A topology and control method for a fault-tolerant bridge arm multiplexed MMC

Abstract

This invention belongs to the technical field of modular multilevel converters, and relates to a fault-tolerant bridge arm multiplexing MMC topology and control method. It includes a three-phase four-bridge arm converter and an AC-side fault-tolerant unit topology. Each phase four-bridge arm converter and AC-side fault-tolerant unit topology includes a bridge arm unit, a switching unit, an AC-side fault-tolerant unit, and a controller. The bridge arm unit includes an upper bridge arm, a first multiplexed bridge arm, a second multiplexed bridge arm, and a lower bridge arm connected in series. The switching unit includes three bridge arm switching switches connected in parallel. The AC-side fault-tolerant unit includes a full-bridge submodule connected in series. The controller controls the on / off state of each bridge arm switching switch, allowing each multiplexed bridge arm to connect to the upper or lower bridge arm, changing the operating mode of the upper and lower bridge arms. When a bridge arm unit or switching unit fails, DC-side voltage support control and AC-side waveform reshaping control are performed based on the operating modes of the upper and lower bridge arms.

Description

Technical Field

[0001] This invention relates to the field of modular multilevel converter technology, and in particular to a fault-tolerant bridge arm multiplexing MMC topology and control method. Background Technology

[0002] With the acceleration of the global energy transition, offshore wind power has become a strategic focus for renewable energy development due to its abundant and clean resources. Flexible high-voltage direct current (HVDC) transmission technology based on voltage source converters (VSCs) is widely recognized as the optimal solution for grid connection of large-scale offshore wind farms due to its outstanding advantages such as independent control of active and reactive power, no need for grid commutation, and ease of constructing multi-terminal DC grids. Among them, modular multilevel converters (MMCs) have become the mainstream topology in the field of flexible DC transmission due to their low output voltage harmonic content, low switching frequency, and strong scalability.

[0003] Traditional half-bridge MMCs consist of two arms per phase, with each arm composed of numerous cascaded half-bridge sub-modules (HBSMs) and an arm reactor connected in series. However, their application in offshore wind power scenarios presents two major drawbacks: 1. The harsh operating environment of offshore platforms, characterized by high humidity, high salinity, and strong corrosion, exacerbates the failure rate of offshore MMC devices. Furthermore, high-voltage, high-capacity MMCs contain thousands of sub-modules, resulting in significant weight and volume, and the large number of sub-module devices further increases the risk of MMC failure. 2. The construction difficulty and cost of offshore converter station platforms are directly related to their size and weight. While arm-reuse MMCs can effectively save on sub-module capacitors, thereby reducing the weight and volume of the MMC converter station, the additional devices and control logic added by the reuse mechanism lead to a more severe failure rate compared to conventional MMCs, highlighting reliability issues.

[0004] In summary, traditional MMCs have problems with large weight and size and high failure rate when used in offshore wind power scenarios. While the bridge arm reusable MMC reduces the weight and size of the MMC, its failure rate is higher than that of the traditional MMC. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problems of large weight and volume and high failure rate of traditional MMC when used in offshore wind power scenarios, while the bridge arm reusable MMC reduces the weight and volume of MMC, but has a higher failure rate than traditional MMC.

[0006] To address the aforementioned technical problems, this invention provides a fault-tolerant bridge arm multiplexing MMC topology, comprising a three-phase four-bridge arm converter and an AC-side fault-tolerant unit topology, wherein each phase four-bridge arm converter and AC-side fault-tolerant unit topology includes:

[0007] The bridge arm unit includes an upper bridge arm, a first multiplexed bridge arm, a second multiplexed bridge arm, and a lower bridge arm connected in series. The input terminal of the upper bridge arm is connected to the positive DC bus, and the output terminal of the lower bridge arm is connected to the negative DC bus. Each bridge arm consists of... N / 3 It consists of a series of half-bridge sub-modules. N This indicates the total number of half-bridge sub-modules within the upper or lower bridge arm and the first and second multiplexed bridge arms;

[0008] The switching unit includes three bridge arm switching switches connected in parallel; wherein, the first end of each of the three bridge arm switching switches is connected to the AC bus via an AC side fault-tolerant unit, the second end of the first bridge arm switching switch is connected to the connection between the upper bridge arm and the first multiplex bridge arm, the second end of the second bridge arm switching switch is connected to the connection between the first multiplex bridge arm and the second multiplex bridge arm, and the second end of the third bridge arm switching switch is connected to the connection between the second multiplex bridge arm and the lower bridge arm;

[0009] AC-side fault-tolerant unit, including N / 3 A series of full-bridge sub-modules; wherein, the first end of the series-connected full-bridge sub-module is connected to the AC bus, and the second end is connected to the first end of the three bridge arm switching switches;

[0010] The controller controls the switching of each bridge arm to allow each multiplexed bridge arm to connect to the upper or lower bridge arm, thereby changing the operating mode of the upper and lower bridge arms. When a bridge arm unit or switching unit fails, the controller performs DC-side voltage support control and AC-side waveform reshaping control based on the operating modes of the upper and lower bridge arms, so that the output of the four-bridge arm converter and the AC-side fault-tolerant unit topology is the same as the output when there is no fault.

[0011] Preferably, the controller controls the on / off state of each bridge arm switching switch to connect each multiplexed bridge arm to the upper or lower bridge arm, thereby changing the operating mode of the upper and lower bridge arms and realizing the normal operation of the fault-tolerant bridge arm multiplexing MMC, including:

[0012] The theoretical number of half-bridge submodules in the upper arm and the theoretical number of half-bridge submodules in the lower arm are calculated using the nearest level approximation modulation method.

[0013] When the theoretical number of half-bridge submodules deployed on the upper bridge arm is less than or equal to N / 3 And the theoretical number of half-bridge sub-modules deployed in the lower bridge arm is greater than or equal to 2N / 3When the first bridge arm switching switch is closed, the remaining two bridge arm switching switches are opened, so that the upper bridge arm can operate independently. The first multiplexed bridge arm, the second multiplexed bridge arm and the lower bridge arm are connected in series to form an equivalent lower bridge arm. The upper bridge arm is in normal mode and the lower bridge arm is in multiplexed mode.

[0014] When the theoretical number of half-bridge submodules deployed on the upper bridge arm is greater than or equal to N / 3 And the theoretical number of half-bridge sub-modules deployed in the lower bridge arm is greater than or equal to N / 3 When the second bridge arm switching switch is closed, the remaining two bridge arm switching switches are opened, so that the first multiplexed bridge arm is connected in series with the upper bridge arm to form an equivalent upper bridge arm, and the second multiplexed bridge arm is connected in series with the lower bridge arm to form an equivalent lower bridge arm. Both the upper and lower bridge arms are in multiplexed mode.

[0015] When the theoretical number of half-bridge submodules deployed on the upper bridge arm is greater than or equal to 2N / 3 And the theoretical number of half-bridge sub-modules deployed in the lower bridge arm is less than or equal to N / 3 When the control is activated, the third bridge arm switching switch is closed, and the remaining two bridge arm switching switches are opened, so that the first multiplexed bridge arm, the second multiplexed bridge arm and the upper bridge arm are connected in series to form an equivalent upper bridge arm, and the lower bridge arm operates independently. The upper bridge arm is in multiplexed mode, and the lower bridge arm is in normal mode.

[0016] Preferably, when a bridge arm unit or switching unit fails, DC-side voltage support control and AC-side waveform reshaping control are performed based on the operating modes of the upper and lower bridge arms to achieve fault-tolerant operation of the fault-tolerant bridge arm multiplexing MMC, including:

[0017] When a half-bridge submodule in the upper bridge arm or equivalent upper bridge arm fails, the lower bridge arm or equivalent lower bridge arm is adjusted to engage a half-bridge submodule to supplement the missing level and achieve DC side voltage support.

