Protection method and protection system for ANPC type three-level inverter

Abstract

The invention discloses a protection method and protection system for an ANPC type three-level inverter, and the method comprises the steps: determining a current operation period of the ANPC type three-level inverter in response to a shutdown signal of the ANPC type three-level inverter; determining a to-be-controlled target inner tube, a to-be-controlled target outer tube and a to-be-controlled target clamping tube in the ANPC type three-level inverter according to the current operation period; and sequentially performing the operations of turning off the target outer tube, turning on the target inner tube, turning off the target clamping tube and turning off the target inner tube so as to complete the shutdown protection of the ANPC type three-level inverter. Through the orderly turn-off process, especially the method of firstly turning on the inner tube and then turning off the clamping tube, the problem of overpressure of the inner tube caused by sudden change of neutral-point potential can be effectively avoided.

Description

Technical Field

[0001] The present application relates to the technical field of ANPC type three-level inverter and internal tube high frequency modulation, and in particular to a protection method and a protection system for an ANPC type three-level inverter. Background Art

[0002] In the internal tube high-frequency modulation of the prior art, the internal tube high-frequency chopping mode is a configuration scheme of 2 fast tubes and 4 slow tubes, the outer tube and the clamping tube work in the industrial frequency mode, and the inner tube works in the high-frequency mode; the switching loss is concentrated on the inner tube, and the outer tube and the clamping tube only bear part of the conduction loss. Only the inner tube uses a high-speed tube, which can reduce the cost of the inverter module.

[0003] However, when the inverter needs to limit current or shut down wave by wave, a specific shutdown sequence is usually followed to ensure the safety and stability of the equipment. The common shutdown sequence is: first turn off the outer tube to quickly cut off the direct connection with the DC bus and reduce the current flow; then turn off the inner tube to further isolate the midpoint potential from the output end; finally turn off the clamp tube to ensure that the balance of the midpoint potential will not be affected by sudden power failure. However, when the inner tube high-frequency modulation method is used for control, the switching frequency of the inner tube will be higher than that of the outer tube and the clamp tube. In this case, when the shutdown signal is triggered, the inner tube may be turned off while the outer tube remains on. At this time, after the outer tube is turned off, the inner tube is in the off state. If the clamp tube is turned off directly, the inner tube may be subjected to excessive voltage due to the sudden change in the output potential, thereby causing an overvoltage problem. Summary of the invention

[0004] In view of this, the embodiments of the present application provide a protection method and a protection system for an ANPC type three-level inverter, which not only solves the potential problems of the ANPC inverter during wave-by-wave current limiting or shutdown, but also optimizes the safety of the shutdown process.

[0005] According to one aspect of the present application, a protection method for an ANPC type three-level inverter is provided, the method comprising:

[0006] In response to a shutdown signal of the ANPC type three-level inverter, determining a current operation cycle of the ANPC type three-level inverter;

[0007] According to the current operation cycle, determining a target inner tube, a target outer tube and a target clamping tube to be controlled in the ANPC type three-level inverter;

[0008] The operations of shutting down the target outer tube, opening the target inner tube, shutting down the target clamping tube, and shutting down the target inner tube are sequentially performed to complete the shutdown protection of the ANPC type three-level inverter.

[0009] In an optional implementation, the shutdown signal includes a wave-by-wave current limiting signal and a shutdown signal.

[0010] In an optional implementation manner, the determining a current operation cycle of the ANPC type three-level inverter includes:

[0011] According to the currently turned-on external tubes of the ANPC type three-level inverter, a current operation cycle of the ANPC type three-level inverter is determined.

[0012] In an optional implementation, the ANPC type three-level inverter includes an outer tube T1, an inner tube T2, an inner tube T3, an outer tube T4, a clamping tube T5, and a clamping tube T6;

[0013] The determining, according to the currently turned-on external tube of the ANPC type three-level inverter, the current operation cycle of the ANPC type three-level inverter comprises:

[0014] If the currently turned-on external tube is T1, it is determined that the current operation cycle of the ANPC type three-level inverter is a positive half cycle;

[0015] If the currently turned-on external tube is T4, it is determined that the current operation cycle of the ANPC type three-level inverter is a negative half cycle.

