Method for suppressing ground common-mode voltage of alternating current side of inverter

Abstract

The invention discloses a method for suppressing the ground common-mode voltage of the alternating current side of an inverter, which is applied to the maintenance process of the inverter, a common-mode loop is formed among a bus negative electrode of the inverter, a ground capacitor of the alternating current side and a signal ground, and the method comprises the following steps: a suppression circuit connected to the common-mode loop is used for suppressing the ground common-mode voltage of the alternating current side of the inverter when the inverter is maintained; the suppression circuit is conducted to perform upper limit clamping on the negative voltage to ground of the bus so as to suppress the voltage to ground of the alternating current side; or the suppression circuit is disconnected to disconnect the common-mode loop and cut off the charging loop of the AC-side ground capacitor to suppress the AC-side ground voltage, so that the AC port voltage is kept below the personal safety voltage, and the safety of the maintenance personnel is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter common-mode voltage suppression, and in particular to a method for suppressing the common-mode voltage between the AC side of an inverter and the ground. Background Art

[0002] In existing grid-connected inverters, most of their DC sides and AC sides adopt non-isolated schemes, that is, the signal ground is connected to the negative bus, thereby reducing the cost of the grid-connected inverter. However, this non-isolated scheme has potential safety hazards. For example, when the inverter is being repaired, although the grid-connected switch group between the inverter and the grid is disconnected, due to the existence of the common-mode loop, the AC side-to-ground capacitance will be charged. Especially when the voltage output by the DC side power supply is relatively large, the DC voltage on the ground capacitance will also be relatively large, resulting in a relatively high voltage at the AC side port, thus posing a risk of electric shock to maintenance personnel.

[0003] In related technologies, although the high-frequency common-mode voltage during inverter grid connection is suppressed, when the grid-connected switch group is disconnected for maintenance, a relatively high voltage will still be generated at the AC side port due to the existence of the common-mode loop, posing an electric shock risk to maintenance personnel. Summary of the Invention

[0004] An object of the present invention is to provide a method for suppressing the common-mode voltage between the AC side of an inverter and the ground, so as to solve or alleviate the problem that a relatively large voltage is generated at the AC side during off-grid maintenance of the inverter, posing a safety hazard to maintenance personnel.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for suppressing the common-mode voltage between the AC side of an inverter and the ground, which is applied to the maintenance process of the inverter. A common-mode loop is formed among the negative bus, signal ground, and AC side-to-ground capacitance of the inverter, including: a suppression line connected to the common-mode loop. When the inverter is being maintained, the suppression line is turned on to perform an upper limit clamp on the voltage of the negative bus to the ground, or the suppression line is disconnected to disconnect the common-mode loop, so as to suppress the voltage of the AC side-to-ground capacitance.

[0006] As a preference, the suppression line includes a bypass branch line provided between the negative bus and the ground. When the inverter is operating normally, the bypass branch line is disconnected. When the inverter is being maintained, the bypass branch line is turned on to perform an upper limit clamp on the voltage of the negative bus to the ground.

[0007] As a preference, the bypass branch line includes a bypass switch S dc- , the bypass switch S dc- is connected between the negative bus and the ground. When the inverter is operating normally, the bypass switch S dc- is disconnected. When the inverter is being maintained, the bypass switch S dc-Close to perform upper limit clamping on the ground voltage of the negative busbar.

[0008] As a preference, the bypass branch further includes a bypass resistor R, and the bypass resistor R is connected in series with the bypass switch S dc- .

[0009] As a preference, the resistance value of the resistor R is smaller than the resistance value of the resistor R connected between the positive busbar and the ground dc+ .

[0010] As a preference, the suppression circuit includes a PID power supply disposed between the negative busbar and the ground. When the inverter is under maintenance, adjust the output voltage V of the PID power supply PID to perform upper limit clamping on the ground voltage of the negative busbar.

