Hybrid distributed energy storage modular multilevel converter and control method thereof

Abstract

The application relates to a hybrid distributed energy storage modular multilevel converter and a control method thereof, the modular multilevel converter comprising six bridge arms, wherein each bridge arm is mainly composed of N sub-modules, a bridge arm inductor and a bridge arm equivalent resistor in series, and the upper and lower bridge arms of each phase are combined to form a phase unit; the N sub-modules comprise N Q one full-bridge sub-module and N H one half-bridge sub-module, and the half-bridge sub-module is an energy storage type sub-module. The modular multilevel converter and the control method thereof are beneficial to realizing AC-DC interconnection, energy buffering and maintaining power grid stability, and reducing system construction cost and operation loss.

Description

Technical Field

[0001] This invention belongs to the field of power transmission and distribution technology, specifically relating to a hybrid distributed energy storage modular multilevel converter and its control method. Background Technology

[0002] With the construction of new power systems, new energy sources, represented by wind power and photovoltaics, are being connected to the grid on a large scale. However, the instability of these new energy sources is increasingly posing a threat to the power grid. To support the large-scale integration of new energy sources and ensure the safe operation of the grid, it is often necessary to combine them with energy storage devices. The power decoupling capability of energy storage devices can effectively decouple the input power of new energy sources from the power received by the grid. However, for enhancing the frequency response of large-scale new energy integration and virtual inertia control, only some MMC sub-modules need to be configured with energy storage, thereby reducing system construction and maintenance costs and increasing system reliability.

[0003] The paper "PDJudge,TCGreen, Modular Multilevel Converter With Partially Rated Integrated Energy Storage Suitable for Frequency Support and Ancillary Service Provision[J].IEEE Transactions on Power Delivery,2019,34(01):208-219." proposes a novel partially rated storage MMC (PRS-MMC) structure. To overcome the problem of requiring a large number of energy storage submodules during low-power operation, a control method for injecting circulating current into the branch current is designed. However, when the system is running, this circulating current may cause significant additional losses, therefore the proposed topology is not suitable for energy arbitrage purposes. Summary of the Invention

[0004] The purpose of this invention is to provide a hybrid distributed energy storage modular multilevel converter and its control method. This modular multilevel converter and its control method are beneficial for realizing AC / DC interconnection, energy buffering and maintaining grid stability, and reducing system construction costs and operating losses.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a hybrid distributed energy storage modular multilevel converter, comprising six bridge arms, wherein each bridge arm is mainly composed of N sub-modules, bridge arm inductors, and bridge arm equivalent resistances connected in series, and the upper and lower bridge arms of each phase are combined to form a phase unit; the N sub-modules include N QOne full-bridge submodule and N H Each half-bridge submodule is an energy storage submodule.

[0006] Furthermore, the half-bridge submodule includes two insulated-gate bipolar transistors with anti-parallel diodes, a first submodule DC capacitor, a submodule filter inductor, and an energy storage battery. The two insulated-gate bipolar transistors with anti-parallel diodes are connected in parallel with the series circuit of the first submodule DC capacitor, the submodule filter inductor, and the energy storage battery.

[0007] Furthermore, the current input terminal flowing into the submodule is simultaneously connected to the emitter of the first insulated-gate bipolar transistor and the collector of the second insulated-gate bipolar transistor. The collector of the first insulated-gate bipolar transistor is divided into two paths: one path is connected to one end of the DC capacitor of the first submodule, and the other path is connected to the positive terminal of the energy storage battery through the submodule filter inductor. The other end of the DC capacitor of the first submodule, the negative terminal of the energy storage battery, and the emitter of the second insulated-gate bipolar transistor are simultaneously connected to the current output terminal flowing out of the submodule.

[0008] Furthermore, the half-bridge submodule has three operating states: latched state, engaged state, and disconnected state. The first insulated-gate bipolar transistor (IGBT) and its first anti-parallel diode are considered as the first switching device, and the second IGBT and its second anti-parallel diode are considered as the second switching device. When the half-bridge submodule is in the engaged state, the first switching device is turned on while the second switching device is turned off, allowing current to flow bidirectionally through the first switching device, and the submodule's external voltage is the capacitor voltage U. c When the half-bridge submodule is in the disconnected state, the first switching device is turned off and the second switching device is turned on, and the current flows bidirectionally through the second switching device, and the external voltage of the submodule is 0; while when the half-bridge submodule is in the locked state, the first and second switching devices are intermittently switched on and off.

