. The entire power converter is internally de-energized. After the power converter is powered on but before it begins normal operation, for example, before converting the DC input of the energy storage battery as a DC power source into AC output to supply the load or the power grid, it is necessary to check whether the switching transistors in the power converter are functioning properly to prevent short-circuit faults caused by short circuits in the switching transistors, which could endanger equipment safety.

[0036] In the technical solution provided in this application, the controller selects at least one target capacitor between the first capacitor and the second capacitor, and selects at least one target switch in each phase bridge arm. After the target switch is turned on, the target capacitor is charged or discharged. During this process, the controller determines whether there is a short circuit or open circuit in a specific switch in each phase bridge arm based on whether the charging or discharging process of the target capacitor is normal. Specifically, with Figure 5 Taking the power converter shown as an example, after power-on, the controller first turns on the target switch. The target switch is at least one of the first, second, third, and fourth switches in each bridge arm. For example, if the target switch is the first switch, then the first switch Q11 in phase A, the first switch Q21 in phase B, the first switch Q31 in phase C, and the first switch Q41 in phase N are the target switches. Initially after power-on, the voltage across the first capacitor C1 and the second capacitor C2 is zero. After turning on the target switch, charging begins on the target capacitor, which is at least one of the first capacitor C1 and the second capacitor C2. All switches in each bridge arm except the target switch remain off. Then, if the voltage across the target capacitor after charging does not reach the voltage threshold, the controller determines that a switch in the current power converter has a short circuit and outputs information indicating a short circuit fault in each bridge arm. By detecting faulty switching transistors before the power converter starts operating, abnormal operating conditions such as bus short circuits and short circuit fault propagation can be avoided during the operation of the power converter, thereby improving the reliability of the power converter.

[0037] In some possible embodiments, the power converter described above can comprise a soft-start circuit, which can comprise a soft-start switch and a resistor connected in series to the positive DC bus or the negative DC bus. The controller is configured to control the first switch in each bridge arm to remain conductive and then control the soft-start switch to be conductive when the voltage across the first capacitor and the second capacitor is zero, so as to connect the first capacitor and the second capacitor to the DC power supply and charge the first capacitor and the second capacitor by the DC power supply. The controller is further configured to output information that the third switch is short-circuited when the first capacitor is charged and the voltage across the first capacitor and the second capacitor does not reach the voltage threshold, or output information that the fourth switch is short-circuited when the first capacitor and the second capacitor are charged and the voltage across the first capacitor and the second capacitor does not reach the voltage threshold. See Figure 7 , Figure 7 FIG. 3 is another structural schematic diagram of the power converter provided in the present application. As shown in Figure 7 , Figure 7 The power converter in FIG. 3 comprises four bridge arms, and the structure of each bridge arm can refer to the power converter described above Figure 5 . The power converter can further comprise a soft-start circuit, which comprises a soft-start switch K1 and a resistor R connected in series to the positive DC bus BUS+ or the negative DC bus BUS-. Taking the case where the soft-start switch K1 and the resistor R are connected in series to the positive DC bus BUS+ as an example, during the process of detecting the faulty switch, when the voltage across the first capacitor C1 and the second capacitor C2 is zero, the controller controls the first switch in each bridge arm to remain conductive, for example, controls the first switch Q11, the first switch Q21, the first switch Q31 and the first switch Q41 to be conductive. Then the controller controls the soft-start switch K1 to be conductive, so as to connect the first capacitor C1 and the second capacitor C2 to the DC power supply, and at this time the first capacitor C1 and the second capacitor C2 are charged by the DC power supply. The soft-start circuit described above can be connected in parallel to a switch K2, and the switch K2 is used to be conductive after the detection of the faulty switch is completed, so as to connect the power converter to the DC power supply. Here, since the soft-start circuit comprises the resistor R, the resistor R can limit the inrush current when the power converter is powered on, so that the voltage across the first capacitor C1 and the second capacitor C2 changes at a rate less than a set threshold during the charging of the first capacitor C1 and the second capacitor C2, thereby avoiding the voltage across the first capacitor C1 and the second capacitor C2 from jumping instantaneously, and further preventing a large current from flowing into the bridge arm when there is a short-circuited switch in the bridge arm, which can cause some switches to be damaged by overcurrent. The controller is further configured to determine that the third switch in at least one of the bridge arms is short-circuited and output information that the third switch is short-circuited when it is detected that the first capacitor C1 is charged and the voltage across the first capacitor C1 does not rise synchronously, or the voltage across the first capacitor C1 does not reach the voltage threshold. For example, taking the case where the third switch Q13 in the A-phase bridge arm is short-circuited as an example, see Figure 8 , Figure 8 FIG. 4 is a schematic diagram of a short-circuited switch of the power converter provided in the present application. As shown in Figure 8As shown, when the controller controls the first switch Q11, the first switch Q21, the first switch Q31 and the first switch Q41 to be conductive, the slow start switch K1 is controlled to be conductive, so as to connect the first capacitor C1 and the second capacitor C2 with the DC power supply, and the first capacitor C1 and the second capacitor C2 are charged based on the DC power provided by the DC power supply. If the third switch Q13 is short-circuited and the second switch Q12 is disconnected, the diode connected in parallel with the second switch Q12 can conduct the current flowing from the connection end of the first switch Q11 and the fourth switch Q14 to the connection end of the first capacitor C1 and the second capacitor C2, so that the third switch Q13 and the second switch Q12 cannot cut off the current flowing from the connection end of the first switch Q11 and the fourth switch Q14 to the connection end of the first capacitor C1 and the second capacitor C2, the first capacitor C1 is short-circuited, the short-circuit current Ia flows out from the positive DC bus BUS+, and flows to the second capacitor C2 through the first switch Q11, the second switch Q12 and the third switch Q13 in turn. The first capacitor C1 cannot be normally charged, and the second capacitor C2 can be normally charged. The controller is further configured to determine that the fourth switch of at least one of the plurality of bridge arms is short-circuited when it is detected that the first capacitor C1 and the second capacitor C2 are charged and the voltages at both ends are not synchronously boosted, or the voltages at both ends of the first capacitor C1 and the second capacitor C2 do not reach the voltage threshold, and output information of the short-circuited fourth switch. For example, taking the fourth switch Q14 in the A-phase bridge arm as an example, referring to Figure 9 , Figure 9 is another schematic diagram of the short-circuited switch of the power converter provided by the present application. As shown in Figure 9 , when the controller controls the first switch Q11, the first switch Q21, the first switch Q31 and the first switch Q41 to be conductive, the slow start switch K1 is controlled to be conductive, so as to connect the first capacitor C1 and the second capacitor C2 with the DC power supply, and the first capacitor C1 and the second capacitor C2 are charged based on the DC power provided by the DC power supply. If the fourth switch Q14 is short-circuited, the fourth switch Q14 cannot cut off the current flowing from the positive DC bus BUS+ to the negative DC bus BUS-, the first capacitor C1 and the second capacitor C2 are short-circuited, the short-circuit current Ia flows out from the positive DC bus BUS+, and flows to the negative DC bus BUS- through the first switch Q11 and the fourth switch Q14 in turn, and the first capacitor C1 and the second capacitor C2 cannot be normally charged.