[0016] In an optional implementation manner, determining the target inner tube, target outer tube, and target clamping tube to be controlled in the ANPC type three-level inverter according to the current operation cycle includes:

[0017] If the current operation cycle is a positive half cycle, the outer tube T1 is determined as the target outer tube, the inner tubes T2 and T3 are determined as the target inner tubes, and the clamp tube T6 is determined as the target clamp tube;

[0018] If the current operation cycle is a negative half cycle, the outer tube T4 is determined as the target outer tube, the inner tubes T3 and T2 are determined as the target inner tubes, and the clamping tube T5 is determined as the target clamping tube.

[0019] In an optional implementation, the operations of shutting down the target outer tube, opening the target inner tube, shutting down the target clamping tube, and shutting down the target inner tube are sequentially performed to complete the shutdown protection of the ANPC type three-level inverter, including:

[0020] Turning off the target outer tube and timing the delay time;

[0021] After the delay time t0, the target inner tube is opened and the delay time is re-timed;

[0022] After the delay time t1, the target clamping tube is turned off and the delay time is restarted;

[0023] After the delay time t2, the target internal tube is turned off to complete the shutdown protection of the ANPC type three-level inverter.

[0024] According to another aspect of the present application, a protection system for an ANPC type three-level inverter is provided, comprising:

[0025] ANPC type three-level inverter and controller, wherein the controller is used for:

[0026] receiving a stop signal of the ANPC type three-level inverter, and determining a current operation cycle of the ANPC type three-level inverter in response to the stop signal of the ANPC type three-level inverter;

[0027] According to the current operation cycle, determining a target inner tube, a target outer tube and a target clamping tube to be controlled in the ANPC type three-level inverter;

[0028] The operations of shutting down the target outer tube, opening the target inner tube, shutting down the target clamping tube, and shutting down the target inner tube are sequentially performed to complete the shutdown protection of the ANPC type three-level inverter.

[0029] In an embodiment of the present application, optionally, the shutdown signal includes a wave-by-wave current limiting signal and a shutdown signal.

[0030] In the embodiment of the present application, optionally, the controller is further used to:

[0031] According to the currently turned-on external tubes of the ANPC type three-level inverter, a current operation cycle of the ANPC type three-level inverter is determined.

[0032] In the embodiment of the present application, optionally, the ANPC type three-level inverter includes an outer tube T1, an inner tube T2, an inner tube T3, an outer tube T4, a clamping tube T5, and a clamping tube T6;

[0033] The controller is further configured to:

[0034] If the currently turned-on external tube is T1, it is determined that the current operation cycle of the ANPC type three-level inverter is a positive half cycle;

[0035] If the currently turned-on external tube is T4, it is determined that the current operation cycle of the ANPC type three-level inverter is a negative half cycle.

[0036] In the embodiment of the present application, optionally, the controller is further used to:

[0037] If the current operation cycle is a positive half cycle, the outer tube T1 is determined as the target outer tube, the inner tubes T2 and T3 are determined as the target inner tubes, and the clamp tube T6 is determined as the target clamp tube;

[0038] If the current operation cycle is a negative half cycle, the outer tube T4 is determined as the target outer tube, the inner tubes T3 and T2 are determined as the target inner tubes, and the clamping tube T5 is determined as the target clamping tube.

[0039] In the embodiment of the present application, optionally, the controller is further used to:

[0040] Turning off the target outer tube and timing the delay time;

[0041] After the delay time t0, the target inner tube is opened and the delay time is re-timed;

[0042] After the delay time t1, the target clamping tube is turned off and the delay time is restarted;

[0043] After the delay time t2, the target internal tube is turned off to complete the shutdown protection of the ANPC type three-level inverter.

[0044] According to another aspect of the present application, a storage medium is provided, on which a computer program is stored. When the program is executed by a processor, the protection method of the ANPC type three-level inverter is implemented.

[0045] According to another aspect of the present application, a computer device is provided, including a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor, wherein the processor implements the above-mentioned ANPC type three-level inverter protection method when executing the program.