[0018] When a half-bridge submodule in the lower bridge arm or equivalent lower bridge arm fails, the upper bridge arm or equivalent upper bridge arm is adjusted to engage a half-bridge submodule to supplement the missing voltage level and achieve DC-side voltage support.

[0019] When the half-bridge submodules in the two multiplexed bridge arms fail simultaneously, the upper bridge arm or equivalent upper bridge arm and the lower bridge arm or equivalent lower bridge arm are adjusted to engage the half-bridge submodules to supplement the missing level and achieve DC side voltage support.

[0020] When the bridge arm switching switch in the switching unit fails, the upper bridge arm or equivalent upper bridge arm and the lower bridge arm or equivalent lower bridge arm are adjusted to engage the half-bridge sub-module to supplement the missing level and achieve DC side voltage support.

[0021] When a half-bridge submodule in the bridge arm unit or a bridge arm switching switch in the switching unit fails, the number of full-bridge submodules in the AC side fault-tolerant unit and the output voltage of the full-bridge submodules are controlled to achieve AC side waveform reshaping.

[0022] Preferably, when a half-bridge submodule within the upper bridge arm or equivalent upper bridge arm fails, the lower bridge arm or equivalent lower bridge arm is adjusted to engage a half-bridge submodule to compensate for the missing voltage level and achieve DC-side voltage support, including:

[0023] When the upper bridge arm is in normal mode and the lower bridge arm is in reuse mode, a half-bridge submodule within the upper bridge arm fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, the control equivalent lower bridge arm is re-engaged. One and a half bridge modules;

[0024] When both the upper and lower bridge arms are in reuse mode, it is equivalent to a half-bridge submodule failure within the upper bridge arm, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, the control equivalent lower bridge arm is re-engaged. One and a half bridge modules;

[0025] When the upper bridge arm is in reuse mode and the lower bridge arm is in normal mode, a half-bridge submodule within the upper bridge arm fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than Control the lower bridge arm to re-engage One and a half bridge modules;

[0026] in, Indicates the number of faulty half-bridge sub-modules within the upper bridge arm; This indicates the number of half-bridge submodules with faults in the equivalent upper bridge arm.

[0027] Preferably, when a half-bridge submodule in the lower bridge arm or equivalent lower bridge arm fails, the upper bridge arm or equivalent upper bridge arm is adjusted to engage a half-bridge submodule to compensate for the missing voltage level and achieve DC-side voltage support, including:

[0028] When the upper bridge arm is in normal mode and the lower bridge arm is in reuse mode, it is equivalent to a half-bridge submodule failure within the lower bridge arm, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than At that time, control the upper bridge arm to re-engage. One and a half bridge modules;

[0029] When both the upper and lower bridge arms are in reuse mode, the equivalent failure of a half-bridge submodule within the lower bridge arm, and the theoretical number of half-bridge submodules in the lower bridge arm, are considered to be... Greater than At that time, control the equivalent upper bridge arm to re-engage. One and a half bridge modules;

[0030] When the upper bridge arm is in reuse mode and the lower bridge arm is in normal mode, a half-bridge submodule within the lower bridge arm fails, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than At that time, control the equivalent upper bridge arm to re-engage. One and a half bridge modules;

[0031] in, Indicates the number of faulty half-bridge sub-modules within the lower bridge arm; This indicates the number of half-bridge submodules with faults within the equivalent lower bridge arm.

[0032] Preferably, when the half-bridge submodules in both multiplexed bridge arms fail simultaneously, the upper bridge arm or equivalent upper bridge arm and the lower bridge arm or equivalent lower bridge arm are adjusted to engage the half-bridge submodules to compensate for the missing voltage level and achieve DC-side voltage support, including:

[0033] When the upper bridge arm is in normal mode and the lower bridge arm is in reuse mode, a half-bridge submodule in the first and second reuse bridge arms fails, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than At that time, control the upper bridge arm to re-engage. One and a half bridge modules;

[0034] When both the upper and lower bridge arms are in reuse mode, a half-bridge submodule in the first and second reused bridge arms fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, the control equivalent lower bridge arm is re-engaged. One and a half bridge modules;

[0035] When both the upper and lower bridge arms are in reuse mode, a half-bridge submodule in the first and second reused bridge arms fails, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than Control equivalent upper bridge arm re-investment One and a half bridge modules;

[0036] When the upper bridge arm is in reuse mode and the lower bridge arm is in normal mode, a half-bridge submodule in the first and second reuse bridge arms fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, control the lower bridge arm to re-engage. One and a half bridge modules;

[0037] in, Indicates the number of half-bridge submodules that have failed within the first multiplexed bridge arm; This indicates the number of half-bridge submodules that are faulty within the second multiplexed bridge arm.

[0038] Preferably, when the bridge arm switching switch in the switching unit fails, the upper bridge arm or equivalent upper bridge arm, and the lower bridge arm or equivalent lower bridge arm are adjusted to engage a half-bridge submodule to supplement the missing voltage level and achieve DC-side voltage support, including:

[0039] When the upper bridge arm is in normal mode and the lower bridge arm is in multiplexing mode, if the first or third bridge arm switch fails, the second bridge arm switch will close. This is based on the theoretical number of half-bridge submodules that can be deployed in the lower bridge arm. Greater than Control equivalent upper bridge arm re-investment One and a half bridge modules;

[0040] When the upper bridge arm is in multiplexing mode and the lower bridge arm is in normal mode, if the first or third bridge arm switch fails, the second bridge arm switch will be closed. This is based on the theoretical number of half-bridge submodules of the equivalent upper bridge arm in operation. Greater than Control equivalent bridge arm re-engagement One and a half bridge modules;

[0041] When both the upper and lower bridge arms are in multiplexing mode, and the second bridge arm switching switch fails, if the theoretical number of half-bridge submodules of the upper bridge arm are engaged... The theoretical number of half-bridge submodules deployed is less than that of the lower bridge arm. The control switch for switching with the first bridge arm is closed, and the control switch for the upper bridge arm is closed. All half-bridge sub-modules are engaged, and then the bridge arm under control is engaged. One and a half bridge sub-modules; if the theoretical number of half bridge sub-modules in the upper bridge arm is [number missing] The theoretical number of half-bridge submodules deployed is greater than that of the lower bridge arm. Control the closing of the third bridge arm switching switch and control the lower bridge arm. All one and a half bridge sub-modules are put into operation, and the control equivalent upper bridge arm is then put into operation. One and a half bridge modules.

[0042] Preferably, when a half-bridge submodule in the bridge arm unit or a bridge arm switching switch in the switching unit fails, the number of full-bridge submodules activated in the AC side fault-tolerant unit and the output voltage of the full-bridge submodules are controlled to achieve AC side waveform reshaping, including:

[0043] When a half-bridge submodule in the upper arm or equivalent upper arm fails, all full-bridge submodules in the AC-side fault-tolerant unit output a negative voltage; when a half-bridge submodule in the lower arm or equivalent lower arm fails, all full-bridge submodules in the AC-side fault-tolerant unit output a positive voltage.

[0044] When the bridge arm switching switch in the switching unit fails, if the upper bridge arm or equivalent upper bridge arm is put into a half-bridge submodule again, the full-bridge submodule in the AC side fault-tolerant unit will output a positive voltage; if the lower bridge arm or equivalent lower bridge arm is put into a half-bridge module again, the full-bridge submodule in the AC side fault-tolerant unit will output a negative voltage.