[0038] In some possible embodiments, the controller is configured to, when the voltage across the first capacitor and the second capacitor is zero, control the fourth switch in each bridge arm to keep conducting and then control the slow start switch to conduct, so as to connect the first capacitor and the second capacitor to the DC power supply to charge the first capacitor and the second capacitor by the DC power supply. The controller is further configured to, after the second capacitor is charged and the voltage across the second capacitor does not reach the voltage threshold, output information that the second switch is short-circuited, or, after the first capacitor and the second capacitor are charged and the voltage across the first capacitor and the second capacitor does not reach the voltage threshold, output information that the first switch is short-circuited. Referring again to Figure 7 In the process of detecting the short-circuited switch, when the voltage across the first capacitor C1 and the second capacitor C2 is zero, the controller controls the fourth switch in each bridge arm to keep conducting, for example, the fourth switch Q14, the fourth switch Q24, the fourth switch Q34 and the fourth switch Q44 are controlled to conduct. Then the slow start switch K1 is controlled to conduct, so as to connect the first capacitor C1 and the second capacitor C2 to the DC power supply, at this time, the first capacitor C1 and the second capacitor C2 are charged based on the DC power provided by the DC power supply. Here, since the resistor R is included in the slow start circuit, the resistor R can limit the inrush current when the power converter is powered on, so that the voltage across the first capacitor C1 and the second capacitor C2 changes at a rate less than a set threshold during the charging of the first capacitor C1 and the second capacitor C2, avoiding the voltage across the first capacitor C1 and the second capacitor C2 jumping instantaneously, in addition, preventing a large current from flowing when a short-circuited switch exists in the bridge arm, causing some switches to be damaged by overcurrent. The controller is further configured to, after detecting that the second capacitor C2 is charged and the voltage across the second capacitor C2 is not synchronously boosted, or the voltage across the second capacitor C2 does not reach the voltage threshold, determine that the second switch in at least one of the bridge arms is short-circuited, and output information that the second switch is short-circuited. For example, taking the second switch Q12 in the A-phase bridge arm as an example, referring to Figure 10 , Figure 10 is another schematic diagram of a short-circuited switch of the power converter provided by the present application. As shown in Figure 10As shown, when the controller controls the fourth switch Q14, the fourth switch Q24, the fourth switch Q34 and the fourth switch Q44 to be turned on, it controls the soft start switch K1 to be turned on, so as to connect the first capacitor C1 and the second capacitor C2 to the DC power supply. The first capacitor C1 and the second capacitor C2 are charged based on the DC power provided by the DC power supply. If the second switch Q12 is short-circuited and the third switch Q13 is open, the diode connected in parallel with the third switch Q13 can conduct the current flowing from the connection terminal of the first capacitor C1 and the second capacitor C2 to the connection terminal of the first switch Q11 and the fourth switch Q14. Therefore, neither the second switch Q12 nor the third switch Q13 can cut off the current flowing from the connection terminal of the first capacitor C1 and the second capacitor C2 to the connection terminal of the first switch Q11 and the fourth switch Q14. The second capacitor C2 is short-circuited, and the short-circuit current Ic flows out from the positive DC bus BUS+, through the first capacitor C1, and then sequentially through the third switch Q13, the second switch Q12, and the fourth switch Q14 to the negative DC bus BUS-. The second capacitor C2 cannot be charged normally, while the first capacitor C1 can be charged normally. The controller is also used to determine that the first switch of at least one of the multiple bridge arms is short-circuited when it detects that the first capacitor C1 and the second capacitor C2 are charging and the voltages across them are not synchronously increased, or when the voltages across the first capacitor C1 and the second capacitor C2 are not reaching a voltage threshold, and outputs information indicating that the first switch is short-circuited. For example, taking the short circuit of the first switch Q11 in phase A bridge arm as an example, see again... Figure 9 When the controller turns on the fourth switches Q14, Q24, Q34, and Q44, it turns on the soft-start switch K1 to connect the first capacitor C1 and the second capacitor C2 to the DC power supply. The first capacitor C1 and the second capacitor C2 are then charged by the DC power supply. If the first switch Q11 is short-circuited, it cannot cut off the current flowing from the positive DC bus BUS+ to the negative DC bus BUS-. The first capacitor C1 and the second capacitor C2 are short-circuited, and the short-circuit current Ib flows out from the positive DC bus BUS+, passing through the first switch Q11 and the fourth switch Q14 in sequence to the negative DC bus BUS-. As a result, the first capacitor C1 and the second capacitor C2 cannot be charged normally.

