Power converter

Abstract

To provide a power conversion device.SOLUTION: A power conversion device includes: a DC input; positive and negative DC buses; positive and negative bus capacitors; an inverter circuit; a protection circuit; a first discharge circuit; a reference ground terminal; and a first AC output. The first AC output is configured to be connected to a load. An input of the inverter circuit is separately connected to a DC input via the positive and the negative DC buses. The positive DC bus is connected to the negative DC bus via the positive and negative bus capacitors that are connected in series. A connection point between the positive and negative bus capacitors is connected to the first AC output and connected to the reference ground terminal via the protection circuit. As a rate of change of a current flowing through the protection circuit increases, an impedance value of the protection circuit increases and the first discharge circuit located between the DC input and the reference ground terminal is connected.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application relates to the field of power supply technology, and particularly to a power conversion device.

Background Art

[0002] When the inverter operates in off-grid mode and the neutral output of the inverter remains unconnected, the voltage of the neutral output fluctuates, threatening the safety of users or maintenance personnel. To solve this problem, currently, the inverter mainly uses a method of connecting the neutral output of the inverter to the reference grounding terminal in off-grid mode, thereby grounding the inverter internally to avoid voltage fluctuations of the neutral output of the inverter. However, since the path between the neutral output of the inverter and the grounding terminal is a low-impedance path, when the input of the inverter encounters a common-mode lightning strike, all lightning energy flows through the inverter internally, and the energy is discharged on the low-impedance path between the neutral output of the inverter and the grounding terminal. In this case, the impact energy generated by the common-mode lightning strike damages the components of the power conversion circuit in the inverter. As a conclusion, it can be seen that it is particularly important to prevent the impact energy generated by the common-mode lightning strike from damaging the components of the power conversion circuit while the inverter is reliably grounded internally.

Summary of the Invention

[0003] This application provides a power conversion device. The impact energy generated by the common-mode lightning strike current does not damage the components of the power conversion circuit, and the power conversion device is reliably grounded internally, thereby protecting the power conversion device.

[0004] According to a first aspect, the present application provides a power converter. The power converter includes a DC input, a positive DC bus, a negative DC bus, a positive bus capacitor, a negative bus capacitor, an inverter circuit, a protection circuit, a first discharge circuit, a reference ground terminal, and a first AC output. The DC input is configured to connect to a DC source, and the first AC output is configured to connect to a load. The input to the inverter circuit is connected to the DC input separately via the positive DC bus and the negative DC bus. The positive DC bus is connected to the negative DC bus via a positive bus capacitor and a negative bus capacitor connected in series in order. The connection point between the positive bus capacitor and the negative bus capacitor, i.e., the bus midpoint, is connected to the reference ground terminal via the protection circuit. The bus midpoint is further configured to provide a DC voltage to the first AC output of the power converter. As the rate of change of the current flowing through the protection circuit increases, the impedance value of the protection circuit increases, and the common-mode voltage value of the DC input becomes greater than a first breakover voltage threshold. The first discharge circuit is connected between the DC input of the power converter and the reference ground terminal, and is configured to be connected when the common-mode voltage value of the DC input is greater than the first breakover voltage threshold.

[0005] In this implementation, the bus midpoint is connected to a reference ground terminal via a protection circuit, and the bus midpoint is further connected to the neutral output of the first AC output of the power converter, so that the power converter can be reliably grounded internally in off-grid mode. In addition, when the DC input of the power converter encounters a common-mode lightning strike and the power converter is in off-grid mode, the common-mode lightning strike current flows through the protection circuit, increasing the impedance value of the protection circuit, making the protection circuit equivalent to high impedance. In this way, the common-mode voltage value of the DC input of the power converter reaches the breakover voltage threshold of the first discharge circuit, and most of the common-mode lightning strike current flows and discharges in the first discharge circuit, and does not flow through the power converter circuit within the power converter. In this way, the shock energy generated by the common-mode lightning strike current does not damage the components of the power converter circuit, and the power converter is reliably grounded internally, thereby protecting the power converter.

[0006] Referring to the first embodiment, in the first possible implementation, the power converter further includes a first switch and a controller, the bus midpoint being connected to a reference ground terminal via the first switch and protection circuit connected in series, and the first AC output being further connected to the power grid. The controller is configured to control the first switch to turn on when the voltage of the power grid is below a first breakover voltage threshold, i.e., when a power outage occurs in the power grid.

[0007] In this implementation, the power converter adds a first switch between the bus midpoint and the reference ground terminal. When a power outage occurs in the power grid, the first switch is controlled to turn on, ensuring that the power converter is reliably grounded internally only in off-grid mode. In addition, the first AC output can be connected not only to the load but also to the power grid. This indicates that the first AC output can be used not only as a grid-connected output but also as an off-grid output. Unlike power converters where the grid-connected output and off-grid output are independent of each other, the power converter in this implementation allows the grid-connected output and its associated circuitry to be used in both grid-connected and off-grid modes. This helps reduce the circuit cost of the power converter and allows for a smaller power converter.

[0008] Referencing the first possible implementation of the first embodiment, in the second possible implementation, the controller is further configured to control the first switch to turn off when the power grid voltage is equal to or greater than a first breakover voltage threshold, i.e., when there is no power outage in the power grid.

[0009] In this implementation, when there is no power outage in the power grid, the power converter is controlled to turn off the first switch, and when a power outage occurs in the power grid, it is controlled to turn on the first switch, ensuring that the power converter is reliably grounded internally only in off-grid mode.

[0010] Referring to the first embodiment, in a third possible implementation, the power converter further includes a first switch, a second switch, a third switch, a second AC output, and a controller, wherein the connection point between the positive and negative bus capacitors is connected to a reference ground terminal via the first switch and a protection circuit connected in series, the connection point between the positive and negative bus capacitors is further connected to the first AC output of the power converter via the second switch, and the output of the inverter circuit is further connected separately to the first and second AC outputs of the power converter via the second and third switches, respectively, the second AC output is configured to be connected to the power grid. The controller is configured to control the second switch to turn on and the third switch to turn off when the voltage of the power grid is below a first breakover voltage threshold, i.e., when a power outage occurs in the power grid, and to control the first switch to turn on when the second switch is on and the third switch is off, i.e., when the power converter is in off-grid mode.

[0011] In this implementation, the power converter adds a second switch between the inverter circuit output and the first AC output of the power converter, and a third switch between the inverter circuit output and the second AC output of the power converter, allowing the power converter to flexibly switch between off-grid mode and grid-connected mode. In addition, the power converter in off-grid mode is controlled to turn on the first switch, ensuring that the power converter is reliably grounded internally only in off-grid mode.