[0011] As a preference, the suppression circuit includes a breaking branch. The breaking branch is disposed between the AC side ground capacitance and the negative busbar, or between the AC side ground capacitance and the ground. When the inverter is operating normally, the breaking branch is conducting. When the inverter is under maintenance, the branch line is disconnected to cut off the charging circuit of the AC side ground capacitance.

[0012] As a preference, the breaking branch includes a breaking switch S1. The breaking switch S1 is connected between the AC side ground capacitance and the ground. When the inverter is operating normally, the breaking switch S1 is closed. When the inverter is under maintenance, the breaking switch S1 is disconnected to disconnect between the AC side ground capacitance and the ground.

[0013] As a preference, the breaking branch includes a breaking switch S2. The breaking switch S2 is connected between the signal ground and the negative busbar. When the inverter is operating normally, the breaking switch S2 is closed. When the inverter is under maintenance, the breaking switch S2 is disconnected to disconnect between the AC voltage sampling resistor and the negative busbar.

[0014] As a preference, the bypass switch S dc- , the breaking switch S1, and the breaking switch S2 adopt relays.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] (1) When the inverter is under maintenance, conduct the suppression circuit to perform upper limit clamping on the ground voltage of the negative busbar to suppress the ground voltage of the AC side, so that the AC port voltage is kept below the personal safety voltage, which is beneficial to ensuring the safety of maintenance personnel.

[0017] (2) When the inverter is under maintenance, disconnect the suppression circuit to open the common-mode loop and cut off the charging circuit of the AC-side ground capacitance, so as to suppress the AC-side ground voltage, thereby keeping the AC port voltage below the safe voltage for human body, or making the voltage difference between the AC-side ports zero, which is beneficial to ensuring the safety of maintenance personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a typical photovoltaic system in the related art.

[0019] Figure 2A is a schematic diagram showing complete isolation between the bus side and the signal side of an inverter in the related art.

[0020] Figure 2B is a schematic diagram showing that the bus negative of the bus side and the signal ground of the signal side of an inverter in the related art share the same ground.

[0021] Figure 3 is a circuit schematic diagram showing that the bus negative and the signal ground of an inverter in a photovoltaic system in the related art share the same ground.

[0022] Figure 4A is Figure 3 the equivalent circuit schematic diagram of the circuit schematic diagram shown.

[0023] Figure 4B is Figure 4A the simplified circuit schematic diagram of the equivalent circuit schematic diagram shown.

[0024] Figure 5 is a circuit schematic diagram of a bypass branch connected to the common-mode loop according to an embodiment of the present application.

[0025] Figure 6 is Figure 5 the equivalent circuit schematic diagram of the circuit schematic diagram shown.

[0026] Figure 7 is a circuit schematic diagram of a bypass branch connected to the common-mode loop according to another embodiment of the present application.

[0027] Figure 8 is Figure 7 the equivalent circuit schematic diagram of the circuit schematic diagram shown.

[0028] Figure 9 is a circuit schematic diagram of a PID voltage connected to the common-mode loop according to an embodiment of the present application.

[0029] Figure 10 is Figure 9 the equivalent circuit schematic diagram of the circuit schematic diagram shown.

[0030] Figure 11It is a circuit schematic diagram in which a breaking branch line is connected to a common-mode loop according to an embodiment of the present application.

[0031] Figure 12 is the present application Figure 11 The equivalent circuit schematic diagram of the circuit schematic diagram shown.

[0032] Figure 13 It is a circuit schematic diagram in which a breaking branch line is connected to a common-mode loop according to another embodiment of the present application.

[0033] Figure 14 is the present application Figure 13 The equivalent circuit schematic diagram of the circuit schematic diagram shown.

[0034] Figure 15 It is a circuit schematic diagram in which a breaking branch line in the present application is connected between the bus negative and the signal ground. Detailed implementation manners

[0035] Next, in combination with the detailed implementation manners, the present invention will be further described. It should be noted that, on the premise of no conflict, the following described embodiments or technical features can be arbitrarily combined to form new embodiments.

