A hybrid MMC and its operation strategy based on dual-end sharing of Si / SiC intensive redundant modules

Abstract

The present application provides a hybrid MMC and operation strategy based on dual-end sharing of Si / SiC intensive redundant modules, including: a three-phase circuit topology, an AC side output port, a first DC side energy storage capacitor, and a second DC side energy storage capacitor; the three-phase circuit topology includes three identical single-phase topologies, and the single-phase topology includes an upper bridge arm, a filter inductor, a multiplexing redundant submodule, a lower bridge arm, and a filter inductor; the multiplexing redundant submodule includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube, and a sixth switch tube, as well as a DC capacitor. By introducing the multiplexing redundant submodule, the upper and lower bridge arms are respectively redundantly configured, which reduces the number of configurations of the redundant submodules while also reducing the configuration of devices such as radiators and capacitors, which can effectively optimize the configuration cost of the MMC.

Description

Technical Field

[0001] The present application relates to the technical field of power systems, and in particular to the field of multi-level converter control. Background Art

[0002] In recent years, certain regions have been vigorously developing clean energy sources such as photovoltaics and wind power to build new power systems, which has placed higher demands on power conversion devices. Modular multilevel converters (MMCs), due to their high degree of modularity, good output waveform quality, and strong scalability, are widely used in scenarios such as distributed power grid connection, DC transmission, and power quality management. Compared to traditional two-level converters, MMCs adopt a structure with sub-modules connected in series, which increases the flexibility of output levels and control. However, this requires more power devices, capacitors, and heat sinks, leading to increased MMC costs and failure risks. In medium-voltage flexible power distribution scenarios, the increase in land costs and grid construction density places higher demands on the operating efficiency, configuration costs, and overall reliability of medium-voltage MMCs.

[0003] Traditional MMCs primarily utilize silicon (Si)-based insulated-gate bipolar transistors (IGBTs) as power switching devices. However, due to the physical limitations of Si-based devices, optimizing device operating efficiency is difficult. Third-generation wide-bandgap semiconductor devices, such as silicon carbide field-effect transistors (SiC MOSFETs), offer advantages such as high switching frequency and low switching losses. Their application in medium-voltage MMCs can significantly improve device operating efficiency. However, SiC MOSFETs are 5 to 10 times more expensive than Si IGBTs of the same specification. Furthermore, the large number of power switching devices in MMCs means that replacing Si IGBTs with SiC MOSFETs in large numbers will increase device costs.

[0004] Furthermore, the extensive use of submodules in MMCs can reduce the overall reliability of the device; failure of any one submodule can cause system malfunction. Configuring redundant submodules is the most common method for improving MMC reliability. When an MMC submodule fails, the faulty submodule is removed from operation while a redundant submodule replaces the faulty submodule and resumes normal operation, effectively improving MMC reliability. However, traditional redundant submodules suffer from limited functionality, low utilization, and high configuration costs, failing to balance the MMC's comprehensive requirements for reliability, operational efficiency, and device cost. Summary of the Invention

[0005] In order to overcome the above technical defects, the present application provides a hybrid MMC and operation strategy based on dual-end sharing of Si / SiC intensive redundant modules. To achieve the above objectives, the present application is implemented according to the following technical solutions:

[0006] In the first aspect, the present application provides a hybrid MMC based on Si / SiC intensive redundant module dual-end sharing, including: three-phase circuit topology, AC side output port , the first DC side energy storage capacitor , the second DC side energy storage capacitor ;

[0007] The three-phase circuit topology includes three identical single-phase topologies, wherein the single-phase topology includes an upper bridge arm ARMp, an upper bridge arm filter inductor , multiplexing redundant submodule MRSM, lower bridge arm ARMn, lower bridge arm filter inductor ;

[0008] The multiplexing redundancy submodule MRSM includes a first switch tube , the second switch tube , the third switch tube , the fourth switch tube , the fifth switch tube and the sixth switch tube , and DC capacitors The multiplexing redundancy submodule MRSM is also provided with three external connection ports, namely 、 、 port;

[0009] The first switching tube The collector of the third switch tube The collector and the fifth switch The drains are connected to the DC capacitors The positive electrode of the second switch The emitter of the fourth switch tube The emitter of the sixth switch tube The source is connected to the DC capacitor The negative electrode of the first switch tube The emitter of the second switch tube The collectors are connected to the ports The third switch tube The emitter of the fourth switch tube The collector and the port connected, the fifth switch tube The source of the sixth switch tube The drains are connected to the ports ; port and the upper arm filter inductor One end of the port and the lower bridge arm filter inductor One end of the port and the AC side output port connected;

