Power conversion device

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] TECHNICAL FIELD This application relates to the field of power supply technology, and in particular to power conversion devices. [Background technology]

[0002] When an inverter operates in off-grid mode and the neutral output of the inverter is left unconnected, the voltage of the neutral output will fluctuate, threatening the safety of users or maintenance personnel. To solve this problem, currently inverters mainly use a method of connecting the neutral output of the inverter to a reference ground terminal in off-grid mode, thereby making the inverter grounded internally and avoiding voltage fluctuations of the neutral output of the inverter. However, since the path between the neutral output of the inverter and the ground terminal is a low impedance path, when the input of the inverter encounters a common-mode lightning strike, all the lightning energy flows inside the inverter, and the energy is discharged on the low impedance path of the neutral output and the ground terminal of the inverter. In this case, the shock energy generated by the common-mode lightning strike will damage the components of the power conversion circuit in the inverter. In conclusion, it can be seen that it is particularly important to prevent the shock energy generated by the common-mode lightning strike from damaging the components of the power conversion circuit while the inverter is securely grounded internally. Summary of the Invention

[0003] The present application provides a power converter, in which the shock energy generated by a common-mode lightning current will not damage components of the power converter circuit, and the power converter is internally grounded reliably, thereby protecting the power converter.

[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. An input of the inverter circuit is separately connected to the DC input via a positive DC bus and a 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 turn. A connection point between the positive bus capacitor and the negative bus capacitor, i.e., a bus midpoint, is connected to the reference ground terminal via a protection circuit. The bus midpoint is further configured to provide a DC voltage to the first AC output of the power converter. An impedance value of the protection circuit increases as a rate of change of the current through the protection circuit increases, causing a common mode voltage value of the DC input to be 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 in a connected state when a common mode voltage value of the DC input is greater than a first breakover voltage threshold.

[0005] In this implementation, the bus midpoint is connected to the reference ground terminal through the 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 stroke and the power converter is in off-grid mode, when the common-mode lightning 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 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 current flows and discharges through the first discharge circuit, and does not flow through the power conversion circuit in the power converter. In this way, the impact energy generated by the common-mode lightning current does not damage the components of the power conversion circuit, and the power converter is reliably grounded internally, thereby protecting the power converter.

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

[0007] In this implementation, according to the power conversion device, a first switch is added between the bus midpoint and the reference ground terminal, and when a power outage occurs in the power grid, the first switch is controlled to be turned on, ensuring that the power conversion device is internally grounded only in the 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 a power conversion device in which the grid-connected output and the off-grid output are independent of each other, the power conversion device in this implementation can use the grid-connected output and its associated circuitry in both the grid-connected mode and the off-grid mode. This helps to reduce the circuit cost of the power conversion device and miniaturize the power conversion device.

[0008] With reference to the first possible implementation form of the first aspect, in a second possible implementation form, the controller is further configured to control the first switch to be turned off when the voltage of the power grid is equal to or greater than a first breakover voltage threshold, i.e., when no power outage occurs in the power grid.

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

[0010] With reference to the first aspect, 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, where 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 of the power converter via the second switch, and the output of the inverter circuit is further connected to the first AC output and the second AC output of the power converter separately via the second switch and the third switch, and the second AC output is configured to connect to a power grid. The controller is configured to control the second switch to be on and the third switch to be 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 be on when the second switch is on and the third switch is off, i.e., when the power converter is in an off-grid mode.

[0011] In this implementation, according to the power converter, a second switch is added between the output of the inverter circuit and the first AC output of the power converter, and a third switch is added between the output of the inverter circuit and the second AC output of the power converter, so that the power converter can flexibly switch between an off-grid mode and a grid-connected mode. In addition, the power converter in the off-grid mode controls the first switch to be on, ensuring that the power converter is internally grounded only in the off-grid mode.

[0012] With reference to the third possible implementation form of the first aspect, in a fourth possible implementation form, the controller is further configured to control the second switch to be turned off and the third switch to be turned on when the voltage of the power grid is equal to or greater than a first breakover voltage threshold, and to control the first switch to be turned off when the second switch is turned off and the third switch is turned on, i.e., when the power conversion device is in a grid-connected mode.

