Power conversion device and charging pile

Abstract

This application provides a power conversion device and a charging pile, belonging to the field of power electronics technology. The power conversion device includes a switching transistor connected in series between the power conversion circuit and the DC bus. When a short-circuit fault occurs in the power conversion circuit, resulting in a large short-circuit current (i.e., fault current) on the DC bus, the on-state voltage drop of the switching transistor increases. When the on-state voltage drop of the switching transistor exceeds a threshold voltage, the control circuit in the power conversion device promptly controls the switching transistor to turn off, thereby disconnecting the fault current path and disconnecting the short-circuited power conversion circuit from the DC bus. This allows for rapid isolation of the short-circuited power conversion device from other power conversion devices, preventing the fault from propagating and affecting the reliability of the entire system (such as a charging pile).

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a power conversion device and a charging pile. Background Technology

[0002] Charging stations typically include multiple power conversion devices, one end of which is connected in parallel to a DC bus. In scenarios where multiple power conversion devices are connected in parallel to the DC bus, a short-circuit fault in any one device can easily spread to the entire charging station. This results in low reliability for such charging stations. Summary of the Invention

[0003] This application provides a power conversion device and a charging pile, which can solve the technical problem of low reliability of charging piles.

[0004] In a first aspect, a power conversion device is provided, comprising: a power conversion circuit, a first switching transistor, and a first control circuit. The power conversion circuit has a first DC terminal connected to a first bus in a DC bus configuration, and a second DC terminal connected to a first terminal of the first switching transistor. The second terminal of the first switching transistor is connected to a second bus in the DC bus configuration. The first control circuit is connected to the control terminal of the first switching transistor and is used to control the first switching transistor to turn off when the on-state voltage drop of the first switching transistor is greater than a first threshold voltage. One of the first bus and the second bus is a positive bus, and the other is a negative bus. Furthermore, of the first DC terminal and the second DC terminal, the DC terminal connected to the positive bus is the positive terminal, and the DC terminal connected to the negative bus is the negative terminal.

[0005] Understandably, when a short-circuit fault occurs in the power conversion circuit, resulting in a large short-circuit current (i.e., fault current) on the DC bus, the forward voltage drop of the first switching transistor will increase. When the forward voltage drop of the first switching transistor exceeds the threshold voltage, the first control circuit promptly controls the first switching transistor to turn off, thus disconnecting the fault current path and disconnecting the short-circuited power conversion circuit from the DC bus. This isolates the short-circuited power conversion device from other power conversion devices, preventing the fault from spreading and affecting the reliability of the entire system (such as a charging station).

[0006] In one embodiment, the first voltage threshold is greater than the product of the on-resistance of the first switching transistor and the rated current of the DC bus. The rated current is the quotient of the rated power of the power conversion circuit and the rated voltage of the DC bus. This not only avoids affecting the normal operation of the power conversion circuit but also ensures rapid fault isolation when a fault current exceeding the rated current occurs on the DC bus.

[0007] In one embodiment, the first voltage threshold is 1.5 to 3 times the product. This ensures that the first control circuit can quickly identify the fault current and promptly disconnect the current path of the fault current.

[0008] In one embodiment, the first control circuit is further configured to control the first switch to turn on after controlling the first switch to turn off, upon receiving an unlocking command indicating that the short-circuit fault has been cleared.

[0009] The unlocking command can be issued by the system controller (such as the system controller of a charging pile) after detecting that a short-circuit fault in the power conversion circuit has been cleared. Based on this unlocking command, the first control circuit controls the first switching transistor to turn on again, allowing the power conversion circuit to reconnect to the DC bus and resume operation after the short-circuit fault is cleared. Therefore, for short-circuit faults not caused by hardware damage, the system can recover quickly after the short-circuit fault is cleared without replacing the power conversion equipment, thus significantly reducing the cost of the system (such as a charging pile).

[0010] In one embodiment, the power conversion device further includes a first voltage sampling circuit, which is connected to the first and second terminals of a first switching transistor and is used to detect the on-state voltage drop between the first and second terminals of the first switching transistor. Correspondingly, the first control circuit can acquire the on-state voltage drop of the first switching transistor sampled by the first voltage sampling circuit.

[0011] In one embodiment, the first control circuit includes a comparator and a control sub-circuit. The first input terminal of the comparator receives the on-state voltage drop of the first switching transistor sampled by the first voltage sampling circuit. The second input terminal of the comparator receives a first threshold voltage. The output terminal of the comparator is connected to the control sub-circuit and is used to output a first level when the on-state voltage drop is greater than the first threshold voltage, and to output a second level when the on-state voltage drop is not greater than the first threshold voltage. The control sub-circuit is also connected to the control electrode of the first switching transistor and is used to control the first switching transistor to turn off when it receives the first level output from the comparator, and to control the first switching transistor to turn on when it receives an unlock command or the second level output from the comparator.

[0012] When the comparator outputs the first level, it indicates that the on-state voltage drop of the first switch is greater than the first threshold voltage, signifying a short circuit fault in the power conversion circuit. Therefore, the control sub-circuit can promptly turn off the first switch based on this first level to achieve rapid isolation of the short circuit fault. When the comparator outputs the second level, it indicates that the on-state voltage drop of the first switch is not greater than the first threshold voltage, signifying that no short circuit fault has occurred in the power conversion circuit. Therefore, the control sub-circuit can keep the first switch on based on this second level to ensure normal operation of the power conversion circuit. Furthermore, when the control sub-circuit receives an unlock command, it indicates that the short circuit fault in the power conversion circuit has been cleared, thus allowing the first switch to remain on to ensure normal operation of the power conversion circuit.

[0013] In one embodiment, the control sub-circuit includes a controller, a logic gate circuit, and a driver circuit. The first input terminal of the logic gate circuit is connected to the controller, the second input terminal of the logic gate circuit is connected to the output terminal of the comparator, and the output terminal of the logic gate circuit is connected to the control electrode of the first switching transistor via the driver circuit. The controller outputs a first level to the first input terminal of the logic gate circuit when no unlock command is received, and outputs a second level to the first input terminal of the logic gate circuit when an unlock command is received. The logic gate circuit outputs a first level to the driver circuit when both the first and second input terminals receive the first level, and outputs a second level to the driver circuit when either the first or second input terminal receives the second level. The driver circuit controls the first switching transistor to turn off when the logic gate circuit outputs the first level, and controls the first switching transistor to turn on when the logic gate circuit outputs the second level.

[0014] Based on the working principles of the controller, logic gate circuits, and drive circuits described above, the first switch can be turned off in a timely manner when its on-state voltage drop is greater than the first threshold voltage. Conversely, the first switch can be turned on when its on-state voltage drop is not greater than the first threshold voltage, or when an unlocking command indicating that a short-circuit fault has been cleared is received, thus enabling the power conversion circuit to operate normally.

[0015] In one embodiment, the logic gate is an AND gate, where the first level is high relative to the second level. Alternatively, the logic gate is an OR gate, where the first level is low relative to the second level.

