A network-type SVG device startup topology structure and two-stage startup method thereof

Abstract

The present invention relates to the field of power system energy storage technology, and in particular to a grid-type SVG device startup topology and a two-stage startup method thereof. The topology comprises a startup circuit and an energy storage static VAR generator; the energy storage static VAR generator comprises a modular multi-level converter valve circuit and a supercapacitor circuit; the modular multi-level converter valve circuit comprises an upper bridge arm and a lower bridge arm, each of which comprises a plurality of series-connected half-bridge submodules; the modular multi-level converter valve circuit controls energy conversion between an AC system and a DC system and regulates grid voltage by controlling the half-bridge submodules; each supercapacitor branch of the supercapacitor circuit comprises a plurality of series-connected supercapacitor submodules; the supercapacitor submodules are used for energy storage and discharge. The present invention achieves smooth startup and efficient charging of a grid-type SVG device containing supercapacitors through a two-stage startup method for the grid-type SVG device startup topology.

Description

Technical Field

[0001] The present invention relates to the technical field of power system energy storage technology, and in particular to a grid-type SVG device startup topology structure and a two-stage startup method thereof. Background Art

[0002] With the rapid development of renewable energy power generation technologies, large-scale wind power, photovoltaic power and other renewable energy sources have been connected to the power grid, gradually replacing traditional synchronous generators. This change has brought a series of challenges, especially in terms of frequency and voltage regulation of the power system. Compared with traditional synchronous generators, renewable energy power generation is usually connected to the grid through power electronic converters. However, new energy equipment lacks the necessary system inertia and dynamic response capabilities, resulting in the continuous weakening of the inertia and damping characteristics of the entire power system. This change makes the frequency change faster and the regulation more difficult when the power grid faces short-term power fluctuations. At the same time, the short-circuit ratio of the power grid is reduced, further limiting the absorption capacity of renewable energy and the transmission efficiency of key transmission channels.

[0003] In order to solve the above problems and enhance the active support capability of new energy for the power grid, the introduction of grid-type energy storage devices has become the focus of industry attention. This type of grid-type energy storage device can effectively supplement the inertia and damping of the power system, and improve the stability and transmission capacity of the system. Supercapacitors, as an energy storage element, have demonstrated good performance in high-power applications due to their high power density, fast charging and discharging speed, high efficiency and low maintenance cost. In particular, supercapacitor energy storage devices also have regulation functions such as rapid reactive power support, inertia provision, damping enhancement and primary frequency modulation, which are of great significance for improving the dynamic characteristics of the power system.

[0004] However, in practical applications, achieving reliable startup in grid-type SVG devices containing supercapacitors has become a technical challenge that needs to be addressed urgently. As a key reactive compensation device in power systems, the stability and reliability of the SVG device's startup process are directly related to the safe operation of the entire system. Traditional startup methods often ignore the characteristics of supercapacitors, resulting in current surges, voltage fluctuations, and other problems during startup, which affect the performance and lifespan of the SVG device. Therefore, a method for starting grid-type SVG devices containing supercapacitors is urgently needed to improve the startup performance and operational stability of the SVG device, providing strong support for the safe and stable operation of the power system. Summary of the Invention

[0005] The present invention aims to provide a meshed SVG device startup topology and a two-stage startup method. The two-stage startup method achieves smooth startup and efficient charging of the supercapacitor-based meshed SVG device, thereby improving the system's instantaneous frequency and voltage support capabilities.

[0006] In order to solve the above technical problems, the present invention provides a mesh-type SVG device startup topology structure and a two-stage startup method thereof.