[0013] In this implementation, the power conversion device in grid-connected mode controls the first switch to be off, and the power conversion device in off-grid mode controls the first switch to be on, ensuring that the power conversion device is internally grounded only in off-grid mode.

[0014] With reference to any one of the first to fourth possible implementation forms of the first aspect, in a fifth possible implementation form, the power conversion device further includes a leakage current detection circuit, the leakage current detection circuit being located on a connection line between the output of the inverter circuit and the first AC output of the power conversion device, and the leakage current detection circuit being further located on a connection line between the first AC output of the power conversion device and a 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 leakage current detection circuit is located on the right side of the path between the bus midpoint and the reference ground terminal to avoid the leakage current detection circuit failing in off-grid mode, thereby improving the stability of the power conversion device.

[0016] With reference to any one of the first to fifth possible implementation forms of the first aspect, in a sixth possible implementation form, the protection circuit further includes an air-core inductor or an anti-saturation inductor.

[0017] In this implementation, since there are various types of protection circuits, the structure of the power converter becomes diverse and very flexible.

[0018] With reference to any one of the first to sixth possible implementation forms of the first aspect, in a seventh possible implementation form, the power conversion device further includes a DC / DC conversion circuit, and the DC / DC conversion circuit is configured to perform DC conversion on the DC of a DC input of the power conversion device and output the converted DC to a positive DC bus and a negative DC bus.

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

[0020] With reference to any one of the seventh possible implementation forms of the first aspect to the seventh possible implementation form of the first aspect, in an eighth possible implementation form, 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 conversion device includes a first DC input and a second DC input. A first end of the first protection element is connected to the reference ground terminal, and a second end of the first protection element is connected to the first DC input and the second DC input of the power conversion device via the second protection element and the third protection element, respectively. Each of the first protection element, the second protection element, and the third protection element includes a gas discharge tube, a varistor, or a transient voltage suppression diode.

[0021] In this implementation, since there are various types of protection elements, the structure of the power converter becomes diverse and very flexible.

[0022] With reference to any one of the eighth possible implementation forms of the first aspect to the eighth possible implementation form of the first aspect, in a ninth possible implementation form, the power conversion apparatus further includes a second discharge circuit, the second discharge circuit being connected between the first AC output and a reference ground terminal of the power conversion apparatus. An impedance value of the protection circuit increases as a rate of change of the current through the protection circuit increases, causing the common mode voltage value of the DC input to be greater than the first breakover voltage threshold and the common mode voltage value of the first AC output to be greater than the second breakover voltage threshold. The second discharge circuit is in a connected state when the common mode voltage value of the first AC output is greater than the second breakover voltage threshold.

[0023] In this implementation, in off-grid mode, the power converter 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 converter reaches the breakover voltage threshold of the second discharge circuit, and most of the common-mode surge current flows and discharges through the second discharge circuit, and does not flow through the power converter circuit in the power converter. 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 is reliably grounded internally, thereby protecting the power converter.

[0024] With reference to the ninth possible implementation of the first aspect, in a tenth possible implementation, 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. A first end of the fourth protection element is connected to the reference ground terminal. A 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 via 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, since there are various types of protection elements, the structure of the power converter becomes diverse and very flexible. [Brief description of the drawings]

[0026] [Figure 1] FIG. 2 is a diagram of an application scenario of a power converter according to the present application. [Figure 2a] 1 is a diagram of the structure of a power converter according to the present application; [Figure 2b] FIG. 2 is a diagram of another structure of a power converter according to the present application. [Figure 3a] FIG. 2 is a diagram of another structure of a power converter according to the present application. [Figure 3b] FIG. 2 is a diagram of another structure of a power converter according to the present application. [Figure 3c] FIG. 2 is a diagram of another structure of a power converter according to the present application. [Figure 3d] FIG. 2 is a diagram of another structure of a power converter according to the present application. [Figure 4a] FIG. 2 is a diagram of another structure of a power converter according to the present application. [Figure 4b] FIG. 2 is a diagram of another structure of a power converter according to the present application. [Figure 4c] FIG. 2 is a diagram of another structure of a power converter according to the present application. [Figure 4d] FIG. 2 is a diagram of another structure of a power converter according to the present application. [Figure 4e] FIG. 2 is a diagram of another structure of a power converter according to the present application. [Figure 4f] FIG. 13 is a diagram of yet another configuration of a power converter according to the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The power conversion device provided in the present application can be used in multiple application fields, such as new energy smart microgrid field, power transmission and distribution field, new energy field (for example, photovoltaic power grid connection field or wind power grid connection field), photovoltaic power generation field, energy storage and power generation field, and wind power generation field. The power conversion device provided in the present application can be an inverter (including string inverter and distributed inverter), energy storage inverter, uninterruptible power supply (UPS), etc. The power conversion device can be used in different application scenarios, such as photovoltaic power supply scenarios (including large photovoltaic power station scenarios, small and medium distributed photovoltaic power station scenarios, residential photovoltaic power generation system scenarios, etc.), energy storage power supply scenarios (including large energy storage power plant scenarios, small and medium distributed energy storage power plant scenarios, residential photovoltaic power energy storage and power generation system scenarios, etc.), and power supply scenarios by using uninterruptible power supply (UPS). In the following, the photovoltaic power supply scenario is used as an example for explanation.