[0012] Referencing the third possible implementation of the first embodiment, in the fourth possible implementation, the controller is further configured to control the second switch to turn off and the third switch to turn on when the power grid voltage is greater than or equal to a first breakover voltage threshold, and to control the first switch to turn off when the second switch is off and the third switch is on, i.e., when the power converter is in grid-connected mode.

[0013] In this implementation, power converters in grid-connected mode are controlled to turn off the first switch, and power converters in off-grid mode are controlled to turn on the first switch, ensuring that the power converters are reliably grounded internally only in off-grid mode.

[0014] Referring to any one of the first to fourth possible implementations of the first embodiment, in the fifth possible implementation, the power converter further includes a leakage current detection circuit, the leakage current detection circuit located on the connection line between the output of the inverter circuit and the first AC output of the power converter, and the leakage current detection circuit further located on the connection line between the first AC output of the power converter and the connection point between the positive bus capacitor and the negative bus capacitor.

[0015] In this implementation, the leakage current detection circuit is located on the left side of the path between the bus midpoint and the reference ground terminal, and the failure of the leakage current detection circuit in off-grid mode by having the leakage current detection circuit located on the right side of the path between the bus midpoint and the reference ground terminal is avoided, thereby improving the stability of the power converter.

[0016] Referring to any one of the first to fifth possible implementations of the first embodiment, in the sixth possible implementation, the protection circuit further includes an air-core inductor or a saturation-preventing inductor.

[0017] In this implementation configuration, various types of protection circuits are available, resulting in a diverse and highly flexible structure for the power converter.

[0018] Referring to any one of the first to sixth possible implementations of the first embodiment, in the seventh possible implementation, the power converter further includes a DC / DC converter circuit configured to perform a DC conversion on the DC input of the power converter and output the converted DC to a positive DC bus and a negative DC bus.

[0019] In this implementation, the power converter may further include a DC / DC conversion circuit, thereby making the functions and circuit structure of the power converter more diverse and highly flexible.

[0020] Referring to any one of the seventh possible implementations of the first aspect, in the eighth possible implementation, the first discharge circuit includes a first protection element, a second protection element, and a third protection element, and the DC input of the power converter includes a first DC input and a second DC input. The first end of the first protection element is connected to a reference ground terminal, and the second end of the first protection element is connected to the first DC input and the second DC input of the power converter via the second and third protection elements, respectively. Each of the first, second, and third protection elements includes a gas discharge tube, a varistor, or a transient voltage suppression diode.

[0021] In this implementation configuration, the structure of the power converter becomes diverse and highly flexible due to the availability of various types of protection elements.

[0022] Referring to any one of the eighth possible implementations of the first embodiment, in the ninth possible implementation, the power converter further includes a second discharge circuit, which is connected between the first AC output and the reference ground terminal of the power converter. As the rate of change of the current flowing through the protection circuit increases, the impedance value of the protection circuit increases, the common-mode voltage of the DC input becomes greater than a first breakover voltage threshold, and the common-mode voltage of the first AC output becomes greater than a second breakover voltage threshold. The second discharge circuit is connected when the common-mode voltage of the first AC output is greater than the second breakover voltage threshold.

[0023] In this implementation mode, in the off-grid mode, the power conversion device is grounded internally. When the first AC output encounters a common-mode surge and the common-mode surge current flows through the protection circuit, the impedance value of the protection circuit increases, and the protection circuit becomes equivalent to a high impedance. In this case, the common-mode voltage value of the first AC output of the power conversion device reaches the breakdown voltage threshold of the second discharge circuit, and most of the common-mode surge current flows through the second discharge circuit for discharging and does not flow through the power conversion circuit in the power conversion device. In this way, the impact energy generated by the common-mode surge current does not damage the components of the power conversion circuit, and the power conversion device is reliably grounded internally, thereby protecting the power conversion device.

[0024] Referring to the ninth possible implementation mode of the first aspect, in the tenth possible implementation mode, the second discharge circuit includes a fourth protection element, a fifth protection element, a sixth protection element, and a seventh protection element, and the first AC output of the power conversion device includes a first AC sub-output, a second AC sub-output, and a third AC sub-output. The first end of the fourth protection element is connected to the reference ground terminal. The second end of the fourth protection element is connected to the first AC sub-output, the second AC sub-output, and the third AC sub-output of the power conversion device through the fifth protection element, the sixth protection element, and the seventh protection element respectively. Each of the fourth protection element, the fifth protection element, the sixth protection element, and the seventh protection element includes a gas discharge tube, a varistor, or a transient voltage suppression diode.

[0025] In this implementation mode, since there are various types of protection elements, the structure of the power conversion device is diverse and very flexible.

Brief Description of the Drawings

[0026] [Figure 1] It is a diagram of the application scenario of the power conversion device according to the present application. [Figure 2a] It is a diagram of the structure of the power conversion device according to the present application. [Figure 2b] It is a diagram of another structure of the power conversion device according to the present application. [Figure 3a] It is a diagram of another structure of the power conversion device according to the present application. [Figure 3b] It is a diagram of another structure of the power conversion device according to the present application. [Figure 3c] It is a diagram of another structure of the power conversion device according to the present application. [Figure 3d] It is a diagram of another structure of the power conversion device according to the present application. [Figure 4a] It is a diagram of another structure of the power conversion device according to the present application. [Figure 4b] It is a diagram of another structure of the power conversion device according to the present application. [Figure 4c] It is a diagram of another structure of the power conversion device according to the present application. [Figure 4d] It is a diagram of another structure of the power conversion device according to the present application. [Figure 4e] It is a diagram of another structure of the power conversion device according to the present application. [Figure 4f] It is a diagram of yet another structure of the power conversion device according to the present application.

Embodiments for Carrying Out the Invention

[0027] The power converters provided in this application can be used in multiple application areas, including the new energy smart microgrid field, the power transmission and distribution field, the new energy field (e.g., the solar power grid connection field or the wind power grid connection field), the solar power field, the energy storage and generation field, and the wind power field. The power converters provided in this application may include inverters (including string inverters and distributed inverters), energy storage inverters, and uninterruptible power supplies (UPS). The power converters can be used in different application scenarios, such as solar power supply scenarios (including large-scale solar power station scenarios, small and medium-scale distributed solar power station scenarios, and residential solar power system scenarios), energy storage power supply scenarios (including large-scale energy storage power plant scenarios, small and medium-scale distributed energy storage power plant scenarios, and residential solar power energy storage and generation system scenarios), and power supply scenarios using uninterruptible power supplies (UPS). In the following, the solar power supply scenario will be used as an example for explanation.