[0036] The terms "comprise" and "have" in the description and claims of the present application and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0037] In the description of the present invention, it should also be noted that, unless otherwise clearly defined and limited, the terms "set", "install", "connected", "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection; it can be directly connected, contact connection or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0038] For the convenience of understanding the following solutions, the present application will be described by a photovoltaic system. As Figure 1 shown, for a typical photovoltaic system in the related art, several PV units pass through the DC / DC circuit, DC / AC circuit of the photovoltaic inverter, and the grid-connected switch group T a 、T b and T cConnected to the power grid. Among them, the common ground impedance of the photovoltaic system includes the capacitor C connected between the positive pole of the PV unit and the ground PV+ , the capacitor C connected between the negative pole of the PV unit and the ground PV- ; the capacitor C connected between the positive bus and the ground dc+ , the resistor R dc+ , the capacitor C connected between the negative bus Bus- and the ground dc- , the resistor R dc- ; and the capacitors C connected between each phase wire on the AC side and the ground a , C b and C c . Through the above-mentioned ground impedance, the insulation of the photovoltaic system is improved and the power loss is reduced, thus ensuring the stable operation of the photovoltaic system. In the photovoltaic system, as Figure 2A and Figure 2B shown, usually after taking power from the bus, a weak power supply is obtained through an isolated DC / DC unit to supply power to communication equipment, monitoring systems, sensors, etc. Among them, as Figure 2A shown, the signal ground can be not connected to the negative bus Bus-. At this time, the inverter needs to meet the basic insulation requirements to ensure sufficient electrical isolation in a high-voltage and high-current environment. Furthermore, the electrical clearance and creepage distance are large, and the switching tube drive circuit needs to be designed according to basic insulation, resulting in an increase in the overall volume and cost of the inverter. As Figure 2B shown, the signal ground can also be connected to the negative bus Bus-. At this time, since the potential difference between the signal ground and the negative bus Bus- is small, the inverter only needs to meet the functional insulation. Furthermore, the electrical clearance and creepage distance are small, and the switching tube drive circuit with the lower bridge arm and the negative bus grounded together does not require electrical isolation. Therefore, the overall volume of the inverter is small and the cost is low, so it is widely used.

[0039] Further, taking a PV unit connected to the power grid through the DC / DC circuit, DC / AC circuit of the photovoltaic inverter, and the grid-connected switch group T a , T b and T c as an example for analysis, it should be understood that the following analysis method is also applicable to the case of multiple PV units. As Figures 3 - 4B shown, the common voltage sampling resistors of the photovoltaic system include the voltage sampling resistors R a , R b and R c connected to each phase wire, the voltage sampling resistor R dc of the bus, and the voltage sampling resistor R PV on the PV side. Each of the above voltage sampling resistors is connected to the signal ground and then to the negative bus Bus-. Specifically, when the inverter is under maintenance, although the grid-connected switch group Ta , T b and T c are disconnected, so as to cut off the connection between the inverter and the grid. However, as Figure 4A shown, there is still a common - mode loop in the photovoltaic system: "the negative bus of the inverter → signal ground → voltage sampling resistors R a , R b , R c → AC - side capacitance to ground C a , C b , C c → ground". Among them, the voltages of the AC - side capacitances to ground C a , C b and C c are respectively denoted as V a , V b and V c . Specifically, and V a , V b and V c are all direct - current voltages. That is to say, the voltages of the AC - side capacitances to ground C a , C b and C c are consistent with the voltage of the negative bus to ground. When the voltage V PV of the PV unit is relatively large, the voltage values of the AC - side capacitances to ground C a , C b and C c are also relatively large, which further leads to higher voltages of the AC - side port voltages v a , v b and v c , and it is easy to cause the risk of electric shock to maintenance personnel.