[0039] Optionally, during the fault switch detection, the controller can first control the first switch in each bridge arm to be kept on, control the slow-acting switch to be on so as to charge the first capacitor and the second capacitor, and perform short-circuit fault detection on the third switch and the fourth switch in each bridge arm based on the voltage variation across the first capacitor and the second capacitor. If the third switch and the fourth switch in each bridge arm are normal, the controller controls the slow-acting switch to be off, so as to discharge the first capacitor and the second capacitor until the voltage across the first capacitor and the second capacitor is zero. Then, the controller controls the fourth switch in each bridge arm to be kept on, controls the slow-acting switch to be on so as to charge the first capacitor and the second capacitor, and performs short-circuit fault detection on the first switch and the second switch in each bridge arm based on the voltage variation across the first capacitor and the second capacitor, thereby completing the fault detection on all switches in each bridge arm.

[0040] Optionally, during the fault switch detection, the controller can first control the fourth switch in each bridge arm to be kept on, control the slow-acting switch to be on so as to charge the first capacitor and the second capacitor, and perform short-circuit fault detection on the first switch and the second switch in each bridge arm based on the voltage variation across the first capacitor and the second capacitor. If the first switch and the second switch in each bridge arm are normal, the controller controls the slow-acting switch to be off, so as to discharge the first capacitor and the second capacitor until the voltage across the first capacitor and the second capacitor is zero. Then, the controller controls the first switch in each bridge arm to be kept on, controls the slow-acting switch to be on so as to charge the first capacitor and the second capacitor, and performs short-circuit fault detection on the third switch and the fourth switch in each bridge arm based on the voltage variation across the first capacitor and the second capacitor, thereby completing the fault detection on all switches in each bridge arm.

[0041] In some possible embodiments, a discharging circuit can be connected in parallel across the first capacitor and the second capacitor in the power converter. During the process in which the controller controls the slow-acting switch to be off so as to discharge the first capacitor and the second capacitor, the discharging circuit can be used to accelerate the discharging of the first capacitor and the second capacitor until the voltage across the first capacitor and the second capacitor is zero. Here, the discharging circuit can include at least one resistor, or the discharging circuit can be an auxiliary power supply used to accelerate the power consumption of the first capacitor and the second capacitor during the discharging process.

[0042] In some possible embodiments, when the controller controls the first switch in each bridge arm to remain conductive, controls the slow start switch to be conductive to charge the first capacitor and the second capacitor, and performs short-circuit fault detection on the third switch and the fourth switch in each bridge arm based on voltage changes across the first capacitor and the second capacitor, if the first switch is open, the controller controls the first switch in the bridge arm to remain conductive, and no current can flow through the first switch, so that the first capacitor and the second capacitor can still be normally boosted in the case that the fourth switch is short-circuited. If the first switch is open and the fourth switch cannot be normally detected to be short-circuited, a short-circuit loop is formed in the normal operation of the power converter due to the short-circuit of the fourth switch, so that the second capacitor cannot be normally charged and some switches bear excessive short-circuit current. If the first switch is open and the second switch or the third switch is short-circuited, a short-circuit loop is not formed in the normal operation of the power converter, so that the device is not damaged. Therefore, when the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, the fourth switch is detected for a second time for short-circuit fault. Specifically, the controller controls the slow start switch to be conductive to connect the first capacitor and the second capacitor to the DC power supply to charge the first capacitor and the second capacitor through the DC power supply after the controller controls the first switch Q11 in the A-phase bridge arm to remain conductive. If the voltage across the first capacitor C1 and the voltage across the second capacitor C2 are both greater than or equal to the voltage threshold, the controller controls the slow start switch to be open to disconnect the first capacitor C1 and the second capacitor C2 from the DC power supply to discharge the first capacitor C1 and the second capacitor C2 through the discharge circuit. When the voltage across the first capacitor C1 and the voltage across the second capacitor C2 are both zero, the second switch Q12 is controlled to remain conductive, and the slow start switch is controlled to be conductive to connect the first capacitor C1 and the second capacitor C2 to the DC power supply to charge the first capacitor C1 and the second capacitor C2 through the DC power supply. At this time, if the fourth switch Q14 is short-circuited, the second capacitor C2 is short-circuited, the short-circuit current flows from the positive DC bus BUS+ to the negative DC bus BUS- through the first capacitor C1, the third switch Q13, the second switch Q12, and the fourth switch Q14 in sequence, and the second capacitor C2 cannot be normally charged. The specific short-circuit path can be referred to the above description. Figure 7 For example, as shown in the power converter, if the first switch Q11 in the A-phase bridge arm is open, the controller controls the first switch Q11 to remain conductive, and no current can flow through the first switch Q11, so that the first capacitor C1 and the second capacitor C2 can still be normally boosted in the case that the fourth switch Q14 is short-circuited. If the first switch Q11 is open and the fourth switch Q14 cannot be normally detected to be short-circuited, a short-circuit loop is formed in the normal operation of the power converter due to the short-circuit of the fourth switch Q14, so that the second capacitor C2 cannot be normally charged and some switches bear excessive short-circuit current. If the first switch Q11 is open and the second switch Q12 or the third switch Q13 is short-circuited, a short-circuit loop is not formed in the normal operation of the power converter, so that the device is not damaged. Therefore, when the voltage across the first capacitor C1 and the voltage across the second capacitor C2 are both greater than or equal to the voltage threshold, the fourth switch Q14 is detected for a second time for short-circuit fault. Specifically, the controller controls the slow start switch to be conductive to connect the first capacitor C1 and the second capacitor C2 to the DC power supply to charge the first capacitor C1 and the second capacitor C2 through the DC power supply after the controller controls the first switch Q11 in the A-phase bridge arm to remain conductive. If the voltage across the first capacitor C1 and the voltage across the second capacitor C2 are both greater than or equal to the voltage threshold, the controller controls the slow start switch to be open to disconnect the first capacitor C1 and the second capacitor C2 from the DC power supply to discharge the first capacitor C1 and the second capacitor C2 through the discharge circuit. When the voltage across the first capacitor C1 and the voltage across the second capacitor C2 are both zero, the second switch Q12 is controlled to remain conductive, and the slow start switch is controlled to be conductive to connect the first capacitor C1 and the second capacitor C2 to the DC power supply to charge the first capacitor C1 and the second capacitor C2 through the DC power supply. At this time, if the fourth switch Q14 is short-circuited, the second capacitor C2 is short-circuited, the short-circuit current flows from the positive DC bus BUS+ to the negative DC bus BUS- through the first capacitor C1, the third switch Q13, the second switch Q12, and the fourth switch Q14 in sequence, and the second capacitor C2 cannot be normally charged. The specific short-circuit path can be referred to the above description. Figure 10The controller outputs information of short circuit of the fourth switch tube after the second capacitor is charged and the voltage across the second capacitor does not reach the voltage threshold, which can avoid the situation that the fourth switch tube cannot be normally detected due to the open circuit of the first switch tube, and improve the accuracy of the short circuit fault detection of the switch tube.