[0028] Figure 1 is a diagram illustrating an application scenario of the power converter according to this application. In a solar power supply scenario, the power converter provided in this application may be the inverter shown in Figure 1. The DC input of the inverter is connected to a solar power string, and the first AC output is connected to an AC load such as a household appliance. The inverter includes a DC input, a positive DC bus BUS+, a negative DC bus BUS-, a positive bus capacitor C1, a negative bus capacitor C2, a DC / DC converter circuit, an inverter circuit, a protection circuit, a first discharge circuit, a reference ground terminal PE, and a first AC output. The input of the inverter circuit is connected to the output of the DC / DC converter circuit via the positive DC bus BUS+ and the negative DC bus BUS- separately. The input of the DC / DC converter circuit is connected to the DC input of the inverter. The output of the inverter circuit is connected to the first AC output of the inverter. The positive DC bus BUS+ is connected to the negative DC bus BUS- sequentially via the positive bus capacitor C1 and the negative bus capacitor C2 connected in series. The connection point between the positive bus capacitor C1 and the negative bus capacitor C2 is connected to the reference ground terminal PE via a protection circuit. The connection point between the positive bus capacitor C1 and the negative bus capacitor C2 is further connected to the first AC output of the inverter. The first discharge circuit is connected between the inverter input and the reference ground terminal PE.

[0029] After the inverter starts operating, the DC / DC conversion circuit performs a DC conversion on the DC generated by the solar power string connected to the inverter input, and then outputs the converted DC to the inverter circuit. The inverter circuit converts the DC obtained after the DC conversion and input from the inverter circuit to AC to supply power to various types of electrical equipment, such as AC loads. In addition, if a common-mode lightning strike occurs between the inverter input and the reference ground terminal during the process of the inverter supplying power to the AC load, the common-mode lightning strike current flows through the protection circuit, increasing the rate of change of the current in the protection circuit. As the rate of change of the current flowing through the protection circuit increases, the impedance value of the protection circuit increases, and the common-mode voltage value of the inverter's DC input becomes greater than the first breakover voltage threshold. When the common-mode voltage value of the inverter's DC input is greater than the first breakover voltage threshold, the first discharge circuit is connected, so most of the common-mode lightning strike current can be discharged through the first discharge circuit and does not flow through the power conversion circuit (including the inverter circuit) within the inverter. In this way, the shock energy generated by the common-mode lightning current does not damage the components of the power conversion circuit, thereby protecting the inverter. The above is merely one example of an application scenario for the power conversion device provided in this application, and is not exhaustive. Application scenarios are not limited in this application.

[0030] Referring to Figures 2a to 4f, an example of the operating principle of the power converter provided in this application will be described below.

[0031] Figure 2a is a diagram of the structure of the power converter according to this application. As shown in Figure 2a, the power converter 1 includes a DC input, a positive DC bus BUS+, a negative DC bus BUS-, a positive bus capacitor C1, a negative bus capacitor C2, an inverter circuit 11, a protection circuit 12, a first discharge circuit 13, and a first AC output. The DC input of the power converter 1 includes a first DC input i1+ and a second DC input i1-. The first AC output of the power converter 1 includes a first AC sub-output o111, a second AC sub-output o112, and a third AC sub-output o11N. The first DC input i1+ and the second DC input i1- are configured to be connected to a DC source. The first input i11+ and second input i11- of the inverter circuit 11 are connected to the first DC input i1+ and second DC input i1- of the power converter 1 via a positive DC bus BUS+ and a negative DC bus BUS-, respectively. The first output o1111 and second output o1112 of the inverter circuit 11 are connected to the first AC sub-output o111 and second AC sub-output o112 of the power converter 1, respectively. The positive DC bus BUS+ is connected to the negative DC bus BUS- via a positive bus capacitor C1 and a negative bus capacitor C2 connected in series, respectively. The connection point N between the positive bus capacitor C1 and the negative bus capacitor C2 (i.e., the bus midpoint) is connected to the reference ground terminal PE via a protection circuit 12. The bus midpoint N is further configured to provide a DC voltage to the first AC output of the power converter 1. Correspondingly, the connection relationship between the bus midpoint N and the first AC output of the power converter 1 is as follows: The bus midpoint N is further connected to the third AC sub-output o11N of the power converter 1, i.e., the neutral output of the power converter. The first AC sub-output o111, the second AC sub-output o112, and the third AC sub-output o11N of the power converter 1 are configured to be connected to a load. The first discharge circuit 13 is connected between the DC input of the power converter 1 and the reference ground terminal PE. Specifically, the two inputs of the first discharge circuit 13 are connected to the first DC input i1+ and the second DC input i1- of the power converter 1, respectively, and the output of the first discharge circuit 13 is connected to the reference ground terminal PE.

[0032] In one implementation configuration, during the process in which the power converter 1 supplies power to the load, a common-mode lightning strike occurs between the first DC input i1+ or the second DC input i1- of the power converter 1 and the reference ground terminal PE. When the common-mode lightning strike current flows through the protection circuit 12, the rate of change of the current in the protection circuit 12 increases rapidly. As the rate of change of the current flowing through the protection circuit 12 increases, the impedance value of the protection circuit 12 increases. Consequently, the common-mode voltage value between the DC input of the power converter 1 and the reference ground terminal PE becomes greater than the first breakover voltage threshold. In addition, when the common-mode voltage value of the power converter 1 is greater than the first breakover voltage threshold, the first discharge circuit 13 is connected. Therefore, most of the common-mode lightning strike current flows into the first discharge circuit 13 and discharges, and does not flow through the power conversion circuit within the power converter 1.

[0033] It should be noted that in this application, the connection of A to B may be either a direct connection of A to B or an indirect connection of A to B via C. This is not limited to this application. Specifically, the first input i11+ and the second input i11- of the inverter circuit 11 may be directly connected to the first DC input i1+ and the second DC input i1- of the power converter 1 via a positive DC bus BUS+ and a negative DC bus BUS-, respectively. In addition, a DC / DC conversion circuit may be further connected between the DC input of the power converter 1 and the positive DC bus BUS+ and the negative DC bus BUS-. The DC / DC conversion circuit is configured to perform DC conversion on the DC output by a DC source connected to the DC input of the power converter 1. If the power converter 1 is a photovoltaic inverter, the DC source may be a photovoltaic string. In this case, the DC / DC conversion circuit performs DC conversion on the DC output from the DC source and further implements maximum power point tracking (MPPT) control for the solar power string to ensure high-efficiency power generation of the solar power string. For specific connection relationships of the DC / DC conversion circuit, please refer to the power converter 1 shown in Figure 2b. As shown in Figure 2b, the power converter 1 further includes a DC / DC conversion circuit 14. The first input i11+ of the inverter circuit 11 is connected to the first output o14+ of the DC / DC conversion circuit 14 via a positive DC bus BUS+. The second input i11- of the inverter circuit 11 is connected to the second output o14- of the DC / DC conversion circuit 14 via a negative DC bus BUS-. The first input i14+ and second input i14- of the DC / DC conversion circuit 14 are connected to the first DC input i1+ and second DC input i1- of the power converter 1, respectively. The structure of the power converter 1 is diverse and offers a high degree of flexibility.