[0040] Based on the above content, in order to solve or alleviate the problem that a large voltage is generated on the AC side during off - grid maintenance of the inverter, which poses a safety hazard to maintenance personnel, the present application provides a method for suppressing the common - mode voltage of the inverter's AC side to ground. It is applied to the maintenance process of the inverter. A common - mode loop is formed among the negative bus of the inverter Bus -, the signal ground, and the AC - side capacitances to ground C a , C b , C c . It includes: a suppression line connected to the common - mode loop. When the inverter is under maintenance, the suppression line is turned on to clamp the upper limit of the voltage of the negative bus to ground, so as to suppress the voltage of the AC side to ground, so that the AC - side port voltages v a , v b and v c are maintained below the safe voltage for the human body; or the suppression line is disconnected to disconnect the common - mode loop and cut off the AC - side capacitances to ground C a , C b and Cc The charging circuit is used to suppress the voltage of the AC-side-to-ground capacitance, so that the AC port voltage v a 、v b and v c are maintained below the safe voltage for human body, or the voltage difference between the AC-side ports is made zero. By adopting the above method, it is beneficial to ensure the safety of maintenance personnel during the maintenance of the inverter and improve the safety of maintenance operations.

[0041] In some embodiments, as Figures 5 - 8 shown, the suppression circuit includes a bypass branch line disposed between the negative bus Bus- and the ground. Specifically, when the inverter is operating normally, the bypass branch line is disconnected, and the negative bus Bus- is connected to the ground through the resistor R dc- , and is connected to the ground through the capacitor C dc- , thereby playing a protective role for the inverter and being beneficial to the normal operation of the photovoltaic system. When the inverter is being maintained, the bypass branch line is conducted to clamp the upper limit of the voltage of the negative bus Bus- to the ground, so that the voltage of the negative bus Bus- to the ground is 0, or the voltage of the negative bus Bus- to the ground is maintained below the safe voltage for human body, thereby suppressing the voltage of the above-mentioned common-mode circuit to ensure the safety of maintenance personnel.

[0042] In some embodiments, as Figure 5 and Figure 6 shown, the bypass branch line includes a bypass switch S dc- , and the bypass switch S dc- is connected between the negative bus Bus- and the ground. When the inverter is operating normally, the bypass switch S dc- is disconnected, the bypass branch line is not conducted, and the negative bus Bus- is connected to the ground through the resistor R dc- , and is connected to the ground through the capacitor C dc- , thereby playing a protective role for the inverter and enabling the normal operation of the photovoltaic system. When the inverter is being maintained, the bypass switch S dc- is closed, that is, the negative bus Bus- is directly connected to the ground through the bypass branch line, so that the voltage of the negative bus Bus- to the ground is clamped to 0 or approaches 0, so that the AC port voltages v a 、v b and v c can be 0 or approach 0 to ensure the safety of maintenance personnel.

[0043] In some embodiments, as Figure 7 and Figure 8 shown, the bypass branch line further includes a bypass resistor R, and the bypass resistor R is connected in series with the bypass switch S dc- . That is to say, when the inverter is operating normally, the bypass switch S dc- is disconnected, and the bypass branch line is not conducted. When the inverter is being maintained, the bypass switch Sdc- Closed, the negative bus of the bus, Bus-, is connected to the ground through a bypass resistor R, so that the voltage of the negative bus of the bus, Bus-, to the ground is clamped to approach 0 or maintained below the safe voltage for personnel to ensure the safety of maintenance personnel.

[0044] Specifically, at this time, the capacitances C a 、C b and C c between the AC side and the ground have voltages of That is to say, by adjusting the resistance value of the resistor R to the ground, the capacitances C a 、C b and C c between the AC side and the ground can be adjusted. In at least one embodiment, the resistance value of the resistor R is less than that of the resistor R dc+ , preferably, the resistance value of the resistor R is much less than that of the resistor R dc+ , so that the voltages of the capacitances C a 、C b and C c between the AC side and the ground after voltage division are extremely small or even approach 0, further improving the safety of maintenance operations.

[0045] It should be understood that the specific resistance value of the bypass resistor R can be adjusted according to the actual situation of the photovoltaic system and the range of the required safe voltage for personnel. For example, by adjusting the resistance value of the bypass resistor R, the voltage of the negative bus of the bus, Bus-, to the ground is maintained below 12V, or below 6V, or below other voltage values. This application does not make specific limitations on this.