[0028] FIG. 1 is a diagram of an application scenario of a power converter according to the present application. In a photovoltaic power supply scenario, the power converter provided in the present application can be an inverter as shown in FIG. 1. The DC input of the inverter is connected to a photovoltaic 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 conversion 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 conversion circuit via the positive DC bus BUS+ and the negative DC bus BUS-, respectively. The input of the DC / DC conversion 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 junction 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 junction between the positive bus capacitor C1 and the negative bus capacitor C2 is further connected to a first AC output of the inverter. A first discharge circuit is connected between the input of the inverter and the reference ground terminal PE.

[0029] After the inverter starts to operate, the DC / DC conversion circuit performs DC conversion on the DC generated by the photovoltaic power generation string connected to the input of the inverter, 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 input of the inverter circuit into AC to supply power to various types of electrical equipment, such as AC loads. In addition, in the process of the inverter supplying power to the AC load, when a common-mode lightning strike occurs between the input of the inverter and the reference ground terminal, the common-mode lightning strike current flows through the protection circuit, thereby increasing the rate of change of the current in the protection circuit, and 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 of the inverter becomes greater than the first breakover voltage threshold. When the common-mode voltage value of the DC input of the inverter is greater than the first breakover voltage threshold, the first discharge circuit is in a connected state, so that 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) in the inverter. In this way, the shock energy generated by the common mode lightning current will not damage the components of the power conversion circuit, thereby protecting the inverter. The above is only one example of the application scenario of the power conversion device provided in this application, and is not exhaustive. The application scenario is not limited in this application.

[0030] With reference to Figs. 2a to 4f, an example of the working principle of the power converter provided in the present application is described below.

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

[0032] In one implementation, in the process of the power conversion device 1 supplying power to the load, when a common mode lightning strike occurs between the first DC input i1+ or the second DC input i1- of the power conversion device 1 and the reference ground terminal PE, and 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, so that the impedance value of the protection circuit 12 increases as the rate of change of the current flowing through the protection circuit 12 increases. Therefore, the common mode voltage value between the DC input and the reference ground terminal PE of the power conversion device 1 becomes greater than the first breakover voltage threshold. In addition, when the common mode voltage value of the power conversion device 1 is greater than the first breakover voltage threshold, the first discharge circuit 13 is in a connected state, so that most of the common mode lightning strike current flows and discharges through the first discharge circuit 13, and does not flow through the power conversion circuit in the power conversion device 1.

[0033] It should be noted that in the present application, A being connected to B may be that A is directly connected to B, or that A is indirectly connected to B via C. This is not limited in the present 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 conversion device 1 via the positive DC bus BUS+ and the negative DC bus BUS-, respectively. In addition, a DC / DC conversion circuit may be further connected between the DC input of the power conversion device 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 conversion device 1. If the power conversion device 1 is a solar power generation inverter, the DC source may be a solar power generation string. In this case, the DC / DC conversion circuit performs DC conversion on the DC output by the DC source, and further performs maximum power point tracking (MPPT) control on the solar power string to ensure high-efficiency power generation of the solar power string. Here, for a specific connection relationship of the DC / DC conversion circuit, please refer to the power conversion device 1 shown in FIG. 2b. As shown in FIG. 2b, the power conversion device 1 further includes a DC / DC conversion circuit 14. A first input i11+ of the inverter circuit 11 is connected to a first output o14+ of the DC / DC conversion circuit 14 via a positive DC bus BUS+. A second input i11- of the inverter circuit 11 is connected to a second output o14- of the DC / DC conversion circuit 14 via a negative DC bus BUS-. A first input i14+ and a second input i14- of the DC / DC conversion circuit 14 are respectively connected to a first DC input i1+ and a second DC input i1- of the power conversion device 1. The structure of the power conversion device 1 is diverse and has a high degree of freedom.