[0045] When a half-bridge submodule in the bridge arm unit or a bridge arm switching switch in the switching unit fails, the capacitor voltage of the re-engaged half-bridge submodule is superimposed with the capacitor voltage of the missing half-bridge module in the failed bridge arm to obtain the voltage. , 0.5 The quotient of the voltage across the capacitors of the full-bridge submodule is used as the input number of the full-bridge submodule.

[0046] Preferably, if 0.5 If the quotient of the voltage of the capacitor in the full-bridge submodule is not an integer, a rounding function is used to round the calculated quotient to the nearest integer.

[0047] The present invention also provides a control method for a fault-tolerant bridge arm multiplexing MMC, the method being applied to a controller in the aforementioned fault-tolerant bridge arm multiplexing MMC topology, comprising:

[0048] By controlling the on / off state of each bridge arm switching switch, each multiplexed bridge arm can be connected to the upper or lower bridge arm, thereby changing the operating mode of the upper and lower bridge arms.

[0049] When a bridge arm unit or switching unit fails, DC-side voltage support control and AC-side waveform reshaping control are performed based on the operating modes of the upper and lower bridge arms, so that the output of the four-bridge arm converter and the AC-side fault-tolerant unit topology are the same as the output when there is no fault.

[0050] The fault-tolerant bridge arm multiplexing MMC topology provided in this application has the following advantages:

[0051] This application constructs a phase unit topology consisting of three switches, four bridge arms, and a full-bridge submodule connected in series. Through power electronic switch control, the two sets of multiplexed bridge arms and the AC-side fault-tolerant unit can be flexibly scheduled, thus transforming fixed hardware resources into dynamically allocable flexible resources. This achieves redundancy and fault tolerance without significantly increasing the number of components. Specifically, each phase four-bridge-arm converter and AC-side fault-tolerant unit topology is configured with upper and lower bridge arms, two multiplexed bridge arms, three bridge arm switching switches, and an AC-side fault-tolerant unit. Each bridge arm is constructed using cascaded half-bridge submodules, fully utilizing the low cost and low loss advantages of half-bridge submodules. The AC-side fault-tolerant unit uses a full-bridge submodule, utilizing its bidirectional voltage output capability to provide supplementary voltage levels for faults in the upper and lower bridge arm submodules within the MMC, thus imparting a stronger waveform to the MMC. Reconfigurability; While ensuring consistent operational performance of the fault-tolerant bridge arm multiplexing MMC before and after a fault, the controller, based on the three different functions of the bridge arm switching switches in the three-switch, four-bridge arm multiplexing MMC and the various fault types and potential fault numbers existing in the four different types of bridge arms, and using the AC and DC side voltage constraints of the MMC as a foundation, determines the number of full-bridge sub-modules connected in series in the AC side fault-tolerant unit by adjusting the bridge arm switching switches, the number of half-bridge sub-modules in each bridge arm, and the number and polarity of the full-bridge sub-modules, maintaining the constant output level of the DC and AC circuits of the phase unit. This ensures the high reliability and economy of the fault-tolerant bridge arm multiplexing MMC, and compared with the traditional MMC and bridge arm multiplexing MMC in the existing technology, it has the advantages of small size, light weight, and low failure rate. Attached Figure Description

[0052] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0053] Figure 1 A schematic diagram of the topology of the fault-tolerant bridge arm multiplexing MMC provided in this application;

[0054] Figure 2 A schematic diagram of the topology of the a-phase four-arm converter and the AC-side fault-tolerant unit provided in this application;

[0055] Figure 3 This is a schematic diagram of the topology of the half-bridge submodule provided in this application;

[0056] Figure 4 This is a schematic diagram of the bridge arm switching topology provided in this application;

[0057] Figure 5 This is a schematic diagram of the topology of the full-bridge submodule provided in this application;

[0058] Figure 6The fault-tolerant control flowchart provided for this application;

[0059] Explanation of reference numerals in the accompanying drawings: 1. Bridge arm unit; 11. Upper bridge arm; 12. First multiplex bridge arm; 13. Second multiplex bridge arm; 14. Lower bridge arm; 15. Half-bridge submodule; 2. Switching unit; 21. First bridge arm switching switch; 22. Second bridge arm switching switch; 23. Third bridge arm switching switch; 3. AC side fault-tolerant unit; 31. Full-bridge submodule. Detailed Implementation

[0060] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0061] Please see Figure 1 , Figure 1 The diagram shows the topology of the fault-tolerant bridge arm multiplexing MMC provided in this application. The topology of the fault-tolerant bridge arm multiplexing MMC includes a three-phase (a-phase, b-phase, c-phase) four-bridge arm converter and an AC-side fault-tolerant unit topology. The topology of each phase four-bridge arm converter and the AC-side fault-tolerant unit is the same.

[0062] Please see Figure 2 , Figure 2 The diagram shows the topology of a phase four-arm converter and AC side fault-tolerant unit. Each phase four-arm converter and AC side fault-tolerant unit topology includes arm unit 1, switching unit 2, AC side fault-tolerant unit 3 and controller (not shown in the figure).

[0063] Bridge arm unit 1 includes an upper bridge arm 11, a first multiplexed bridge arm 12, a second multiplexed bridge arm 13, and a lower bridge arm 14 connected in series. The input terminal of the upper bridge arm 11 is connected to the positive DC bus, and the output terminal of the lower bridge arm 14 is connected to the negative DC bus. Each bridge arm consists of... N / 3 It consists of 15 half-bridge sub-modules connected in series. N This indicates the total number of half-bridge sub-modules within the upper or lower bridge arm and the first and second multiplexed bridge arms.

[0064] Specifically, the input terminal of the upper bridge arm 11 is connected to the bridge arm inductor. Connected to the positive DC bus, the output terminal of the lower bridge arm 14 is connected to the bridge arm inductor. Connected to the negative DC bus.

[0065] Please see Figure 3 , Figure 3 The diagram shown is a schematic of the half-bridge submodule topology provided in this application. Each half-bridge submodule (HBSM) 15 contains two IGBTs. Two diodes connected in reverse parallel and a capacitor C. By controlling and The trigger signal (1 indicates on, 0 indicates off) enables the HBSM to achieve the following three operating states:

[0066] 1. Activation Status: Trigger signal configured as follows , The current path in this operating state depends on the bridge arm current. The direction when the bridge arm current At that time, current flows through the diode When the bridge arm current At that time, current flows through the conducting upper switching transistor. Output voltage: Bridge arm current through or When capacitor C is charged and discharged, regardless of the direction of the bridge arm current, the output voltage of the HBSM is always... .

[0067] 2. Bypass state: Trigger signal configured as follows , In this operating state, capacitor C is bypassed and does not participate in charging and discharging; when the bridge arm current... At that time, current flows through the diode When the bridge arm current At that time, current flows through the conducting lower switching transistor. Output voltage: Regardless of the direction of the bridge arm current, the output voltage of the HBSM is always the same. .

[0068] 3. Locked State: Trigger signal configured as follows , In this operating state, all active switching transistors are turned off, and the operating state is entirely determined by the direction of the bridge arm current; when the bridge arm current... At this time, current is forced to flow through the diode. The current charges capacitor C, causing its voltage to rise. The HBSM then enters a switched-on state. When the bridge arm current... At this time, current is forced to flow through the diode. HBSM is bypassed; Output voltage: The output voltage is determined by the direction of the current, when the bridge arm current... At that time, the output voltage of HBSM is When the bridge arm current At that time, the output voltage of HBSM is .

[0069] The switching unit 2 includes three bridge arm switching switches connected in parallel. The first ends of each of the three bridge arm switching switches are connected to the AC bus via the AC side fault-tolerant unit 3. The second end of the first bridge arm switching switch 21 is connected to the connection between the upper bridge arm 11 and the first multiplexed bridge arm 12. The second end of the second bridge arm switching switch 22 is connected to the connection between the first multiplexed bridge arm 12 and the second multiplexed bridge arm 13. The second end of the third bridge arm switching switch 23 is connected to the connection between the second multiplexed bridge arm 13 and the lower bridge arm 14.