[0043] Similarly, when the controller controls the fourth switch tube in each bridge arm to keep conducting, controls the slow start switch to conduct to charge the first capacitor and the second capacitor, and performs the short circuit fault detection on the first switch tube and the second switch tube in each bridge arm based on the voltage change across the first capacitor and the second capacitor, if the fourth switch tube is open, the controller controls the fourth switch tube in the bridge arm to keep conducting, and no current can flow through the fourth switch tube, so that the first capacitor and the second capacitor can still be normally boosted in the case of the short circuit of the first switch tube, i.e. the voltage across the first capacitor and the second capacitor is greater than or equal to the voltage threshold after the first capacitor and the second capacitor are charged. Figure 7In the power converter shown, if the fourth switch Q14 in the A-phase bridge arm is open, the controller controls the fourth switch Q14 to remain on, and no current can flow through the fourth switch Q14. In this case, the first capacitor C1 and the second capacitor C2 can still be charged by controlling the slow start switch to turn on, even if the first switch Q11 is short-circuited. If the fourth switch Q14 is open and the first switch Q11 cannot be normally detected to be short-circuited, a short-circuit loop can be formed due to the short-circuit of the first switch Q11, so that the first capacitor C1 cannot be normally charged and some switches can bear excessive short-circuit current. Therefore, when the voltage across the first capacitor C1 and the second capacitor C2 is greater than or equal to the voltage threshold after the first capacitor C1 and the second capacitor C2 are charged, the short-circuit fault of the first switch Q11 is detected alone. Specifically, after the controller controls the fourth switch Q14 to remain on and controls the slow start switch to turn on to connect the first capacitor C1 and the second capacitor C2 to the DC power supply to charge the first capacitor C1 and the second capacitor C2 by the DC power supply, if the voltage across the first capacitor C1 and the voltage across the second capacitor C2 are both greater than or equal to the voltage threshold, the controller controls the slow start switch to turn off to disconnect the first capacitor C1 and the second capacitor C2 from the DC power supply, so that the discharge circuit discharges the first capacitor C1 and the second capacitor C2, and when the voltage across the first capacitor C1 and the voltage across the second capacitor C2 are both zero, the controller controls the third switch Q13 to remain on and controls the slow start switch to turn on to connect the first capacitor C1 and the second capacitor C2 to the DC power supply to charge the first capacitor C1 and the second capacitor C2 by the DC power supply. At this time, if the first switch Q11 is short-circuited, the first capacitor C1 is short-circuited, and the short-circuit current flows from the positive DC bus BUS+ to the second capacitor C2 through the first capacitor C1, the second switch Q12 and the third switch Q13 in turn. The first capacitor C1 cannot be normally charged, and the specific short-circuit path can be referred to the description of the above Figure 10 When the first capacitor is charged and the voltage across the first capacitor does not reach the voltage threshold, the controller outputs information of the short-circuit of the first switch, which can avoid the situation that the first switch cannot be normally detected to be short-circuited due to the open fourth switch, and improves the accuracy of the short-circuit fault detection of the switch.

[0044] In some possible embodiments, the controller is configured to, control the first switch in each bridge arm to be kept on, control the slow-acting switch to be turned on to charge the first capacitor and the second capacitor, and perform short-circuit fault detection on the third switch and the fourth switch in each bridge arm based on voltage changes across the first capacitor and the second capacitor, or control the fourth switch in each bridge arm to be kept on, control the slow-acting switch to be turned on to charge the first capacitor and the second capacitor, and perform short-circuit fault detection on the first switch and the second switch in each bridge arm based on voltage changes across the first capacitor and the second capacitor. If it is detected that the first switch or the fourth switch has no short-circuit fault, secondary short-circuit fault detection can be performed on the first switch or the fourth switch to avoid false judgment of short-circuit fault due to disconnection of the first switch or the fourth switch. Specifically, after the controller controls the first switch or the fourth switch in each bridge arm to be kept on and controls the slow-acting switch to be turned on to connect the first capacitor and the second capacitor to the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to a voltage threshold, the controller controls the slow-acting switch to be turned off to disconnect the first capacitor and the second capacitor from the DC power supply, so that the discharge circuit discharges the first capacitor and the second capacitor, and when the voltage across the first capacitor and the voltage across the second capacitor are both zero, the controller controls the slow-acting switch to be turned on to connect the first capacitor and the second capacitor to the DC power supply to charge the first capacitor and the second capacitor by the DC power supply. At this time, the switches in each bridge arm are all turned off, and if the first switch and the fourth switch are short-circuited, the first capacitor and the second capacitor are short-circuited, the short-circuit current flows out of the positive DC bus, sequentially passes through the first switch and the fourth switch, and flows to the negative DC bus, and the first capacitor and the second capacitor cannot be normally charged. The specific short-circuit path can be referred to the description of the above Figure 9 If the voltage across the first capacitor and the voltage across the second capacitor do not reach the voltage threshold, the controller outputs information that the first switch and the fourth switch are short-circuited. Further, if the voltage across the first capacitor and the voltage across the second capacitor are equal to the voltage across the filter capacitor connected to any bridge arm after the first capacitor and the second capacitor are charged, the controller outputs information that the first switch or the fourth switch is short-circuited. Specifically, if the voltage across the first capacitor is equal to the voltage across the filter capacitor connected to any bridge arm, the controller outputs information that the first switch is short-circuited, and if the voltage across the second capacitor is equal to the voltage across the filter capacitor connected to any bridge arm, the controller outputs information that the fourth switch is short-circuited. Please refer again to the description of the above Figure 6The power converter shown, when the first capacitor C1 and the second capacitor C2 are charged, if the voltage across the filter inductor L1 connected to the A-phase bridge arm is equal to the voltage across the first capacitor C1, it is determined that the first switch Q11 in the A-phase bridge arm is short-circuited, so that the first capacitor C1 and the filter inductor L1 are connected in parallel, and the information of the short-circuit of the first switch is output. Alternatively, if the voltage across the filter inductor L1 connected to the A-phase bridge arm is equal to the voltage across the second capacitor C2, it is determined that the second switch Q12 in the A-phase bridge arm is short-circuited, so that the second capacitor C2 and the filter inductor L1 are connected in parallel, and the information of the short-circuit of the second switch is output.