[0034] In this embodiment of the present application, the bus midpoint is connected to the reference ground terminal through the 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 stroke and the common-mode lightning current flows through 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 current flows and discharges through the first discharge circuit 13, and does not flow through the power conversion circuit in the power converter 1. In this way, the impact energy generated by the common-mode lightning current does not damage the components of the power conversion circuit, and the power converter 1 is reliably grounded internally, thereby protecting the power converter 1.

[0035] FIG. 3a is a diagram of another structure of a power converter according to the present application. As shown in FIG. 3a, compared with the power converter 1 shown in FIG. 2a, the power converter 1 shown in FIG. 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 protection circuit 12 and a first switch K1 connected in series. 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 connect 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 conversion device 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 to the first AC sub-output o111 and the second AC sub-output o112 of the power conversion device 1, respectively, via the leakage current detection circuit 16 and the second switch K2 connected in series. The bus midpoint N is connected to the third AC sub-output o11N of the power conversion device 1, via the leakage current detection circuit 16 and the second switch K2 connected in series. Optionally, the power conversion device 1 further includes a second discharge circuit 17. The second discharge circuit 17 is connected between the first AC output of the power conversion device 1 and the reference ground terminal PE. Specifically, 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 conversion device 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 FIG. 3a is a single-phase power converter. The power converter 1 provided in the present application is also applicable to a three-phase power converter. For details, please refer to the power converter 1 shown in FIG. 3b. As shown in FIG. 3b, compared with the power converter 1 shown in FIG. 3a, the first AC output of the power converter 1 shown in FIG. 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 through the leakage current detection circuit 16 and the second switch K2 connected in series. 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 output 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 operation principle. Therefore, for ease of explanation, the single-phase power converter shown in FIG. 3a will be specifically described below with reference to the power converter shown in FIG. 3c.

[0037] FIG. 3c is a diagram of another structure of the power converter according to the present application. As shown in FIG. 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. A first end of the first protection element is connected to the reference ground terminal PE, and a 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 through 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 aforementioned three protection elements 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 protection element and the third protection element 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. A first end of the fourth protection element is connected to the reference ground terminal PE, and a 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 conversion device 1 through 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 aforementioned four protection elements may be the same or different. This is not limited in the present application. For example, the fourth protection element is a gas discharge tube GDT2, and the fifth protection element, the sixth protection element, and the seventh protection element 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 a first group first input i21 and a first group second input i22. The second group input includes a second group first input i31 and a second group second input i32. The third group input includes a third group first input i41 and a third group second input i42. The first output o1111 of the inverter circuit 11 is connected to the first group first input i21. The first group second input i22 is connected to the first AC sub-output o111 of the power conversion device 1 via the switch K21. The second output o1112 of the inverter circuit 11 is connected to the third group first input i41. The third group second input i42 is connected to the second AC sub-output o112 of the power conversion device 1 via the 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 conversion device 1 via the 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 first group second output o22. The second group output includes the second group first output o31 and the second group second output o32. The third group output includes the third group first output o41 and the third group second output o42. The controller 15 can obtain the leakage current value of the first AC output of the power conversion device 1 by obtaining the current values ​​of the outputs of the three groups of the leakage current detection circuit 16. Therefore, when the leakage current value of the first AC output is larger than the leakage current threshold, the power conversion device 1 is protected, and for example, the second switch K2 is controlled to be turned off.

[0039] In an optional implementation, after the power conversion device 1 starts to operate, the controller 15 controls the switches K21 to K23 of the second switch K2 to be all turned on. When the voltage of the AC power grid is less than the first breakover voltage threshold, it indicates that a power outage occurs in the AC power grid and the power conversion device 1 is in an off-grid mode. In this case, the first AC output of the power conversion device 1 is connected to an AC load, and the controller 15 controls the first switch K1 to be turned on, so that the power conversion device 1 is ensured to be grounded internally in the off-grid mode.