[0070] Please see Figure 4 , Figure 4 The diagram shown is a schematic of the bridge arm switching topology provided in this application. Each bridge arm switching switch is composed of multiple IGBTs connected in series, and its circuit is divided into two functional stages:

[0071] 1. The switching mechanism consists of two voltage ratings. The two IGBTs are connected in reverse series to ensure that the switch can bidirectionally block current when it is off. It should be noted that the two IGBTs receive the same trigger signal.

[0072] 2. The pressure resistance section consists of (N / 2-1) pressure resistance ratings. The IGBTs are connected in series, and the gates of these IGBTs are connected in parallel with the gates of the IGBTs in the switching circuit, receiving the same trigger signal.

[0073] Working process: When the trigger signal is high, all IGBTs in the switching circuit and the withstand voltage circuit are turned on simultaneously, and the switch exhibits a low resistance state; when the trigger signal is low, all IGBTs are turned off simultaneously. At this time, the switching circuit achieves rapid bidirectional blocking of current, and the withstand voltage circuit shares and bears most of the reverse blocking voltage.

[0074] AC-side fault-tolerant unit 3 includes N / 3 A series of full-bridge submodules 31; wherein, the first end of the series-connected full-bridge submodules 31 is connected to the AC bus, and the second end is connected to the first end of the three bridge arm switching switches.

[0075] Please see Figure 5 , Figure 5 The diagram shown is a schematic of the full-bridge submodule topology provided in this application. Each full-bridge submodule (FBSM) 31 contains four IGBTs. Four reverse parallel diodes And a DC capacitor C. By independently controlling the trigger signals of the four IGBTs, the FBSM can achieve the following four operating states:

[0076] 1. In active state: Trigger signal configured as follows , , , In this state, capacitor C is connected to the circuit and outputs a positive voltage; when the bridge arm current... At that time, current flows through the diode Capacitor C, Diode The capacitor is charged; when the bridge arm current... At that time, current flows through the switching transistor. Capacitor C, Switching transistor The capacitor discharges through the switching transistor; regardless of the current direction, the output voltage of the FBSM is... .

[0077] 2. Negative input state: Trigger signal configured as follows , , , In this state, capacitor C is connected to the circuit in reverse, outputting a negative voltage; when the bridge arm current... When, the current flows through Capacitor C The capacitor discharges through the switching transistor; when the bridge arm current... At that time, current flows through the diode Capacitor C, Diode The capacitor is charged; regardless of the current direction, the output voltage of the FBSM is - It should be noted that this state is a key characteristic that distinguishes FBSM from HBSM, enabling it to output negative levels.

[0078] 3. Bypass state: Trigger signal configured as follows , , , In this state, capacitor C is completely bypassed and does not participate in the charging and discharging process; when the bridge arm current... When, the current flows through , The formed loop flows; when the bridge arm current... When, the current flows through , The formed loop is open; the output voltage of the FBSM is 0.

[0079] 4. Locked-out state: Trigger signal configured as follows , , , In this state, all switches are turned off, and the circuit path is naturally formed by the diode network; when the bridge arm current... At that time, the current was forced to flow through , And charge capacitor C; when the bridge arm current At that time, the current was forced to flow through , And it charges capacitor C; the output voltage of the FBSM is determined by the direction of the current, when the bridge arm current... At that time, the output voltage of the FBSM is When the bridge arm current At that time, the output voltage of the FBSM is .

[0080] The controller is connected to the bridge arm unit 1, the switching unit 2, and the AC side fault-tolerant unit 3. It is used to control the on / off state of each bridge arm switching switch so that the first multiplexed bridge arm 12 or the second multiplexed bridge arm 13 can be connected to the upper bridge arm 11 or the lower bridge arm 14, thereby changing the operating mode of the upper bridge arm 11 and the lower bridge arm 14. When the bridge arm unit 1 or the switching unit 2 fails, DC side voltage support control and AC side waveform reshaping control are performed based on the operating mode of the upper bridge arm 11 and the lower bridge arm 14, so that the output of the four-phase bridge arm converter and the AC side fault-tolerant unit topology is the same as the output when there is no fault.

[0081] Specifically, the controller controls the on / off state of each bridge arm switching switch to connect each multiplexed bridge arm to the upper or lower bridge arm, thereby changing the operating mode of the upper and lower bridge arms and realizing the normal operation of the fault-tolerant bridge arm multiplexing MMC, including steps 1-1 to 1-4:

[0082] Step 1-1: Calculate the theoretical number of half-bridge submodules in the upper arm and the theoretical number of half-bridge submodules in the lower arm using the nearest level approximation modulation method.

[0083] Specifically, when using the nearest level modulation (NLM) method in a conventional MMC, both the upper and lower bridge arms output an N+1 level stepped wave to approximate the sinusoidal modulation wave. The theoretical number of half-bridge submodules in each bridge arm are as follows:

[0084] ,

[0085] ,

[0086] in, This represents the theoretical number of half-bridge sub-modules deployed in the upper bridge arm; This represents the theoretical number of half-bridge sub-modules deployed in the lower bridge arm; This indicates the capacitor voltage of the half-bridge submodule. ; This represents the rounding function; This represents the modulation wave command voltage of the phase unit; This indicates the modulated wave command voltage of the lower bridge arm; This indicates the modulated wave command voltage of the upper bridge arm.

[0087] Furthermore, similar to conventional MMC, fault-tolerant bridge arm multiplexing MMC achieves normal operation by controlling the combination of the on and off states of three bridge arm switching switches. The controller enables the upper and lower bridge arms of the fault-tolerant bridge arm multiplexing MMC to have the same number of half-bridge sub-modules as the upper and lower bridge arms of conventional MMC through the on and off states of the bridge arm switching switches, thus achieving equivalent operation of conventional MMC.

[0088] Specifically, under the control of the trigger signal of the half-bridge submodule, all four bridge arms can output... There are a total of N / 3+1 voltage levels. The upper and lower bridge arms have two operating modes: normal mode and multiplexing mode. In normal mode, the upper and lower bridge arms operate independently. In multiplexing mode, the multiplexing bridge arm is connected to either the upper or lower bridge arm.

[0089] Steps 1-2: When the theoretical number of half-bridge submodules of the upper bridge arm are put into operation... Less than or equal to N / 3 And the theoretical number of half-bridge sub-modules deployed in the lower bridge arm Greater than or equal to 2N / 3 When the first bridge arm switching switch is closed, the remaining two bridge arm switching switches are opened, so that the upper bridge arm operates independently. The first multiplexed bridge arm, the second multiplexed bridge arm and the lower bridge arm are connected in series to form an equivalent lower bridge arm. The upper bridge arm is in normal mode and the lower bridge arm is in multiplexed mode.

[0090] Specifically, the current flow path of the upper bridge arm is as follows: positive DC bus - upper bridge arm - bridge arm switching switch connected to the output terminal of the upper bridge arm - AC side unit - AC bus; the current flow path of the lower bridge arm is as follows: negative DC bus - lower bridge arm - first multiplexed bridge arm - second multiplexed bridge arm - bridge arm switching switch connected to the output terminal of the upper bridge arm - AC side module - AC bus.

[0091] Steps 1-3: When the theoretical number of half-bridge submodules deployed in the upper bridge arm is greater than or equal to... N / 3 And the theoretical number of half-bridge sub-modules deployed in the lower bridge arm is greater than or equal to N / 3 When the second bridge arm switching switch is closed, the remaining two bridge arm switching switches are opened, so that the first multiplexed bridge arm is connected in series with the upper bridge arm to form an equivalent upper bridge arm, and the second multiplexed bridge arm is connected in series with the lower bridge arm to form an equivalent lower bridge arm. Both the upper and lower bridge arms are in multiplexed mode.