[0034] In this embodiment of the present application, the bus midpoint is connected to a reference grounding terminal via a protection circuit, and the bus midpoint is further connected to the neutral output of the power converter 1, so that the power converter 1 can be reliably grounded internally in off-grid mode. In addition, when the DC input of the power converter 1 encounters a common-mode lightning strike and the common-mode lightning strike current flows into the protection circuit 12, the impedance value of the protection circuit 12 increases. In this case, the common-mode voltage value of the DC input of the power converter 1 reaches the breakover voltage threshold of the first discharge circuit 13, and most of the common-mode lightning strike current flows into the first discharge circuit 13 and discharges, and does not flow through the power converter circuit within the power converter 1. In this way, the shock energy generated by the common-mode lightning strike current does not damage the components of the power converter circuit, and the power converter 1 is reliably grounded internally, thereby protecting the power converter 1.

[0035] Figure 3a is a diagram of another structure of the power converter according to the present application. As shown in Figure 3a, compared with the power converter 1 shown in Figure 2a, the power converter 1 shown in Figure 3a further includes a first switch K1 and a controller 15. The bus midpoint N is connected to the reference ground terminal PE via a series-connected protection circuit 12 and the first switch K1. The first AC sub-output o111, the second AC sub-output o112, and the third AC sub-output o11N of the power converter 1 are further configured to be connected to an AC power grid. Optionally, the power converter 1 further includes a second switch K2. The first output o1111 and the second output o1112 of the inverter circuit 11 are connected to the first AC sub-output o111 and the second AC sub-output o112 of the power converter 1 via the second switch K2. The bus midpoint N is further connected to the third AC sub-output o11N of the power converter 1 via the second switch K2. Optionally, the power converter 1 further includes a leakage current detection circuit 16. The first output o1111 and the second output o1112 of the inverter circuit 11 are connected in series to the first AC sub-output o111 and the second AC sub-output o112 of the power converter 1 via the leakage current detection circuit 16 and the second switch K2. The bus midpoint N is connected in series to the third AC sub-output o11N of the power converter 1 via the leakage current detection circuit 16 and the second switch K2. Optionally, the power converter 1 further includes a second discharge circuit 17. The second discharge circuit 17 is connected between the first AC output of the power converter 1 and the reference ground terminal PE. Specifically, the three inputs of the second discharge circuit 17 are connected to the first AC sub-output o111, the second AC sub-output o112, and the third AC sub-output o11N of the power converter 1, respectively. The output of the second discharge circuit 17 is connected to the reference ground terminal PE.

[0036] The power converter 1 shown in Figure 3a is a single-phase power converter. The power converter 1 provided in this application is also applicable to a three-phase power converter. For details, please refer to the power converter 1 shown in Figure 3b. As shown in Figure 3b, compared to the power converter 1 shown in Figure 3a, the first AC output of the power converter 1 shown in Figure 3b further includes a fourth AC sub-output o113, the output of the inverter circuit 11 includes a third output o1113, and the third output o1113 of the inverter circuit 11 is connected to the fourth AC sub-output o113 of the power converter 1 via a series-connected leakage current detection circuit 16 and a second switch K2. The first AC sub-output o111, the second AC sub-output o112, and the fourth AC sub-output o113 of the power converter 1 correspond to the three-phase AC outputs of the power converter 1. Whether the power converter 1 is a single-phase power converter or a three-phase power converter, the power converter 1 has the same operating principle. Therefore, to facilitate the explanation, the single-phase power converter shown in Figure 3a will be described in detail below with reference to the power converter shown in Figure 3c.

[0037] Figure 3c is a diagram of another structure of the power converter according to the present application. As shown in Figure 3c, the protection circuit 12 is an air-core inductor L1. The first discharge circuit 13 includes a first protection element, a second protection element, and a third protection element. The first end of the first protection element is connected to a reference ground terminal PE, and the second end of the first protection element is connected to the first DC input i1+ and the second DC input i1- of the power converter 1 via the second protection element and the third protection element, respectively. Each protection element of the first discharge circuit 13 includes a gas discharge tube, a varistor, a transient voltage suppression diode, or a fuse. The types of the three protection elements described above may be the same or different. This is not limited in the present application. For example, the first protection element is a gas discharge tube GDT1, and the second and third protection elements are varistors RV1 and RV2, respectively. The second discharge circuit 17 includes a fourth protection element, a fifth protection element, a sixth protection element, and a seventh protection element. The first end of the fourth protection element is connected to the reference ground terminal PE, and the second end of the fourth protection element is connected to the first AC sub-output o111, the second AC sub-output o112, and the third AC sub-output o11N of the power converter 1 via the fifth protection element, the sixth protection element, and the seventh protection element, respectively. Each protection element of the second discharge circuit 17 includes a gas discharge tube, a varistor, a transient voltage suppression diode, or a fuse. The types of the four protection elements described above may be the same or different. This is not limited in this application. For example, the fourth protection element is a gas discharge tube GDT2, and the fifth, sixth, and seventh protection elements are varistors RV3, RV4, and RV5, respectively.

[0038] The second switch K2 includes switches K21, K22, and K23. The leakage current detection circuit 16 includes a first group input, a second group input, and a third group input. The first group input includes the first input i21 and the second input i22 of the first group. The second group input includes the first input i31 and the second input i32 of the second group. The third group input includes the first input i41 and the second input i42 of the third group. The first output o1111 of the inverter circuit 11 is connected to the first input i21 of the first group. The second input i22 of the first group is connected to the first AC sub-output o111 of the power converter 1 via switch K21. The second output o1112 of the inverter circuit 11 is connected to the first input i41 of the third group. The third group second input i42 is connected to the second AC sub-output o112 of the power converter 1 via switch K23. The bus midpoint N is connected to the second group first input i31. The second group second input i32 is connected to the third AC sub-output o11N of the power converter 1 via switch K22. The leakage current detection circuit 16 further includes a first group output, a second group output, and a third group output. The first group output includes the first group first output o21 and the second group second output o22. The second group output includes the first group first output o31 and the second group second output o32. The third group output includes the first group first output o41 and the second group second output o42. The controller 15 can obtain the leakage current value of the first AC output of the power converter 1 by obtaining the current values ​​of the three groups of outputs of the leakage current detection circuit 16. Therefore, if the leakage current value of the first AC output is greater than the leakage current threshold, the power converter 1 is protected, and for example, the second switch K2 is controlled to turn off.