[0040] After the power converter 1 is securely grounded internally, when a common-mode lightning current exists 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 exists when no common-mode lightning current exists 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 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. Therefore, the following can be obtained: when the common-mode lightning current flows through the air-core inductor L1, the air-core inductor L1 is equivalent to a high impedance, so that the common-mode voltage value of the DC input of the power converter 1 reaches the first breakover voltage threshold. The common mode voltage value of the DC input includes a voltage value between the first DC input i1+ and the reference ground terminal PE of the power converter 1, or a 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 a first breakover voltage threshold, the gas discharge tube GDT1 breaks down, the first discharge circuit 13 is in a connected state, and the impedance value of the varistor RV1 or RV2 drops sharply. That is, the first discharge circuit 13 is in a connected state. Therefore, most of the common mode lightning current flows and discharges in the first discharge circuit 13, and does not flow through the power conversion circuit in the power converter 1. In this way, the shock energy generated by the common mode lightning current does not damage the components of the power conversion circuit, and the power converter is reliably grounded inside, thereby protecting the power converter 1. The first breakover voltage threshold can 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 securely grounded internally, when no common-mode lightning current exists in 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, when the rate of change of the current 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 exists in 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 exists in the DC input of the power converter 1 and the power converter 1 is in off-grid mode, the ground 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 conversion device 1 is securely grounded internally, when the first AC output of the power conversion device 1 encounters a common-mode surge, by using the air-core inductor L1 and the second discharge circuit 17 of the power conversion device 1, most of the common-mode surge current can flow to and be discharged through the second discharge circuit 17, thereby protecting the power conversion device 1.

[0043] Specifically, when a common mode surge current exists in 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 exists when a common mode lightning current does not exist in 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 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. Therefore, the following can be obtained: when the common mode surge current flows through the air-core inductor L1, the air-core inductor L1 is equivalent to a high impedance, so that 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 is in a connected state, and the impedance value of the varistor RV3, RV4, or RV5 drops sharply. That is, the second discharge circuit 17 is in a connected state. 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 in 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, and the power converter is reliably grounded inside, thereby protecting the power converter 1. The second breakover voltage threshold can be the sum of the breakover voltage threshold of the gas discharge tube GDT2 and the breakover voltage threshold of the varistor RV3, RV4, or RV5.

[0044] It was noted that, when the power conversion device 1 is externally grounded, an operator may send a disable instruction to the power conversion device 1, indicating that the power conversion device 1 is externally grounded, by using an external device connected to the power conversion device 1. The controller 15 in the power conversion device 1 controls the first switch K1 to be turned off according to the received disable instruction, to ensure that the power conversion device 1 in off-grid mode is not grounded internally and externally at the same time. In this way, the following case is avoided: the power conversion device 1 is grounded at multiple points, which generates circulating current. Therefore, the stability of the power conversion device 1 is improved.

[0045] In another optional implementation, after the power converter 1 starts to operate, the controller 15 controls the switches K21 to K23 of the second switch K2 to be all turned on. When the voltage of the AC power grid is equal to or greater than the first breakover voltage threshold, it indicates that no power outage occurs in the AC power grid and the power converter 1 is in a 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 conversion device 1 may further include a DC / DC conversion circuit 14. For details, please refer to the power conversion device 1 shown in Fig. 3d. Here, for the specific connection relationship of the DC / DC conversion circuit 14 shown in Fig. 3d, please refer to the connection relationship of the DC / DC conversion circuit 14 in the power conversion device 1 shown in Fig. 2b. The details will not be described again in this specification.

[0047] In this embodiment of the present application, the power converter 1 in off-grid mode controls the first switch K1 to be turned on, so that the bus midpoint N is connected to the reference ground terminal PE through the protection circuit 12, and the bus midpoint is controlled to be connected to the neutral output of the power converter 1, thereby implementing internal solid grounding. In addition, when the common-mode lightning current flows through the protection circuit 12, the protection circuit 12 becomes equivalent to a high impedance, so that 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 there is a common-mode lightning current in the DC input of the power converter 1, most of the common-mode lightning current flows to the first discharge circuit 13 to be discharged. In this way, the impact energy generated by the common-mode lightning current does not damage the components of the power converter circuit, and the power converter 1 is internally solidly grounded, 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, so that the common-mode voltage value of the first AC output of the power conversion device 1 reaches the breakover voltage threshold of the second discharge circuit 17. Therefore, when a common-mode surge current exists in the first AC output of the power conversion device 1, most of the common-mode surge current flows to the second discharge circuit 17 and is discharged. In this way, the shock energy generated by the common-mode surge current does not damage the components of the power conversion circuit, and the power conversion device 1 is reliably grounded internally, thereby protecting the power conversion device 1.