[0046] By means of the above technical solution, an ANPC type three-level inverter protection method and protection system provided in an embodiment of the present application can effectively avoid the problem of inner tube overvoltage caused by a sudden change in output terminal potential by sequentially executing the orderly switching process of shutting down the target outer tube, opening the target inner tube, shutting down the target clamping tube, and shutting down the target inner tube, especially the method of first opening the inner tube and then shutting down the clamping tube. Moreover, following such a shutdown sequence can reduce unnecessary stress on key components, extend equipment life, and reduce maintenance costs and failure rates.

[0047] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0049] Figure 1 A schematic diagram of a flow chart of a protection method for an ANPC type three-level inverter provided in an embodiment of the present application is shown;

[0050] Figure 2 A schematic diagram of the structure of an ANPC type three-level inverter topology provided in an embodiment of the present application is shown;

[0051] Figure 3 A schematic diagram of a flow chart of a protection method for an ANPC type three-level inverter provided in an embodiment of the present application is shown;

[0052] Figure 4 A protection control logic diagram of an ANPC type three-level inverter provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0053] The present application will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0054] In this embodiment, a protection method for an ANPC type three-level inverter is provided. Figure 1 As shown, the method includes:

[0055] Step 101: In response to a shutdown signal of an ANPC type three-level inverter, determine a current operation cycle of the ANPC type three-level inverter.

[0056] Step 102: Determine a target inner tube, a target outer tube, and a target clamping tube to be controlled in the ANPC type three-level inverter according to the current operation cycle.

[0057] Step 103 , sequentially executing the operations of shutting down the target outer tube, opening the target inner tube, shutting down the target clamping tube, and shutting down the target inner tube to complete the shutdown protection of the ANPC type three-level inverter.

[0058] In the embodiment of the present application, when the shutdown signal of the ANPC type three-level inverter is received, the current operation cycle of the inverter is first detected and determined to ensure that the subsequent operation can be synchronized with the working state of the inverter, thereby achieving safe and effective shutdown. Then, according to the determined current operation cycle, the specific devices that need to be controlled are identified, namely the target inner tube, the target outer tube and the target clamp tube, to ensure that the action of each switch is targeted, to avoid misoperation and redundant control, wherein the switch tubes of the ANPC type three-level inverter in the embodiment of the present application include but are not limited to IGBT, SICMOSFET, MOSFET, etc., and the topology is not limited to ANPC and split ANPC. Finally, the shutdown control operation of the inverter is performed. Specifically, the target outer tube is first turned off to quickly cut off the connection of the DC bus and reduce the current flow. Then the target inner tube is turned on to provide a current path to prevent the output terminal potential from suddenly changing and causing the inner tube to overvoltage due to the clamp tube being turned off immediately after the outer tube is turned off. Then the target clamp tube is turned off. Before that, keeping the inner tube turned on can ensure that even if the clamp tube is turned off, it will not cause overvoltage to the inner tube. Finally, the target inner tube is turned off because the collector potential of the inner tube is clamped to 0 level after it is turned on, and a current path is provided at the same time, so the closing of the inner tube will not cause abnormal voltage increase. This technical solution not only solves the potential problems of ANPC inverters during wave-by-wave current limiting or shutdown, but also optimizes the safety of the shutdown process.

[0059] By applying the technical solution of this embodiment, through this orderly shutdown process, especially the method of opening the inner tube first and then shutting down the clamping tube, the inner tube overvoltage problem caused by sudden potential changes can be effectively avoided, and the unstable factors that may be caused by incorrect shutdown sequence can be reduced. And following such a shutdown sequence can reduce unnecessary stress on key components, extend the life of the equipment, and reduce maintenance costs and failure rates.

[0060] In an embodiment of the present application, optionally, the shutdown signal includes a wave-by-wave current limiting signal and a shutdown signal.

[0061] In the embodiment of the present application, optionally, determining the current operation cycle of the ANPC type three-level inverter includes: determining the current operation cycle of the ANPC type three-level inverter according to a currently turned-on external tube of the ANPC type three-level inverter.