[0039] In the optional implementation configuration, after the power converter 1 starts operating, the controller 15 controls the switches K21 to K23 of the second switch K2 to all be turned on. When the voltage of the AC power grid is below the first breakover voltage threshold, it indicates that a power outage has occurred in the AC power grid and the power converter 1 is in off-grid mode. In this case, the first AC output of the power converter 1 is connected to an AC load, and the controller 15 controls the first switch K1 to be turned on, thereby ensuring that the power converter 1 is reliably grounded internally in off-grid mode.

[0040] After the power converter 1 is reliably grounded internally, if a common-mode lightning current is present at the DC input of the power converter 1, the rate of change of the common-mode lightning current is greater than the rate of change of the operating current of the power converter 1 that would exist if the common-mode lightning current were not present at the DC input of the power converter 1. Therefore, when the common-mode lightning current flows through the air-core inductor L1, the rate of change of the current in the air-core inductor L1 increases rapidly, and as the rate of change of the current flowing through the air-core inductor L1 increases, the impedance value of the air-core inductor L1 increases. In this case, the air-core inductor L1 is equivalent to a high impedance. Thus, the following can be obtained: when the common-mode lightning current flows through the air-core inductor L1, the air-core inductor L1 becomes equivalent to a high impedance, and the common-mode voltage value at the DC input of the power converter 1 reaches the first breakover voltage threshold. The common-mode voltage value of the DC input includes the voltage value between the first DC input i1+ and the reference ground terminal PE of the power converter 1, or the voltage value between the second DC input i1- and the reference ground terminal PE of the power converter 1. In addition, when the common-mode voltage value of the DC input of the power converter 1 reaches the first breakover voltage threshold, the gas discharge tube GDT1 breaks down, the first discharge circuit 13 becomes connected, and the impedance value of the varistor RV1 or RV2 drops sharply. That is, the first discharge circuit 13 is connected. Therefore, most of the common-mode lightning strike current flows and discharges in the first discharge circuit 13 and does not flow in the power conversion circuit within the power converter 1. In this way, the shock energy generated by the common-mode lightning strike current does not damage the components of the power conversion circuit, the power converter is reliably grounded internally, and thereby protects the power converter 1. The first breakover voltage threshold may be the sum of the breakover voltage threshold of the gas discharge tube GDT1 and the breakover voltage threshold of the varistor RV1 or RV2.

[0041] After the power converter 1 is reliably grounded internally, when no common-mode lightning current is present at the DC input of the power converter 1, the rate of change of the operating current of the power converter 1 is small. In addition, as the rate of change of the current flowing through the air-core inductor L1 decreases, the impedance value of the air-core inductor L1 decreases accordingly, and the air-core inductor L1 becomes equivalent to a low impedance. In this case, the voltage value between the bus midpoint N and the reference ground terminal PE is less than the second breakover voltage threshold. That is, when no common-mode lightning current is present at the DC input of the power converter 1, the impedance value of the air-core inductor L1 can be ignored. Furthermore, when no common-mode lightning current is present at the DC input of the power converter 1 and the power converter 1 is in off-grid mode, the grounding path between the bus midpoint N and the reference ground terminal PE is a low-impedance path, thereby ensuring that the bus midpoint N and the reference ground terminal PE are at the same potential.

[0042] In addition, after the power converter 1 is securely grounded internally, if the first AC output of the power converter 1 encounters a common-mode surge, the air-core inductor L1 and the second discharge circuit 17 of the power converter 1 can be used to allow most of the common-mode surge current to flow into the second discharge circuit 17 and discharge, thereby protecting the power converter 1.

[0043] Specifically, when a common-mode surge current is present at the first AC output of the power converter 1, the rate of change of the common-mode surge current is greater than the rate of change of the operating current of the power converter 1 that would exist if a common-mode lightning strike current were not present at the DC input of the power converter 1. Therefore, when the common-mode surge current flows through the air-core inductor L1, the rate of change of the current in the air-core inductor L1 increases rapidly, and as the rate of change of the current flowing through the air-core inductor L1 increases, the impedance value of the air-core inductor L1 increases. In this case, the air-core inductor L1 is equivalent to a high impedance inductor. Therefore, the following can be obtained: when a common-mode surge current flows through the air-core inductor L1, the air-core inductor L1 becomes equivalent to a high impedance inductor, and the common-mode voltage value of the first AC output of the power converter 1 reaches the second breakover voltage threshold. In addition, when the common-mode voltage value of the first AC output of the power converter 1 reaches the second breakover voltage threshold, the gas discharge tube GDT2 breaks down, the second discharge circuit 17 becomes connected, and the impedance values ​​of the varistors RV3, RV4, or RV5 drop sharply. That is, the second discharge circuit 17 is connected. Therefore, most of the common-mode surge current flows and discharges in the second discharge circuit 17 and does not flow through the power conversion circuit within the power converter 1. In this way, the shock energy generated by the common-mode surge current does not damage the components of the power conversion circuit, the power converter is reliably grounded internally, and thereby protects the power converter 1. The second breakover voltage threshold may be the sum of the breakover voltage threshold of the gas discharge tube GDT2 and the breakover voltage threshold of the varistors RV3, RV4, or RV5.

[0044] It was noted that if the power converter 1 is externally grounded, an operator can send a deactivation instruction to the power converter 1 indicating that the power converter 1 is externally grounded by using an external device connected to the power converter 1. The controller 15 within the power converter 1 controls the first switch K1 to turn off in accordance with the received deactivation instruction, ensuring that the power converter 1 in off-grid mode is not simultaneously grounded internally and externally. In this way, the following is avoided: the power converter 1 is grounded at multiple points and circulating current is generated. Therefore, the stability of the power converter 1 is improved.

[0045] In another optional implementation, after the power converter 1 starts operating, the controller 15 controls switches K21 to K23 of the second switch K2 to all be turned on. When the voltage of the AC power grid is above the first breakover voltage threshold, it indicates that there is no power outage in the AC power grid and the power converter 1 is in grid-connected mode. In this case, the first AC output of the power converter 1 is connected to the AC grid, and the controller 15 controls the first switch K1 to be turned off.

[0046] Optionally, the power converter 1 may further include a DC / DC converter circuit 14. For details, please refer to the power converter 1 shown in Figure 3d. Here, for the specific connection relationships of the DC / DC converter circuit 14 shown in Figure 3d, please refer to the connection relationships of the DC / DC converter circuit 14 in the power converter 1 shown in Figure 2b. Further details are not described herein.