[0045] In some possible embodiments, the power converter further comprises an electric energy transfer unit. The controller is configured to, after detecting the short-circuit fault of the third switch and the fourth switch in each bridge arm, control the electric energy transfer unit to discharge one of the first capacitor and the second capacitor, and then charge the discharged first capacitor or the discharged second capacitor to detect the short-circuit fault of the first switch or the second switch. Specifically, the controller controls the first switch in each bridge arm to remain conductive, controls the slow start switch to be conductive to charge the first capacitor and the second capacitor, and detects the short-circuit fault of the third switch and the fourth switch in each bridge arm based on the voltage change across the first capacitor and the second capacitor. If the first capacitor and the second capacitor are charged and the voltage across the first capacitor and the second capacitor is greater than or equal to a voltage threshold, i.e., the third switch and the fourth switch in each bridge arm are normal, the controller controls the electric energy transfer unit to discharge the first capacitor through the electric energy transfer unit. When the first capacitor is discharged to zero voltage, the controller controls the third switch in each bridge arm to remain conductive, and controls the electric energy transfer unit to charge the first capacitor through the electric energy transfer unit. When the first capacitor is charged and the voltage across the first capacitor does not reach the voltage threshold, the controller outputs the information of the short-circuit of the first switch. Alternatively, when the third switch and the fourth switch in each bridge arm are normal, the controller controls the electric energy transfer unit to discharge the second capacitor through the electric energy transfer unit. When the second capacitor is discharged to zero voltage, the controller controls the fourth switch in each bridge arm to remain conductive, and controls the electric energy transfer unit to charge the second capacitor through the electric energy transfer unit. When the second capacitor is charged and the voltage across the second capacitor does not reach the voltage threshold, the controller outputs the information of the short-circuit of the second switch.

[0046] It can be understood that when the controller detects the short-circuit fault of the third switch tube and the fourth switch tube in each bridge arm, and the third switch tube and the fourth switch tube in each bridge arm are normal, the controller can first detect the short-circuit fault of the first switch tube in each bridge arm, and then detect the short-circuit fault of the second switch tube in each bridge arm, so as to complete the fault detection of all switch tubes in each bridge arm. Alternatively, the controller can first detect the short-circuit fault of the second switch tube in each bridge arm, and then detect the short-circuit fault of the first switch tube in each bridge arm, so as to complete the fault detection of all switch tubes in each bridge arm. Taking the example of first detecting the short-circuit fault of the first switch tube in each bridge arm, and then detecting the short-circuit fault of the second switch tube in each bridge arm, specifically, the above-mentioned electric energy transfer unit can be a balance bridge arm, and the balance bridge arm includes an inductor, a fifth switch tube and a sixth switch tube connected in series, the fifth switch tube is connected with the positive DC bus, the sixth switch tube is connected with the negative DC bus, and the connection end of the fifth switch tube and the sixth switch tube is connected with the connection end of the first capacitor and the second capacitor through the inductor. Please see Figure 11 , Figure 11 is another structural schematic diagram of the power converter provided by the present application. As shown in Figure 11 , the power converter in Figure 11 includes four bridge arms, and the structure of each bridge arm can refer to the above-mentioned Figure 5The power converter can further comprise a soft-start circuit and an energy transfer unit. The soft-start circuit comprises a soft-start switch K1 and a resistor R, which can be connected in series on the positive DC bus BUS+. The energy transfer unit can be a balancing bridge arm, which comprises an inductor L0, a switch Q5 connected to the positive DC bus BUS+ and a switch Q6 connected to the negative DC bus BUS-, and a connection end of the switch Q5 and the switch Q6 connected to connection ends of a first capacitor C1 and a second capacitor C2 through the inductor L0. When the controller completes the short-circuit fault detection of the third switch and the fourth switch in each bridge arm, and the third switch and the fourth switch in each bridge arm are normal, voltages across the first capacitor C1 and the second capacitor C2 after charging are greater than or equal to a voltage threshold, and the controller controls the switch Q5 and the switch Q6 to act, so as to transfer the energy of the first capacitor C1 to the second capacitor C2 through the inductor L0, and discharge the first capacitor C1. When the controller discharges the first capacitor C1 to zero voltage, the controller controls the third switch in each bridge arm to keep conducting, i.e. controls the third switch Q13, the third switch Q23, the third switch Q33 and the third switch Q43 to conduct. Then the controller controls the switch Q5 and the switch Q6 to act, so as to transfer the energy of the second capacitor C2 to the first capacitor C1 through the inductor L0, and charge the first capacitor C1. When the controller charges the first capacitor C1 and the voltage across the first capacitor C1 does not reach the voltage threshold, it is determined that the first switch of at least one bridge arm in the plurality of bridge arms is short-circuited, and information of the first switch short-circuit is output. When the voltage across the first capacitor C1 after charging is greater than or equal to the voltage threshold, i.e. the first switch in each bridge arm is normal, the controller controls the switch Q5 and the switch Q6 to act, so as to transfer the energy of the second capacitor C2 to the first capacitor C1 through the inductor L0, and discharge the second capacitor C2. When the controller discharges the second capacitor C2 to zero voltage, the controller controls the fourth switch in each bridge arm to keep conducting, i.e. controls the fourth switch Q14, the fourth switch Q24, the fourth switch Q34 and the fourth switch Q44 to conduct. Then the controller controls the switch Q5 and the switch Q6 to act, so as to transfer the energy of the first capacitor C1 to the second capacitor C2 through the inductor L0, and charge the second capacitor C2. When the controller charges the second capacitor C2 and the voltage across the second capacitor C2 does not reach the voltage threshold, it is determined that the second switch of at least one bridge arm in the plurality of bridge arms is short-circuited, and information of the second switch short-circuit is output, so as to complete the fault detection of all switches in each bridge arm.