[0016] It is understood that the logic gate circuit can also be a circuit composed of other logic gate devices. This application embodiment does not limit this, as long as it ensures that the logic gate circuit can realize the above-mentioned logical relationship between the output level and the input level.

[0017] In one embodiment, the power conversion device further includes a second switching transistor and a second control circuit. The second terminal of the first switching transistor is connected to a second bus in the DC bus via the second switching transistor, and the second terminals of the first and second switching transistors are connected together. Furthermore, the second terminals of the first and second switching transistors have the same polarity; that is, both terminals are either source or drain terminals. Based on the connection relationship between the first and second switching transistors, they are connected in reverse series between the second DC terminal and the second bus of the power conversion circuit. The second control circuit is connected to the control terminal of the second switching transistor, and is used to control the second switching transistor to turn off when the forward voltage drop between the first and second terminals of the second switching transistor is greater than a second threshold voltage.

[0018] In this configuration, the two switches connected in reverse series can refer to their opposite connection directions. This reverse series connection allows for effective detection and blocking of fault currents flowing in two different directions, enabling bidirectional fault current detection and blocking. For example, the first switch can detect and block fault current flowing from the positive busbar to the negative busbar, while the second switch can detect and block fault current flowing from the negative busbar to the positive busbar. This effectively improves the isolation effect against short-circuit faults, thereby enhancing the reliability of the entire system (such as a charging station). It is understood that the structure and operating principle of the second control circuit can be the same as those of the first control circuit. Furthermore, the controller in the second control circuit can be the same controller as the controller in the first control circuit.

[0019] In one embodiment, the power conversion device further includes a second switching transistor and a second control circuit. The first DC terminal of the power conversion circuit is connected to the first terminal of the second switching transistor, and the second terminal of the second switching transistor is connected to the first bus. Furthermore, the second terminals of the first and second switching transistors have the same polarity; that is, both second terminals are either source terminals or both are drain terminals. Based on the above connection relationship of the second switching transistor, it can be understood that the connection direction of the second switching transistor is opposite to that of the first switching transistor, or it can be understood that the first and second switching transistors are connected in reverse series between the first and second bus. The second control circuit is connected to the control terminal of the second switching transistor, and the second control circuit is used to control the second switching transistor to turn off when the forward voltage drop between the first and second terminals of the second switching transistor is greater than a second threshold voltage.

[0020] Because the two switching transistors are connected in opposite directions, that is, the two switching transistors are connected in reverse series between the first busbar and the second busbar, it is possible to effectively detect and block fault currents in two different directions, that is, to detect and block bidirectional fault currents.

[0021] In one embodiment, the second voltage threshold is greater than the product of the on-resistance of the second switch and the rated current of the DC bus. The rated current is the quotient of the rated power of the power conversion circuit and the rated voltage of the DC bus. For example, the second voltage threshold is 1.5 to 3 times the product. Furthermore, the second voltage threshold can be equal to the first voltage threshold.

[0022] In one embodiment, the switching transistor (i.e., the first switching transistor, or the first switching transistor and the second switching transistor) connected in series between the DC terminal and the DC bus of the power conversion circuit in the power conversion device is a metal-oxide-semiconductor field-effect transistor (MOSFET) or an insulated-gate bipolar transistor (IGBT), etc.

[0023] When the switching transistor is a MOSFET, the control electrode of the first switching transistor mentioned above can refer to the gate. The first electrode can be one of the source (S) and drain (D), and the second electrode can be the other of the source and drain. When the switching transistor is an IGBT, the control electrode of the first switching transistor mentioned above can refer to the base (also called the gate). The first electrode can be one of the emitter (E) and collector (C), and the second electrode can be the other of the emitter and collector.

[0024] In one embodiment, the power conversion circuit is an AC / DC power conversion circuit or a DC / DC power conversion circuit. The AC / DC power conversion circuit's AC terminal can be connected to the power grid and can convert the AC power from the grid into DC power before outputting it to the DC bus. The DC / DC power conversion circuit's load terminal can be connected to a load or an energy storage battery. Furthermore, the DC / DC power conversion circuit can convert the DC power from the DC bus to supply power to the load or charge the energy storage battery. Alternatively, the DC / DC power conversion circuit can convert the DC power supplied by the energy storage battery to the DC bus and output it to the DC bus.

[0025] Secondly, a charging pile is provided, comprising: a plurality of power conversion devices as described in the first aspect above and a DC bus, wherein each of the plurality of power conversion devices includes a power conversion circuit and a first switching transistor. The first DC terminal of the power conversion circuit is connected to a first bus in the DC bus, and the second terminal of the first switching transistor is connected to a second bus in the DC bus.

[0026] In one embodiment, the plurality of power conversion devices includes at least one AC / DC conversion device and at least one DC / DC conversion device. Each AC / DC conversion device has an AC / DC power conversion circuit, and each DC / DC conversion device has a DC / DC power conversion circuit. The AC terminal of the AC / DC power conversion circuit is connected to the power grid, the first DC terminal of the AC / DC power conversion circuit is connected to a first bus, and the second terminal of the first switching transistor in each AC / DC conversion device is connected to a second bus. The load terminal of the DC / DC power conversion circuit is connected to a load, the first DC terminal of the DC / DC power conversion circuit is connected to the first bus, and the second terminal of the first switching transistor in each DC / DC conversion device is connected to the second bus. The load may be an electric vehicle.

[0027] In summary, this application provides a power conversion device and a charging pile. The power conversion device includes a switching transistor connected in series between the power conversion circuit and the DC bus. When a short-circuit fault occurs in the power conversion circuit, resulting in a large short-circuit current (i.e., fault current) on the DC bus, the on-state voltage drop of the switching transistor increases. When the on-state voltage drop of the switching transistor exceeds a threshold voltage, the control circuit in the power conversion device promptly controls the switching transistor to turn off, thereby disconnecting the fault current path and disconnecting the short-circuited power conversion circuit from the DC bus. This allows for rapid isolation of the short-circuited power conversion device from other power conversion devices, preventing the fault from propagating and affecting the reliability of the entire system (e.g., the charging pile). Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of a charging pile provided in an embodiment of this application;

[0029] Figure 2 This is a schematic diagram of the structure of a power conversion device provided in an embodiment of this application;

[0030] Figure 3 This is a schematic diagram of another power conversion device provided in an embodiment of this application;

[0031] Figure 4 This is a schematic diagram of the structure of another power conversion device provided in the embodiments of this application;

[0032] Figure 5 This is a schematic diagram of another power conversion device provided in the embodiments of this application;

[0033] Figure 6 This is a schematic diagram of another power conversion device provided in the embodiments of this application;

[0034] Figure 7This is a schematic diagram of another power conversion device provided in the embodiments of this application;

[0035] Figure 8 This is a schematic diagram of the working process of a first control circuit provided in an embodiment of this application;

[0036] Figure 9 This is a schematic diagram of another charging pile provided in an embodiment of this application. Detailed Implementation

[0037] The power conversion device and charging pile provided in the embodiments of this application are described in detail below with reference to the accompanying drawings.