[0009] Furthermore, when both the first and second insulated-gate bipolar transistors (IGBTs) are turned off, the half-bridge submodule is in a locked state. Based on the conduction status of the first anti-parallel diode on the first IGBT and the second anti-parallel diode on the second IGBT, there are two operating modes: mode (a) and mode (b). In mode (a), the first anti-parallel diode is on, and the submodule current charges the first submodule DC capacitor through the first anti-parallel diode, resulting in an output voltage equal to the capacitor voltage. In mode (b), the second anti-parallel diode is on, and the submodule current bypasses the capacitor through the second anti-parallel diode, resulting in an output voltage of 0.

[0010] When the first insulated-gate bipolar transistor (IGBT) is given an on signal and the second IGBT is given an off signal, the half-bridge submodule is in the active state. Based on the current flow direction of the submodule, it operates in two modes: mode (c) and mode (d). In mode (c), the first anti-parallel diode is on, while the first IGBT is subjected to a reverse voltage. Despite the on signal, it remains off. The submodule current charges the capacitor through the first anti-parallel diode, and the output voltage is the capacitor voltage. In mode (d), the first IGBT is on, while the first anti-parallel diode is off due to the reverse voltage. The submodule current discharges the first submodule DC capacitor through the first IGBT, and the output voltage is the capacitor voltage.

[0011] When the first insulated-gate bipolar transistor (IGBT) is turned off and the second IGBT is turned on, the half-bridge submodule is in a disconnected state. Based on the current flow direction, it operates in two modes: mode (e) and mode (f). In mode (e), the second IGBT is turned on, while the second anti-parallel diode is turned off due to reverse voltage. The submodule current bypasses the capacitor through the second IGBT, resulting in a zero output voltage. In mode (f), the second anti-parallel diode is turned on, while the second IGBT is turned off despite the applied turn-on signal. The submodule current bypasses the capacitor through the second anti-parallel diode, resulting in a zero output voltage.

[0012] Furthermore, the full-bridge submodule includes four insulated-gate bipolar transistors with anti-parallel diodes and a second submodule DC capacitor. The series circuit of the four insulated-gate bipolar transistors with anti-parallel diodes connected in pairs is simultaneously connected in parallel with the second submodule DC capacitor.

[0013] Furthermore, the emitter of the third insulated-gate bipolar transistor (IGBT) is connected to the collector of the fourth IGBT, the emitter of the fifth IGBT is connected to the collector of the sixth IGBT, the collectors of the third and fifth IGBTs are simultaneously connected to one end of the DC capacitor of the second submodule, and the emitters of the fourth and sixth IGBTs are simultaneously connected to the other end of the DC capacitor of the second submodule. The current input terminal flowing into the submodule is connected between the third and fourth IGBTs, and the current output terminal flowing out of the submodule is connected between the fifth and sixth IGBTs.

[0014] Furthermore, the full-bridge submodule has four operating states; the third insulated-gate bipolar transistor and its third anti-parallel diode are considered as the third switching device, the fourth insulated-gate bipolar transistor and its fourth anti-parallel diode are considered as the fourth switching device, the fifth insulated-gate bipolar transistor and its fifth anti-parallel diode are considered as the fifth switching device, and the sixth insulated-gate bipolar transistor and its sixth anti-parallel diode are considered as the sixth switching device; when the third and sixth switching devices are turned on, current flows bidirectionally through the third and sixth switching devices, and the submodule port voltage is the positive capacitance voltage U. c When the third and fifth switching devices are turned on, current flows bidirectionally through them, and the submodule port voltage is 0. When the fourth and sixth switching devices are turned on, current flows bidirectionally through them, and the submodule port voltage is 0. When the fourth and fifth switching devices are turned on, current flows bidirectionally through them, and the submodule port voltage is the negative capacitor voltage -U. c .