[0047] Further, after the controller controls the first switch in each bridge arm to keep conducting, controls the slow-acting switch to conduct to charge the first capacitor and the second capacitor, and performs short-circuit fault detection on the third switch and the fourth switch in each bridge arm based on the voltage change across the first capacitor and the second capacitor, if the first switch is open, the controller controls the first switch in the bridge arm to keep conducting, and no current can flow through the first switch, which causes the first capacitor and the second capacitor to still be able to normally boost in the case that the fourth switch is short-circuited, i.e., the voltage across the first capacitor and the second capacitor after charging is greater than or equal to the voltage threshold, and there is also a false judgment of the short-circuit fault of the fourth switch. Therefore, after the controller performs fault detection on all the switches in each bridge arm, the controller performs secondary short-circuit fault detection on the fourth switch. Specifically, the controller can control the switch Q5 and the switch Q6 to act to transfer the electric energy of the second capacitor C2 to the first capacitor C1 through the inductor L0 to discharge the second capacitor C2. When the voltage across the second capacitor C2 is zero after discharging, the controller controls the second switch in each bridge arm to keep conducting, i.e., controls the second switch Q12, the second switch Q22, the second switch Q32, and the second switch Q42 to conduct. Then, the controller controls the switch Q5 and the switch Q6 to act to transfer the electric energy of the first capacitor C1 to the second capacitor C2 through the inductor L0 to charge the second capacitor C2. When the voltage across the second capacitor C2 does not reach the voltage threshold after charging, the controller determines that the fourth switch in at least one of the bridge arms is short-circuited, and outputs information of the short-circuited fourth switch.

[0048] In some possible embodiments, when the controller performs short-circuit fault detection on the first switch and the second switch in each bridge arm, and the first switch and the second switch in each bridge arm are normal, the controller can first perform short-circuit fault detection on the third switch in each bridge arm, and then perform short-circuit fault detection on the fourth switch in each bridge arm, thereby completing fault detection on all the switches in each bridge arm. Alternatively, the controller can first perform short-circuit fault detection on the fourth switch in each bridge arm, and then perform short-circuit fault detection on the third switch in each bridge arm, thereby completing fault detection on all the switches in each bridge arm. Taking the case of first performing short-circuit fault detection on the third switch in each bridge arm, and then performing short-circuit fault detection on the fourth switch in each bridge arm as an example, specifically, the electric energy transfer unit can be a balance bridge arm, which includes an inductor, a fifth switch, and a sixth switch connected in series, the fifth switch is connected to the positive DC bus, the sixth switch is connected to the negative DC bus, and the connection end of the fifth switch and the sixth switch is connected to the connection end of the first capacitor and the second capacitor through the inductor. Please refer again to Figure 11When the controller completes the short-circuit fault detection of the first switch and the second switch in each bridge arm, and the first switch and the second switch in each bridge arm are normal, the voltage across the first capacitor C1 and the second capacitor C2 after charging is greater than or equal to the voltage threshold, the controller can control the switch Q5 and the switch Q6 to act, so as to transfer the electric energy of the first capacitor C1 to the second capacitor C2 through the inductor L0, so as to discharge the first capacitor C1. When the voltage across the first capacitor C1 after discharging is zero, the controller controls the first switch in each bridge arm to keep conducting, that is, the first switch Q11, the first switch Q21, the first switch Q31 and the first switch Q41 are controlled to conduct. Then the switch Q5 and the switch Q6 are controlled to act, so as to transfer the electric energy of the second capacitor C2 to the first capacitor C1 through the inductor L0, so as to charge the first capacitor C1. When the voltage across the first capacitor C1 after charging does not reach the voltage threshold, the controller determines that the third switch of at least one bridge arm in the plurality of bridge arms is short-circuited, and outputs the information of the short-circuited third switch. If the voltage across the first capacitor C1 after charging is greater than or equal to the voltage threshold, that is, the third switch in each bridge arm is normal, the controller controls the switch Q5 and the switch Q6 to act, so as to transfer the electric energy of the second capacitor C2 to the first capacitor C1 through the inductor L0, so as to discharge the second capacitor C2. When the voltage across the second capacitor C2 after discharging is zero, the controller controls the second switch in each bridge arm to keep conducting, that is, the second switch Q12, the second switch Q22, the second switch Q32 and the second switch Q42 are controlled to conduct. Then the switch Q5 and the switch Q6 are controlled to act, so as to transfer the electric energy of the first capacitor C1 to the second capacitor C2 through the inductor L0, so as to charge the second capacitor C2. When the voltage across the second capacitor C2 after charging does not reach the voltage threshold, the controller determines that the fourth switch of at least one bridge arm in the plurality of bridge arms is short-circuited, and outputs the information of the short-circuited fourth switch, so as to complete the fault detection of all switches in each bridge arm.

[0049] Further, when the controller controls the fourth switch in each bridge arm to keep conducting, controls the slow-acting switch to conduct to charge the first capacitor and the second capacitor, and performs short-circuit fault detection on the first switch and the second switch in each bridge arm based on the voltage change across the first capacitor and the second capacitor, if the fourth switch is open, the controller controls the fourth switch in the bridge arm to keep conducting, and no current can flow through the fourth switch, which causes the first capacitor and the second capacitor to still be able to normally boost in the case of short circuit of the first switch, i.e., the voltage across the first capacitor and the second capacitor after charging is greater than or equal to the voltage threshold, and the first switch short-circuit fault is misjudged. Therefore, after the above fault detection on all switches in each bridge arm, the second short-circuit fault detection is performed on the first switch. Specifically, the controller can control the switch Q5 and the switch Q6 to act to transfer the electric energy of the first capacitor C1 to the second capacitor C2 through the inductor L0 to discharge the first capacitor C1. When the voltage across the first capacitor C1 is zero after discharging by the controller, the controller controls the third switch in each bridge arm to keep conducting, i.e., controls the third switch Q13, the third switch Q23, the third switch Q33, and the third switch Q43 to conduct. Then, the controller controls the switch Q5 and the switch Q6 to act to transfer the electric energy of the second capacitor C2 to the first capacitor C1 through the inductor L0 to charge the first capacitor C1. When the voltage across the first capacitor C1 does not reach the voltage threshold after charging by the controller, it is determined that the first switch in at least one of the bridge arms is short-circuited, and information of the first switch short-circuit is output.