[0010] The upper bridge arm ARMp and the lower bridge arm ARMn each include multiple half-bridge sub-modules The multiple half-bridge sub-modules are connected in series, and one end of the last half-bridge sub-module in the upper bridge arm ARMp is connected to the upper bridge arm filter inductor The other end of the first half-bridge sub-module in the lower bridge arm ARMn is connected to the lower bridge arm filter inductor The other end of the upper bridge arm ARMp in the first half-bridge sub-module and the first DC side energy storage capacitor The last half-bridge sub-module in the lower bridge arm ARMn is connected to the positive electrode of the second DC side energy storage capacitor The negative electrode of the first DC side energy storage capacitor is connected to The negative electrode and the second DC side energy storage capacitor The positive poles are connected to the ground terminal.

[0011] Optionally, the first switch tube The second switch tube , the third switch tube , the fourth switch tube All are Si IGBT tubes, the fifth switch tube The sixth switch tube All are SiC MOSFET tubes.

[0012] In a second aspect, the present application provides an operating strategy for a modular multilevel converter. For a hybrid MMC based on dual-end sharing of Si / SiC intensive redundant modules according to the first aspect, the fault handling method operating strategy includes a normal operation processing strategy, a first fault handling strategy, and a second fault handling strategy, wherein the normal operation processing strategy includes:

[0013] Calculating the number of levels of the step wave output by the modular multi-level converter;

[0014] Determining whether the level number changes;

[0015] If yes, collect the DC side capacitor voltage value of the multiplexing redundant submodule and the average DC side current and voltage of the upper and lower bridge arms;

[0016] Determining whether the DC link capacitor voltage value is less than the DC link capacitor voltage average value;

[0017] If so, determine whether the direction of the system circulating current is greater than zero;

[0018] If yes, the multiplexing redundancy submodule operates in the first working mode;

[0019] If the direction of the system circulating current is less than or equal to zero, the multiplexing redundancy submodule operates in the second working mode.

[0020] Optionally, if the result of determining whether the DC link capacitor voltage value is greater than the average DC link current and voltage value is no, the method further includes:

[0021] Determine whether the direction of the system circulating current is greater than zero;

[0022] If yes, the multiplexing redundancy submodule operates in the second working mode;

[0023] If not, the multiplexing redundancy submodule operates in the first working mode;

[0024] Optionally, the first fault handling strategy includes:

[0025] When a submodule in the upper or lower bridge arm fails;

[0026] Determine a fault location, and determine a first number of bridge arm neutron modules currently in operation corresponding to the fault location;

[0027] Determining whether the first quantity currently invested in the work is equal to the initial configuration quantity;

[0028] If yes, then based on the initial configuration quantity, the first quantity of the submodule currently put into operation is updated, and the multiplexing redundant submodule is operated in the first working mode;

[0029] If not, the multiplexing redundancy submodule operates according to the normal operation processing strategy.

[0030] Optionally, the second fault handling strategy includes:

[0031] When one submodule in the upper and lower bridge arms fails;

[0032] Determining a second number of upper arm neutron modules currently in operation;

[0033] Determining whether the second number of currently invested jobs is equal to the initial configuration number;

[0034] If yes, determining the third number of lower bridge arm neutron modules currently in operation;

[0035] Determining whether the third number currently invested in the work is equal to the initial configuration number;

[0036] If so, based on the initial configuration quantity, the second quantity currently put into operation and the third quantity currently put into operation are updated simultaneously, and the multiplexing redundancy submodule is operated in the first working mode.

[0037] Optionally, when the determination result of determining whether the second number currently engaged in work is equal to the initial configuration number is no, the method includes:

[0038] Determining the third number of lower bridge arm neutron modules currently in operation;

[0039] Determining whether the third number currently invested in the work is equal to the initial configuration number;

[0040] If so, then based on the initial configuration quantity, the third quantity currently put into operation is updated, and the multiplexing redundancy submodule is operated in the first working mode;

[0041] If not, the multiplexing redundant submodule is operated according to the normal operation processing strategy.

[0042] Optionally, when the determination result of determining whether the third number currently engaged in work is equal to the initial configuration number is no, the method includes:

[0043] Based on the initial configuration quantity, the second quantity currently put into operation is updated, and the multiplexing redundancy submodule is operated in the first working mode.