[0038] This application provides a charging pile, such as Figure 1 As shown, the charging pile includes a DC bus and multiple power conversion devices, one end of which is connected in parallel to the DC bus (also called a DC busbar or DC bus). The power conversion devices, also known as charging equipment or charging modules, are used to convert received power and output it to the DC bus, or to convert power on the DC bus and output it. In situations such as... Figure 1 In the charging pile shown, because multiple power conversion devices are connected in parallel on the DC bus, a short circuit fault occurring on the DC bus side (i.e., the end connected to the DC bus) of any power conversion device can easily cause the fault to spread to the entire charging pile. Therefore, if the power conversion devices are not designed with short-circuit protection, the reliability of the entire charging pile will be reduced, the failure rate will be high, and the maintenance cost will be high.

[0039] To improve the reliability of power conversion equipment, in some embodiments, a fuse can be installed on the DC bus side of each power conversion device. When a short circuit occurs on the DC bus side of a power conversion device, the fuse can trip (i.e., blow), isolating the power conversion device with the short circuit fault from the DC bus. However, fuse tripping requires a large current, which can lower the voltage of the entire DC bus and may cause fuses in other power conversion devices to also blow, thus escalating the fault.

[0040] In other embodiments, overcurrent detection and protection circuits can also be included in each power conversion device. However, this approach results in a more complex circuit structure, larger size, and higher cost. Furthermore, the protection circuit has a longer protection delay and cannot promptly interrupt short-circuit faults.

[0041] This application provides a power conversion device that can be applied to, for example... Figure 1In the application scenario shown, this power conversion device can quickly disconnect from the DC bus when a short-circuit fault occurs on the DC bus side. That is, it can quickly isolate the power conversion device with a short-circuit fault from other power conversion devices, preventing the escalation of a single point of failure. Figure 2 As shown, the power conversion device includes: a power conversion circuit 10, a first switching transistor M1, and a first control circuit 20.

[0042] The power conversion circuit 10, which is used to connect to the DC bus, includes a first DC terminal and a second DC terminal. One of the first DC terminal and the second DC terminal is a positive terminal (+), and the other is a negative terminal (-).

[0043] refer to Figure 2 The first DC terminal of the power conversion circuit 10 is connected to the first bus in the DC bus, and the second DC terminal of the power conversion circuit 10 is connected to the first terminal of the first switching transistor M1. The second terminal of the first switching transistor M1 is connected to the second bus in the DC bus. That is, the first switching transistor M1 is connected in series between the second DC terminal of the power conversion circuit 10 and the second bus. One of the first bus and the second bus is the positive bus BUS+, and the other is BUS-. For example, Figure 2 The following diagram illustrates the process using the first busbar as the positive busbar BUS+ and the second busbar as the negative busbar BUS-. It can be understood that in the first and second DC terminals of the power conversion circuit 10, the terminal connected to the positive busbar BUS+ is the positive terminal +, and the terminal connected to the negative busbar BUS- is the negative terminal -.

[0044] It is understood that the power conversion circuit 10 is used to output DC power to the DC bus via the conducting first switch M1, or to perform voltage conversion on the DC power on the DC bus. For example, the power conversion circuit 10 can be an AC / DC converter circuit, the AC terminal of which can be connected to the power grid. Furthermore, this AC / DC converter circuit can convert the AC power from the power grid into DC power and output it to the DC bus. Alternatively, the power conversion circuit 10 can be a DC / DC converter circuit, which also has a load terminal, which can be connected to a load or an energy storage battery. Furthermore, the DC / DC converter circuit can perform voltage conversion on the DC power on the DC bus to power the load or charge the energy storage battery. Alternatively, the DC / DC converter circuit can perform voltage conversion on the DC power supplied by the energy storage battery and output it to the DC bus.

[0045] The first control circuit 20 is connected to the control electrode of the first switching transistor M1. The first control circuit 20 is used to control the first switching transistor M1 to turn off when the forward voltage drop between the first and second electrodes of the first switching transistor M1 is greater than a first threshold voltage. The forward voltage drop between the first and second electrodes of the first switching transistor M1 refers to the voltage difference between the first and second electrodes of the first switching transistor M1 when the first and second electrodes are forward-biased. In other words, this forward voltage drop is the forward voltage drop of the switching transistor.

[0046] It is understandable that when the first and second terminals of the first switching transistor M1 are turned on, the current on the DC bus increases, meaning that as the current flowing through the first switching transistor M1 increases, the forward voltage drop between its first and second terminals also increases. In other words, the magnitude of the forward voltage drop between the first and second terminals of the first switching transistor M1 is positively correlated with the magnitude of the current on the DC bus. Based on this, the forward voltage drop between the first and second terminals of the first switching transistor M1 can be used as a characteristic variable of the fault current on the DC bus.

[0047] The first threshold voltage can be determined based on the on-resistance of the first switching transistor M1 and the rated current of the DC bus. The rated current is the quotient of the rated power of the power conversion circuit and the rated voltage of the DC bus, i.e., rated current = rated power / rated voltage. In one embodiment, the first threshold voltage can be greater than the product of the on-resistance of the first switching transistor M1 and the rated current. This not only avoids affecting the normal operation of the power conversion circuit but also ensures rapid fault isolation when a fault current greater than the rated current occurs on the DC bus. For example, the first threshold voltage can be 1.5 to 3 times the product, such as twice the product.

[0048] It is understandable that, since the forward voltage drop of the first switch M1 is positively correlated with the current on the DC bus, when this forward voltage drop exceeds the first threshold voltage, it indicates that the current on the DC bus is greater than the rated current (e.g., more than twice the rated current), meaning there is a large short-circuit current (also known as a fault current) on the DC bus. Accordingly, the first control circuit 20 can determine that a short-circuit fault exists on the DC bus side of the power conversion circuit 10. To achieve short-circuit protection of the DC bus, the first control circuit 20 can control the first switch M1 to turn off. This disconnects the fault current path, i.e., disconnects the power conversion circuit 10 with the short-circuit fault from the DC bus, thereby isolating the power conversion device with the short-circuit fault from other power conversion devices, preventing the fault from spreading and affecting the reliability of the entire system (such as a charging pile), and ensuring the system can operate continuously and stably. Furthermore, by designing the first threshold voltage to be 1.5 to 3 times the product mentioned above, it can be ensured that the fault current can be quickly identified and its current path promptly disconnected when the fault current is still small.

[0049] Furthermore, the solution provided in this application uses a switching transistor to achieve fault isolation, and the on / off state of this switching transistor can be controlled by a control circuit. Compared to a fuse solution, since there is no need for a large current on the DC bus to blow the fuse, the problem of large currents causing fuses in other power conversion equipment to also blow can be effectively avoided. Moreover, the time required for a fuse to blow is relatively long, for example, on the order of milliseconds (ms), while the switching transistor has a faster turn-off speed, for example, on the order of microseconds (µs). Therefore, by turning off the switching transistor to block the fault current, rapid isolation of short-circuit faults can be achieved, effectively improving the speed of short-circuit protection.