[0015] This invention also provides a control method for the above-mentioned hybrid distributed energy storage modular multilevel converter. During the charging process of the energy storage sub-module, the voltage equalization of the sub-module is achieved through the following control method:

[0016] Set P dc P represents the DC power transferred from the DC power supply to the modular multilevel converter. ac For the AC power output of the modular multilevel converter, i arm For the bridge arm current of the modular multilevel converter, N arm U represents the number of sub-modules that can be opened in the bridge arm. c_max U c_min These are the maximum and minimum allowable voltage values ​​for the submodule, respectively.

[0017] When the bridge arm current charges the bridge arm submodule, i.e. arm If N ≥ 0, then the energy storage submodule will be charged first; when N arm >N H All energy storage sub-modules and N were put into operation. arm -N H The full-bridge submodule with the lowest voltage; when N arm ≤N H , will N arm The energy storage submodule with the lowest voltage is put into operation, and N is selected. H -N arm If there are k full-bridge submodules with the highest voltage, and the voltage of any k submodules is greater than U... c_min Then, invest k energy storage submodules and invest k -Uc Full-bridge submodule;

[0018] When the bridge arm current discharges to the bridge arm submodule, i.e. arm If the voltage is less than 0, then the full-bridge submodule will be discharged first; that is, the submodule with a voltage greater than U will be prioritized for discharge. c_max The full-bridge submodule is then connected, followed by the energy storage submodule, and finally the submodule with a voltage less than U. c_max The full-bridge submodule.

[0019] When the bridge arm current discharges to the bridge arm submodule, i.e. arm If the voltage is less than 0, then the full-bridge submodule will be discharged first; specifically: the submodule with a voltage greater than or equal to U will be prioritized for discharge. c_max The full-bridge submodule is then connected, followed by the energy storage submodule, and finally the submodule with a voltage less than U. c_max The full-bridge submodule.

[0020] Compared with existing technologies, this invention has the following advantages: It provides a hybrid distributed energy storage modular multilevel converter and its control method. By using energy storage half-bridge submodules and full-bridge submodules, this invention enables the modular multilevel converter system to achieve AC / DC interconnection, energy buffering, and grid stability maintenance when energy storage is configured in the distributed part. Furthermore, the control method proposed in this invention prioritizes the two types of submodules under different operating states of the modular multilevel converter, eliminating the need for injecting additional circulating current or adding extra hardware circuitry, thus reducing system construction and operating costs. Attached Figure Description

[0021] Figure 1 This is a topology diagram of the hybrid distributed energy storage modular multilevel converter according to an embodiment of the present invention;

[0022] Figure 2 This is a topology diagram of the half-bridge submodule in an embodiment of the present invention;

[0023] Figure 3 This is a topology diagram of the full-bridge submodule in an embodiment of the present invention;

[0024] Figure 4 This is a schematic diagram of three switching states of the half-bridge submodule in an embodiment of the present invention;

[0025] Figure 5 This is a schematic diagram of the switching state of the full-bridge submodule in an embodiment of the present invention;

[0026] Figure 6 This is a schematic diagram of the structure of the DC power transmission system in an embodiment of the present invention;

[0027] Figure 7This is a steady-state simulation waveform diagram of the system under 6MW charging state in an embodiment of the present invention;

[0028] Figure 8 This is a steady-state simulation waveform diagram of the system under 3MW charging state in an embodiment of the present invention;

[0029] Figure 9 This is a dynamic simulation waveform diagram of the system under variable power charging state in an embodiment of the present invention. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] This invention provides a hybrid distributed energy storage modular multilevel converter (MMC-BESS) and its control method. By combining a full-bridge submodule (FBSM) and a half-bridge energy storage submodule (HBSM), it achieves AC / DC interconnection, energy buffering, and grid stability maintenance, while reducing system construction costs and operating losses.