[0062] In this embodiment, determining the current operating cycle of the ANPC type three-level inverter is achieved by analyzing the state of its currently turned-on external tube. This method allows the system to accurately identify which specific working stage the inverter is in, so that subsequent protection measures can be performed more accurately. The following is a detailed explanation of this process and its impact on the technical solution: Since the external tubes are directly connected to the high and low potentials of the DC bus and control the main current path, their states can directly reflect the current working mode or cycle of the inverter. For example, in different working cycles, different combinations of external tubes will be activated to generate the required output waveform. By monitoring which external tubes are turned on, the operating cycle of the inverter can be inferred based on this information. Specifically, a mapping table from the external tube turn-on state to the specific operating cycle can be established, so that once a specific external tube state is detected, the corresponding operating cycle can be quickly determined to quickly locate and respond to the shutdown signal. Determining the current operating cycle in this way can make the protection mechanism act more accurately on the correct switch component and avoid the possibility of misoperation.

[0063] In the embodiment of the present application, optionally, Figure 2 As shown, the ANPC three-level inverter includes an outer tube T1, an inner tube T2, an inner tube T3, an outer tube T4, a clamping tube T5, and a clamping tube T6; the determining the current operation cycle of the ANPC three-level inverter according to the currently turned-on outer tube of the ANPC three-level inverter includes: if the currently turned-on outer tube belongs to a positive half cycle, then determining that the current operation cycle of the ANPC three-level inverter is a positive half cycle; if the currently turned-on outer tube belongs to a negative half cycle, then determining that the current operation cycle of the ANPC three-level inverter is a negative half cycle.

[0064] In this embodiment, the ANPC type three-level inverter is divided into an outer tube T1, an inner tube T2 and a clamping tube T6 corresponding to the positive half cycle, and an outer tube T4, an inner tube T3 and a clamping tube T5 corresponding to the negative half cycle. If the outer tube (i.e., T1) belonging to the positive half cycle is currently turned on, it can be determined that the ANPC type three-level inverter is currently in the operation cycle of the positive half cycle. If the outer tube (i.e., T4) belonging to the negative half cycle is currently turned on, it can be determined that the ANPC type three-level inverter is currently in the operation cycle of the negative half cycle. In order to select the most appropriate protection strategy based on the current operation cycle, for example, different shutdown sequences are adopted during the positive half cycle or the negative half cycle to ensure safety.

[0065] In the embodiment of the present application, optionally, determining the target inner tube, target outer tube and target clamping tube to be controlled in the ANPC three-level inverter according to the current operating cycle includes: if the current operating cycle is a positive half cycle, determining the outer tube T1 as the target outer tube, determining the inner tube T2 and the inner tube T3 as the target inner tube, and determining the clamping tube T6 as the target clamping tube; if the current operating cycle is a negative half cycle, determining the outer tube T4 as the target outer tube, determining the inner tube T3 and the inner tube T2 as the target inner tube, and determining the clamping tube T5 as the target clamping tube.

[0066] In this embodiment, when determining the target inner tube, target outer tube and target clamping tube to be controlled in the ANPC type three-level inverter according to the current operation cycle, the following rules should be followed: if the current operation cycle is a positive half-cycle operation cycle, the target outer tube is T1 (used to connect the DC bus high potential), the target inner tube is T2 (located between the midpoint potential and the outer tube T1), and the target clamping tube is T6 (responsible for controlling the midpoint potential balance). If the current operation cycle is a negative half-cycle operation cycle, the target outer tube is T4 (used to connect the DC bus low potential), the target inner tube is T3 (located between the midpoint potential and the outer tube T4), and the target clamping tube is T5 (responsible for controlling the midpoint potential balance). In this way, it can be ensured that the operation of each switch strictly corresponds to the current working state, thereby achieving more accurate and safe control. This not only improves the response speed and accuracy of the system, but also enhances the overall safety and stability.

[0067] In an embodiment of the present application, optionally, the operations of shutting down the target outer tube, turning on the target inner tube, shutting down the target clamping tube, and shutting down the target inner tube are sequentially performed to complete the shutdown protection of the ANPC type three-level inverter, including: shutting down the target outer tube and timing the delay time; after the delay time t0, turning on the target inner tube and re-timing the delay time; after the delay time t1, shutting down the target clamping tube and re-timing the delay time; after the delay time t2, shutting down the target inner tube to complete the shutdown protection of the ANPC type three-level inverter.