[0048] FIG. 4a is a diagram of another structure of a power converter according to the present application. As shown in FIG. 4a, compared with the power converter 1 shown in FIG. 3a, the power converter 1 shown in FIG. 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 connect 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 conversion device 1. A 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 conversion device 1. Optionally, the power conversion device 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 to the fifth AC sub-output o121 and the sixth AC sub-output o122 of the power conversion device 1, respectively, via the leakage current detection circuit 18 and the third switch K3 connected in series. Optionally, the power conversion device 1 further includes a third discharge circuit 19. The third discharge circuit 19 is connected between the second AC output of the power conversion device 1 and the reference ground terminal PE. Specifically, three inputs of a 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 conversion device 1. An output of the third discharge circuit 19 is connected to the reference ground terminal PE.

[0049] The power converter 1 shown in FIG. 4a is a single-phase power converter. The power converter 1 provided in the present application is also applicable to a three-phase power converter. For details, please refer to the power converter 1 shown in FIG. 4b. As shown in FIG. 4b, compared with the power converter 1 shown in FIG. 4a, the first AC output of the power converter 1 shown in FIG. 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 leakage current detection circuit 16 and a second switch K2 connected in series. 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 leakage current detection circuit 18 and a third switch K3 connected in series. Regardless of 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, for ease of explanation, the single-phase power converter shown in Fig. 4a will be specifically described below with reference to the power converter shown in Fig. 4c.

[0050] FIG. 4c is a diagram of another structure of the power converter according to the present application. As shown in FIG. 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 the 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 the 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 conversion device 1 by obtaining the current values ​​of the outputs of the two groups of the leakage current detection circuit 18. Therefore, when the leakage current value of the second AC output is greater than the leakage current threshold value, the power conversion device 1 is protected, and for example, the third switch K3 is controlled to be turned 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 protection element, the ninth protection element, and the tenth protection element are connected in series between the fifth AC sub-output o121 and the sixth AC sub-output o122 of the power conversion device 1, and the eleventh protection element and the twelfth protection element are connected in series and then in parallel with the ninth protection element. The connection point between the eleventh protection element and the twelfth protection element is connected to the seventh AC sub-output o12N of the power conversion device 1 via the thirteenth protection element, and further, the connection point between the eleventh protection element and the twelfth protection element is connected to the reference ground terminal PE via the fourteenth protection element. Each protection element of the third discharge circuit 19 includes a gas discharge tube, a varistor, a transient voltage suppression diode, or a fuse. The types of the aforementioned seven protection elements may be the same or different. This is not limited in the present application.For example, the eighth to thirteenth protection elements are varistors RV6 to RV11, respectively, and the fourteenth protection element is a gas discharge tube GDT3. The specific structures 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 described with reference to the description of the corresponding parts of the power conversion device 1 shown in Fig. 3c. The details will not be described again in this specification.

[0051] In an optional implementation, when the voltage of the AC power grid is less than the first breakover voltage threshold, it indicates that a power outage has occurred on the AC power grid, and the controller 15 controls the switches K21-K23 of the second switch K2 to all be turned on, and the switches K31 and K32 of the third switch K3 to both be turned off, thereby causing the power conversion device 1 to be in an off-grid mode. In this case, the first AC output of the power conversion device 1 is connected to an AC load. Then, 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 be turned on, thereby ensuring that the power conversion device 1 is internally grounded in the off-grid mode.

[0052] After the power converter 1 is securely grounded inside, when there is a common-mode lightning current in the DC input of the power converter 1, the impact energy generated by the common-mode lightning current will not damage the components of the power converter circuit by using the air-core inductor L1 and the first discharge circuit 13 of the power converter 1. For specific implementation, please refer to the description of the corresponding part of the power converter 1 shown in FIG. 3c. The details will not be described again in this specification.