[0092] Specifically, the current flow path of the upper bridge arm is as follows: positive DC bus - upper bridge arm - first multiplexed bridge arm - bridge arm switching switch connected to the output terminal of the first multiplexed bridge arm - AC side unit - AC bus; the current flow path of the lower bridge arm is as follows: negative DC bus - lower bridge arm - second multiplexed bridge arm - bridge arm switching switch connected to the output terminal of the first multiplexed bridge arm - AC side module - AC bus.

[0093] Steps 1-4: When the theoretical number of half-bridge submodules deployed in the upper bridge arm is greater than or equal to... 2N / 3 And the theoretical number of half-bridge sub-modules deployed in the lower bridge arm is less than or equal to N / 3 When the control is activated, the third bridge arm switching switch is closed, and the remaining two bridge arm switching switches are opened, so that the first multiplexed bridge arm, the second multiplexed bridge arm and the upper bridge arm are connected in series to form an equivalent upper bridge arm, and the lower bridge arm operates independently. The upper bridge arm is in multiplexed mode, and the lower bridge arm is in normal mode.

[0094] Specifically, the current flow path of the upper bridge arm is as follows: positive DC bus - upper bridge arm - first multiplexed bridge arm - second multiplexed bridge arm - bridge arm switching switch connected to the output terminal of the second multiplexed bridge arm - AC side unit - AC bus; the current flow path of the lower bridge arm is as follows: negative DC bus - lower bridge arm - bridge arm switching switch connected to the output terminal of the second multiplexed bridge arm - AC side module - AC bus.

[0095] Furthermore, when a bridge arm unit or switching unit fails, DC-side voltage support control and AC-side waveform reshaping control are performed based on the operating modes of the upper and lower bridge arms to achieve fault-tolerant operation of the fault-tolerant bridge arm multiplexing MMC, including steps 2-1 to 2-5:

[0096] Step 2-1: When a half-bridge submodule in the upper bridge arm or equivalent upper bridge arm fails, adjust the lower bridge arm or equivalent lower bridge arm to engage a half-bridge submodule to supplement the missing voltage level and achieve DC-side voltage support.

[0097] Step 2-2: When a half-bridge submodule in the lower bridge arm or equivalent lower bridge arm fails, adjust the upper bridge arm or equivalent upper bridge arm to engage a half-bridge submodule to supplement the missing voltage level and achieve DC-side voltage support.

[0098] Steps 2-3: When the half-bridge submodules in the two multiplexed bridge arms fail simultaneously, adjust the upper bridge arm or equivalent upper bridge arm, and the lower bridge arm or equivalent lower bridge arm to engage the half-bridge submodules to supplement the missing level and achieve DC side voltage support.

[0099] Steps 2-4: When the bridge arm switching switch in the switching unit fails, adjust the upper bridge arm or equivalent upper bridge arm, and the lower bridge arm or equivalent lower bridge arm to engage the half-bridge sub-module to supplement the missing level and achieve DC side voltage support.

[0100] Steps 2-5: When a half-bridge submodule in the bridge arm unit or a bridge arm switching switch in the switching unit fails, control the number of full-bridge submodules in the AC side fault-tolerant unit and the output voltage of the full-bridge submodules to achieve AC side waveform reshaping.

[0101] Please see Figure 6 , Figure 6The diagram shown is a fault-tolerant control flowchart of the controller provided in this application. When a device failure occurs in the bridge arm unit or switching unit, the fault-tolerant control strategy is immediately activated to maintain the reliable and high-quality operation of the MMC after the failure. Specifically, the fault-tolerant operation control mainly includes three parts: 1. Fault isolation control; 2. DC side voltage support control; 3. AC side waveform reshaping control.

[0102] Specifically, for a faulty half-bridge submodule within a bridge arm, fault isolation control primarily identifies the faulty half-bridge submodule by real-time monitoring of its capacitor voltage, bridge arm current, and switch status. By removing the switch signal of the faulty half-bridge submodule, a bypass switch at its output port is triggered, preventing bridge arm current from flowing through the faulty half-bridge submodule and thus isolating it. For a faulty bridge arm switching switch within a switching unit, fault isolation control primarily detects the bridge arm current status in real-time, removes the switch signals of the power devices used in the faulty bridge arm switching switch unit, simultaneously opens adjacent bridge arm switching switches to provide a current flow path, and bypasses the faulty bridge arm switching switch, achieving fault isolation.

[0103] Furthermore, the control principle of DC-side voltage support is as follows: based on the number of faults and the operating status of the upper and lower bridge arms, the number of half-bridge sub-modules put into the equivalent upper bridge arm when all the reused bridge arms are connected in series with the upper bridge arm, and the number of half-bridge sub-modules put into the equivalent lower bridge arm when all the reused bridge arms are connected in series with the lower bridge arm, is always equal to N, thereby maintaining the voltage stress of the devices in the remaining non-faulty half-bridge sub-modules consistent with that during normal operation.

[0104] The control principle of AC side waveform reshaping is as follows: based on the adjustment of each bridge arm according to the DC side voltage support control, combined with the AC loop model, the output of the AC side is reconstructed by adjusting the number of full-bridge submodules and the polarity of the full-bridge submodules, so that it is consistent with the output of the AC side under the integrated operation.

[0105] Specifically, when a half-bridge submodule in the upper bridge arm or equivalent upper bridge arm fails, the lower bridge arm or equivalent lower bridge arm is adjusted to engage a half-bridge submodule to compensate for the missing voltage level and achieve DC-side voltage support, including steps 3-1 to 3-3:

[0106] Step 3-1: When the upper bridge arm is in normal mode and the lower bridge arm is in reuse mode, a half-bridge submodule in the upper bridge arm fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, the control equivalent lower bridge arm is re-engaged. One and a half bridge modules.

[0107] Step 3-2: When both the upper and lower bridge arms are in reuse mode, it is equivalent to a half-bridge submodule failure within the upper bridge arm, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, the control equivalent lower bridge arm is re-engaged. One and a half bridge modules.

[0108] Step 3-3: When the upper bridge arm is in reuse mode and the lower bridge arm is in normal mode, a half-bridge submodule in the upper bridge arm fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, control the lower bridge arm to re-engage. One and a half bridge modules.

[0109] in, Indicates the number of faulty half-bridge sub-modules within the upper bridge arm; This indicates the number of half-bridge submodules with faults in the equivalent upper bridge arm.

[0110] Furthermore, when a half-bridge submodule in the lower bridge arm or equivalent lower bridge arm fails, the upper bridge arm or equivalent upper bridge arm is adjusted to engage a half-bridge submodule to compensate for the missing voltage level and achieve DC-side voltage support, including steps 4-1 to 4-3:

[0111] Step 4-1: When the upper bridge arm is in normal mode and the lower bridge arm is in reuse mode, it is equivalent to a half-bridge submodule failure within the lower bridge arm, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than At that time, control the upper bridge arm to re-engage. One and a half bridge modules.

[0112] Step 4-2: When both the upper and lower bridge arms are in reuse mode, the equivalent half-bridge submodule failure in the lower bridge arm is considered, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than At that time, control the equivalent upper bridge arm to re-engage. One and a half bridge modules.

[0113] Step 4-3: When the upper bridge arm is in reuse mode and the lower bridge arm is in normal mode, a half-bridge submodule in the lower bridge arm fails, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than At that time, control the equivalent upper bridge arm to re-engage. One and a half bridge modules.