[0007] In a first aspect, the present invention provides a grid-type SVG device startup topology, comprising a control system, a main circuit breaker connected to the control system, a startup circuit, and a supercapacitor-based energy storage static VAR generator; the main circuit breaker is connected to the energy storage static VAR generator via the startup circuit; the supercapacitor-based energy storage static VAR generator comprises a modular multi-level converter valve circuit and a supercapacitor circuit connected in parallel;

[0008] The modular multilevel converter valve circuit includes a plurality of modular multilevel converter valve branches connected in parallel, each of the modular multilevel converter valve branches includes an upper bridge arm and a lower bridge arm connected in series, and each of the upper bridge arm and the lower bridge arm includes a plurality of half-bridge sub-modules connected in series; the modular multilevel converter valve circuit is used to control energy conversion between an AC system and a DC system, and to regulate the grid voltage by controlling the switching state of the half-bridge sub-modules;

[0009] The supercapacitor circuit includes a plurality of supercapacitor branches, each of which includes a plurality of supercapacitor submodules connected in series; the supercapacitor submodules are used for energy storage and discharge;

[0010] The control system is used to enter the modular multi-level converter valve circuit charging phase by controlling the switching actions of the main circuit breaker and the energy storage type static VAR generator in response to the start signal;

[0011] Furthermore, the half-bridge submodules are unlocked in an orderly manner by controlling and starting an active charging strategy, so that the modular multi-level converter valve circuit charges the supercapacitor branch, entering the supercapacitor charging phase.

[0012] In a further embodiment, the half-bridge submodule includes a first switch module, a second switch module, a first DC capacitor, a bypass switch, and a turning thyristor;

[0013] The first switch module and the second switch module are connected in series and then connected in parallel with the first DC capacitor; the bypass switch and the turning thyristor are connected in parallel with the second switch module.

[0014] In a further embodiment, the supercapacitor submodule includes a third switch module, a fourth switch module, a second DC capacitor and a supercapacitor;

[0015] The third switch module and the fourth switch module are connected in series and then connected in parallel with the second DC capacitor, and the supercapacitor is connected in parallel with the second DC capacitor.

[0016] In a further embodiment, the first switch module includes a first switch tube and a first diode anti-parallel connected to the first switch tube;

[0017] The second switch module includes a second switch tube and a second diode connected in anti-parallel with the second switch tube.

[0018] In a further embodiment, the third switch module includes a third switch tube and a third diode anti-parallel connected to the third switch tube;

[0019] The fourth switch module includes a fourth switch tube and a fourth diode connected in anti-parallel with the fourth switch tube.

[0020] In a further embodiment, the modular multi-level converter valve circuit also includes two first current-limiting reactors connected in series between the upper bridge arm and the lower bridge arm, and the first current-limiting reactors are used to reduce the DC current fluctuations generated by the supercapacitor during the switching process.

[0021] In a further embodiment, the starting circuit includes a starting resistor, a starting isolating switch, a first DC side switch, and a second DC side switch;

[0022] The first DC side switch and the second DC side switch are respectively arranged at two common ends between the modular multi-level converter valve circuit and the supercapacitor circuit. The first DC side switch and the second DC side switch are used to control the modular multi-level converter valve circuit to charge the supercapacitor branch by switching the electrical connection state between the modular multi-level converter valve circuit and the supercapacitor branch.

[0023] In a further embodiment, one end of the starting resistor connected in parallel with the starting isolating switch is connected to the common end between the two first current limiting reactors, and the other end of the starting resistor connected in parallel with the starting isolating switch is connected to the main circuit breaker; the starting resistor is used to limit overcurrent during the charging process of the supercapacitor circuit.

[0024] In a further embodiment, each of the supercapacitor branches further includes a second current limiting reactor; the second current limiting reactor is used to reduce the DC current fluctuations generated by the supercapacitor during charging and discharging;

[0025] The second DC side switch is connected to one end of a plurality of super capacitor submodules connected in series through the second current limiting reactor, and the other end of the plurality of super capacitor submodules connected in series is connected to the first DC side switch.