[0053] After the power converter 1 is securely grounded internally, when there is no common-mode lightning current in 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, when the rate of change of the current through the air-core inductor L1 is less than a 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 in the DC input of the power converter 1 and the power converter 1 is in off-grid mode, the ground 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.

[0054] In addition, after the power conversion device 1 is securely grounded inside, when the first AC output of the power conversion device 1 encounters a common mode surge, by using the air-core inductor L1 and the second discharge circuit 17 of the power conversion device 1, most of the common mode surge current can flow to the second discharge circuit 17 and be discharged, thereby protecting the power conversion device 1. Here, by using the air-core inductor L1 and the second discharge circuit 17 of the power conversion device 1, the shock energy generated by the common mode surge current does not damage the components of the power conversion circuit. For specific implementation, please refer to the description of the corresponding part of the power conversion device 1 shown in FIG. 3c. The details will not be described again in this specification.

[0055] Optionally, the second discharge circuit 17 may further use a circuit structure shown in Fig. 4d. As shown in Fig. 4d, the second discharge circuit 17 includes fuses FU1 and FU2, a gas discharge tube GDT4, and varistors RV12 to RV15. The fuse FU1 and varistor RV12 are connected in series between the first AC sub-output o111 and the third AC sub-output o11N, and the 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 the fuse FU1 and varistor RV12 is connected to the reference ground terminal PE through the varistor RV15 and the gas discharge tube GDT4 in sequence, and the connection point between the fuse FU2 and varistor RV14 is connected to the reference ground terminal PE through the varistor RV15 and the gas discharge tube GDT4 in sequence. When a common mode surge current or a differential mode surge current exists in the first AC output of the power converter 1, most of the common mode surge current or the 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 FIG. 4d can further include gas discharge tubes GDT5 and GDT6. For details, please refer to the second discharge circuit 17 in the power converter 1 shown in FIG. 4e. In addition, the circuit structure of all the discharge circuits provided in this application can be adjusted accordingly according to actual requirements. This is not limited in this application.

[0056] It was noted that, when the power conversion device 1 is externally grounded, an operator may send a disable instruction to the power conversion device 1, indicating that the power conversion device 1 is externally grounded, by using an external device connected to the power conversion device 1. The controller 15 in the power conversion device 1 controls the first switch K1 to be turned off according to the received disable instruction, to ensure that the power conversion device 1 in off-grid mode is not grounded internally and externally at the same time. In this way, the following case is avoided: the power conversion device 1 is grounded at multiple points, which generates circulating current. Therefore, the stability of the power conversion device 1 is improved.

[0057] In another optional implementation, when the voltage of the AC power grid is equal to or greater than the first breakover voltage threshold, it indicates that no power outage occurs in the AC power grid, and the controller 15 controls the switches K21-K23 of the second switch K2 to all be turned off, and controls the switches K31 and K32 of the third switch K3 to both be turned on, thereby causing the power converter 1 to be in a 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 be turned off.

[0058] In addition, after the power converter 1 is in the 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 the varistors RV6, RV7, RV9, and RV10 will rapidly decrease, and the gas discharge tube GDT3 will 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, so that the common-mode voltage value of the second AC output of the power converter 1 rapidly decreases, thereby implementing overvoltage protection of the second output of the power converter 1.

[0059] Optionally, the power conversion device 1 may further include a DC / DC conversion circuit 14. For details, please refer to the power conversion device 1 shown in Fig. 4f. Here, for the specific connection relationship of the DC / DC conversion circuit 14 shown in Fig. 4f, please refer to the connection relationship of the DC / DC conversion circuit 14 in the power conversion device 1 shown in Fig. 2b. The details will not be described again in this specification.

[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, so that the power converter 1 can flexibly switch between the off-grid mode and the grid-connected mode. Through the manner of adding the protection circuit 12 and the first switch K1 between the bus midpoint N and the reference ground terminal PE, and adding the first discharge circuit 13 and the second discharge circuit 17 to the power converter 1, the power converter 1 can be surely grounded internally in the off-grid mode, and when there is a common-mode lightning current on the input, most of the common-mode lightning current can flow to the first discharge circuit 13 to be discharged in the off-grid mode. In addition, when there is a common-mode surge current on the first output in the off-grid mode, most of the common-mode surge current can flow to the second discharge circuit 17 to be discharged, thereby protecting the power converter 1.