Claims

1. A power converter, characterized by, The power converter comprises a controller, at least one bridge arm, and a first capacitor and a second capacitor connected in series, the first capacitor being connected to a positive DC bus, and the second capacitor being connected to a negative DC bus; Each bridge arm in the at least one bridge arm comprises a first switch tube, a second switch tube, a third switch tube, and a fourth switch tube, the first switch tube and the fourth switch tube being connected in series and then connected in parallel across the first capacitor and the second capacitor connected in series, and the connection end of the first switch tube and the fourth switch tube being connected to the connection end of the first capacitor and the second capacitor through the second switch tube and the third switch tube connected in reverse series; The controller is configured to control a target switch tube in each bridge arm to be kept on after the power converter is started, wherein other switch tubes in the each bridge arm except the target switch tube are kept off, and a target capacitor starts to charge after the target switch tube in the each bridge arm is turned on, the target capacitor being at least one of the first capacitor and the second capacitor, and the target switch tube being at least one of the first switch tube, the second switch tube, the third switch tube, and the fourth switch tube in the each bridge arm; The controller is further configured to output information that a short circuit fault exists in the each bridge arm when the voltage across the target capacitor does not reach a voltage threshold after the target capacitor is charged.

2. The power converter of claim 1, wherein, The power converter comprises a slow start switch and a resistor connected in series across the positive DC bus or the negative DC bus, the target capacitor being the first capacitor and the second capacitor, and the target switch tube being the first switch tube in the each bridge arm; The target capacitor starts to charge after the target switch tube in the each bridge arm is turned on, specifically as follows: After the first switch tube in the each bridge arm is kept on, the controller controls the slow start switch to be turned on to turn on the connection of the first capacitor and the second capacitor to a DC power supply so as to start charging the first capacitor and the second capacitor through the DC power supply; The controller is further configured to output information that the third switch tube is short-circuited when the voltage across the first capacitor does not reach the voltage threshold after the DC power supply charges the first capacitor and the second capacitor, or output information that the fourth switch tube is short-circuited when the voltage across the first capacitor and the voltage across the second capacitor do not reach the voltage threshold after the DC power supply charges the first capacitor and the second capacitor.

3. The power converter of claim 1, wherein, The power converter comprises a slow start switch and a resistor connected in series across the positive DC bus or the negative DC bus, the target capacitor being the first capacitor and the second capacitor, and the target switch tube being the fourth switch tube in the each bridge arm; The target capacitor starts to charge after the target switch tube in the each bridge arm is turned on, specifically as follows: After the fourth switch tube in the each bridge arm is kept on, the controller controls the slow start switch to be turned on to turn on the connection of the first capacitor and the second capacitor to a DC power supply so as to start charging the first capacitor and the second capacitor through the DC power supply; The controller is further configured to control the slow start switch to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply after the fourth switch in each bridge arm is controlled to be kept on. The controller is further configured to output information that the second switch is short-circuited when the voltage across the second capacitor does not reach the voltage threshold after the DC power supply charges the first capacitor and the second capacitor, or output information that the first switch is short-circuited when the voltage across the first capacitor and the voltage across the second capacitor do not reach the voltage threshold after the DC power supply charges the first capacitor and the second capacitor.

4. The power converter of claim 2, wherein, A discharge circuit is connected in parallel across the first capacitor and the second capacitor, and the controller is configured to control the slow start switch to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply after the fourth switch in each bridge arm is controlled to be kept on. If the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, the fourth switch is controlled to be turned off, and the slow start switch is controlled to be turned off to disconnect the first capacitor and the second capacitor from the DC power supply, so that the discharge circuit discharges the first capacitor and the second capacitor, and when the voltage across the first capacitor and the second capacitor is zero, the third switch in each bridge arm is controlled to be kept on, and the slow start switch is controlled to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, and information that the first switch is short-circuited is outputted when the voltage across the first capacitor does not reach the voltage threshold after the first capacitor is charged.

5. The power converter of claim 3, wherein, A discharge circuit is connected in parallel across the first capacitor and the second capacitor, and the controller is configured to control the slow start switch to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply after the fourth switch in each bridge arm is controlled to be kept on. If the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, the fourth switch is controlled to be turned off, and the slow start switch is controlled to be turned off to disconnect the first capacitor and the second capacitor from the DC power supply, so that the discharge circuit discharges the first capacitor and the second capacitor, and when the voltage across the first capacitor and the second capacitor is zero, the third switch in each bridge arm is controlled to be kept on, and the slow start switch is controlled to be turned on to turn on the connection between the first capacitor and the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, and information that the first switch is short-circuited is outputted when the voltage across the first capacitor does not reach the voltage threshold after the first capacitor is charged.