[0026] In a second aspect, the present invention provides a two-stage startup method for a meshed SVG device startup topology structure, using the meshed SVG device startup topology structure described above, wherein the startup circuit includes a startup resistor, a startup isolation switch, a first DC side switch, and a second DC side switch; the two-stage startup method includes the following steps:

[0027] In response to the start signal, controlling the main circuit breaker to close so that the grid-type SVG device starts the topology structure and establishes a connection with the external power system;

[0028] Control the bypass paths of all half-bridge submodules in the modular multi-level converter valve circuit to be in a non-blocking state, and connect the starting resistor to the starting loop;

[0029] The half-bridge submodule in the modular multi-level converter valve circuit is charged through the AC system, entering the modular multi-level converter valve circuit charging phase;

[0030] Controlling the start isolation switch of the start loop to close, so as to initiate the active charging strategy to orderly unlock the half-bridge sub-module, and during the unlocking process, controlling the voltage on the modular multi-level converter valve circuit side to zero;

[0031] Close the first DC side switch and the second DC side switch to charge the supercapacitor branch through the modular multi-level converter valve circuit, and raise the DC voltage to the rated voltage, entering the supercapacitor charging phase;

[0032] After the DC voltage reaches the rated voltage, the supercapacitor branch is unlocked and charged with constant power current limiting until the supercapacitor branch is charged. The AC system is switched from the charging mode to the grid control operation mode.

[0033] The present invention provides a grid-type SVG device startup topology and a two-stage startup method thereof. The grid-type SVG device startup topology includes a main circuit breaker, a startup circuit, and a supercapacitor-based energy storage static VAR generator. The startup circuit includes a starting resistor, a starting disconnect switch, a first DC side switch, and a second DC side switch. The supercapacitor-based energy storage static VAR generator includes a modular multilevel converter valve circuit and a supercapacitor circuit connected in parallel. The modular multilevel converter valve circuit includes multiple parallel-connected modular multilevel converter valve branches, each of which includes an upper bridge arm and a lower bridge arm connected in series, each of which includes multiple half-bridge sub-modules connected in series. The modular multilevel converter valve circuit is used to control energy conversion between an AC system and a DC system and regulate the grid voltage by controlling the switching states of the half-bridge sub-modules. The supercapacitor circuit includes multiple supercapacitor branches, each of which includes multiple supercapacitor sub-modules connected in series. The supercapacitor sub-modules are used to store and discharge energy. Compared with existing technologies, this grid-type SVG device startup topology achieves smooth startup and efficient charging of grid-type SVG devices containing supercapacitors through an orderly two-stage startup method. It effectively suppresses current fluctuations during startup, reduces power impact on the power grid, and improves the system's instantaneous frequency and voltage support capabilities. It solves the problems of poor grid stability caused by fluctuations when new energy is connected to the grid, and the large power impact on the grid caused by traditional startup methods during the startup of SVG devices, thereby improving the reliability and flexibility of power grid operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the startup topology structure of a meshed SVG device provided in an embodiment of the present invention;

[0035] Figure 2 Schematic diagram of a half-bridge submodule provided by an embodiment of the present invention;

[0036] Figure 3 Schematic diagram of a supercapacitor submodule provided by an embodiment of the present invention;

[0037] Figure 4 1. A schematic flow chart of a two-stage startup method for a meshed SVG device to start a topology structure according to an embodiment of the present invention;

[0038] Figure 5 This is a two-stage startup logic block diagram provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following describes the embodiments of the present invention in detail with reference to the accompanying drawings. The embodiments are provided for illustrative purposes only and are not to be construed as limiting the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute a limitation on the scope of protection of the present invention. Many changes may be made to the present invention without departing from the spirit and scope of the present invention.

[0040] refer to Figure 1 , the embodiment of the present invention provides a network-type SVG device startup topology structure, such as Figure 1 As shown, the grid-type SVG device startup topology includes a control system, a main circuit breaker QF1 connected to the control system, a startup circuit, and a supercapacitor-based energy storage static VAR generator. The main circuit breaker is connected to the energy storage static VAR generator via the startup circuit. The control system is used to respond to a startup signal and enter the modular multi-level converter valve circuit charging phase by controlling the switching actions of the main circuit breaker and the energy storage static VAR generator. The control system is also used to sequentially unlock the half-bridge sub-modules by controlling the startup active charging strategy, so that the modular multi-level converter valve circuit charges the supercapacitor branch, entering the supercapacitor charging phase.