[0034] Figure 1 This is a topology diagram of the hybrid distributed energy storage modular multilevel converter in this embodiment. (See diagram for example.) Figure 1 As shown, the hybrid distributed energy storage modular multilevel converter provided in this embodiment includes six bridge arms, each of which mainly consists of N sub-modules, a bridge arm inductor L, and a bridge arm equivalent resistance R connected in series. The upper and lower bridge arms of each phase are combined to form a phase unit. The N sub-modules include N... Q One full-bridge submodule (Full-BridgeSM, FBSM) and N HA half-bridge submodule (HBSM). The half-bridge submodule is an energy storage type submodule. The bridge arm inductors have three main functions: 1. Suppressing the starting current during MMC startup; 2. Suppressing the bridge arm circulating current during normal MMC operation; 3. Suppressing the short-circuit current during MMC DC faults. The bridge arm equivalent resistance is used to represent the bridge arm losses. Figure 1 In the diagram, point O represents the zero-potential reference point, and the voltage between the positive and negative DC buses is U. dc .

[0035] There are three main types of submodule topologies: Half-BridgeSM (HBSM), Full-BridgeSM (FBSM), and Clamp-DoubleSM (CDSM). Considering that the bridge arm current may exhibit a short-duration zero-crossing current or even no zero-crossing current during high-power charging and discharging of the MMC-BESS, the MMC topology proposed in this invention uses a hybrid of full-bridge submodules and energy storage-type half-bridge submodules to achieve balanced voltage control of the submodules under these conditions.

[0036] Figure 2 This is a topology diagram of the half-bridge submodule in this embodiment. For example... Figure 2 As shown, the half-bridge submodule includes two insulated-gate bipolar transistors T1 and T2 with anti-parallel diodes, a first submodule DC capacitor C0, and a submodule filter inductor L. SM The two insulated-gate bipolar transistors (IGBTs) with anti-parallel diodes are connected in parallel with the series circuit of the first submodule DC capacitor C0, the submodule filter inductor, and the energy storage battery. The current input terminal flowing into the submodule is simultaneously connected to the emitter of the first IGBT T1 and the collector of the second IGBT T2. The collector of the first IGBT T1 is divided into two paths: one path is connected to one end of the first submodule DC capacitor C0, and the other path passes through the submodule filter inductor L. SM The positive terminal of the energy storage battery is connected, and the other end of the DC capacitor C0 of the first submodule, the negative terminal of the energy storage battery, and the emitter of the second insulated gate bipolar transistor T2 are simultaneously connected to the current output terminal of the submodule. Figure 2 In the diagram, D1 and D2 represent anti-parallel diodes, u c Represents capacitor voltage, u sm i represents the voltage across the submodule. sm V represents the current flowing into the submodule. c This represents the voltage across the battery terminals.

[0037] Figure 3 This is a topology diagram of the full-bridge submodule in this embodiment. For example... Figure 3As shown, the full-bridge submodule includes four insulated-gate bipolar transistors T3, T4, T5, and T6 with anti-parallel diodes and a second submodule DC capacitor C0. The series circuit of the four insulated-gate bipolar transistors with anti-parallel diodes connected in pairs is simultaneously connected in parallel with the second submodule DC capacitor C0. The emitter of the third insulated-gate bipolar transistor T3 is connected to the collector of the fourth insulated-gate bipolar transistor T4, and the emitter of the fifth insulated-gate bipolar transistor T5 is connected to the collector of the sixth insulated-gate bipolar transistor T6. The collectors of the third insulated-gate bipolar transistor T3 and the fifth insulated-gate bipolar transistor T5 are simultaneously connected to one end of the DC capacitor of the second submodule. The emitters of the fourth insulated-gate bipolar transistor T4 and the sixth insulated-gate bipolar transistor T6 are simultaneously connected to the other end of the DC capacitor of the second submodule. The current input terminal flowing into the submodule is connected between the third insulated-gate bipolar transistor T3 and the fourth insulated-gate bipolar transistor T4, and the current output terminal flowing out of the submodule is connected between the fifth insulated-gate bipolar transistor T5 and the sixth insulated-gate bipolar transistor T6. Figure 3 In the diagram, D3, D4, D5, and D6 represent anti-parallel diodes, respectively. c Represents capacitor voltage, u sm i represents the voltage across the submodule. sm This represents the current flowing into the submodule.