[0046] It is worth mentioning that by setting a bypass switch S dc- and a bypass capacitor R connected in series on the bypass branch, the impact during the closing of the bypass switch S dc- can be reduced, which is beneficial to avoiding damage to electrical components caused by surge current and improving the reliability of the photovoltaic system.

[0047] In some embodiments, as shown in Figure 9 and Figure 10 , the suppression circuit includes a PID power supply arranged between the negative bus of the bus, Bus-, and the ground. When the inverter is being maintained, the output voltage V PID of the PID power supply is adjusted to perform an upper limit clamp on the voltage of the negative bus of the bus, Bus-, to the ground. It should be understood that by setting the output voltage V PID of the PID power supply to 0 or approaching 0, the voltage of the negative bus of the bus, Bus-, to the ground is controlled to be 0 or approach 0, so that the voltages of the capacitances C a 、C b and C c between the AC side and the ground are extremely small or even approach 0, that is, V a =Vb = V c ≈ 0. At this time, the AC port voltages v a , v b and v c are also 0 or approach 0 to ensure the safety of maintenance personnel during inverter maintenance. In addition, the output voltage V PID of the PID power supply can also be set to a voltage value less than the human safety voltage, so that the voltage of the negative bus Bus- to ground is clamped below the human safety voltage to ensure the safety of maintenance personnel.

[0048] It is worth mentioning that when the inverter is operating normally, the PID power supply can be turned off, thus simplifying the structure of the photovoltaic system and helping to avoid power consumption caused by the PID power supply. When the inverter is operating normally, the PID power supply can also be enabled to optimize the output performance of the inverter, so that the inverter maintains a stable output when the load changes on the grid side or the input voltage fluctuates on the photovoltaic side. That is to say, when the inverter is operating normally, the PID power supply can be turned off or still enabled according to the actual situation, and this application does not make specific restrictions on this.

[0049] In some embodiments, as Figures 11 - 15 shown, the suppression circuit includes a breaking branch line, which is arranged between the AC side ground capacitances C a , C b and C c and the negative bus Bus-, or between the AC side ground capacitances C a , C b and C c and the ground. When the inverter is operating normally, the breaking branch line is conducting, so that one ends of the AC side ground capacitances C a , C b , C c are connected to the ground, and the other ends are respectively connected to the signal ground through the voltage sampling resistors R a , R b , R c , and then connected to the negative bus Bus-, enabling the stable operation of the photovoltaic system. When the inverter is being maintained, the branch line is disconnected to cut off the charging circuit of the AC side ground capacitances C a , C b , C c , so that the voltages V a , V b , and V c of the AC side ground capacitances C a , V b , and V c gradually drop to 0 or approach zero, and then the AC port voltages v a , v b and v cCan be 0 or approach 0 to ensure the safety of maintenance personnel.

[0050] In some embodiments, such as Figure 11 and Figure 12 shown, the branch disconnection includes a disconnection switch S1, and the disconnection switch S1 is connected between the AC side ground capacitance C a , C b , C c and the ground. When the inverter is operating normally, the disconnection switch S1 is closed to keep the AC side capacitances C a , C b , C c grounded, thereby ensuring the stable operation of the photovoltaic system. When the inverter is under maintenance, the disconnection switch S1 is opened to disconnect the AC side ground capacitances C a , C b , C c from the ground. That is to say, the common mode loop of "inverter's bus negative Bus-→signal ground→voltage sampling resistors R a , R b , R c →AC side ground capacitances C a , C b , C c →ground" is cut off. Furthermore, the bus negative Bus- cannot charge the AC side ground capacitances C a , C b and C c . And due to the existence of the voltage sampling resistors R a , R b and R c , as well as the dielectric losses of each AC side ground capacitance itself, the voltages V a , C b and C c of the AC side ground capacitances C a , V b and V c gradually decrease until they drop to 0 or approach 0. At this time, the AC port voltages v a , v b and v c are also 0 or approach 0 to ensure the safety of maintenance personnel during inverter maintenance.