[0041] In this embodiment, the supercapacitor-based energy storage static VAR generator includes a modular multilevel converter valve circuit and a supercapacitor circuit connected in parallel. The modular multilevel converter valve circuit (MMC converter valve circuit) and the supercapacitor circuit can be connected through a bidirectional DC-DC converter. The bidirectional DC-DC converter can be used to control the energy exchange between the modular multilevel converter valve circuit and the supercapacitor branch, thereby realizing energy charging and discharging control, ensuring that the supercapacitor provides energy to the MMC converter valve when needed, and the MMC converter valve charges the supercapacitor when it needs to be charged.

[0042] In this embodiment, the main circuit breaker QF1 is used to connect the meshed SVG device startup topology structure to the external power supply system, so that the main circuit breaker QF1 can be used to cut off or connect the power supply before the meshed SVG device startup topology structure is started. For example, during the startup process, this embodiment connects the meshed SVG device startup topology structure to the external power supply system by closing the main circuit breaker QF1, preparing to enter the startup process, thereby ensuring safe startup and normal operation of the device.

[0043] The startup circuit includes a startup resistor R1, a startup isolating switch QS1, a first DC side switch QS2, and a second DC side switch QS3; wherein the startup resistor R1 is used to provide current limiting in the startup circuit to limit overcurrent during the charging process of the supercapacitor circuit. In this embodiment, the startup resistor is used as a current limiting resistor during the startup process. By adding the startup resistor to the startup circuit, the overcurrent phenomenon occurring during the charging process is effectively suppressed, ensuring the smooth startup of the SVG device (static VAR generator); the startup isolating switch QS1 is used to control the on-off of the startup circuit. In this embodiment, by closing the startup isolating switch QS1, an active charging strategy can be initiated to orderly unlock the half-bridge sub-module in the MMC converter valve circuit; the first DC side switch QS2 and the second DC side switch QS3 are used to control the electrical connection between the MMC converter valve circuit and the supercapacitor branch. In this embodiment, by closing the first DC side switch QS2 and the second DC side switch QS3, the MMC converter valve can be controlled as a power supply to charge the supercapacitor branch, raising the DC voltage to the rated voltage.

[0044] In this embodiment, the modular multilevel converter valve circuit includes a plurality of modular multilevel converter valve branches connected in parallel. Each of the modular multilevel converter valve branches includes an upper bridge arm and a lower bridge arm connected in series, and two first current-limiting reactors connected in series between the upper bridge arm and the lower bridge arm. One end of the starting resistor connected in parallel with the starting disconnect switch is connected to a common end between the two first current-limiting reactors, and the other end of the starting resistor connected in parallel with the starting disconnect switch is connected to the main circuit breaker. The upper bridge arm and the lower bridge arm each include a plurality of half-bridge sub-modules SM connected in series. In this embodiment, the modular multilevel converter valve circuit is used to control energy conversion between an AC system and a DC system and regulate the grid voltage by controlling the switching states of the half-bridge sub-modules. It should be noted that the number of half-bridge sub-modules in the upper bridge arm and the lower bridge arm may be the same or different. Those skilled in the art may adjust the number of half-bridge sub-modules in the upper bridge arm and the lower bridge arm according to specific implementation circumstances, and are not limited to the embodiments of the present invention.