[0038] Depend on Figure 2 and Figure 3 Thus, each submodule is connected to the main circuit topology via AB series connection, and the MMC supports the bus voltage through the capacitor voltage in each submodule.

[0039] Under normal operating conditions, T1 and T2 are complementary switches, alternately turning on and off. For example... Figure 4 As shown, the half-bridge submodule has three working states: locked state, engaged state, and disconnected state.

[0040] When both the first and second insulated-gate bipolar transistors (IGBTs) are turned off, the half-bridge submodule is in a locked state. Based on the conduction status of the first anti-parallel diode on the first IGBT and the second anti-parallel diode on the second IGBT, there are two operating modes: mode (a) and mode (b). In mode (a), the first anti-parallel diode is on, and the submodule current charges the first submodule's DC capacitor through the first anti-parallel diode, resulting in an output voltage equal to the capacitor voltage. In mode (b), the second anti-parallel diode is on, and the submodule current bypasses the capacitor through the second anti-parallel diode, resulting in an output voltage of 0.

[0041] When the first insulated-gate bipolar transistor (IGBT) is given an on signal and the second IGBT is given an off signal, the half-bridge submodule is in the active state. Based on the current flow direction of the submodule, it operates in two modes: mode (c) and mode (d). In mode (c), the first anti-parallel diode is turned on, while the first IGBT is subjected to a reverse voltage. Despite the applied on signal, it remains off. The submodule current charges the capacitor through the first anti-parallel diode, and the output voltage is the capacitor voltage. In mode (d), the first IGBT is turned on, while the first anti-parallel diode is turned off due to the reverse voltage. The submodule current discharges the first submodule DC capacitor through the first IGBT, and the output voltage is the capacitor voltage.

[0042] When the first insulated-gate bipolar transistor (IGBT) is turned off and the second IGBT is turned on, the half-bridge submodule is in a disconnected state. Based on the current flow direction, it operates in two modes: mode (e) and mode (f). In mode (e), the second IGBT is turned on, while the second anti-parallel diode is turned off due to reverse voltage. The submodule current bypasses the capacitor through the second IGBT, resulting in a zero output voltage. In mode (f), the second anti-parallel diode is turned on, while the second IGBT is turned off despite the applied turn-on signal. The submodule current bypasses the capacitor through the second anti-parallel diode, resulting in a zero output voltage.

[0043] The above analysis shows that when the submodule enters steady-state mode, only one transistor is in the conducting state. If we consider the first insulated-gate bipolar transistor and its first anti-parallel diode as the first switching device, and the second insulated-gate bipolar transistor and its second anti-parallel diode as the second switching device; when the half-bridge submodule is in the active state, the first switching device is turned on while the second switching device is turned off. Current flows bidirectionally through the first switching device, and the submodule's external voltage is the capacitor voltage U. c When the half-bridge submodule is in the disconnected state, the first switching device is turned off and the second switching device is turned on, and the current flows bidirectionally through the second switching device, and the external voltage of the submodule is 0; while when the half-bridge submodule is in the locked state, the first and second switching devices are intermittently switched on and off.

[0044] Under normal operating conditions, the full-bridge submodule can output -U by controlling the switching states of the four IGBTs. c , 0 and U c Three levels offer a high degree of control flexibility. Figure 5 The four operating states of the full-bridge submodule under normal operation are shown.

[0045] Similar to the analysis of the half-bridge submodule, the third insulated-gate bipolar transistor (IGBT) and its third anti-parallel diode are considered as the third switching device; the fourth IGBT and its fourth anti-parallel diode are considered as the fourth switching device; the fifth IGBT and its fifth anti-parallel diode are considered as the fifth switching device; and the sixth IGBT and its sixth anti-parallel diode are considered as the sixth switching device. When the third and sixth switching devices are turned on, current flows bidirectionally through them, and the submodule port voltage is the positive capacitor voltage U. c When the third and fifth switching devices are turned on, current flows bidirectionally through them, and the submodule port voltage is 0. When the fourth and sixth switching devices are turned on, current flows bidirectionally through them, and the submodule port voltage is 0. When the fourth and fifth switching devices are turned on, current flows bidirectionally through them, and the submodule port voltage is the negative capacitor voltage -U. c .