[0044] This application has the following beneficial effects:

[0045] The proposed MRSM, as a redundant submodule, can also coordinate with the upper and lower bridge arms (SMs) to output a superimposed high- and low-frequency voltage during normal MMC operation, thereby improving the utilization of the redundant submodules. Furthermore, the reliability improvement method proposed in this invention eliminates the need for separate redundant configurations for the upper and lower bridge arms, reducing the number of redundant submodules required and the number of components such as heat sinks and capacitors, effectively optimizing the configuration costs of the MMC.

[0046] In addition to the above-described purposes, features and advantages, the present application has other purposes, features and advantages. The present application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0048] Figure 1 This is a schematic diagram of the topological structure of the hybrid MMC of the existing SiC-based device and Si-based device of the present application;

[0049] Figure 2 This is a schematic diagram of a hybrid MMC topology structure based on multi-terminal sharing of intensive redundant modules provided by an embodiment of the present application;

[0050] Figure 3 Schematic diagram of an equivalent circuit of a multiplexing redundant submodule and upper and lower bridge arms provided in an embodiment of the present application;

[0051] Figure 4 This is a flow chart of the mode switching and voltage stabilization strategy when the multiplexing redundant submodule provided in the embodiment of the present application is in the normal operation processing strategy;

[0052] Figure 5 This is a flow chart of a first fault handling strategy for a multiplexing redundant submodule provided in an embodiment of the present application;

[0053] Figure 6 This is a flow chart of the second fault handling strategy for the multiplexing redundant submodule provided in an embodiment of the present application;

[0054] Figure 7 This is a schematic diagram of the MMC voltage waveform when the multiplexing redundant submodule is in the normal operation processing strategy during the experimental simulation analysis of the embodiment of the present application; Figure 7 (a) is the upper arm output voltage Waveform diagram, Figure 7 (b) is the upper arm output voltage Waveform diagram, Figure 7 (c) is the output voltage of phase A Waveform diagram, Figure 7 (d) is the output voltage of MRSM in the upper arm Waveform diagram, Figure 7 (e) is the upper bridge arm DC side capacitor voltage Waveform diagram, Figure 7 (f) is the MRSM DC side capacitor voltage Waveform diagram;

[0055] Figure 8 This is a schematic diagram of the MMC voltage waveform when the multiplexing redundant submodule is in the first fault handling strategy during the experimental simulation analysis of the embodiment of the present application; Figure 8 (a) is the upper arm output voltage Waveform diagram, Figure 8 (b) is the upper arm output voltage Waveform diagram, Figure 8 (c) is the output voltage of phase A Waveform diagram, Figure 8 (d) is the output voltage of MRSM in the upper arm Waveform diagram, Figure 8 (e) is the upper bridge arm DC side capacitor voltage Waveform diagram, Figure 8 (f) is the MRSM DC side capacitor voltage Waveform diagram;

[0056] Figure 9 This is a schematic diagram of the MMC voltage waveform when the multiplexing redundant submodule is in the second fault handling strategy during the experimental simulation analysis of the embodiment of the present application; Figure 9 (a) is the upper arm output voltage Waveform diagram, Figure 9 (b) is the upper arm output voltage Waveform diagram, Figure 9 (c) is the output voltage of phase A Waveform diagram, Figure 9 (d) is the output voltage of MRSM in the upper arm Waveform diagram, Figure 9 (e) is the upper bridge arm DC side capacitor voltage Waveform diagram, Figure 9 (f) is the MRSM DC side capacitor voltage Waveform diagram. DETAILED DESCRIPTION

[0057] The embodiments of the present application are described in detail below with reference to the accompanying drawings, but the present application can be implemented in many different ways as defined and covered by the claims.

[0058] It should be noted that the terms "first", "second", "third", etc. in the claims, description and drawings of the present application are used to distinguish similar objects and are not used to describe a specific order or sequence. The data used in this way are interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in a sequence other than that illustrated or described herein. In addition, the terms "including", "having" and their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0059] In order to provide a more vivid explanation of the issues raised in the background technology, Figure 1 As shown, an existing MMC topology uses a hybrid of SiC and Si-based devices. Each phase of this topology consists of symmetrical upper and lower bridge arms. Compared to traditional MMCs, one of the N half-bridge sub-modules (SMs) in each bridge arm is replaced with two full-bridge sub-modules (FSMs). The SM consists of two Si IGBTs, and the FSMs consist of four SiC MOSFETs. This topology shifts the majority of switching from Si-based devices to SiC-based devices by changing the modulation strategy, reducing overall device operating losses. However, compared to traditional MMCs, this topology adds a total of 12 FSMs composed of SiC MOSFETs, significantly increasing overall device cost. Furthermore, when configuring redundant sub-modules, redundancy must be configured for both the SM and FSM in each bridge arm, further increasing device configuration costs.