[0045] like Figure 2As shown, the half-bridge submodule SM includes a first switch module S1, a second switch module S2, a first DC capacitor C1, a bypass switch KM, and a turning thyristor T1. The first switch module S1 and the second switch module S2 are connected in series and then in parallel with the first DC capacitor C1. The bypass switch KM and the turning thyristor T1 are connected in parallel with the second switch module S2. The first switch module S1 includes a first switch transistor IGBT1 and a first diode VD1 connected in anti-parallel with the first switch transistor IGBT1. The second switch module S2 includes a second switch transistor IGBT2 and a second diode VD2 connected in anti-parallel with the second switch transistor IGBT2. In this embodiment, the first current-limiting reactor is used to reduce the DC current fluctuation generated by the supercapacitor during the switching process. The startup circuit realizes orderly unlocking of the half-bridge submodule during the startup process of the grid-type SVG device startup topology structure and controls the voltage on the MMC converter valve circuit side to 0, ensuring that the grid-type SVG device startup topology structure can be started safely and stably.

[0046] In this embodiment, the supercapacitor circuit includes multiple supercapacitor branches, each supercapacitor branch includes a second current limiting inductor and multiple supercapacitor submodules CM connected in series, the supercapacitor submodules are used for energy storage and discharge, and this embodiment provides reactive power support and voltage regulation functions required by the power grid by storing and quickly releasing energy through the supercapacitor submodules. In this embodiment, the second DC side switch is connected to one end of the multiple supercapacitor submodules connected in series through the second current limiting inductor, and the other end of the multiple supercapacitor submodules connected in series is connected to the first DC side switch. The second current limiting inductor is used to reduce the DC current fluctuations generated by the supercapacitor during the charging and discharging process.

[0047] like Figure 3 As shown, the supercapacitor submodule CM includes a third switch module S3, a fourth switch module S4, a second DC capacitor C2 and a supercapacitor SC; the third switch module S3 and the fourth switch module S4 are connected in series and then connected in parallel with the second DC capacitor C2, and the supercapacitor SC is connected in parallel with the second DC capacitor C2; wherein, the third switch module S3 includes a third switch tube IGBT3 and a third diode VD3 anti-parallel to the third switch tube IGBT3; the fourth switch module S4 includes a fourth switch tube IGBT4 and a fourth diode VD4 anti-parallel to the fourth switch tube IGBT4.

[0048] In this embodiment, the first DC side switch and the second DC side switch are respectively arranged at two common ends between the modular multilevel converter valve circuit and the supercapacitor circuit. The first DC side switch and the second DC side switch are used to control the modular multilevel converter valve circuit to charge the supercapacitor branch by switching the electrical connection state between the modular multilevel converter valve circuit and the supercapacitor branch.

[0049] An embodiment of the present invention provides a grid-type SVG device startup topology structure, which includes a main circuit breaker, a startup circuit, and a supercapacitor-based energy storage static VAR generator; the startup circuit includes a startup resistor, a startup disconnect switch, a first DC side switch, and a second DC side switch; the supercapacitor-based energy storage static VAR generator includes a modular multilevel converter valve circuit and a supercapacitor circuit connected in parallel; the modular multilevel converter valve circuit includes multiple modular multilevel converter valve branches connected in parallel, each of the multilevel converter valve branches includes an upper bridge arm and a lower bridge arm connected in series, and the upper bridge arm and the lower bridge arm each include multiple half-bridge sub-modules connected in series; the modular multilevel converter valve circuit is used to control energy conversion between an AC system and a DC system, and to adjust the grid voltage by controlling the switching state of the half-bridge sub-modules; the supercapacitor circuit includes multiple supercapacitor branches, each of which includes multiple supercapacitor sub-modules connected in series; the supercapacitor sub-modules are used to store and discharge energy. Compared with the existing technology, the grid-type SVG device startup topology adopted in this embodiment uses a modular multi-level converter valve circuit and supercapacitor circuit, combined with a two-stage startup method. It can achieve smooth startup and efficient charging of the supercapacitor-based grid-type SVG device. It effectively suppresses current fluctuations during startup, reduces power impact on the power grid, improves the system's instantaneous frequency and voltage support capabilities, and provides the power grid with more stable and efficient dynamic regulation capabilities.