[0046] The total DC voltage control of the three-phase modular multilevel converter and the parallel structure of the three phase units can maintain the DC voltage balance of the phase units. As the switching states of the upper and lower bridge arm sub-modules of the phase unit change, voltage balance can also be achieved between the upper and lower bridge arm sub-modules. Therefore, the voltage balance control of the three-phase modular multilevel converter can be based on one bridge arm.

[0047] The traditional capacitor voltage balancing strategy is as follows:

[0048] 1. Detect the voltage value of each SM capacitor using a voltage sensor.

[0049] 2. Detect the current direction of each bridge arm using a current sensor.

[0050] 3. Based on the number N of modules N that are in real-time engaged in the valve group level control output bridge arm, the controller sorts the bridge arm voltages.

[0051] However, during high-power charging and discharging, the bridge arm current of the energy storage MMC may have a short period of zero-crossing current or even no zero-crossing current, which causes the overall voltage of the bridge arm submodule to rise and deviate from the rated voltage value.

[0052] In view of this, this embodiment proposes a control method applicable to the above-mentioned hybrid distributed energy storage modular multilevel converter, namely, a submodule voltage equalization strategy applicable to the above-mentioned hybrid distributed energy storage modular multilevel converter.

[0053] Taking the charging process of the energy storage submodule as an example (i.e., P) dc >P acThe discharging process is similar and will not be described in detail here. The specific steps of its charging process are as follows:

[0054] 1. Set P dc P represents the DC power transferred from the DC power supply to the modular multilevel converter. ac For the AC power output of the modular multilevel converter, i arm For the bridge arm current of the modular multilevel converter, N arm U represents the number of sub-modules that can be opened in the bridge arm. c_max U c_min These represent the maximum and minimum allowable voltage values ​​for the submodule, respectively.

[0055] 2. When the bridge arm current charges the bridge arm submodule, i.e. arm If N ≥ 0, then the energy storage submodule will be charged first; when N arm >N H All energy storage sub-modules and N were put into operation. arm -N H The full-bridge submodule with the lowest voltage; when N arm ≤N H , will N arm The energy storage submodule with the lowest voltage is put into operation, and N is selected. H -N arm If there are k full-bridge submodules with the highest voltage, and the voltage of any k submodules is greater than U... c_min Then, invest k energy storage submodules and invest k -U c Full-bridge submodule.

[0056] 3. When the bridge arm current discharges to the bridge arm submodule, i.e. arm If the voltage is less than 0, then the full-bridge submodule will be discharged first; that is, the submodule with a voltage greater than or equal to U will be prioritized for discharge. c_max The full-bridge submodule is then connected, followed by the energy storage submodule, and finally the submodule with a voltage less than U. c_max The full-bridge submodule.

[0057] The above describes the control method for the hybrid distributed energy storage modular multilevel converter proposed in this invention. This control method provides comprehensive balanced control for energy storage submodules and non-energy storage submodules. By controlling the activation priority of energy storage and non-energy storage submodules under different operating states of the MMC-BESS, it achieves balanced voltage control of the bridge arm submodules. This strategy does not require the injection of additional circulating current or the addition of additional hardware circuitry, which helps to further reduce system construction and operating costs.

[0058] This embodiment uses MATLAB / Simulink to build a system as follows: Figure 6The single-ended MMC-BESS type VSC-HVDC system shown has been verified through simulation, proving its feasibility. The parameters of the MMC-BESS and control system in the simulation are shown in Table 1.

[0059] Table 1 Simulation System Parameters

[0060]

[0061]

[0062] The simulation verification will be carried out from the following two aspects to verify the feasibility of the present invention: (1) comparison of simulation results under steady state of the system; (2) comparison of simulation results under variable power of the system.

[0063] (1) Comparison of simulation results under steady state of the system

[0064] The simulation verification takes the upper arm of phase A as the research object. Figure 7 When the charging power of the energy storage MMC is 6MW (P dc =8MW, P ac =2MW) system steady-state simulation waveform diagram, from top to bottom are AC phase a voltage, phase a bridge arm current, phase a bridge arm submodule capacitor voltage.