[0050] Furthermore, based on the above analysis, it is clear that in the solution provided in this application embodiment, the first switching transistor M1 is not only a detection device for detecting the current on the DC bus, but also a protection device for implementing short-circuit protection. That is, the first switching transistor M1 has both current detection and short-circuit protection functions. Therefore, compared to traditional current detection methods, it saves on current detection devices, thereby saving circuit cost and size. Moreover, compared to current sensors and other current detection devices, the solution provided in this application embodiment detects fault current by directly sampling the on-state voltage drop, which can effectively improve the fault current detection speed, avoid protection delay, and improve protection speed.

[0051] Continue to refer to Figure 2The power conversion device may further include a first voltage sampling circuit 30, which is connected to the first and second terminals of the first switching transistor M1 and is used to detect the on-state voltage drop between the first and second terminals of the first switching transistor M1. Correspondingly, the first control circuit 20 can acquire the on-state voltage drop of the first switching transistor M1 detected by the first voltage sampling circuit 30.

[0052] It is also understandable that the first switch M1 is in the on state by default to ensure that the power conversion circuit 10 can be connected to the DC bus and operate normally. Furthermore, during the operation of the power conversion circuit 10, the first voltage sampling circuit 30 can continuously sample the on-state voltage drop of the first switch M1. When the on-state voltage drop of the first switch M1 sampled by the first voltage sampling circuit 30 is not greater than the first threshold voltage, the first control circuit 20 determines that the current on the DC bus is within the normal range, and therefore can control the first switch M1 to remain in the on state.

[0053] In one embodiment, the first switching transistor M1 is a MOSFET or an IGBT, etc. Furthermore, the first switching transistor M1 can be an N-type switching transistor or a P-type switching transistor; this embodiment does not limit the specific type.

[0054] When the first switching transistor M1 is a MOSFET (Metal-Oxide-Semiconductor), the control electrode of the first switching transistor M1 mentioned above can refer to the gate. The first electrode can refer to one of the source (S) and drain (D), and the second electrode can refer to the other of the source and drain. For example, the first electrode can be the drain D, and the second electrode can be the source S. Furthermore, the on-state voltage drop between the first and second electrodes of the first switching transistor M1 can refer to the voltage difference between the drain D and the source S, i.e., the drain-source voltage Vds.

[0055] When the first switching transistor M1 is an IGBT, the control terminal of the first switching transistor M1 mentioned above can refer to the base (also called the gate). The first terminal can refer to one of the emitter (E) and collector (C), and the second terminal can refer to the other of the emitter and collector. For example, the first terminal can be the collector C, and the second terminal can be the emitter E. Furthermore, the forward voltage drop between the first and second terminals of the first switching transistor M1 can refer to the voltage difference between the collector C and the emitter E, i.e., the collector-emitter voltage Vce.

[0056] In one embodiment, such as Figure 2 As shown, the power conversion device may include a switching transistor (i.e., a first switching transistor M1) connected in series between the second DC terminal and the second bus of the power conversion circuit 10. Furthermore, when the second bus is the negative bus BUS-, refer to... Figure 2The source S (or emitter) of the first switching transistor M1 can be connected to the negative bus BUS-, and the drain D (or collector) can be connected to the second DC terminal (i.e., the negative terminal) of the power conversion circuit 10. Alternatively, refer to... Figure 3 The source S (or emitter) of the first switching transistor M1 is connected to the second DC terminal (i.e., the negative terminal) of the power conversion circuit 10, and the drain D (or collector) is connected to the negative bus BUS-.

[0057] It is understandable that when the first switching transistor M1 is a MOSFET, it also includes a body diode, also known as a parasitic diode. The anode of this body diode is connected to the source (S), and the cathode is connected to the drain (D). Correspondingly, when the first switching transistor M1 uses… Figure 2 When connected as shown, fault current flowing from the positive busbar BUS+ to the negative busbar BUS- can be blocked. That is, after the first switch M1 is turned off, it can block currents such as... Figure 2 The fault current path 1 is shown. When the fault current flows from the negative busbar BUS- to the positive busbar BUS+, even if the first switch M1 is turned off, the body diode can still conduct and provide a current path for the fault current, resulting in the fault current flowing from the negative busbar BUS- to the positive busbar BUS+ being unable to be effectively blocked. That is, after the first switch M1 is turned off, it cannot block fault currents such as... Figure 3 The fault current path 2 is shown.

[0058] The first switching transistor M1 is used Figure 3 When connected as shown, fault current flowing from the negative busbar BUS- to the positive busbar BUS+ can be blocked. That is, after the first switch M1 is turned off, it can block currents such as... Figure 3 The fault current path 2 is shown. When the fault current flows from the positive bus BUS+ to the negative bus BUS-, even if the first switch M1 is turned off, the body diode can still conduct and provide a current path for the fault current, resulting in the inability to effectively block the flow from the negative bus BUS- to the positive bus BUS+. In other words, after the first switch M1 is turned off, it cannot block currents such as... Figure 2 The fault current path 1 is shown.

[0059] When the first switching transistor M1 is an IGBT, since the IGBT is a bipolar device, current can only flow in one direction, that is, from the collector to the emitter. Therefore, the IGBT should avoid being subjected to reverse voltage. Accordingly, the IGBT is used in anti-parallel connection with a diode, which provides a conduction path for the reverse current. Therefore, an IGBT and its anti-parallel diode can only block fault current in one direction. For example, when using... Figure 2 When connected as shown, the IGBT can block fault current flowing from the positive busbar BUS+ to the negative busbar BUS-. When using, for example... Figure 3 When connected as shown, the IGBT can block fault current flowing from the negative bus BUS- to the positive bus BUS+.

[0060] In one embodiment, such as Figure 4 As shown, the power conversion device may include two switching transistors connected in series between the DC terminal and the DC bus of the power conversion circuit 10: a first switching transistor M1 and a second switching transistor M2. For example, Figure 4 The first switch M1 and the second switch M2 shown are connected in series between the second DC terminal and the second bus of the power conversion circuit 10, that is, the second terminal of the first switch M1 is connected to the second bus through the second switch M2. Figure 4 The following example illustrates the situation using the second busbar as the negative busbar (BUS-). Furthermore, from... Figure 4 It can be seen that the power conversion device also includes a second control circuit 40.

[0061] refer to Figure 4 It can be seen that the first switch M1 and the second switch M2 are connected in reverse series. Reverse series connection, also known as back-to-back series connection, means that the first and second terminals of the two switches are connected in opposite directions. Alternatively, it can be understood as: the same terminals of the two switches are connected to each other, that is, the second terminal of the first switch M1 is connected to the second terminal of the second switch M2. Furthermore, the polarities of the second terminals of the first switch M1 and the second switch M2 are the same, meaning that the second terminals of both switches are either the source (S) or the drain (D). For example, Figure 4 In the structure shown, the second terminal of both switching transistors is the source terminal S, that is, the source terminal S of the first switching transistor M1 is connected to the source terminal S of the second switching transistor M2.