[0051] It is worth mentioning that even if the electrical energy in the AC side ground capacitances C a , C b and C c is not released or not fully released, since the bus negative Bus- can no longer charge the AC side ground capacitances C a , C b and C c , therefore, the voltages V of the three AC side ground capacitancesa and V b are the same or approximately the same, so that the voltage difference v c -v a -v b and v b -v c and v c -v a at the AC ports is 0 or approaches 0. In addition, when the disconnect switch S1 is open, the AC side-to-ground capacitors C a and C b and C c are floating, which helps prevent voltage from being conducted to the inverter housing or other parts, thus reducing the risk of electric shock to maintenance personnel; moreover, the voltages V a and C b and C c of the AC side-to-ground capacitors C a and V b and V c do not increase significantly either, enabling the voltages v a and v b and v c to be maintained within a range less than the safe voltage for the human body.

[0052] In at least one embodiment, one end of each of the AC side-to-ground capacitors C a and C b and C c is connected to a phase line respectively, and the other end is connected to the same switch. That is to say, the disconnect switch S1 is implemented as a single switch, and only one switch is needed to disconnect the AC side-to-ground capacitors C a and C b and C c from the ground, thereby improving the synchronization when each AC side-to-ground capacitor is disconnected from the ground, and reducing the number of switching devices, lowering the complexity of the PV system, and simplifying the control of the PV system.

[0053] In at least one embodiment, one end of each of the AC side-to-ground capacitors C a and C b and C c is connected to a phase line respectively, and the other ends are connected to different switches respectively. That is to say, the disconnect switch S1 is implemented as a switch group, and each AC side-to-ground capacitor is separately disconnected from the ground through a switch. It should be understood that when the PV module is operating normally, the current can flow dispersedly through multiple paths, thereby reducing the heat loss and voltage drop caused by excessive current.

[0054] In some embodiments, such as Figures 13 - 15As shown, the disconnection branch line includes a disconnection switch S2, which is connected between the signal ground and the negative bus Bus-. When the inverter is operating normally, the disconnection switch S2 is closed, so that the signal ground and the negative bus Bus- are electrically connected, ensuring the stable operation of the photovoltaic system. When the inverter is being repaired, the disconnection switch S2 is opened, so that the negative bus Bus- is disconnected from the signal ground, causing the AC voltage sampling resistors R a and R b and R c to be disconnected from the negative bus Bus-. That is, the common-mode loop of "negative bus Bus- of the inverter → signal ground → voltage sampling resistors R a and R b and R c → AC side ground capacitors C a and C b and C c → ground" is cut off, and the negative bus Bus- cannot charge the AC side ground capacitors C a and C b and C c . Moreover, due to the existence of the voltage sampling resistors R a and R b and R c , and the dielectric losses of each AC side ground capacitor itself, the voltages V a and V b and V c of the AC side ground capacitors C a and V b and V c gradually decrease until they drop to 0 or approach 0. At this time, the AC port voltages v a and v b and v c are also 0 or approach 0, ensuring the safety of maintenance personnel during inverter repair.

[0055] In some embodiments, the above bypass switch S dc- , disconnection switch S1, and disconnection switch S2 are implemented as relays to achieve a better electrical isolation effect, which is beneficial to avoiding the influence of interference signals on the control circuit and improving the reliability of the photovoltaic system. It should be understood that the above bypass switch S dc- , disconnection switch S1, and disconnection switch S2 can also be implemented as solid-state relays, MOSFETs, etc., and the present application does not make specific limitations on this.

[0056] It is worth mentioning that through the above embodiments, the AC side ground voltage can be effectively suppressed during inverter repair, thereby reducing the risk of electric shock to maintenance personnel and ensuring the safety of maintenance personnel. Moreover, the above embodiments add fewer components, only the bypass switch S dc-, any one of the bypass resistor R, the disconnect switch S1, the disconnect switch S2, and the PID power supply can be used. The implementation method is simple, and the modification to the original photovoltaic system is less, which is beneficial to reducing the transformation cost of the photovoltaic system and is applicable to many scenarios.