[0065] Figure 8 When the charging power of the energy storage MMC is 3MW (P dc =8MW, P ac =5MW) system steady-state simulation waveform diagram, from top to bottom: AC phase a voltage, phase a bridge arm current, phase a bridge arm submodule capacitor voltage.

[0066] (2) Comparison of simulation results under system variable power

[0067] Similarly, the simulation verification takes the upper arm of phase A as the research object. Figure 9 The charging power for energy storage MMC increases from 3MW to 6MW within 0.2 seconds (P). dc =8MW, P ac =2MW) system dynamic simulation waveform diagram, from top to bottom are AC phase a voltage, phase a bridge arm current, phase a bridge arm submodule capacitor voltage.

[0068] In summary, as shown by the simulation results above, the proposed topology and its submodule voltage balancing strategy can achieve good control performance under both dynamic and steady-state conditions, meeting the practical needs of engineering.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A hybrid distributed energy storage modular multilevel converter characterized by, It includes six bridge arms, each of which consists of N sub-modules, bridge arm inductors, and bridge arm equivalent resistances connected in series. The upper and lower bridge arms of each phase are combined to form a phase unit; the N sub-modules include N Q One full-bridge submodule and N H Each half-bridge submodule is an energy storage submodule; The half-bridge submodule includes two insulated-gate bipolar transistors with anti-parallel diodes, a first submodule DC capacitor, a submodule filter inductor, and an energy storage battery. The two insulated-gate bipolar transistors with anti-parallel diodes are connected in parallel with the series circuit of the first submodule DC capacitor, the submodule filter inductor, and the energy storage battery. The current input terminal flowing into the submodule is simultaneously connected to the emitter of the first insulated gate bipolar transistor and the collector of the second insulated gate bipolar transistor. The collector of the first insulated gate bipolar transistor is divided into two paths: one path is connected to one end of the DC capacitor of the first submodule, and the other path is connected to the positive terminal of the energy storage battery through the submodule filter inductor. The other end of the DC capacitor of the first submodule, the negative terminal of the energy storage battery, and the emitter of the second insulated gate bipolar transistor are simultaneously connected to the current output terminal flowing out of the submodule. The full-bridge submodule includes four insulated-gate bipolar transistors (IGBTs) with anti-parallel diodes and a second submodule DC capacitor. The series circuit of the four IGBTs with anti-parallel diodes connected in pairs is simultaneously connected in parallel with the second submodule DC capacitor. The emitter of the third IGBT is connected to the collector of the fourth IGBT, and the emitter of the fifth IGBT is connected to the collector of the sixth IGBT. The collectors of the third and fifth IGBTs are simultaneously connected to one end of the second submodule DC capacitor, and the emitters of the fourth and sixth IGBTs are simultaneously connected to the other end of the second submodule DC capacitor. The current input terminal flowing into the submodule is connected between the third and fourth IGBTs, and the current output terminal flowing out of the submodule is connected between the fifth and sixth IGBTs.

2. The hybrid distributed energy storage modular multilevel converter according to claim 1, characterized in that, The half-bridge submodule has three operating states: latched state, engaged state, and disconnected state. The first insulated-gate bipolar transistor (IGBT) and its first anti-parallel diode are considered as the first switching device, and the second IGBT and its second anti-parallel diode are considered as the second switching device. When the half-bridge submodule is in the engaged state, the first switching device is turned on while the second switching device is turned off, allowing current to flow bidirectionally through the first switching device, and the submodule's external voltage is the capacitor voltage U. c When the half-bridge submodule is in the disconnected state, the first switching device is turned off and the second switching device is turned on, and the current flows bidirectionally through the second switching device, and the external voltage of the submodule is 0; while when the half-bridge submodule is in the locked state, the first and second switching devices are intermittently switched on and off.