[0060] In order to solve the above problems, Figure 2 As shown, the present application proposes a hybrid MMC based on dual-end sharing of Si / SiC intensive redundant modules, including:

[0061] Three-phase circuit topology, AC side output port , the first DC side energy storage capacitor , the second DC side energy storage capacitor The three-phase circuit topology includes three identical single-phase topologies, namely A, B, and C. The three phases share a DC bus port, and the DC bus voltage is ;

[0062] The single-phase topology includes an upper bridge arm ARMp, an upper bridge arm filter inductor , multiplexing redundant submodule MRSM, lower bridge arm ARMn, lower bridge arm filter inductor ;

[0063] The multiplexing redundancy submodule MRSM includes a first switch tube , the second switch tube , the third switch tube , the fourth switch tube , the fifth switch tube and the sixth switch tube , and DC capacitors The multiplexing redundancy submodule MRSM is also provided with three external connection ports, namely 、 、 port;

[0064] The first switching tube The collector of the third switch tube The collector and the fifth switch The drains are connected to the DC capacitors The positive electrode of the second switch The emitter of the fourth switch tube The emitter of the sixth switch tube The source of the capacitor is connected to the DC The negative electrode of the first switch tube The emitter of the second switch tube The collectors are connected to the ports The third switch tube The emitter of the fourth switch tube The collector and port connected, the fifth switch tube The source of the sixth switch tube The drains are connected to the ports ; port and the upper arm filter inductor One end is connected, port and the lower bridge arm filter inductor One end is connected, port and the AC side output port u oa connected;

[0065] The upper bridge arm ARMp and the lower bridge arm ARMn each include a plurality of half-bridge sub-modules SM aN The multiple half-bridge sub-modules are connected in series, and one end of the last half-bridge sub-module in the upper bridge arm ARMp is connected to the upper bridge arm filter inductor The other end of the first half-bridge sub-module in the lower bridge arm ARMn is connected to the lower bridge arm filter inductor The other end of the upper bridge arm ARMp in the first half-bridge sub-module and the first DC side energy storage capacitor The last half-bridge sub-module in the lower bridge arm ARMn is connected to the positive electrode of the second DC side energy storage capacitor The negative electrode of the first DC side energy storage capacitor is connected to The negative electrode and the second DC side energy storage capacitor The positive poles are connected to the ground.

[0066] It should also be noted that the first switch tube The second switch tube , the third switch tube , the fourth switch tube All are Si IGBT tubes, the fifth switch tube The sixth switch tube All are SiCMOSFET tubes.

[0067] Based on the above-mentioned hybrid MMC based on dual-end sharing of Si / SiC intensive redundant modules, the operation of the redundant sub-modules of the present application is divided into three operating modes according to the fault conditions of the upper and lower bridge arms SM: normal operation, one SM fault in the upper or lower bridge arm (first fault handling strategy), and one SM fault in each of the upper and lower bridge arms (second fault handling strategy). These three operating strategies are described in detail below.

[0068] 1) Normal operation processing strategy:

[0069] Under normal operation, the upper and lower bridge arms of MMC N (Initial configuration number) SMs are operating normally. At this time, the MRSM can cooperate with the upper and lower bridge arms to concentrate most of the switching actions on the SiC MOSFET devices in the MRSM through the combination of nearest level modulation (NLM) and pulse width modulation (PWM). 、 ) and utilize the advantages of SiC MOSFET’s high switching frequency and low switching loss to improve the operating efficiency of MMC.

[0070] The equivalent circuit of MRSM and the upper and lower bridge arms working together to output is as follows: Figure 3 As shown. Among them, the output voltage of the upper bridge arm is , the output voltage of the lower bridge arm is , the output voltage of MRSM in the upper arm is , the output voltage of MRSM in the lower bridge arm is .

[0071] According to the different switching states of the devices in the MRSM, its operating states are shown in Table 1. According to the MRSM output voltage The positive and negative polarities are different, and the operating states 1 and 2 can be defined as the first operating mode 1, and the operating states 3 and 4 can be defined as the second operating mode 2. By adjusting the MRSM operating mode, the DC side capacitor voltage can be maintained stable.