[0047] In this embodiment of the present application, the power converter 1 in off-grid mode is controlled to turn on the first switch K1 so that the bus midpoint N is connected to the reference ground terminal PE via the protection circuit 12, and the bus midpoint is controlled to be connected to the neutral output of the power converter 1, thereby ensuring reliable internal grounding. In addition, when a common-mode lightning strike current flows through the protection circuit 12, the protection circuit 12 becomes equivalent to a high impedance, so the common-mode voltage value of the DC input of the power converter 1 reaches the breakover voltage threshold of the first discharge circuit 13. Therefore, when a common-mode lightning strike current is present at the DC input of the power converter 1, most of the common-mode lightning strike current flows into the first discharge circuit 13 and discharges. In this way, the shock energy generated by the common-mode lightning strike current does not damage the components of the power converter circuit, and the power converter 1 is reliably grounded internally, thereby protecting the power converter 1. Furthermore, when a common-mode surge current flows through the protection circuit 12, the protection circuit 12 becomes equivalent to a high impedance, causing the common-mode voltage value of the first AC output of the power converter 1 to reach the breakover voltage threshold of the second discharge circuit 17. Therefore, when a common-mode surge current is present at the first AC output of the power converter 1, most of the common-mode surge current flows into the second discharge circuit 17 and discharges. In this way, the shock energy generated by the common-mode surge current does not damage the components of the power converter circuit, and the power converter 1 is reliably grounded internally, thereby protecting the power converter 1.

[0048] Figure 4a is a diagram of another structure of the power converter according to the present application. As shown in Figure 4a, compared with the power converter 1 shown in Figure 3a, the power converter 1 shown in Figure 4a further includes a second AC output, a third switch K3, a first output capacitor C3, and a second output capacitor C4. The second AC output of the power converter 1 includes a fifth AC sub-output o121, a sixth AC sub-output o122, and a seventh AC sub-output o12N. The fifth AC sub-output o121, the sixth AC sub-output o122, and the seventh AC sub-output o12N of the power converter 1 are configured to be connected to an AC power grid. The first output o1111 and the second output o1112 of the inverter circuit 11 are further connected to the fifth AC sub-output o121 and the sixth AC sub-output o122 of the power converter 1 via the third switch K3. The first output capacitor C3 and the second output capacitor C4 are connected in series between the fifth AC sub-output o121 and the sixth AC sub-output o122 of the power converter 1. The connection point between the first output capacitor C3 and the second output capacitor C4 is connected to the seventh AC sub-output o12N of the power converter 1. Optionally, the power converter 1 further includes a leakage current detection circuit 18. The first output o1111 and the second output o1112 of the inverter circuit 11 are connected in series to the fifth AC sub-output o121 and the sixth AC sub-output o122 of the power converter 1 via the series-connected leakage current detection circuit 18 and the third switch K3. Optionally, the power converter 1 further includes a third discharge circuit 19. The third discharge circuit 19 is connected between the second AC output of the power converter 1 and the reference ground terminal PE. Specifically, the three inputs of the third discharge circuit 19 are connected to the fifth AC sub-output o121, the sixth AC sub-output o122, and the seventh AC sub-output o12N of the power converter 1, respectively. The output of the third discharge circuit 19 is connected to the reference ground terminal PE.

[0049] The power converter 1 shown in Figure 4a is a single-phase power converter. The power converter 1 provided in this application is also applicable to a three-phase power converter. For details, please refer to the power converter 1 shown in Figure 4b. As shown in Figure 4b, compared to the power converter 1 shown in Figure 4a, the first AC output of the power converter 1 shown in Figure 4b further includes a fourth AC sub-output o113, the second AC output of the power converter 1 further includes an eighth AC sub-output o123, and the output of the inverter circuit 11 includes a third output o1113. The third output o1113 of the inverter circuit 11 is connected to the fourth AC sub-output o113 of the power converter 1 via a series-connected leakage current detection circuit 16 and a second switch K2. The third output o1113 of the inverter circuit 11 is further connected to the eighth AC sub-output o123 of the power converter 1 via a series-connected leakage current detection circuit 18 and a third switch K3. Regardless of whether power converter 1 is a single-phase power converter or a three-phase power converter, power converter 1 operates on the same principle. Therefore, to facilitate the explanation, the single-phase power converter shown in Figure 4a will be specifically described below with reference to the power converter shown in Figure 4c.

[0050] Figure 4c is a diagram of another structure of the power converter according to this application. As shown in Figure 4c, the third switch K3 includes switches K31 and K32. The leakage current detection circuit 18 includes a fourth group input and a fifth group input. The fourth group input includes a fourth group first input i51 and a fourth group second input i52. The fifth group input includes a fifth group first input i61 and a fifth group second input i62. The first output o1111 of the inverter circuit 11 is connected to the fourth group first input i51. The fourth group second input i52 is connected to the fifth AC sub-output o121 of the power converter 1 via switch K31. The second output o1112 of the inverter circuit 11 is connected to the fifth group first input i61. The fifth group second input i62 is connected to the sixth AC sub-output o122 of the power converter 1 via switch K32. The leakage current detection circuit 18 further includes a fourth group output and a fifth group output. The fourth group output includes a fourth group first output o51 and a fourth group second output o52. The fifth group output includes a fifth group first output o61 and a fifth group second output o62. The controller 15 can obtain the leakage current value of the second AC output of the power converter 1 by obtaining the current values ​​of the two groups of outputs of the leakage current detection circuit 18. Therefore, if the leakage current value of the second AC output is greater than the leakage current threshold, the power converter 1 is protected, and for example, the third switch K3 is controlled to turn off. The third discharge circuit 19 includes an eighth protection element, a ninth protection element, a tenth protection element, an eleventh protection element, a twelfth protection element, a thirteenth protection element, and a fourteenth protection element. The eighth, ninth, and tenth protection elements are connected in series between the fifth AC sub-output o121 and the sixth AC sub-output o122 of the power converter 1, and the eleventh and twelfth protection elements are connected in series and then in parallel with the ninth protection element. The connection point between the eleventh and twelfth protection elements is connected to the seventh AC sub-output o12N of the power converter 1 via the thirteenth protection element, and further, the connection point between the eleventh and twelfth protection elements is connected to the reference ground terminal PE via the fourteenth protection element. Each protection element in the third discharge circuit 19 includes a gas discharge tube, a varistor, a transient voltage suppression diode, or a fuse. The types of the seven protection elements described above may be the same or different; this is not limited in this application.For example, the 8th to 13th protection elements are varistors RV6 to RV11, respectively, and the 14th protection element is a gas discharge tube GDT3. The specific structure and connection relationships of the protection circuit 12, the first discharge circuit 13, the second switch K2, and the leakage current detection circuit 16 will be explained by referring to the description of the corresponding parts of the power converter 1 shown in Figure 3c. Further details will not be explained again in this specification.