[0062] The second control circuit 40 is connected to the control electrode of the second switch M2. The second control circuit 40 is used to control the second switch M2 to turn off when the on-state voltage drop between the first and second electrodes of the second switch M2 is greater than the second threshold voltage.

[0063] The second threshold voltage can be determined based on the on-resistance of the second switch M2 and the rated current of the DC bus. For example, the second threshold voltage can be greater than the product of the on-resistance of the second switch M2 and the rated current. For instance, the second threshold voltage can be 1.5 to 3 times the product, such as twice the product. Furthermore, the second threshold voltage can be equal to or different from the first threshold voltage described above; this embodiment does not limit this.

[0064] Understandably, since the on-state voltage drop of the second switch M2 is also positively correlated with the current on the DC bus, when this on-state voltage drop exceeds the second threshold voltage, it indicates that the current on the DC bus is greater than the rated current, meaning there is a large short-circuit current (also known as a fault current) on the DC bus. Accordingly, the second control circuit 40 can determine that there is a short-circuit fault on the DC bus side of the power conversion circuit 10. In order to achieve short-circuit protection for the DC bus, the second control circuit 40 can control the second switch M2 to turn off in a timely manner.

[0065] Furthermore, since the first switch M1 and the second switch M2 are connected in reverse series between the DC terminal and the DC bus of the power conversion circuit 10, when one of the switches is turned off, it can block the fault current flowing from the positive bus BUS+ to the negative bus BUS-, that is, it can block currents such as... Figure 2 The fault current path 1 is shown. When the other switch is turned off, it can block the fault current flowing from the negative bus BUS- to the positive bus BUS+, that is, it can block fault current such as... Figure 3 The fault current path 2 is shown. It can be seen that by connecting two switches in reverse series between the DC terminal and the DC bus of the power conversion circuit 10, effective detection and blocking of fault currents in different directions can be achieved, thereby further improving the reliability of fault protection. Furthermore, for fault currents in a single direction, the control circuit in the power conversion equipment can control one switch to turn off while the other switch remains on.

[0066] Example, reference Figure 4 Assume that the drain (D) of the first switch M1 is connected to the negative terminal of the power conversion circuit 10, and its source (S) is connected to the source (S) of the second switch M2. The drain (D) of the second switch M2 is connected to the negative bus BUS-. Then, when the first switch M1 is turned off, it can block the fault current flowing from the positive bus BUS+ to the negative bus BUS-. When the second switch M2 is turned off, it can block the fault current flowing from the negative bus BUS- to the positive bus BUS+.

[0067] It is understandable that the second switch M2 can be of the same type as the first switch M1, meaning it can be a MOSFET or an IGBT. Furthermore, the second switch M2 can be either an N-type or a P-type switch. It is also understandable that when both the first and second switches M1 are MOSFETs, both switches include a body diode. When both the first and second switches M1 are IGBTs, each IGBT is connected in reverse parallel with a diode. Here, reverse parallel connection of the diodes means that the anode of the diode is connected to the emitter, and the cathode is connected to the collector.

[0068] Furthermore, it can be understood that a MOSFET, once turned on, can allow current to flow bidirectionally; that is, current can flow from the source (S) to the drain (D), and also from the drain (D) to the source (S). Therefore, in the scenario where both the first switch M1 and the second switch M2 are MOSFETs, during normal operation of the power conversion circuit 10, both the first switch M1 and the second switch M2 are turned on, and the current on the DC bus flows through both turned-on switches. However, when an IGBT is turned on, current can only flow in one direction; that is, current can only flow from the collector to the emitter. Therefore, in the scenario where both the first switch M1 and the second switch M2 are IGBTs, during normal operation of the power conversion circuit 10, both the first switch M1 and the second switch M2 are turned on, and the current on the DC bus flows through one of the turned-on IGBTs and through the diode connected in reverse parallel to the other IGBT.

[0069] Continue to refer to Figure 4 The power conversion device further includes a second voltage sampling circuit 50, which is connected to the first and second terminals of the second switching transistor M2 and is used to detect the on-state voltage drop between the first and second terminals of the second switching transistor M2. Correspondingly, the second control circuit 40 can acquire the on-state voltage drop of the second switching transistor M2 detected by the second voltage sampling circuit 50.

[0070] The above explanation uses the negative bus BUS- as an example, meaning that the switching transistors (e.g., the first switching transistor M1, or the first switching transistor M1 and the second switching transistor M2) are connected in series between the negative terminal - and the negative bus BUS- of the power conversion circuit 10. It can be understood that the second bus can also be the positive bus BUS+, meaning that the switching transistors (e.g., the first switching transistor M1, or the first switching transistor M1 and the second switching transistor M2) can also be connected in series between the positive terminal + and the positive bus BUS+ of the power conversion circuit 10. For example, refer to... Figure 5 The first switch M1 and the second switch M2 are connected in reverse series between the positive terminal + and the positive bus BUS+ of the power conversion circuit 10.

[0071] Alternatively, in a scenario where the power conversion device includes a first switch M1 and a second switch M2, the first switch M1 and the second switch M2 can be connected in series between different DC terminals and buses. That is, the second switch M2 can be connected in series between the first DC terminal of the power conversion circuit 10 and the first bus, and the first DC terminal of the power conversion circuit 10 is connected to the first terminal of the second switch M2, while the second terminal of the second switch M2 is used to connect to the first bus. Alternatively, it can be understood that the first switch M1 and the second switch M2 are connected in reverse series between the first bus and the second bus. For example, see reference... Figure 6The first switch M1 is connected in series between the negative terminal - and the negative bus BUS- of the power conversion circuit 10, while the second switch M2 is connected in series between the positive terminal + and the positive bus BUS+ of the power conversion circuit 10. Furthermore, the two switches are connected in opposite directions. For example, as... Figure 6 As shown, the source S of the first switching transistor M1 can be connected to the negative bus BUS-, and the drain D can be connected to the negative terminal - of the power conversion circuit 10. The drain D of the second switching transistor M2 can be connected to the positive terminal + of the power conversion circuit 10, and the source S can be connected to the positive bus BUS+.

[0072] Alternatively, the power conversion circuit may include two sets of detection and protection circuits. Each set includes a first switch M1 and a second switch M2 connected in reverse series, along with corresponding voltage sampling and control circuits. In one set of detection and protection circuits, the two switches can be connected in reverse series between the positive terminal of the power conversion circuit 10 and the positive bus BUS+, while in the other set, the two switches can be connected in reverse series between the negative terminal of the power conversion circuit 10 and the negative bus BUS-. This effectively improves the accuracy of fault current detection and the blocking effect, thereby enhancing the reliability of the system (such as a charging station).