6. The power converter of claim 2 or 3, wherein, The first capacitor and the second capacitor are connected in parallel with a discharging circuit, and the connection end of the first switch tube and the fourth switch tube in each bridge arm is connected with the connection end of the first capacitor and the second capacitor through a filter capacitor, and the controller is configured to control the slow start switch to be turned on to connect the first capacitor and the second capacitor with the DC power supply to charge the first capacitor and the second capacitor through the DC power supply, and then The controller is further configured to control the target switch tube to be turned off and control the slow start switch to be turned off to disconnect the first capacitor and the second capacitor from the DC power supply if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, so that the discharging circuit discharges the first capacitor and the second capacitor, and when the voltage across the first capacitor and the voltage across the second capacitor are both zero, the slow start switch is turned on to connect the first capacitor and the second capacitor with the DC power supply to charge the first capacitor and the second capacitor through the DC power supply, and if the first capacitor and the second capacitor are charged, and the voltage across the first capacitor and the voltage across the second capacitor are both less than the voltage threshold, the controller outputs information that the first switch tube and the fourth switch tube are short-circuited, Or, The controller is further configured to control the target switch tube to be turned off and control the slow start switch to be turned off to disconnect the first capacitor and the second capacitor from the DC power supply if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, so that the discharging circuit discharges the first capacitor and the second capacitor, and when the voltage across the first capacitor and the voltage across the second capacitor are both zero, the slow start switch is turned on to connect the first capacitor and the second capacitor with the DC power supply to charge the first capacitor and the second capacitor through the DC power supply, and if the first capacitor and the second capacitor are charged, and the voltage across the first capacitor and the voltage across the second capacitor are both less than the voltage threshold, the controller outputs information that the first switch tube and the fourth switch tube are short-circuited.

7. The power converter of claim 2 or 3, wherein, The power converter further comprises an electric energy transfer unit, and the controller is configured to control the slow start switch to be turned on to connect the first capacitor and the second capacitor with the DC power supply to charge the first capacitor and the second capacitor through the DC power supply, and then If the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, the controller controls the target switch tube to be turned off and controls the electric energy transfer unit to discharge the first capacitor through the electric energy transfer unit; The controller is further configured to control the third switch tube in each bridge arm to be kept turned on and control the electric energy transfer unit to charge the first capacitor through the electric energy transfer unit when the voltage across the first capacitor is zero through the electric energy transfer unit. The controller is further configured to output information that the first switch tube is short-circuited if the voltage across the first capacitor does not reach the voltage threshold after the first capacitor is charged by the power transfer unit.

8. The power converter of claim 2, wherein, The power converter further comprises a power transfer unit, and the controller is configured to, after controlling the slow-start switch to be turned on to turn on the connection between the first capacitor, the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, control the fourth switch tube to be turned off, and control the power transfer unit to discharge the first capacitor by the power transfer unit; the controller is further configured to, after the first capacitor is discharged to zero voltage across by the power transfer unit, control the first switch tube in each bridge arm to remain turned on, and control the power transfer unit to charge the first capacitor by the power transfer unit; the controller is further configured to output information that the second switch tube is short-circuited if the voltage across the second capacitor does not reach the voltage threshold after the second capacitor is charged by the power transfer unit.

9. The power converter of claim 3, wherein, The power converter further comprises a power transfer unit, and the controller is configured to, after controlling the slow-start switch to be turned on to turn on the connection between the first capacitor, the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, control the fourth switch tube to be turned off, and control the power transfer unit to discharge the first capacitor by the power transfer unit; the controller is further configured to, after the first capacitor is discharged to zero voltage across by the power transfer unit, control the first switch tube in each bridge arm to remain turned on, and control the power transfer unit to charge the first capacitor by the power transfer unit; the controller is further configured to output information that the third switch tube is short-circuited if the voltage across the first capacitor does not reach the voltage threshold after the first capacitor is charged by the power transfer unit.

10. The power converter of claim 2 or 3, wherein, The power converter further comprises a power transfer unit, and the controller is configured to, after controlling the slow-start switch to be turned on to turn on the connection between the first capacitor, the second capacitor and the DC power supply to charge the first capacitor and the second capacitor by the DC power supply, if the voltage across the first capacitor and the voltage across the second capacitor are both greater than or equal to the voltage threshold, control the target switch tube to be turned off, and control the power transfer unit to discharge the second capacitor by the power transfer unit; the controller is further configured to, after the second capacitor is discharged to zero voltage across by the power transfer unit, control the second switch tube in each bridge arm to remain turned on, and control the power transfer unit to charge the second capacitor by the power transfer unit; the controller is further configured to output information that the third switch tube is short-circuited if the voltage across the first capacitor does not reach the voltage threshold after the first capacitor is charged by the power transfer unit. The controller is further configured to output information that the fourth switch tube is short-circuited if the second capacitor is charged by the power transfer unit and a voltage across the second capacitor does not reach a voltage threshold.

11. The power converter of claim 7 or 9, wherein, The power transfer unit comprises an inductor, a fifth switch tube and a sixth switch tube connected in series, the fifth switch tube is connected to a positive DC bus, the sixth switch tube is connected to a negative DC bus, and a connection end of the fifth switch tube and the sixth switch tube is connected to connection ends of the first capacitor and the second capacitor through the inductor. The controller controls the power transfer unit to discharge the first capacitor through the power transfer unit, specifically: The controller controls the fifth switch tube and the sixth switch tube to act, so that the power of the first capacitor is transferred to the second capacitor through the inductor to discharge the first capacitor. The controller controls the power transfer unit to charge the first capacitor through the power transfer unit, specifically: The controller controls the fifth switch tube and the sixth switch tube to act, so that the power of the second capacitor is transferred to the first capacitor through the inductor to charge the first capacitor.

12. The power converter of claim 8 or 10, wherein, The power transfer unit comprises an inductor, a fifth switch tube and a sixth switch tube connected in series, the fifth switch tube is connected to a positive DC bus, the sixth switch tube is connected to a negative DC bus, and a connection end of the fifth switch tube and the sixth switch tube is connected to connection ends of the first capacitor and the second capacitor through the inductor. The controller controls the power transfer unit to discharge the second capacitor through the power transfer unit, specifically: The controller controls the fifth switch tube and the sixth switch tube to act, so that the power of the second capacitor is transferred to the first capacitor through the inductor to discharge the second capacitor. The controller controls the power transfer unit to charge the second capacitor through the power transfer unit, specifically: The controller controls the fifth switch tube and the sixth switch tube to act, so that the power of the first capacitor is transferred to the second capacitor through the inductor to charge the second capacitor.

13. The power converter of claim 1, wherein, During the charging process of the target capacitor, a voltage change rate across the target capacitor is less than a set threshold.

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