[0051] In an optional implementation, when the voltage of the AC power grid is below the first breakover voltage threshold, it indicates that a power outage has occurred in the AC power grid, and that the controller 15 controls switches K21 to K23 of the second switch K2 to turn on, and switches K31 and K32 of the third switch K3 to turn off, thereby indicating that the power converter 1 is in off-grid mode. In this case, the first AC output of the power converter 1 is connected to an AC load. Next, when the second switch K2 is turned on and the third switch K3 is turned off, the controller 15 controls the first switch K1 to turn on, thereby ensuring that the power converter 1 is internally grounded in off-grid mode.

[0052] After the power converter 1 is securely grounded internally, if a common-mode lightning current is present at the DC input of the power converter 1, the air-core inductor L1 and the first discharge circuit 13 of the power converter 1 prevent the shock energy generated by the common-mode lightning current from damaging the components of the power converter circuit. For specific implementations, please refer to the description of the corresponding parts of the power converter 1 shown in Figure 3c. Further details are not described herein.

[0053] After the power converter 1 is reliably grounded internally, if there is no common-mode lightning current at the DC input of the power converter 1, the rate of change of the operating current of the power converter 1 is small. In addition, if the rate of change of the current flowing through the air-core inductor L1 is less than the second rate of change threshold, the impedance value of the air-core inductor L1 can be ignored. In this way, when there is no common-mode lightning current at the DC input of the power converter 1 and the power converter 1 is in off-grid mode, the grounding path between the bus midpoint N and the reference grounding terminal PE is a low-impedance path, thereby ensuring that the bus midpoint N and the reference grounding terminal PE are at the same potential.

[0054] In addition, after the power converter 1 is securely grounded internally, if the first AC output of the power converter 1 encounters a common-mode surge, the air-core inductor L1 and the second discharge circuit 17 of the power converter 1 allow most of the common-mode surge current to flow into the second discharge circuit 17 and discharge, thereby protecting the power converter 1. Here, by using the air-core inductor L1 and the second discharge circuit 17 of the power converter 1, the shock energy generated by the common-mode surge current does not damage the components of the power converter circuit. For specific implementations, please refer to the description of the corresponding parts of the power converter 1 shown in Figure 3c. Further details are not described herein.

[0055] Optionally, the second discharge circuit 17 may further utilize the circuit configuration shown in Figure 4d. As shown in Figure 4d, the second discharge circuit 17 includes fuses FU1 and FU2, a gas discharge tube GDT4, and varistors RV12 to RV15. Fuse FU1 and varistor RV12 are connected in series between the first AC sub-output o111 and the third AC sub-output o11N, and fuse FU2 and varistor RV13 are connected in series between the second AC sub-output o112 and the third AC sub-output o11N. The connection point between fuse FU1 and varistor RV12 is connected to the reference ground terminal PE via varistor RV15 and gas discharge tube GDT4 in sequence, and the connection point between fuse FU2 and varistor RV14 is connected to the reference ground terminal PE via varistor RV15 and gas discharge tube GDT4 in sequence. If a common-mode surge current or differential-mode surge current is present at the first AC output of the power converter 1, the majority of the common-mode surge current or differential-mode surge current can be discharged through the second discharge circuit 17, thereby protecting the power converter 1. Optionally, the second discharge circuit 17 shown in Figure 4d may further include gas discharge tubes GDT5 and GDT6. For further details, see the second discharge circuit 17 in the power converter 1 shown in Figure 4e. In addition, the circuit structures of all discharge circuits provided in this application can be appropriately adjusted according to actual requirements. This is not limited to this application.

[0056] It was noted that if the power converter 1 is externally grounded, an operator can send a deactivation instruction to the power converter 1 indicating that the power converter 1 is externally grounded by using an external device connected to the power converter 1. The controller 15 within the power converter 1 controls the first switch K1 to turn off in accordance with the received deactivation instruction, ensuring that the power converter 1 in off-grid mode is not simultaneously grounded internally and externally. In this way, the following is avoided: the power converter 1 is grounded at multiple points and circulating current is generated. Therefore, the stability of the power converter 1 is improved.

[0057] In another optional implementation, when the AC power grid voltage is above the first breakover voltage threshold, it indicates that there is no power outage in the AC power grid, and that the controller 15 controls switches K21-K23 of the second switch K2 to turn off and switches K31 and K32 of the third switch K3 to turn on, thereby indicating that the power converter 1 is in grid-connected mode. In this case, the first AC output of the power converter 1 is connected to the AC power grid. Then, when the second switch K2 is turned off and the third switch K3 is turned on, the controller 15 controls the first switch K1 to turn off.

[0058] In addition, after the power converter 1 enters grid-connected mode, if the common-mode voltage value of the second AC output of the power converter 1 is excessively high, for example, if the voltage value between the fifth AC sub-output o121 of the power converter 1 and the reference ground terminal PE is greater than the third breakover voltage threshold, the impedance values ​​of varistors RV6, RV7, RV9, and RV10 rapidly decrease, causing the gas discharge tube GDT3 to break down and enter a connected state. In other words, the third discharge circuit 19 is in a connected state, and the voltage value between the fifth AC sub-output o121 of the power converter 1 and the reference ground terminal PE is discharged through the third discharge circuit 19, thereby rapidly decreasing the common-mode voltage value of the second AC output of the power converter 1, and thereby providing overvoltage protection for the second output of the power converter 1.

[0059] Optionally, the power converter 1 may further include a DC / DC conversion circuit 14. For details, please refer to the power converter 1 shown in Figure 4f. Here, for the specific connection relationships of the DC / DC conversion circuit 14 shown in Figure 4f, please refer to the connection relationships of the DC / DC conversion circuit 14 in the power converter 1 shown in Figure 2b. Further details are not described herein.

[0060] In this embodiment of the present application, a second switch K2 is added between the output of the inverter circuit 11 of the power converter 1 and the first AC output, and a third switch K3 is added between the output of the inverter circuit 11 of the power converter 1 and the second AC output, thereby allowing the power converter 1 to flexibly switch between off-grid mode and grid-connected mode. By adding a protection circuit 12 and the first switch K1 between the bus midpoint N and the reference ground terminal PE, and by adding a first discharge circuit 13 and a second discharge circuit 17 to the power converter 1, the power converter 1 can be reliably grounded internally in off-grid mode, and when a common-mode lightning current is present on the input, most of the common-mode lightning current can flow into the first discharge circuit 13 and be discharged in off-grid mode. In addition, when a common-mode surge current is present at the first output in off-grid mode, most of the common-mode surge current can flow into the second discharge circuit 17 and be discharged, thereby protecting the power converter 1.