[0073] It is understood that the structures of the first voltage sampling circuit 30 and the second voltage sampling circuit 50 described above can be identical. For example, since the on-state voltage drop of the switching transistor is low, while the voltage between its first and second terminals is high when it is off, each voltage sampling circuit can include a limiting circuit. This limiting circuit can limit the voltage between the first and second terminals of the sampled switching transistor to restrict the amplitude of the voltage within the input voltage range of the control circuit (such as the first control circuit 20 and the second control circuit 40).

[0074] In one embodiment, the first control circuit 20 is further configured to: after controlling the first switch M1 to turn off, control the first switch M1 to turn on when receiving an unlocking command indicating that the short-circuit fault has been cleared.

[0075] The unlocking command can be issued by the system controller of the system to which the power conversion device belongs (such as a charging pile). Furthermore, this system controller can issue an unlocking command to the first control circuit 20 after determining that the short-circuit fault in the power conversion device has been cleared. For example, after maintenance personnel detect that the short-circuit fault in the power conversion device has been cleared, they can instruct the system controller to issue an unlocking command to the first control circuit 20 in the power conversion device to turn on the first switch M1. Alternatively, maintenance personnel can directly control the power conversion device to be powered on again. After the power conversion device is powered on again, the first switch M1 is in the on state by default.

[0076] Once the first switching transistor M1 is turned on, the power conversion equipment can resume operation (reset) and reconnect to the DC bus. Therefore, for short-circuit faults in the power conversion equipment caused by non-hardware damage, the system can be quickly restored after the fault is cleared without needing to replace the power conversion equipment.

[0077] Figure 7 This is a schematic diagram of another power conversion device provided in an embodiment of this application. For example... Figure 7 As shown, the first control circuit 20 may include a comparator 21 and a control sub-circuit 22.

[0078] In this circuit, the first input terminal of comparator 21 is connected to the first voltage sampling circuit 30 and is used to receive the on-state voltage drop of the first switching transistor M1 sampled by the first voltage sampling circuit 30. The second input terminal of comparator 21 is used to receive the first threshold voltage (also called the reference voltage). The output terminal of comparator 21 is connected to the control sub-circuit 22 and is used to output a first level or a second level to the control sub-circuit 22. Specifically, comparator 21 is used to: output a first level when the on-state voltage drop of the first switching transistor M1 is greater than the first threshold voltage; and output a second level when the on-state voltage drop of the first switching transistor M1 is not greater than the first threshold voltage.

[0079] For example, the first input terminal of comparator 21 can be a positive input terminal, and the second input terminal can be a negative input terminal. Accordingly, when the forward voltage drop received at the positive input terminal is greater than the first threshold voltage received at the negative input terminal, the first output level of comparator 21 can be a high level. When the forward voltage drop received at the positive input terminal is not greater than the first threshold voltage received at the negative input terminal, the second output level of comparator 21 can be a low level.

[0080] The control sub-circuit 22 is also connected to the control electrode of the first switching transistor M1, and is used to control the first switching transistor M1 to turn off when the first level output by the comparator 21 is received, and to control the first switching transistor M1 to turn on when the unlock command or the second level output by the comparator 21 is received.

[0081] As mentioned earlier, when comparator 21 outputs the first level, it indicates that the forward voltage drop of the first switch M1 is greater than the first threshold voltage, meaning there is a fault current on the DC bus. Therefore, control sub-circuit 22 can promptly control the first switch M1 to turn off, thus cutting off the current path of the fault current. When control sub-circuit 22 receives an unlock command, it can determine that the short-circuit fault has been resolved, and therefore can control the first switch M1 to turn on. Alternatively, when control sub-circuit 22 receives the second level output from comparator 21, it indicates that the forward voltage drop of the first switch M1 is not greater than the first threshold voltage, meaning there is no fault current on the DC bus. Therefore, control sub-circuit 22 can control the first switch M1 to remain on.

[0082] In one embodiment, reference continues... Figure 3 The control sub-circuit 22 may include: a controller 221, a logic gate circuit 222, and a driver circuit 223. The first input terminal of the logic gate circuit 222 is connected to the controller 221, the second input terminal of the logic gate circuit 222 is connected to the output terminal of the comparator 21, and the output terminal of the logic gate circuit 222 is connected to the control electrode of the first switching transistor M1 of the logic gate circuit 222 via the driver circuit 223.

[0083] The controller 221 is used to output a first level to the first input terminal of the logic gate circuit 222 when no unlock command is received, and to output a second level to the first input terminal of the logic gate circuit 222 when an unlock command is received.

[0084] Logic gate 222 is used to output a first level to drive circuit 223 when both the first and second input terminals receive a first level, and to output a second level to drive circuit 223 when either the first or second input terminal receives a second level. That is, logic gate 222 can output a first level when both input terminals are at the first level, and can output the second level when either input terminal is at the second level.

[0085] The driving circuit 223 is used to control the first switch M1 to turn off when the logic gate circuit 222 outputs the first level, and to control the first switch M1 to turn on when the logic gate circuit 222 outputs the second level.

[0086] Based on the working principle of comparator 21 and logic gate 222, it can be seen that when the on-state voltage drop of the first switch M1 is greater than the first threshold voltage, comparator 21 outputs a first level to the second input terminal of logic gate 222. At this time, when the controller 221 does not receive an unlock command, it can output a first level to the first input terminal of logic gate 222. Correspondingly, logic gate 222 can output a first level to the drive circuit 223. The drive circuit 223 can then control the first switch M1 to turn off in a timely manner based on this first level.

[0087] After the drive circuit 223 controls the first switch M1 to turn off, when the controller 221 receives the unlock command, it can output a second level to the first input terminal of the logic gate circuit 222. Correspondingly, the logic gate circuit 222 can output a second level to the drive circuit 223. The drive circuit 223 can then control the first switch M1 to turn on again based on this second level, so that the power conversion circuit 10 can be reconnected to the DC bus and resume operation.

[0088] When the on-state voltage drop of the first switch M1 is not greater than the first threshold voltage, comparator 21 outputs a second level to the second input of logic gate 222. At this time, when controller 221 does not receive an unlock command, it can output a first level to the first input of logic gate 222. Correspondingly, logic gate 222 can output a second level to drive circuit 223. Drive circuit 223 can then control the first switch M1 to remain on.

[0089] It is understandable that the first switching transistor M1 can be an N-type switching transistor. Correspondingly, when the driving circuit 223 receives the first level output from the logic gate circuit 222, it can output a low-level driving signal to the control electrode of the first switching transistor M1 to turn it off. When the driving circuit 223 receives the second level output from the logic gate circuit 222, it can output a high-level driving signal to the control electrode of the first switching transistor M1 to turn it on.

[0090] In one embodiment, the first level can be a high level relative to the second level. Furthermore, the logic gate 222 can be an AND gate. Based on the working principle of an AND gate, it is known that an AND gate can output a high level (i.e., the first level) when both inputs are high, and can output a low level (i.e., the second level) when either input is low.