3. The hybrid distributed energy storage multilevel converter of claim 2, wherein, When both the first and second insulated-gate bipolar transistors (IGBTs) are turned off, the half-bridge submodule is in a locked state. Based on the conduction status of the first anti-parallel diode on the first IGBT and the second anti-parallel diode on the second IGBT, there are two operating modes: mode (a) and mode (b). In mode (a), the first anti-parallel diode is on, and the submodule current charges the first submodule's DC capacitor through the first anti-parallel diode, resulting in an output voltage equal to the capacitor voltage. In mode (b), the second anti-parallel diode is on, and the submodule current bypasses the capacitor through the second anti-parallel diode, resulting in an output voltage of 0. When the first insulated-gate bipolar transistor (IGBT) is given an on signal and the second IGBT is given an off signal, the half-bridge submodule is in the active state. Based on the current flow direction of the submodule, it operates in two modes: mode (c) and mode (d). In mode (c), the first anti-parallel diode is on, while the first IGBT is subjected to a reverse voltage. Despite the on signal, it remains off. The submodule current charges the capacitor through the first anti-parallel diode, and the output voltage is the capacitor voltage. In mode (d), the first IGBT is on, while the first anti-parallel diode is off due to the reverse voltage. The submodule current discharges the first submodule DC capacitor through the first IGBT, and the output voltage is the capacitor voltage. When the first insulated-gate bipolar transistor (IGBT) is turned off and the second IGBT is turned on, the half-bridge submodule is in a disconnected state. Based on the current flow direction of the submodule, it operates in two modes: mode (e) and mode (f). In mode (e), the second IGBT is turned on, while the second anti-parallel diode is turned off due to reverse voltage. The submodule current bypasses the capacitor through the second IGBT, resulting in an output voltage of 0. In mode (f), the second anti-parallel diode is turned on, while the second IGBT is turned off despite the applied turn-on signal. The submodule current bypasses the capacitor through the second anti-parallel diode, resulting in an output voltage of 0.

4. The hybrid distributed energy storage multilevel converter of claim 1, wherein, The full-bridge submodule has four operating states; the third insulated-gate bipolar transistor and its third anti-parallel diode are considered as the third switching device, the fourth insulated-gate bipolar transistor and its fourth anti-parallel diode are considered as the fourth switching device, the fifth insulated-gate bipolar transistor and its fifth anti-parallel diode are considered as the fifth switching device, and the sixth insulated-gate bipolar transistor and its sixth anti-parallel diode are considered as the sixth switching device; when the third and sixth switching devices are turned on, current flows bidirectionally through the third and sixth switching devices, and the submodule port voltage is the positive capacitance voltage U. c When the third and fifth switching devices are turned on, current flows bidirectionally through them, and the submodule port voltage is 0. When the fourth and sixth switching devices are turned on, current flows bidirectionally through them, and the submodule port voltage is 0. When the fourth and fifth switching devices are turned on, current flows bidirectionally through them, and the submodule port voltage is the negative capacitor voltage -U. c .

5. The control method of the hybrid distributed energy storage multilevel converter according to any one of claims 1-4, characterized in that, During the charging process of the energy storage submodule, voltage balancing of the submodule is achieved through the following control method: Setting a direct current power transmitted by a direct current source to a modular multilevel converter, an alternating current power output by the modular multilevel converter, a bridge arm current of the modular multilevel converter, a number of bridge arm on submodules, a maximum and a minimum of the allowed submodule voltage, respectively; When the bridge arm current charges the bridge arm submodule, that is... In this case, the energy storage submodule will be charged first; when All energy storage sub-modules and The lowest voltage full-bridge submodule; when ,Will The energy storage submodule with the lowest voltage is put into operation, and takes... If there are k sub-modules with the highest voltage in the full-bridge circuit, and the voltage of any of these sub-modules is greater than [a certain value]... Then, invest k energy storage submodules and invest k... Full-bridge submodule; When the bridge arm current discharges the bridge arm sub-module, that is , the full-bridge sub-module is preferentially discharged; specifically, the full-bridge sub-module with a sub-module voltage greater than or equal to is preferentially put into operation, the energy storage type sub-module is then put into operation, and finally the full-bridge sub-module with a sub-module voltage less than is put into operation.

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