[0057] The basic principle, main features, and advantages of the present invention have been described above. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for suppressing the common-mode voltage between the AC side of an inverter and the ground, which is applied to the maintenance process of the inverter. A common-mode loop is formed among the negative bus, signal ground, and the capacitance between the AC side and the ground of the inverter. The method is characterized in that, Comprising: A suppression circuit connected to the common-mode circuit. When the inverter is under maintenance, the suppression circuit is turned on to perform upper-limit clamping on the ground voltage of the negative bus, so as to suppress the AC-side ground voltage; Or the suppression circuit is disconnected to disconnect the common-mode circuit and cut off the charging circuit of the AC-side ground capacitance, so as to suppress the AC-side ground voltage.

2. The method for suppressing the common-mode voltage between the AC side of the inverter and the ground according to claim 1, characterized in that, The suppression circuit includes a bypass branch line disposed between the negative bus and the ground. When the inverter is operating normally, the bypass branch line is disconnected. When the inverter is under maintenance, the bypass branch line is turned on to perform upper-limit clamping on the ground voltage of the negative bus.

3. The method for suppressing the common-mode voltage between the AC side of the inverter and the ground according to claim 2, wherein The bypass branch line includes a bypass switch S dc- , and the bypass switch S dc- is connected between the negative bus and the ground. When the inverter is operating normally, the bypass switch S dc- is disconnected. When the inverter is under maintenance, the bypass switch S dc- is closed to clamp the upper limit of the voltage of the negative bus to the ground.

4. The method for suppressing the common-mode voltage between the AC side of the inverter and the ground according to claim 3, wherein The bypass branch further includes a bypass resistor R, and the bypass resistor R is connected in series with the bypass switch S dc- .

5. The method for suppressing the common-mode voltage between the AC side of the inverter and the ground according to claim 4, characterized in that, The resistance value of resistor R is less than the resistance value of resistor R connected between the positive bus and the ground. dc+ of.

6. The method for suppressing the common-mode voltage between the AC side of the inverter and the ground according to claim 1, characterized in that, The suppression circuit includes a PID power supply disposed between the negative bus and the ground. When the inverter is under maintenance, the output voltage V of the PID power supply is adjusted PID to perform an upper limit clamp on the voltage of the negative bus to the ground.

7. The method for suppressing the common-mode voltage between the AC side of the inverter and the ground according to claim 1, wherein The suppression circuit includes a breaking branch line. The breaking branch line is disposed between the AC-side ground capacitance and the negative bus, or between the AC-side ground capacitance and the ground. When the inverter is operating normally, the breaking branch line is turned on. When the inverter is under maintenance, the branch line is disconnected to cut off the charging circuit of the AC-side ground capacitance.

8. The method for suppressing the common-mode voltage between the AC side of the inverter and the ground according to claim 7, characterized in that, The breaking branch line includes a breaking switch S1. The breaking switch S1 is connected between the AC-side ground capacitance and the ground. When the inverter is operating normally, the breaking switch S1 is closed. When the inverter is under maintenance, the breaking switch S1 is disconnected, so that the connection between the AC-side ground capacitance and the ground is disconnected.

9. The method for suppressing the common-mode voltage between the AC side of the inverter and the ground according to claim 7, wherein, The breaking branch line includes a breaking switch S2. The breaking switch S2 is connected between the signal ground and the negative bus. When the inverter is operating normally, the breaking switch S2 is closed. When the inverter is under maintenance, the breaking switch S2 is disconnected, so that the connection between the AC voltage sampling resistor and the negative bus is disconnected.

10. The method for suppressing the common-mode voltage between the AC side of the inverter and the ground according to any one of claims 3, 4, 5, 8, and 9, characterized in that, Bypass switch S dc- , the disconnect switches S1 and S2 use relays.

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