[0091] Of course, the first level can also be low relative to the second level. Correspondingly, the logic gate 222 described above can be an OR gate. This application embodiment does not limit the type of the logic gate 222, only requiring that the input and output levels of the logic gate 222 have the aforementioned logical relationship. Furthermore, the logic gate 222 can be a logic gate chip (such as an AND gate chip) or a circuit composed of discrete components.

[0092] It is understandable that the signal output by controller 221 to logic gate 222 can be called the enable signal EN. Furthermore, in the default state, the enable signal EN output by controller 221 can be at a first level (e.g., high level). When controller 221 receives an unlock command, it can adjust the level of its output enable signal EN to a second level (e.g., low level), and then adjust the level of enable signal EN back to the first level (e.g., high level). That is, after receiving the unlock command, controller 221 can output a pulse of the second level (e.g., a low-level pulse). This ensures that when comparator 21 detects the fault current again and outputs the first level, logic circuit 222 can output the first level, so that drive circuit 223 controls the first switch M1 to turn off.

[0093] The working process of the first control circuit 20 described above can be referred to Figure 8,and Figure 8 Taking the first switching transistor M1 as an N-type switching transistor as an example, and using logic gate circuit 222 as an AND gate as an example, the explanation will be provided. Figure 8 As shown, under fault conditions, the fault current on the DC bus causes an increase in the drain current Id (or collector current Ic) of the first switching transistor M1. Correspondingly, the on-state voltage drop Vds (or Vce) of the first switching transistor M1 increases. When the on-state voltage drop Vds (or Vce) exceeds the first threshold voltage, the output level of comparator 21 flips from the second level to the first level (i.e., low level flips to high level). At this time, when the enable signal EN output by controller 221 is at an effective level (i.e., high level), the AND gate circuit outputs a high level. The drive circuit 223 can then output a low level to the control electrode (i.e., gate) of the first switching transistor M1 based on this high level, thereby turning off the first switching transistor M1.

[0094] Understandably, after the driving circuit 223 outputs a low level to the gate of the first switching transistor M1, the gate-source voltage difference Vgs (or gate-emitter voltage Vge) of the first switching transistor M1 will decrease. This will increase the on-resistance of the first switching transistor M1 and keep the on-state voltage drop Vds (or Vce) above the first threshold voltage. Correspondingly, the comparator 21 continuously outputs the first level, and with the enable signal EN also at the first level, the logic gate circuit 222 can continuously output the first level. The driving circuit 223 can then control the first switching transistor M1 to remain in the off state based on this first level. That is, the first control circuit 20 has an automatic lock-up function; after the on-state voltage drop of the first switching transistor M1 exceeds the first threshold voltage, the first control circuit 20 can lock the first switching transistor M1 in the off state.

[0095] The controller 221 can be a microcontroller unit (MCU), a complex programmable logic device (CPLD), or a field-programmable gate array (FPGA), etc. The driving circuit 223 can be a gate driving circuit, which provides a driving signal with appropriate driving capability to the gate of the first switch M1 according to the level output of the logic gate circuit 222, so as to effectively drive the first switch M1 to turn on or off. Furthermore, the driving circuit 223 can be an integrated circuit (IC) or a circuit composed of discrete components; this embodiment does not limit this.

[0096] The structure and working principle of the first control circuit 20 have been described above. It is understood that the structure and working principle of the second control circuit 40 can be the same as that of the first control circuit 20. For example, after controlling the second switch M2 to turn off, the second control circuit 40 can control the second switch M2 to turn back on upon receiving an unlocking command. The structure and working principle of the second control circuit 40 can be referred to the relevant description of the first control circuit 20, and will not be repeated here. Furthermore, the controller in the second control circuit 40 and the controller 221 in the first control circuit 20 can share the same controller, or they can be set independently. This application embodiment does not limit this.

[0097] When the controller in the second control circuit 40 shares the same controller as the controller 221 in the first control circuit 20, the controller can output enable signals EN to different logic gates through different ports, and the levels of the enable signals EN output from different ports can be different. Alternatively, the controller can also output enable signals EN to different logic gates through the same port, meaning that the levels of the enable signals EN received by different logic gates are the same.

[0098] In summary, this application provides a power conversion device including a switching transistor connected in series between the power conversion circuit and the DC bus. When a short-circuit fault occurs in the power conversion circuit, resulting in a large short-circuit current (i.e., fault current) on the DC bus, the on-state voltage drop of the switching transistor increases. When the on-state voltage drop of the switching transistor exceeds a threshold voltage, the control circuit in the power conversion device promptly controls the switching transistor to turn off, thereby disconnecting the fault current path and disconnecting the short-circuited power conversion circuit from the DC bus. This isolates the short-circuited power conversion device from other power conversion devices, preventing the fault from propagating and affecting the reliability of the entire system (such as a charging pile).

[0099] Furthermore, the solution provided in this application uses a switching transistor to detect and isolate fault current. This effectively improves the detection speed of fault current and enables faster short-circuit protection, ensuring stable system operation. Since the switching transistor combines current detection and short-circuit protection functions, it achieves the reuse of detection and blocking components, thus effectively saving circuit cost and size.

[0100] Furthermore, upon receiving an unlocking command indicating that the short-circuit fault has been cleared, the control circuit can also control the switching transistor to turn on again, i.e., unlock the switching transistor, so that the power conversion circuit can be reconnected to the DC bus and resume operation. Since the solution provided in this embodiment also has an unlocking function, the system can quickly recover from short-circuit faults not caused by hardware damage without replacing the power conversion equipment, thereby effectively reducing system maintenance costs.

[0101] This application also provides a charging pile, such as... Figure 1 As shown, the charging pile includes a DC bus and multiple power conversion devices as provided in the above embodiments. Each of the multiple power conversion devices includes a power conversion circuit and a first switching transistor. The first DC terminal of the power conversion circuit is connected to the first bus in the DC bus, and the second terminal of the first switching transistor is connected to the second bus in the DC bus.

[0102] Example, reference Figure 9 The plurality of power conversion devices may include at least one AC / DC conversion device and at least one DC / DC conversion device. For example Figure 9 The document shows multiple AC / DC conversion devices and multiple DC / DC conversion devices.

[0103] Each AC / DC converter contains an AC / DC power conversion circuit, and each DC / DC converter contains a DC / DC power conversion circuit. The AC terminal of the AC / DC power conversion circuit is connected to the power grid, the first DC terminal is connected to the first bus, and the second terminal of the first switching transistor in each AC / DC converter is connected to the second bus. This AC / DC power conversion circuit converts the AC power from the power grid into DC power and outputs it to the DC bus.

[0104] The load terminal of this DC / DC power conversion circuit is used to connect a load, such as an electric vehicle. The first DC terminal of the DC / DC power conversion circuit is connected to a first bus, and the second terminal of the first switching transistor in each DC / DC converter is connected to a second bus. This DC / DC power conversion circuit is used to convert the DC power on the DC bus to voltage and then supply power to the load. It can be understood that the connection method between the aforementioned AC / DC converter and DC / DC converter and the DC bus can also be referred to as a back-to-back connection.