[0050] In one embodiment, Figure 4 As shown, an embodiment of the present invention provides a two-stage startup method for a meshed SVG device startup topology structure. The two-stage startup method uses the meshed SVG device startup topology structure described above. The two-stage startup method includes the following steps:

[0051] S1 in response to the start signal, the control main circuit breaker is closed, so that the network-type SVG device starts the topology structure and establishes a connection with the external power system;

[0052] S2. Control the bypass paths of all half-bridge submodules in the modular multi-level converter valve circuit to be in a non-blocking state and connect the starting resistor to the starting loop;

[0053] S3. The half-bridge submodule in the modular multi-level converter valve circuit is charged through the AC system, and the modular multi-level converter valve circuit charging phase is entered;

[0054] S4. The start isolation switch of the control start circuit is closed to start the active charging strategy to orderly unlock the half-bridge sub-module, and during the unlocking process, control the voltage on the modular multi-level converter valve circuit side to zero;

[0055] S5. Close the first DC side switch and the second DC side switch to charge the supercapacitor branch through the modular multi-level converter valve circuit and raise the DC voltage to the rated voltage, entering the supercapacitor charging phase;

[0056] S6. After the DC voltage reaches the rated voltage, unlock the supercapacitor branch and charge the supercapacitor branch with constant power current limiting until the supercapacitor branch is fully charged. Then, switch the AC system from the charging mode to the network control operation mode.

[0057] Specifically, such as Figure 5As shown, this embodiment closes the main circuit breaker QF1, establishing a connection between the grid-type SVG device startup topology and the external power system. The startup resistor is connected to the startup circuit to suppress overcurrent during the startup process. At the same time, the bypass switch KM of the half-bridge submodule is closed to put the bypass paths of all half-bridge submodules in the modular multilevel converter valve circuit in a non-blocking state. That is, the bypass paths of all half-bridge submodules are open, allowing current to flow. The supercapacitor branch (i.e., the circuit path where the supercapacitor is located) is ensured to be in a locked state to prevent sudden current from flowing into the supercapacitor before charging begins. The AC system (or AC power supply) then charges the first DC capacitor of the half-bridge submodule in the MMC converter valve circuit through the startup circuit to establish an initial voltage in the MMC converter valve circuit and avoid excessive current surges during the subsequent charging process. The startup isolation switch QS1 of the startup circuit is then closed to initiate the active charging phase. The active charging strategy is used to sequentially unlock the half-bridge submodules in the MMC converter valve to ensure voltage stability. During the unlocking process, the voltage on the MMC converter valve side is controlled to be maintained at 0. V is set to prevent excessive voltage fluctuations during the unlocking process. This completes the first startup phase. In the grid-type SVG device startup topology, DC-side switches QS2 and QS3 control the on / off circuit on the DC side. In this embodiment, the first and second DC-side switches QS2 and QS3 are closed to charge the supercapacitor branch through the MMC converter valve circuit. As charging progresses, the DC voltage gradually rises to the rated voltage, entering the supercapacitor charging phase. When the DC voltage reaches the rated value, the supercapacitor branch is unlocked. In this embodiment, constant-power, current-limited charging of the supercapacitor SC begins, ensuring that the supercapacitor is not affected by overcurrent during charging and ensuring charging efficiency. When the supercapacitor is fully charged, the grid-type SVG device startup topology completes the startup process, transitioning the system from charging mode to grid-type control mode. In this grid-type control mode, the supercapacitor energy storage system participates in the dynamic regulation of the power grid, providing reactive power support, frequency regulation, and voltage support, thereby improving the stability and reliability of the power grid and providing the power grid with more stable and efficient dynamic regulation capabilities.