[0068] In this embodiment, if Figure 3 and Figure 4As shown, when performing shutdown control, first turn off the target outer tube, quickly cut off the connection of the DC bus, reduce the current flow, and start the timing of the delay time t0 immediately after turning off the outer tube. After the delay time t0 is over, open the target inner tube to provide a current path to prevent the sudden change of the output potential from affecting other components. After opening the inner tube, start the timing of the delay time t1 again. After the delay time t1 is over, turn off the target clamping tube. To ensure that the clamping tube is completely turned off, start the timing of the delay time t2 again after turning off the clamping tube. After the delay time t2 is over, finally turn off the target inner tube to complete the entire shutdown protection process. The embodiment of the present application can effectively reduce the sudden interruption of current through staged operation, especially turning off the outer tube first and then turning on the inner tube, thereby avoiding the generation of excessively high voltage stress. By gradually adjusting the switch state instead of shutting down all at once, the impact of the power system can be significantly reduced. Introducing an appropriate delay time between each operation makes it possible to more accurately control the action sequence of each switch and improve the stability of the overall operation. The delayed shut-off time of the inner tube ensures a smooth transition of the output terminal potential and reduces the stress on the inner tube and other components.

[0069] Further, as Figure 1 The specific implementation of the method, the embodiment of the present application provides a protection system for an ANPC type three-level inverter, including:

[0070] ANPC type three-level inverter and controller, wherein the controller is used for:

[0071] receiving a stop signal of the ANPC type three-level inverter, and determining a current operation cycle of the ANPC type three-level inverter in response to the stop signal of the ANPC type three-level inverter;

[0072] According to the current operation cycle, determining a target inner tube, a target outer tube and a target clamping tube to be controlled in the ANPC type three-level inverter;

[0073] The operations of shutting down the target outer tube, opening the target inner tube, shutting down the target clamping tube, and shutting down the target inner tube are sequentially performed to complete the shutdown protection of the ANPC type three-level inverter.

[0074] In an embodiment of the present application, optionally, the shutdown signal includes a wave-by-wave current limiting signal and a shutdown signal.

[0075] In the embodiment of the present application, optionally, the controller is further used to:

[0076] According to the currently turned-on external tubes of the ANPC type three-level inverter, a current operation cycle of the ANPC type three-level inverter is determined.

[0077] In the embodiment of the present application, optionally, the ANPC type three-level inverter includes an outer tube T1, an inner tube T2, an inner tube T3, an outer tube T4, a clamping tube T5, and a clamping tube T6;

[0078] The controller is further configured to:

[0079] If the current open external tube belongs to the positive half cycle, then determine that the current operation cycle of the ANPC type three-level inverter is the positive half cycle;

[0080] If the current opening of the external tube belongs to the negative half cycle, it is determined that the current operation cycle of the ANPC type three-level inverter is the negative half cycle.

[0081] In the embodiment of the present application, optionally, the controller is further used to:

[0082] If the current operation cycle is a positive half cycle, the outer tube T1 is determined as the target outer tube, the inner tubes T2 and T3 are determined as the target inner tubes, and the clamp tube T6 is determined as the target clamp tube;

[0083] If the current operation cycle is a negative half cycle, the outer tube T4 is determined as the target outer tube, the inner tubes T3 and T2 are determined as the target inner tubes, and the clamping tube T5 is determined as the target clamping tube.

[0084] In the embodiment of the present application, optionally, the controller is further used to:

[0085] Turning off the target outer tube and timing the delay time;

[0086] After the delay time t0, the target inner tube is opened and the delay time is re-timed;

[0087] After the delay time t1, the target clamping tube is turned off and the delay time is restarted;

[0088] After the delay time t2, the target internal tube is turned off to complete the shutdown protection of the ANPC type three-level inverter.

[0089] It should be noted that for other corresponding descriptions of the functional units involved in the protection system of an ANPC type three-level inverter provided in the embodiment of the present application, reference can be made to Figures 1 to 3 The corresponding description in the method will not be repeated here.