[0105] It is also understood that the solutions provided in this application can be applied not only to charging piles in charging stations, but also to other fields, such as energy storage stations, or to photovoltaic-energy storage-charging integrated scenarios. Here, a photovoltaic-energy storage-charging integrated scenario refers to a scenario that combines photovoltaics, energy storage, and charging. For example, the inverter system in a photovoltaic-energy storage-charging integrated scenario can adopt, for example... Figure 1 or Figure 9 The diagram illustrates a common DC bus design architecture. Furthermore, in energy storage stations or applications integrating photovoltaic, energy storage, and charging, when the power conversion device is a DC / DC converter, the load terminal of the DC / DC power conversion circuit within this device can also be connected to the energy storage battery. This DC / DC converter is used to convert the DC power on the DC bus to a voltage to charge the energy storage battery, or to convert the DC power supplied by the energy storage battery to a voltage and output it to the DC bus.

[0106] In the embodiments of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "at least one" refers to one or more, and "multiple" refers to two or more.

[0107] The above description is merely an optional implementation of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A power conversion device, characterized in that, The power conversion device includes: a power conversion circuit, a first switching transistor, and a first control circuit; Wherein, the first DC terminal of the power conversion circuit is used to connect to the first bus in the DC bus, the second DC terminal of the power conversion circuit is connected to the first pole of the first switching transistor, and the second pole of the first switching transistor is used to connect to the second bus in the DC bus; The first control circuit is connected to the control electrode of the first switching transistor. The first control circuit is used to control the first switching transistor to turn off when the on-state voltage drop between the first electrode and the second electrode of the first switching transistor is greater than the first threshold voltage.

2. The power conversion device according to claim 1, characterized in that, The first voltage threshold is greater than the product of the on-resistance of the first switch and the rated current of the DC bus; The rated current is the quotient of the rated power of the power conversion circuit and the rated voltage of the DC bus.

3. The power conversion device according to claim 2, characterized in that, The first voltage threshold is 1.5 to 3 times the product.

4. The power conversion device according to any one of claims 1 to 3, characterized in that, The first control circuit is further configured to: After the first switch is turned off, the first switch is turned on upon receiving an unlocking command indicating that the short-circuit fault has been cleared.

5. The power conversion device according to claim 4, characterized in that, The power conversion device further includes a first voltage sampling circuit, which is used to detect the on-state voltage drop between the first and second terminals of the first switching transistor. The first control circuit includes a comparator and a control sub-circuit. The first input terminal of the comparator is used to receive the on-state voltage drop of the first switch detected by the first voltage sampling circuit, the second input terminal of the comparator is used to receive the first threshold voltage, and the output terminal of the comparator is connected to the control sub-circuit and used to output a first level or a second level to the control sub-circuit. The control sub-circuit is also connected to the control electrode of the first switch transistor and is used to control the first switch transistor to turn off when the first level output by the comparator is received, and to control the first switch transistor to turn on when the unlock command or the second level output by the comparator is received. The comparator is used for: When the on-state voltage drop is greater than the first threshold voltage, the first level is output; When the on-state voltage drop is not greater than the first threshold voltage, the second level is output.

6. The power conversion device according to claim 5, characterized in that, The control sub-circuit includes: a controller, logic gate circuits, and a drive circuit; The first input terminal of the logic gate circuit is connected to the controller, the second input terminal of the logic gate circuit is connected to the output terminal of the comparator, and the output terminal of the logic gate circuit is connected to the control electrode of the first switching transistor through the driving circuit. The controller is configured to output the first level to the first input terminal of the logic gate circuit when no unlocking instruction is received, and to output the second level to the first input terminal of the logic gate circuit when the unlocking instruction is received; The logic gate circuit is used to output the first level to the driving circuit when both the first input terminal and the second input terminal receive the first level, and is used to output the second level to the driving circuit when either the first input terminal or the second input terminal receives the second level; The driving circuit is used to control the first switch to turn off when the logic gate circuit outputs the first level, and to control the first switch to turn on when the logic gate circuit outputs the second level.

7. The power conversion device according to claim 6, characterized in that, The logic gate circuit is an AND gate circuit, and the first level is a high level relative to the second level; Alternatively, the logic gate circuit is an OR gate circuit, where the first level is low relative to the second level.

8. The power conversion device according to any one of claims 1 to 7, characterized in that, The power conversion device further includes: a second switching transistor and a second control circuit; The second terminal of the first switch is connected to the second busbar through the second switch, and the second terminal of the first switch is connected to the second terminal of the second switch, wherein the second terminal of the first switch and the second terminal of the second switch have the same polarity; The second control circuit is connected to the control electrode of the second switching transistor. The second control circuit is used to control the second switching transistor to turn off when the forward voltage drop between the first and second electrodes of the second switching transistor is greater than the second threshold voltage.

9. The power conversion device according to any one of claims 1 to 7, characterized in that, The power conversion device further includes: a second switching transistor and a second control circuit; The first DC terminal of the power conversion circuit is connected to the first terminal of the second switching transistor, the second terminal of the second switching transistor is used to connect to the first bus, and the polarity of the second terminal of the first switching transistor and the second terminal of the second switching transistor are the same. The second control circuit is connected to the control electrode of the second switching transistor. The second control circuit is used to control the second switching transistor to turn off when the forward voltage drop between the first and second electrodes of the second switching transistor is greater than the second threshold voltage.

10. The power conversion device according to claim 8 or 9, characterized in that, The second voltage threshold is greater than the product of the on-resistance of the second switch and the rated current of the DC bus; The rated current is the quotient of the rated power of the power conversion circuit and the rated voltage of the DC bus.

11. The power conversion device according to claim 10, characterized in that, The second voltage threshold is 1.5 to 3 times the product.

12. A charging pile, characterized in that, The charging pile includes: a plurality of power conversion devices and a DC bus as described in any one of claims 1 to 11, each power conversion device including a power conversion circuit and a first switching transistor, the first DC terminal of the power conversion circuit being connected to the first bus in the DC bus, and the second terminal of the first switching transistor being connected to the second bus in the DC bus.

13. The charging pile according to claim 12, characterized in that, The plurality of power conversion devices include: at least one AC / DC conversion device and at least one DC / DC conversion device, wherein the power conversion circuit in each AC / DC conversion device is an AC / DC power conversion circuit and the power conversion circuit in each DC / DC conversion device is a DC / DC power conversion circuit; The AC terminal of the AC / DC power conversion circuit is used to connect to the power grid, the first DC terminal of the AC / DC power conversion circuit is connected to the first bus, and the second terminal of the first switching transistor in each AC / DC conversion device is connected to the second bus. The load terminal of the DC / DC power conversion circuit is used to connect the load, the first DC terminal of the DC / DC power conversion circuit is connected to the first bus, and the second terminal of the first switching transistor in each DC / DC conversion device is connected to the second bus.

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