[0058] It should be noted that unlocking refers to making the circuit path conductive through a control mechanism such as a relay or switch, allowing current to flow, thereby transitioning the supercapacitor branch (composed of multiple supercapacitor submodules CM connected in series) from an initially locked or isolated state to an operational state. Once the supercapacitor branch is unlocked, the supercapacitor is actively charged. During the charging process, the voltage of each supercapacitor submodule is monitored, and charging continues until the voltage of all supercapacitor submodules reaches the rated voltage. Once the voltage of all supercapacitor submodules reaches the rated voltage, the system switches from charging mode to network control operation mode. In summary, the two-stage startup method adopted in this embodiment achieves safe and efficient startup of the SVG device by first charging and orderly unlocking the half-bridge submodule SM (first stage) and then charging the supercapacitor (second stage). This method enables a smooth startup and gradual transition to a fully functional operation state, while effectively avoiding overvoltage issues during startup, reducing impact on the power grid, and improving the stability and reliability of the SVG device.

[0059] It should be noted that the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of this application.

[0060] For the specific definition of the two-stage startup method for a mesh-type SVG device startup topology structure, please refer to the above-mentioned definition of a mesh-type SVG device startup topology structure, which will not be repeated here. A person of ordinary skill in the art will appreciate that the various modules and steps described in conjunction with the embodiments disclosed in this application can be implemented in hardware, software, or a combination of both. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0061] An embodiment of the present invention provides a two-stage startup method for a startup topology of a meshed SVG device. The two-stage startup method includes controlling a main circuit breaker to close in response to a startup signal so that the meshed SVG device startup topology establishes a connection with an external power system; controlling the bypass paths of all half-bridge submodules in a modular multilevel converter valve circuit to be in a non-blocking state and connecting a startup resistor to a startup circuit; charging the half-bridge submodules in the modular multilevel converter valve circuit via an AC system, thereby entering a modular multilevel converter valve circuit charging phase; controlling a startup isolating switch of the startup circuit to close to initiate an active charging strategy to sequentially unlock the half-bridge submodules, and controlling the voltage on the modular multilevel converter valve circuit side to zero during the unlocking process; closing a first DC side switch and a second DC side switch to charge a supercapacitor branch via the modular multilevel converter valve circuit and raise the DC voltage to a rated voltage, thereby entering a supercapacitor charging phase; unlocking the supercapacitor branch after the DC voltage reaches the rated voltage and charging the supercapacitor branch with constant power current limiting until charging of the supercapacitor branch is complete, thereby switching the AC system from a charging mode to a meshed control operation mode. Compared with existing technologies, this embodiment solves the grid stability issues caused by fluctuations when renewable energy is connected to the grid, as well as the problem of large power shocks to the grid during SVG device startup, through an orderly two-stage startup method. This method achieves smooth startup and efficient charging of supercapacitor-based grid-connected SVG devices, effectively suppresses current fluctuations during startup, reduces power shocks to the grid during startup, improves the system's instantaneous frequency and voltage support capabilities, and ensures safe and stable operation of the power system.

[0062] The above-described embodiments merely represent several preferred implementations of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art could make several improvements and substitutions without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be based on the scope of protection of the claims.

Claims

1. A mesh-type SVG device startup topology structure, characterized by: The invention comprises a control system, a main circuit breaker connected to the control system, a starting circuit, and a supercapacitor-based energy storage type static VAR generator; the main circuit breaker is connected to the energy storage type static VAR generator via the starting circuit; the supercapacitor-based energy storage type static VAR generator comprises a modular multi-level converter valve circuit and a supercapacitor circuit connected in parallel; The modular multilevel converter valve circuit includes a plurality of modular multilevel converter valve branches connected in parallel, each of the modular multilevel converter valve branches includes an upper bridge arm and a lower bridge arm connected in series, and each of the upper bridge arm and the lower bridge arm includes a plurality of half-bridge sub-modules connected in series; the modular multilevel converter valve circuit is used to control energy conversion between an AC system and a DC system, and to regulate the grid voltage by controlling the switching state of the half-bridge sub-modules; The supercapacitor circuit includes a plurality of supercapacitor branches, each of which includes a plurality of supercapacitor submodules connected in series; The supercapacitor submodule is used for energy storage and discharge; The control system is used to enter the modular multi-level converter valve circuit charging phase by controlling the switching actions of the main circuit breaker and the energy storage type static VAR generator in response to the start signal; Furthermore, the half-bridge submodules are unlocked in an orderly manner by controlling and starting an active charging strategy, so that the modular multi-level converter valve circuit charges the supercapacitor branch, entering the supercapacitor charging phase.