[0061] It should be noted that the protection circuit 12 provided in the present application may further include an optional protection component, for example, an anti-saturation inductor, which shows high impedance characteristics when a common mode lightning current flows through the protection component and shows low impedance characteristics when a non-common mode lightning current flows through the protection component, in addition to the air-core inductor. This is not limited in the present application. In addition, the operation principle of the protection circuit 12 when the protection circuit 12 is another protection component such as an anti-saturation inductor is consistent with the operation principle of the protection circuit 12 when the protection circuit 12 is an air-core inductor L1. Details will not be described again in this specification. In addition, in the power conversion device 1 provided in the present 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 above embodiment, an example in which the number of positive bus capacitors and the number of negative bus capacitors are both 1 is used for explanation. When the number of positive bus capacitors and the number of negative bus capacitors are both multiple, the operating principle of the power conversion device 1 remains unchanged, and the circuit structure and operating principle of the power conversion device 1 when the number of positive bus capacitors and the number of negative bus capacitors are multiple are not described in this specification.

[0062] The above description is merely a specific implementation form of the present application, and does not limit the protection scope of the present application. Any variation or replacement that is easily conceived by a person skilled in the art within the technical scope disclosed in this application shall fall within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A power converter 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 connect to a DC source and the first AC output is configured to connect to a load, and the inputs of the inverter circuit are separately connected 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; an impedance value of the protection circuit increases as a rate of change of current through the protection circuit increases, causing a common mode voltage value of the DC input to be greater than a first breakover voltage threshold; the first discharge circuit is connected between the DC input and the reference ground terminal and configured to be in a connected state when the common mode voltage value is greater than the first breakover voltage threshold. Power conversion equipment.

2. the power converter further comprises a first switch and a controller, the junction 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 connect to a power grid; the controller is configured to control the first switch to be on when a voltage of the power grid is below a first breakover voltage threshold; The power conversion device according to claim 1 .

3. The power converter of claim 2 , wherein the controller is further configured to control the first switch to be off when the voltage of the power grid is greater than or equal to 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, 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, an output of the inverter circuit is separately connected to the first AC output and the second AC output of the power converter via the second switch and the third switch, and the second AC output is configured to connect to a power grid; the controller is configured to control the second switch to be on and the third switch to be off when a voltage of the power grid is below a first breakover voltage threshold, and to control the first switch to be on when the second switch is on and the third switch is off. The power conversion device according to claim 1 .

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

6. The power conversion device of any one of claims 1 to 5, further comprising a leakage current detection circuit, the leakage current detection circuit being located on a connection line between the output of the inverter circuit and the first AC output of the power conversion device, and the leakage current detection circuit being further located on a connection line between the first AC output of the power conversion device and the connection point between the positive bus capacitor and the negative bus capacitor.

7. The power converter of claim 1 , wherein the protection circuit comprises an air-core inductor or an anti-saturation inductor.

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

9. the first discharge circuit includes a first protection element, a second protection element, and a third protection element; the DC input of the power conversion device includes a first DC input and a second DC input; a first end of the first protection element is connected to the reference ground terminal, and a second end of the first protection element is connected to the first DC input and the second DC input of the power conversion device via the second protection element and the third protection element, respectively, and each of the first protection element, the second protection element, and the third protection element comprises a gas discharge tube, a varistor, or a transient voltage suppression diode; The power conversion device according to any one of claims 1 to 8.

10. The power conversion device further includes a second discharge circuit, the impedance value of the protection circuit increases as the rate of change of the current through the protection circuit increases, the common mode voltage value of the DC input increases above the first breakover voltage threshold, and the common mode voltage value of the first AC output increases above a second breakover voltage threshold; the second discharge circuit is connected between the first AC output and the reference ground terminal of the power converter and configured to be in a connected state when the common mode voltage value of the first AC output is greater than a second breakover voltage threshold. The power conversion device according to any one of claims 1 to 9.

11. the second discharge circuit includes a fourth protection element, a fifth protection element, a sixth protection element, and a seventh protection element; 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; a first end of the fourth protection element is connected to the reference ground terminal, and a 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 via 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 comprises a gas discharge tube, a varistor, or a transient voltage suppression diode; The power converter according to claim 10.

Images