[0114] in, Indicates the number of faulty half-bridge sub-modules within the lower bridge arm; This indicates the number of half-bridge submodules with faults within the equivalent lower bridge arm.

[0115] Furthermore, when the half-bridge submodules in both multiplexed bridge arms fail simultaneously, the upper bridge arm or equivalent upper bridge arm and the lower bridge arm or equivalent lower bridge arm are adjusted to engage the half-bridge submodules to compensate for the missing voltage level and achieve DC-side voltage support, including steps 5-1 to 5-4:

[0116] Step 5-1: When the upper bridge arm is in normal mode and the lower bridge arm is in reuse mode, a half-bridge submodule in the first and second reuse bridge arms fails, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than At that time, control the upper bridge arm to re-engage. One and a half bridge modules.

[0117] Step 5-2: When both the upper and lower bridge arms are in multiplexing mode, a half-bridge submodule in the first and second multiplexing bridge arms fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, the control equivalent lower bridge arm is re-engaged. One and a half bridge modules.

[0118] Step 5-3: When both the upper and lower bridge arms are in multiplexing mode, a half-bridge submodule in the first and second multiplexing bridge arms fails, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than Control equivalent upper bridge arm re-investment One and a half bridge modules.

[0119] Step 5-4: When the upper bridge arm is in multiplexing mode and the lower bridge arm is in normal mode, a half-bridge submodule in the first and second multiplexing bridge arms fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, control the lower bridge arm to re-engage. One and a half bridge modules.

[0120] in, Indicates the number of half-bridge submodules that have failed within the first multiplexed bridge arm; This indicates the number of half-bridge submodules that are faulty within the second multiplexed bridge arm.

[0121] Furthermore, when the bridge arm switching switch within the switching unit fails, the upper bridge arm or equivalent upper bridge arm, and the lower bridge arm or equivalent lower bridge arm are adjusted to engage a half-bridge submodule to compensate for the missing voltage level and achieve DC-side voltage support, including steps 6-1 to 6-3:

[0122] Step 6-1: When the upper bridge arm is in normal mode and the lower bridge arm is in multiplexing mode, if the first or third bridge arm switching switch fails, the second bridge arm switching switch will be closed. If the theoretical number of half-bridge submodules of the lower bridge arm is [number missing], [further details missing]. Greater than Control equivalent upper bridge arm re-investment One and a half bridge modules.

[0123] Step 6-2: When the upper bridge arm is in multiplexing mode and the lower bridge arm is in normal mode, if the first or third bridge arm switching switch fails, the second bridge arm switching switch will be closed. If the theoretical number of half-bridge submodules of the upper bridge arm is [number missing], [further details missing]. Greater than Control equivalent bridge arm re-engagement One and a half bridge modules.

[0124] Step 6-3: When both the upper and lower bridge arms are in multiplexing mode, and the second bridge arm switching switch fails, if the theoretical number of half-bridge submodules of the upper bridge arm are engaged... The theoretical number of half-bridge submodules deployed is less than that of the lower bridge arm. The control switch for switching with the first bridge arm is closed, and the control switch for the upper bridge arm is closed. All half-bridge sub-modules are engaged, and then the bridge arm under control is engaged. One and a half bridge sub-modules; if the theoretical number of half bridge sub-modules in the upper bridge arm is [number missing] The theoretical number of half-bridge submodules deployed is greater than that of the lower bridge arm. Control the closing of the third bridge arm switching switch and control the lower bridge arm. All one and a half bridge sub-modules are put into operation, and the control equivalent upper bridge arm is then put into operation. One and a half bridge modules.

[0125] Furthermore, when a half-bridge submodule in the bridge arm unit or a bridge arm switching switch in the switching unit fails, the number of full-bridge submodules activated in the AC side fault-tolerant unit and the output voltage of the full-bridge submodules are controlled to achieve AC side waveform reshaping, including steps 7-1 to 7-3:

[0126] Step 7-1: When a half-bridge submodule in the upper arm or equivalent upper arm fails, all full-bridge submodules in the AC side fault-tolerant unit output negative voltage; when a half-bridge submodule in the lower arm or equivalent lower arm fails, all full-bridge submodules in the AC side fault-tolerant unit output positive voltage.

[0127] Step 7-2: When the bridge arm switching switch in the switching unit fails, if the upper bridge arm or equivalent upper bridge arm is put into a half-bridge submodule again, the full-bridge submodule in the AC side fault-tolerant unit will output a positive voltage; if the lower bridge arm or equivalent lower bridge arm is put into a half-bridge submodule again, the full-bridge submodule in the AC side fault-tolerant unit will output a negative voltage.

[0128] Step 7-3: When a half-bridge submodule in the bridge arm unit or a bridge arm switching switch in the switching unit fails, the capacitor voltage of the re-engaged half-bridge submodule is superimposed with the capacitor voltage of the missing half-bridge submodule in the faulty bridge arm to obtain the result. , 0.5 The quotient of the voltage across the capacitors of the full-bridge submodule is used as the input number of the full-bridge submodule.

[0129] Furthermore, in step 7-3 if 0.5 If the quotient of the voltage of the capacitor in the full-bridge submodule is not an integer, a rounding function is used to round the calculated quotient to the nearest integer.

[0130] In summary, this application configures each phase unit with an upper bridge arm, a lower bridge arm, two multiplexed bridge arms, three bridge arm switching switches, and an AC-side fault-tolerant unit composed of full-bridge submodules connected in series. The upper and lower bridge arms, as well as the two multiplexed bridge arms, all employ cascaded half-bridge submodules. The bridge arm switching switch consists of a switching element and a withstand voltage element. The switching element uses a reverse series structure of power electronic switches, while the withstand voltage element uses a series structure of multiple power electronic switches in the same direction. The AC-side fault-tolerant unit is located at the AC output of each phase unit and uses a full-bridge submodule. This topology fully utilizes the low cost and low loss of the half-bridge submodules to maintain the AC and DC power transmission efficiency during normal MMC operation. Simultaneously, it leverages the bidirectional voltage output capability of the full-bridge submodules to provide supplementary voltage levels for faults in the upper and lower bridge arm submodules within the MMC, giving the MMC strong waveform reshaping capabilities. Meanwhile, to ensure the high reliability and economy of the fault-tolerant bridge arm multiplexing MMC, the configuration of the number of full-bridge submodules in its AC side module is based on the following: Under the premise of ensuring consistent operational performance of the fault-tolerant bridge arm multiplexing MMC before and after a fault, and considering the various fault types and potential fault numbers present in the three-switch, four-bridge arm multiplexing MMC with three different functions and four different types of bridge arms, based on the AC and DC side voltage constraints of the MMC and the principle of maintaining constant output levels in the DC and AC circuits of the phase unit, the number of full-bridge submodules connected in series in each AC submodule is determined to be N / 3. Furthermore, to fully utilize the capabilities of the above fault-tolerant topology, the corresponding fault-tolerant control method is as follows:

[0131] 1. Isolation control between each operating bridge arm and the changeover switch

[0132] To address faults in power electronic switches (IGBTs, diodes) and their drivers, capacitors, and other power devices within submodules of the upper and lower bridge arms, as well as power electronic switches within the switching switches, a rapid switching strategy for operating bridge arms and switching switches is proposed. This strategy can quickly disconnect a bridge arm or switching switch from the system upon detecting a fault, isolating the faulty submodule or switching switch and reducing the impact of the fault on other healthy units and devices, thus preventing cascading damage and system downtime in the MMC system.