[0090] The processor involved in each embodiment provided in this application may be a general-purpose processor, a digital signal processor, a programmable logic device, etc., but is not limited thereto.

[0091] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0092] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A protection method for an ANPC type three-level inverter, characterized in that: The method comprises: In response to a shutdown signal of the ANPC type three-level inverter, determining a current operation cycle of the ANPC type three-level inverter; According to the current operation cycle, determining a target inner tube, a target outer tube and a target clamping tube to be controlled in the ANPC type three-level inverter; The operations of shutting down the target outer tube, opening the target inner tube, shutting down the target clamping tube, and shutting down the target inner tube are sequentially performed to complete the shutdown protection of the ANPC type three-level inverter.

2. The method according to claim 1, characterized in that The shutdown signal includes a wave-by-wave current limiting signal and a shutdown signal.

3. The method according to claim 1, characterized in that Determining the current operation cycle of the ANPC type three-level inverter includes: According to the currently turned-on external tubes of the ANPC type three-level inverter, a current operation cycle of the ANPC type three-level inverter is determined.

4. The method according to claim 3, characterized in that: The ANPC type three-level inverter includes an outer tube T1, an inner tube T2, an inner tube T3, an outer tube T4, a clamping tube T5, and a clamping tube T6; The determining, according to the currently turned-on external tube of the ANPC type three-level inverter, the current operation cycle of the ANPC type three-level inverter comprises: If the currently turned-on external tube is T1, it is determined that the current operation cycle of the ANPC type three-level inverter is a positive half cycle; If the currently turned-on external tube is T4, it is determined that the current operation cycle of the ANPC type three-level inverter is a negative half cycle.

5. The method according to claim 4, characterized in that The step of determining a target inner tube, a target outer tube, and a target clamping tube to be controlled in the ANPC type three-level inverter according to the current operation cycle includes: If the current operation cycle is a positive half cycle, the outer tube T1 is determined as the target outer tube, the inner tubes T2 and T3 are determined as the target inner tubes, and the clamp tube T6 is determined as the target clamp tube; If the current operation cycle is a negative half cycle, the outer tube T4 is determined as the target outer tube, the inner tubes T3 and T2 are determined as the target inner tubes, and the clamping tube T5 is determined as the target clamping tube.

6. The method according to any one of claims 1 to 5, characterized in that The operations of sequentially shutting down the target outer tube, opening the target inner tube, shutting down the target clamping tube, and shutting down the target inner tube to complete the shutdown protection of the ANPC type three-level inverter include: Turning off the target outer tube and timing the delay time; After the delay time t0, the target inner tube is opened and the delay time is re-timed; After the delay time t1, the target clamping tube is turned off and the delay time is restarted; After the delay time t2, the target internal tube is turned off to complete the shutdown protection of the ANPC type three-level inverter.

7. A protection system for an ANPC type three-level inverter, characterized in that: include: ANPC type three-level inverter and controller, wherein the controller is used for: receiving a stop signal of the ANPC type three-level inverter, and determining a current operation cycle of the ANPC type three-level inverter in response to the stop signal of the ANPC type three-level inverter; According to the current operation cycle, determining a target inner tube, a target outer tube and a target clamping tube to be controlled in the ANPC type three-level inverter; The operations of shutting down the target outer tube, opening the target inner tube, shutting down the target clamping tube, and shutting down the target inner tube are sequentially performed to complete the shutdown protection of the ANPC type three-level inverter.

8. The system according to claim 7, characterized in that The shutdown signal includes a wave-by-wave current limiting signal and a shutdown signal.

9. The system according to claim 7, characterized in that The controller is further used for: According to the currently turned-on external tubes of the ANPC type three-level inverter, a current operation cycle of the ANPC type three-level inverter is determined.

10. The system according to claim 7, characterized in that The controller is further used for: Turning off the target outer tube and timing the delay time; After the delay time t0, the target inner tube is opened and the delay time is re-timed; After the delay time t1, the target clamping tube is turned off and the delay time is restarted; After the delay time t2, the target internal tube is turned off to complete the shutdown protection of the ANPC type three-level inverter.

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