[0072] Table 1 MRSM operation mode

[0073] ;

[0074] The upper and lower bridge arms use NLM. In the first working mode 1, the number of submodules put into operation is 、 It can be expressed as:

[0075] (1)

[0076] Where, is the MMC DC bus voltage, is the DC side capacitor voltage of each submodule of MMC, is the AC side output reference voltage, is the floor function.

[0077] The middle MRSM uses PWM. In mode 1, the MRSM PWM reference voltages in the upper and lower arms can be expressed as:

[0078] (2)

[0079] Where, They are respectively the reference values ​​of the output voltages of the upper and lower bridge arms of the MRSM when operating in the first working mode 1.

[0080] In the second working mode 2, the number of submodules in the upper and lower bridge arms that are put into operation It can be expressed as:

[0081] (3)

[0082] Where, is the ceiling function.

[0083] In the second working mode 2, the MRSM upper and lower arm PWM reference voltages can be expressed as:

[0084] (4)

[0085] Where, They are respectively the reference values ​​of the output voltages of the upper and lower bridge arms of the MRSM when operating in the second working mode 2.

[0086] According to the requirements of DC capacitor voltage regulation, MRSM can flexibly switch between two operating modes to maintain voltage stability. The change of DC side capacitor voltage value of MRSM can be determined by its operating mode and system circulating current. To jointly decide: When the MRSM is operated in the first working mode 1, the voltage value of the DC side capacitor can be controlled to increase, and when it is operated in the second working mode 2, the voltage value of the DC side capacitor can be controlled to decrease; When the MRSM is operated in the second working mode 2, the voltage value of the DC link capacitor can be controlled to increase; when the MRSM is operated in the first working mode 1, the voltage value of the DC link capacitor can be controlled to decrease.

[0087] The specific switching process, such as Figure 4As shown, first calculate the level number of the modular multilevel converter output step wave , The calculation formula is as follows:

[0088] (5)

[0089] When calculating the level of the step wave k After that, judge the level number k Check whether the voltage has changed, that is, compare it with the previous voltage level. If it has changed, collect the voltage value of the MRSM DC side capacitor. , and the average value of the DC side capacitor voltage of the upper and lower bridge arms U AVG , then the MRSM DC side capacitor voltage value and the average value of the DC side capacitor voltage of the upper and lower bridge arms U AVG Compare and judge the DC side capacitor voltage value Is it less than the average value of the DC side capacitor voltage? U AVG If it is less than, then it is necessary to judge the system circulating current Is the direction greater than zero? If it is greater than zero, the MRSM will be operated in the first working mode 1, and the number of submodules in the upper and lower bridge arms that are put into operation is 、 , can be calculated by formula (1). If the system circulating current is direction is less than or equal to zero, it will run in the second working mode 2, and the number of submodules put into operation in the upper and lower bridge arms is It can be calculated by formula (3).

[0090] If the DC side capacitor voltage value Greater than or equal to the average value of the DC link capacitor voltage U AVG At this time, it is also necessary to determine the direction of the system circulating current Is it greater than zero? If so, the MRSM is operated in the second working mode 2, and the number of submodules in the upper and lower bridge arms that are put into operation is It can be calculated by formula (3). If the system loop circuit direction is less than or equal to zero at this time, the MRSM is operated in the first working mode 1, and the number of submodules in the upper and lower bridge arms that are put into operation is , which can be calculated using formula (1).

[0091] If the DC side capacitor voltage value Greater than or equal to the average value of the DC link capacitor voltage U AVGAt this time, it is also necessary to determine whether the system circulating current direction icir is greater than zero. If so, the MRSM is operated in the second working mode 2, and the number of sub-modules put into operation in the upper and lower bridge arms is It can be calculated by formula (3). If the system loop circuit direction is less than or equal to zero at this time, the MRSM is operated in the first working mode 1, and the number of submodules in the upper and lower bridge arms that are put into operation is , which can be calculated using formula (1).

[0092] 2) First fault handling strategy (one SM in the upper / lower bridge arm is faulty):

[0093] When an SM in the upper or lower bridge arm fails, the MRSM can assume the role of level support for the faulty bridge arm, ensuring the stable operation of the MMC without affecting the output quality of the MMC.