[0133] 2. DC-side voltage support control

[0134] Bypassing faulty submodules in the upper and lower bridge arms and the two multiplexed bridge arms, as well as disconnecting the fault switching switch, reduces the output capability of the fault-tolerant bridge arm multiplexed MMC phase unit. The DC-side voltage is then borne by the remaining submodules, causing increased voltage stress on these submodules and threatening their lifespan. To address this issue, a balanced support control for the DC-side voltage is proposed. This involves inserting additional submodules into healthy bridge arms to ensure that the DC-side voltage is always applied to N submodules, maintaining a constant capacitor voltage in each submodule.

[0135] 3. AC side waveform reconstruction control

[0136] The DC-side voltage support control causes a shift in the number of inserted submodules in each bridge arm due to modulation requirements, inevitably leading to distortion of the AC output waveform of the fault-tolerant bridge arm multiplexed MMC. To achieve high-quality fault-tolerant operation, a fault-tolerant bridge arm multiplexed MMC AC side waveform reconstruction control is proposed based on the fault type. This control fully utilizes the positive, negative, and zero-level output capabilities of the full-bridge submodules to actively compensate for voltage defects caused by the DC-side voltage support control, accurately reconstructing the AC output voltage waveform and ensuring the power quality and stability of the connection to the AC grid.

[0137] Based on the fault-tolerant bridge arm multiplexing MMC topology provided in the above embodiments, this application also provides a control method for the fault-tolerant bridge arm multiplexing MMC applied to the controller in the topology, including:

[0138] By controlling the on / off state of each bridge arm switching switch, each multiplexed bridge arm can be connected to the upper or lower bridge arm, thereby changing the operating mode of the upper and lower bridge arms.

[0139] When a bridge arm unit or switching unit fails, DC-side voltage support control and AC-side waveform reshaping control are performed based on the operating modes of the upper and lower bridge arms, so that the output of the four-bridge arm converter and the AC-side fault-tolerant unit topology are the same as the output when there is no fault.

[0140] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0141] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0142] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0143] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0144] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A fault-tolerant bridge arm multiplexing MMC topology, characterized in that, This includes a three-phase four-arm converter and an AC-side fault-tolerant unit topology, wherein each phase of the four-arm converter and AC-side fault-tolerant unit topology includes: The bridge arm unit includes an upper bridge arm, a first multiplexed bridge arm, a second multiplexed bridge arm, and a lower bridge arm connected in series. The input terminal of the upper bridge arm is connected to the positive DC bus, and the output terminal of the lower bridge arm is connected to the negative DC bus. Each bridge arm consists of... N / 3 It consists of a series of half-bridge sub-modules. N This indicates the total number of half-bridge sub-modules within the upper or lower bridge arm and the first and second multiplexed bridge arms; The switching unit includes three bridge arm switching switches connected in parallel; wherein, the first end of each of the three bridge arm switching switches is connected to the AC bus via an AC side fault-tolerant unit, the second end of the first bridge arm switching switch is connected to the connection between the upper bridge arm and the first multiplex bridge arm, the second end of the second bridge arm switching switch is connected to the connection between the first multiplex bridge arm and the second multiplex bridge arm, and the second end of the third bridge arm switching switch is connected to the connection between the second multiplex bridge arm and the lower bridge arm; AC-side fault-tolerant unit, including N / 3 A series of full-bridge sub-modules; wherein, the first end of the series-connected full-bridge sub-module is connected to the AC bus, and the second end is connected to the first end of the three bridge arm switching switches; The controller controls the switching of each bridge arm to allow each multiplexed bridge arm to connect to the upper or lower bridge arm, thereby changing the operating mode of the upper and lower bridge arms. When a bridge arm unit or switching unit fails, the controller performs DC-side voltage support control and AC-side waveform reshaping control based on the operating modes of the upper and lower bridge arms, so that the output of the four-bridge arm converter and the AC-side fault-tolerant unit topology is the same as the output when there is no fault.

2. The topology of the fault-tolerant bridge arm multiplexing MMC according to claim 1, characterized in that, The controller controls the on / off state of each bridge arm switching switch, allowing each multiplexed bridge arm to connect to the upper or lower bridge arm, thereby changing the operating mode of the upper and lower bridge arms and enabling the normal operation of the fault-tolerant bridge arm multiplexing MMC, including: The theoretical number of half-bridge submodules in the upper arm and the theoretical number of half-bridge submodules in the lower arm are calculated using the nearest level approximation modulation method. When the theoretical number of half-bridge submodules deployed on the upper bridge arm is less than or equal to N / 3 And the theoretical number of half-bridge sub-modules deployed in the lower bridge arm is greater than or equal to 2N / 3 When the first bridge arm switching switch is closed, the remaining two bridge arm switching switches are opened, so that the upper bridge arm can operate independently. The first multiplexed bridge arm, the second multiplexed bridge arm and the lower bridge arm are connected in series to form an equivalent lower bridge arm. The upper bridge arm is in normal mode and the lower bridge arm is in multiplexed mode. When the theoretical number of half-bridge submodules deployed on the upper bridge arm is greater than or equal to N / 3 And the theoretical number of half-bridge sub-modules deployed in the lower bridge arm is greater than or equal to N / 3 When the second bridge arm switching switch is closed, the remaining two bridge arm switching switches are opened, so that the first multiplexed bridge arm is connected in series with the upper bridge arm to form an equivalent upper bridge arm, and the second multiplexed bridge arm is connected in series with the lower bridge arm to form an equivalent lower bridge arm. Both the upper and lower bridge arms are in multiplexed mode. When the theoretical number of half-bridge submodules deployed on the upper bridge arm is greater than or equal to 2N / 3 And the theoretical number of half-bridge sub-modules deployed in the lower bridge arm is less than or equal to N / 3 When the control is activated, the third bridge arm switching switch is closed, and the remaining two bridge arm switching switches are opened, so that the first multiplexed bridge arm, the second multiplexed bridge arm and the upper bridge arm are connected in series to form an equivalent upper bridge arm, and the lower bridge arm operates independently. The upper bridge arm is in multiplexed mode, and the lower bridge arm is in normal mode.

3. The topology of the fault-tolerant bridge arm multiplexing MMC according to claim 2, characterized in that, When a bridge arm unit or switching unit fails, DC-side voltage support control and AC-side waveform reshaping control are performed based on the operating modes of the upper and lower bridge arms to achieve fault-tolerant operation of the fault-tolerant bridge arm multiplexing MMC, including: When a half-bridge submodule in the upper bridge arm or equivalent upper bridge arm fails, the lower bridge arm or equivalent lower bridge arm is adjusted to engage a half-bridge submodule to supplement the missing level and achieve DC side voltage support. When a half-bridge submodule in the lower bridge arm or equivalent lower bridge arm fails, the upper bridge arm or equivalent upper bridge arm is adjusted to engage a half-bridge submodule to supplement the missing voltage level and achieve DC-side voltage support. When the half-bridge submodules in the two multiplexed bridge arms fail simultaneously, the upper bridge arm or equivalent upper bridge arm and the lower bridge arm or equivalent lower bridge arm are adjusted to engage the half-bridge submodules to supplement the missing level and achieve DC side voltage support. When the bridge arm switching switch in the switching unit fails, the upper bridge arm or equivalent upper bridge arm and the lower bridge arm or equivalent lower bridge arm are adjusted to engage the half-bridge sub-module to supplement the missing level and achieve DC side voltage support. When a half-bridge submodule in the bridge arm unit or a bridge arm switching switch in the switching unit fails, the number of full-bridge submodules in the AC side fault-tolerant unit and the output voltage of the full-bridge submodules are controlled to achieve AC side waveform reshaping.