[0061] It should be noted that the protection circuit 12 provided in this application may further include, in addition to the air-core inductor, any protection component, for example, a saturation prevention inductor that exhibits high impedance characteristics when a common-mode lightning current flows through the protection component and low impedance characteristics when a non-common-mode lightning current flows through the protection component. This is not limited to this application. In addition, the operating principle of the protection circuit 12 when the protection circuit 12 is another protection component such as a saturation prevention inductor is consistent with the operating principle of the protection circuit 12 when the protection circuit 12 is an air-core inductor L1. Further details are again not described herein. In addition, in the power converter 1 provided in this application, the number of positive bus capacitors is the same as the number of negative bus capacitors, and both are at least one. In the embodiments described above, for illustrative purposes, an example is used in which both the number of positive bus capacitors and the number of negative bus capacitors are 1. When both the number of positive and negative bus capacitors are multiple, the operating principle of the power converter 1 remains unchanged, and the circuit structure and operating principle of the power converter 1 when the number of positive and negative bus capacitors are multiple are not described herein.

[0062] The foregoing description is merely a specific implementation of this application and does not limit the scope of protection of this application. Any modifications or substitutions that are readily conceivable by a person skilled in the art within the scope of the art disclosed in this application shall fall within the scope of protection of this application. Accordingly, the scope of protection of this application shall be subject to the scope of protection of the claims.

Claims

1. A power conversion device comprising a DC input, a positive DC bus, a negative DC bus, a positive bus capacitor, a negative bus capacitor, an inverter circuit, a protection circuit, a first discharge circuit, a reference ground terminal, and a first AC output. The DC input is configured to be connected to a DC source, the first AC output is configured to be connected to a load, and the inputs of the inverter circuit are connected separately to the DC input via the positive DC bus and the negative DC bus. The positive DC bus is connected to the negative DC bus via the positive bus capacitor and the negative bus capacitor connected in series, the connection point between the positive bus capacitor and the negative bus capacitor is connected to the reference ground terminal via the protection circuit, and the connection point between the positive bus capacitor and the negative bus capacitor is further configured to provide a DC voltage to the first AC output. As the rate of change of the current flowing through the protection circuit increases, the impedance value of the protection circuit increases, and the common-mode voltage value of the DC input becomes greater than the first breakover voltage threshold. The first discharge circuit is connected between the DC input and the reference ground terminal and is configured to be connected when the common-mode voltage value is greater than the first breakover voltage threshold in the power conversion device.

2. The power converter further comprises a first switch and a controller, wherein the connection point between the positive bus capacitor and the negative bus capacitor is connected to the reference ground terminal via the first switch and the protection circuit connected in series, and the first AC output is further configured to be connected to the power grid. The power converter according to claim 1, wherein the controller is configured to control the first switch to turn on when the voltage of the power grid is less than the first breakover voltage threshold.

3. The power converter according to claim 2, wherein the controller is further configured to control the first switch to turn off when the voltage of the power grid is equal to or greater than the first breakover voltage threshold.

4. The power converter further comprises a first switch, a second switch, a third switch, a second AC output, and a controller, wherein the connection point between the positive bus capacitor and the negative bus capacitor is connected to the reference ground terminal via the first switch and the protection circuit connected in series, the connection point between the positive bus capacitor and the negative bus capacitor is further connected to the first AC output via the second switch, the output of the inverter circuit is connected to the first AC output of the power converter via the second switch, and to the second AC output of the power converter via the third switch, and the second AC output is configured to be connected to the power grid. The controller is configured to control the second switch to turn on and the third switch to turn off when the voltage of the power grid is below the first breakover voltage threshold, and to control the first switch to turn on when the second switch is on and the third switch is off. The power conversion device according to claim 1.

5. The power converter according to claim 4, wherein the controller is further configured to control the second switch to turn off and the third switch to turn on when the voltage of the power grid is equal to or greater than the first breakover voltage threshold, and to control the first switch to turn off when the second switch is turned off and the third switch is turned on.

6. The power converter according to claim 1, further comprising a leakage current detection circuit, wherein the leakage current detection circuit is located on a connection line between the output of the inverter circuit and the first AC output of the power converter, and the leakage current detection circuit is further located on a connection line between the first AC output of the power converter and the connection point between the positive bus capacitor and the negative bus capacitor.

7. The power conversion device according to claim 1, wherein the protection circuit comprises an air-core inductor or a saturation prevention inductor.

8. The power converter according to claim 1, further comprising a DC / DC conversion circuit, wherein the DC / DC conversion circuit is configured to perform DC conversion on the DC input and output the converted DC to the positive DC bus and the negative DC bus.

9. The first discharge circuit comprises a first protection element, a second protection element, and a third protection element, and the DC input of the power converter comprises a first DC input and a second DC input. The power converter according to claim 1, wherein the first end of the first protective element is connected to the reference ground terminal, and the second end of the first protective element is connected to the first DC input and the second DC input of the power converter via the second protective element and the third protective element, respectively, and each of the first protective element, the second protective element and the third protective element comprises a gas discharge tube and a varistor or transient voltage suppression diode.

10. The power conversion device further comprises a second discharge circuit, As the rate of change of the current flowing through the protection circuit increases, the impedance value of the protection circuit increases, the common-mode voltage value of the DC input becomes greater than the first breakover voltage threshold, and the common-mode voltage value of the first AC output becomes greater than the second breakover voltage threshold. The power converter according to claim 1, wherein the second discharge circuit is connected between the first AC output and the reference ground terminal of the power converter, and is configured to be connected when the common-mode voltage value of the first AC output is greater than the second breakover voltage threshold.

11. The second discharge circuit comprises a fourth protection element, a fifth protection element, a sixth protection element, and a seventh protection element, and the first AC output of the power converter comprises a first AC sub-output, a second AC sub-output, and a third AC sub-output. The power converter according to claim 10, wherein the first end of the fourth protective element is connected to the reference ground terminal, the second end of the fourth protective element is connected to the first AC sub-output, the second AC sub-output, and the third AC sub-output of the power converter via the fifth protective element, the sixth protective element, and the seventh protective element, respectively, and each of the fourth protective element, the fifth protective element, the sixth protective element, and the seventh protective element comprises a gas discharge tube and a varistor or transient voltage suppression diode.

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