[0094] At this point, it is first necessary to determine the location of the fault, that is, to determine the specific bridge arm where the fault occurred, and then confirm the current first number of submodules put into operation in the bridge arm corresponding to the fault location, and then determine whether the current first number of submodules put into operation is equal to the initial configuration number. The initial configuration number can be understood as a certain number of submodules configured for each bridge arm at the beginning to consider various factors of the system. If the current first number of submodules put into operation is equal to the initial configuration number, then the current first number of submodules put into operation is updated according to the initial configuration number, and the MRSM is operated in the first working mode 1. If it is not equal, it means that the current first number of submodules put into operation is less than the initial configuration number, and the MRSM is operated according to the above-mentioned normal operation processing strategy.

[0095] In order to understand the first fault handling strategy more vividly, Figure 5 As shown, this application takes the occurrence of the upper bridge arm fault as an example to provide the following detailed description:

[0096] After the fault is detected, it is confirmed that the fault is in the upper bridge arm, and then the current first working quantity of the upper bridge arm submodule is determined. After that, the fault protection detection is performed, that is, whether the current first working quantity of the upper bridge arm submodule is equal to the initial configuration quantity. If After that, the fault protection detection is performed, that is, whether the current first working quantity of the upper bridge arm submodule is equal to the initial configuration quantity. If , then the number of SMs put into the upper bridge arm needs to be corrected, so At the same time, the MRSM is operated in Mode 1 to ensure DC bus voltage balance. The same applies to the case of a fault in the lower bridge arm.

[0097] It should be noted that Figure 5A more detailed fault handling process is also shown, but its essence is the same as the processing flow when the upper bridge arm fails. Therefore, in order to avoid brevity, other solutions will not be described in detail one by one.

[0098] 3) Second fault handling strategy (one SM fault in each of the upper and lower bridge arms):

[0099] When one SM in the upper and lower bridge arms fails, the MRSM can simultaneously assume the role of level support for the upper and lower bridge arms to ensure the normal operation of the MMC.

[0100] When a fault is detected in one SM on each of the upper and lower bridge arms, additional fault protection measures need to be added. The specific processing process is as follows: Figure 6 As shown, first determine the second number of the upper arm neutron modules currently put into operation , then determine the second quantity Is it equal to the initial configuration number N? If so, then determine the current working third number in the lower bridge arm , then determine the third quantity Is it equal to the initial configuration quantity N? If so, based on the initial configuration quantity N, the second quantity currently invested in the work and the third number of currently working To update, let , And the MRSM runs in the first working mode 1. If the current working third quantity of the lower bridge arm neutron module If it is not equal to the initial configuration quantity N, then based on the initial configuration quantity N, the second quantity of the current work is To update, , currently the third number of Remain unchanged and run MRSM in the first working mode 1.

[0101] If the above is currently working on the second quantity Not equal to the initial configuration quantity N , then determine the third number of the lower bridge arm neutron modules currently put into operation , determine the third amount of work currently being put into Is it equal to the initial configuration quantity? N , if equal, then based on the initial configuration quantity N , the third amount of current work To update, , currently working on the second Remain unchanged, and operate the MRSM in the first working mode 1. If not equal, operate the MRSM according to the normal operation processing strategy.

[0102] It should be noted that the aforementioned situation in which the number of submodules currently in operation is not equal to the number initially configured only applies to situations where the number of submodules currently in operation is less than the number initially configured. Furthermore, the redundant submodules in this application can only handle the two aforementioned fault scenarios. If more than one submodule in the upper or lower bridge arm fails, the redundant submodules will need to be reconfigured, which is not the specific situation addressed by this application.

[0103] Experimental simulation analysis

[0104] In order to verify the feasibility of the operation strategy of the modular multilevel converter proposed in this application, a simulation experiment platform was built in MATLAB / Simulink software. The simulation parameters are shown in Table 2:

[0105] Table 2 Main simulation parameters

[0106] ;

[0107] Taking the upper bridge arm of phase A as an example, the simulation waveforms of the strategy proposed in the present invention under different operating conditions are as follows.

[0108] (1) Normal operation:

[0109] When MMC is operating normally, the simulated waveform of the A-phase output voltage is as follows: Figure 7 shown. Figure 7 (a) is the output voltage of the upper bridge arm of phase A. The MRSM can cooperate with the eight SMs in the upper bridge arm to output a 9-level voltage with high and low frequency superposition; Figure 7 (b) is the output step wave voltage of the upper bridge arm of phase A, which can be adjusted according to the voltage regulation needs; Figure 7 (c) is the output voltage of phase A, and the total harmonic distortion (THD) is 1.09%; Figure 7 (d) is the output voltage of the MRSM in the upper bridge arm, concentrating most of the switching action on the SiC MOSFET device; Figure 7 (e) is the DC side capacitor voltage of the upper bridge arm of phase A, which can be stabilized at around 1250V; Figure 7 (f) is the capacitor voltage on the DC side of the MRSM, which can be stabilized at around 1250V.