4. The topology of the fault-tolerant bridge arm multiplexing MMC according to claim 3, characterized in that, When a half-bridge submodule within the upper bridge arm or equivalent upper bridge arm fails, the lower bridge arm or equivalent lower bridge arm is adjusted to engage a half-bridge submodule to compensate for the missing voltage level and achieve DC-side voltage support, including: When the upper bridge arm is in normal mode and the lower bridge arm is in reuse mode, a half-bridge submodule within the upper bridge arm fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, the control equivalent lower bridge arm is re-engaged. One and a half bridge modules; When both the upper and lower bridge arms are in reuse mode, it is equivalent to a half-bridge submodule failure within the upper bridge arm, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than Control equivalent bridge arm re-engagement One and a half bridge modules; When the upper bridge arm is in reuse mode and the lower bridge arm is in normal mode, a half-bridge submodule within the upper bridge arm fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than Control the lower bridge arm to re-engage One and a half bridge modules; in, Indicates the number of faulty half-bridge sub-modules within the upper bridge arm; This indicates the number of half-bridge submodules with faults in the equivalent upper bridge arm.

5. The topology of the fault-tolerant bridge arm multiplexing MMC according to claim 3, characterized in that, When a half-bridge submodule in the lower bridge arm or equivalent lower bridge arm fails, the upper bridge arm or equivalent upper bridge arm is adjusted to engage a half-bridge submodule to compensate for the missing voltage level and achieve DC-side voltage support, including: When the upper bridge arm is in normal mode and the lower bridge arm is in reuse mode, it is equivalent to a half-bridge submodule failure within the lower bridge arm, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than At that time, control the upper bridge arm to re-engage. One and a half bridge modules; When both the upper and lower bridge arms are in reuse mode, the equivalent failure of a half-bridge submodule within the lower bridge arm, and the theoretical number of half-bridge submodules in the lower bridge arm, are considered to be... Greater than At that time, control the equivalent upper bridge arm to re-engage. One and a half bridge modules; When the upper bridge arm is in reuse mode and the lower bridge arm is in normal mode, a half-bridge submodule within the lower bridge arm fails, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than At that time, control the equivalent upper bridge arm to re-engage. One and a half bridge modules; in, Indicates the number of faulty half-bridge sub-modules within the lower bridge arm; This indicates the number of half-bridge submodules with faults within the equivalent lower bridge arm.

6. The topology of the fault-tolerant bridge arm multiplexing MMC according to claim 3, characterized in that, When the half-bridge submodules in two multiplexed bridge arms fail simultaneously, the upper bridge arm or equivalent upper bridge arm and the lower bridge arm or equivalent lower bridge arm are adjusted to engage the half-bridge submodules to compensate for the missing voltage level and achieve DC-side voltage support, including: When the upper bridge arm is in normal mode and the lower bridge arm is in reuse mode, a half-bridge submodule in the first and second reuse bridge arms fails, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than At that time, control the upper bridge arm to re-engage. One and a half bridge modules; When both the upper and lower bridge arms are in reuse mode, a half-bridge submodule in the first and second reused bridge arms fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, the control equivalent lower bridge arm is re-engaged. One and a half bridge modules; When both the upper and lower bridge arms are in multiplexing mode, a half-bridge submodule in the first and second multiplexing bridge arms fails, and the theoretical number of half-bridge submodules in the lower bridge arm is [not specified]. Greater than At that time, control the equivalent upper bridge arm to re-engage. One and a half bridge modules; When the upper bridge arm is in reuse mode and the lower bridge arm is in normal mode, a half-bridge submodule in the first and second reuse bridge arms fails, and the theoretical number of half-bridge submodules in the upper bridge arm is [not specified]. Greater than At that time, control the lower bridge arm to re-engage. One and a half bridge modules; in, Indicates the number of half-bridge submodules that have failed within the first multiplexed bridge arm; This indicates the number of half-bridge submodules that are faulty within the second multiplexed bridge arm.

7. The topology of the fault-tolerant bridge arm multiplexing MMC according to claim 3, characterized in that, When the bridge arm switching switch within the switching unit fails, the upper bridge arm or equivalent upper bridge arm, and the lower bridge arm or equivalent lower bridge arm are adjusted to engage a half-bridge submodule to compensate for the missing voltage level and achieve DC-side voltage support, including: When the upper bridge arm is in normal mode and the lower bridge arm is in multiplexing mode, if the first or third bridge arm switch fails, the second bridge arm switch will close. This is based on the theoretical number of half-bridge submodules that can be deployed in the lower bridge arm. Greater than Control equivalent upper bridge arm re-investment One and a half bridge modules; When the upper bridge arm is in multiplexing mode and the lower bridge arm is in normal mode, if the first or third bridge arm switch fails, the second bridge arm switch will be closed. This is based on the theoretical number of half-bridge submodules that can be deployed in the upper bridge arm. Greater than Control equivalent bridge arm re-engagement One and a half bridge modules; When both the upper and lower bridge arms are in multiplexing mode, and the second bridge arm switching switch fails, if the theoretical number of half-bridge submodules of the upper bridge arm are engaged... The theoretical number of half-bridge submodules deployed is less than that of the lower bridge arm. Control the first bridge arm switching switch to close, and control the upper bridge arm internal... All half-bridge sub-modules are engaged, and then the bridge arm under control is engaged. One and a half bridge sub-modules; if the theoretical number of half bridge sub-modules in the upper bridge arm is [number missing] The theoretical number of half-bridge submodules deployed is greater than that of the lower bridge arm. Control the closing of the third bridge arm switching switch and control the lower bridge arm. All one and a half bridge sub-modules are put into operation, and the control equivalent upper bridge arm is then put into operation. One and a half bridge modules.

8. The topology of the fault-tolerant bridge arm multiplexing MMC according to claim 3, characterized in that, When a half-bridge submodule in the bridge arm unit or a bridge arm switching switch in the switching unit fails, the number of full-bridge submodules activated in the AC side fault-tolerant unit and the output voltage of the full-bridge submodules are controlled to achieve AC side waveform reshaping, including: When a half-bridge submodule in the upper arm or equivalent upper arm fails, all full-bridge submodules in the AC-side fault-tolerant unit output a negative voltage; when a half-bridge submodule in the lower arm or equivalent lower arm fails, all full-bridge submodules in the AC-side fault-tolerant unit output a positive voltage. When the bridge arm switching switch in the switching unit fails, if the upper bridge arm or equivalent upper bridge arm is put into a half-bridge submodule again, the full-bridge submodule in the AC side fault-tolerant unit will output a positive voltage; if the lower bridge arm or equivalent lower bridge arm is put into a half-bridge module again, the full-bridge submodule in the AC side fault-tolerant unit will output a negative voltage. When a half-bridge submodule in the bridge arm unit or a bridge arm switching switch in the switching unit fails, the capacitor voltage of the re-engaged half-bridge submodule is superimposed with the capacitor voltage of the missing half-bridge module in the failed bridge arm to obtain the voltage. , will 0.5 The quotient of the voltage across the capacitors of the full-bridge submodule is used as the input number of the full-bridge submodule.

9. The topology of the fault-tolerant bridge arm multiplexing MMC according to claim 8, characterized in that, If 0.5 If the quotient of the voltage of the capacitor in the full-bridge submodule is not an integer, a rounding function is used to round the calculated quotient to the nearest integer.

10. A control method for a fault-tolerant bridge arm multiplexing MMC, characterized in that, The method is applied to the controller in the topology of the fault-tolerant bridge arm multiplexing MMC according to any one of claims 1-9, comprising: By controlling the on / off state of each bridge arm switching switch, each multiplexed bridge arm can be connected to the upper or lower bridge arm, thereby changing the operating mode of the upper and lower bridge arms. When a bridge arm unit or switching unit fails, DC-side voltage support control and AC-side waveform reshaping control are performed based on the operating modes of the upper and lower bridge arms, so that the output of the four-bridge arm converter and the AC-side fault-tolerant unit topology are the same as the output when there is no fault.

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