[0110] (2) There is a SM fault in the upper / lower bridge arm:

[0111] When there is a SM fault in the upper arm of the MMC, the simulated waveform of the output voltage of phase A is as follows: Figure 8 shown. Figure 8 The meaning of each figure and Figure 7The same. After an SM fault in the upper bridge arm is removed, the MRSM can assume the role of supporting the output voltage level of the upper bridge arm, ensuring its own high-frequency PWM voltage output while jointly outputting a 9-level voltage with the 7 SMs operating normally in the upper bridge arm. After the upper bridge arm fails, the asymmetry between the upper and lower bridge arms causes a slight increase in the voltage fluctuation of the DC-side capacitor of the upper bridge arm and the MRSM. However, through the voltage stabilization strategy proposed in the present invention, it can still be controlled within ±5%, meeting the DC-side capacitor voltage stabilization standard.

[0112] (3) There is a SM fault in each of the upper and lower bridge arms:

[0113] When there is a SM fault in each of the upper and lower bridge arms of the MMC, the simulated waveform of the output voltage of phase A is as follows: Figure 9 shown. Figure 9 The meaning of each figure and Figure 8 After a fault is removed in one SM in each of the upper and lower arms, the MRSM can utilize the operating state switching shown in Table 1 to coordinate with the seven SMs in the upper and lower arms to jointly output a nine-level voltage. Furthermore, after a fault occurs, the voltage stabilization strategy proposed in this invention stabilizes the voltage fluctuation of the DC-side capacitors in the upper arm and MRSM to within ±5% of the rated value, meeting the DC-side capacitor voltage regulation standard.

[0114] In summary, the topology and method proposed in this application effectively improve the operating efficiency of the MMC by configuring a multiplexed redundant submodule (MRSM). Furthermore, after a submodule (SM) failure occurs in the upper or lower bridge arm and until the fault is repaired, the MRSM can ensure the normal operation of the MMC. The MRSM utilizes a hybrid Si IGBT and SiC MOSFET device construction method. Through a modulation method, most switching actions are concentrated on the SiC MOSFET, effectively utilizing its advantages of high switching frequency and low switching losses, effectively improving the reliability of the MMC. As a redundant submodule, the MRSM can also cooperate with the upper and lower bridge arm SMs to output a superimposed high- and low-frequency voltage during normal operation of the MMC, thereby improving the utilization rate of the redundant submodule. Furthermore, the reliability improvement method proposed in this invention eliminates the need for separate redundant configurations for the upper and lower bridge arms, reducing the number of redundant submodules required and the configuration of components such as heat sinks and capacitors, effectively optimizing the configuration cost of the MMC.

[0115] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A hybrid MMC based on Si / SiC intensive redundant module dual-end sharing, characterized in that: include: Three-phase circuit topology, AC side output port u oa , the first DC side energy storage capacitor C 1. Second DC side energy storage capacitor C 2; The three-phase circuit topology includes three identical single-phase topologies, wherein the single-phase topology includes an upper bridge arm ARMp, an upper bridge arm filter inductor L arm1 , multiplexing redundant submodule MRSM, lower bridge arm ARMn, lower bridge arm filter inductor L arm2 ; The multiplexing redundancy submodule MRSM includes a first switch tube S R1 , the second switch tube S R2 , the third switch tube S R3 , the fourth switch tube S R4 , the fifth switch tube S R5 and the sixth switch tube S R6 , and DC capacitors C R The multiplexing redundancy submodule MRSM is also provided with three external connection ports, namely p 、 n 、 o port, the first switch tube S R1 The second switch tube S R2 , the third switch tube S R3 , the fourth switch tube S R4 All are Si IGBT tubes, the fifth switch tube S R5 The sixth switch tube S R6 All are SiC MOSFET tubes; The first switching tube S R1 The collector of the third switch tube S R3 The collector and the fifth switch S R5 The drains are connected to the DC capacitors C R The positive electrode of the second switch S R2 The emitter of the fourth switch tube S R4 The emitter of the sixth switch tube S R6 The source is connected to the DC capacitor C R The negative electrode of the first switch tube S R1 The emitter of the second switch tube S R2 The collectors are connected to the ports p The third switch tube S R3 The emitter of the fourth switch tube S R4 The collector and the port n connected, the fifth switch tube S R5 The source of the sixth switch tube S R6 The drains are connected to the ports o ; p port and the upper arm filter inductor L arm1 One end of the n port and the lower bridge arm filter inductor L arm2 One end of the o port and the AC side output port u oa connected; The upper bridge arm ARMp and the lower bridge arm ARMn each include a plurality of half-bridge sub-modules SM aN The multiple half-bridge sub-modules are connected in series, and one end of the last half-bridge sub-module in the upper bridge arm ARMp is connected to the upper bridge arm filter inductor L arm1 The other end of the first half-bridge sub-module in the lower bridge arm ARMn is connected to the lower bridge arm filter inductor L arm2 The other end of the upper bridge arm ARMp in the first half-bridge sub-module and the first DC side energy storage capacitor C 1 is connected to the positive electrode; the last half-bridge sub-module in the lower bridge arm ARMn is connected to the second DC side energy storage capacitor C 2 is connected to the negative electrode of the first DC side energy storage capacitor C 1 and the negative electrode of the second DC side energy storage capacitor C 2 are connected to the ground terminal.

2. An operating strategy for a modular multilevel converter, characterized in that: For the hybrid MMC based on dual-end sharing of Si / SiC intensive redundant modules according to claim 1, the operation strategy includes a normal operation processing strategy, a first fault processing strategy, and a second fault processing strategy, wherein the normal operation processing strategy includes: Calculating the number of levels of the step wave output by the modular multi-level converter; Determining whether the level number changes; If yes, collect the DC side capacitor voltage value of the multiplexing redundant submodule and the average DC side current and voltage of the upper and lower bridge arms; Determining whether the DC link capacitor voltage value is less than the DC link capacitor voltage average value; If so, determine whether the direction of the system circulating current is greater than zero; If yes, the multiplexing redundancy submodule operates in the first working mode; If the direction of the system circulating current is less than or equal to zero, the multiplexing redundancy submodule operates in the second working mode.

3. The strategy according to claim 2, characterized in that If the result of determining whether the DC link capacitor voltage value is greater than the average DC link current and voltage value is no, the method further includes: Determine whether the direction of the system circulating current is greater than zero; If yes, the multiplexing redundancy submodule operates in the second working mode; If not, the multiplexing redundancy submodule operates in the first working mode.

4. The strategy according to claim 2, characterized in that The first fault handling strategy includes: When a submodule in the upper or lower bridge arm fails; Determine the fault location, and determine a first number of bridge arm neutron modules currently in operation corresponding to the fault location; Determining whether the first quantity currently invested in the work is equal to the initial configuration quantity; If yes, then based on the initial configuration quantity, the first quantity of the submodule currently put into operation is updated, and the multiplexing redundant submodule is operated in the first working mode; If not, the multiplexing redundancy submodule operates according to the normal operation processing strategy.

5. The strategy according to claim 2, characterized in that: The second fault handling strategy includes: When one submodule in the upper and lower bridge arms fails; Determining a second number of upper arm neutron modules currently in operation; Determining whether the second number of currently invested jobs is equal to the initial configuration number; If yes, determining the third number of lower bridge arm neutron modules currently in operation; Determining whether the third number currently invested in the work is equal to the initial configuration number; If so, based on the initial configuration quantity, the second quantity currently put into operation and the third quantity currently put into operation are updated simultaneously, and the multiplexing redundancy submodule is operated in the first working mode.

6. The strategy according to claim 5, characterized in that When the result of determining whether the second number of currently engaged jobs is equal to the initial configuration number is no, the method includes: Determining the third number of lower bridge arm neutron modules currently in operation; Determining whether the third number currently invested in the work is equal to the initial configuration number; If so, then based on the initial configuration quantity, the third quantity currently put into operation is updated, and the multiplexing redundancy submodule is operated in the first working mode; If not, the multiplexing redundant submodule is operated according to the normal operation processing strategy.

7. The strategy according to claim 6, characterized in that When the result of determining whether the third number currently put into operation is equal to the initial configuration number is no, the method includes: Based on the initial configuration quantity, the second quantity currently put into operation is updated, and the multiplexing redundancy submodule is operated in the first working mode.

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