2. The mesh-type SVG device startup topology structure according to claim 1, characterized in that: The half-bridge submodule includes a first switch module, a second switch module, a first DC capacitor, a bypass switch and a turning thyristor; The first switch module and the second switch module are connected in series and then connected in parallel with the first DC capacitor; the bypass switch and the turning thyristor are connected in parallel with the second switch module.

3. The mesh-type SVG device startup topology structure according to claim 2, wherein: The supercapacitor submodule includes a third switch module, a fourth switch module, a second DC capacitor and a supercapacitor; The third switch module and the fourth switch module are connected in series and then connected in parallel with the second DC capacitor, and the supercapacitor is connected in parallel with the second DC capacitor.

4. The mesh-type SVG device startup topology structure according to claim 2, wherein: The first switch module includes a first switch tube and a first diode anti-parallel connected to the first switch tube; The second switch module includes a second switch tube and a second diode connected in anti-parallel with the second switch tube.

5. The mesh-type SVG device startup topology structure according to claim 3, wherein: The third switch module includes a third switch tube and a third diode anti-parallel connected to the third switch tube; The fourth switch module includes a fourth switch tube and a fourth diode connected in anti-parallel with the fourth switch tube.

6. The mesh-type SVG device startup topology structure according to claim 3, wherein: The modular multi-level converter valve circuit also includes two first current-limiting reactors connected in series between the upper bridge arm and the lower bridge arm, and the first current-limiting reactors are used to reduce the DC current fluctuations generated by the supercapacitor during switching.

7. The mesh-type SVG device startup topology structure according to claim 6, characterized in that: The starting circuit includes a starting resistor, a starting isolating switch, a first DC side switch and a second DC side switch; The first DC side switch and the second DC side switch are respectively arranged at two common ends between the modular multi-level converter valve circuit and the supercapacitor circuit. The first DC side switch and the second DC side switch are used to control the modular multi-level converter valve circuit to charge the supercapacitor branch by switching the electrical connection state between the modular multi-level converter valve circuit and the supercapacitor branch.

8. The mesh-type SVG device startup topology structure according to claim 7, characterized in that: One end of the starting resistor connected in parallel with the starting isolation switch is connected to the common end between the two first current-limiting reactors, and the other end of the starting resistor connected in parallel with the starting isolation switch is connected to the main circuit breaker; the starting resistor is used to limit overcurrent during the charging process of the supercapacitor circuit.

9. The mesh-type SVG device startup topology structure according to claim 8, characterized in that: Each of the supercapacitor branches further includes a second current limiting reactor; the second current limiting reactor is used to reduce the DC current fluctuations generated by the supercapacitor during the charging and discharging process; The second DC side switch is connected to one end of a plurality of super capacitor submodules connected in series through the second current limiting reactor, and the other end of the plurality of super capacitor submodules connected in series is connected to the first DC side switch.

10. A two-stage startup method for a meshed SVG device to start a topology structure, characterized in that: The meshed SVG device startup topology structure according to any one of claims 1 to 9 is applied, wherein the startup circuit includes a startup resistor, a startup isolation switch, a first DC side switch, and a second DC side switch; and the two-stage startup method includes the following steps: In response to the start signal, controlling the main circuit breaker to close so that the grid-type SVG device starts the topology structure and establishes a connection with the external power system; Control the bypass paths of all half-bridge submodules in the modular multi-level converter valve circuit to be in a non-blocking state, and connect the starting resistor to the starting loop; The half-bridge submodule in the modular multi-level converter valve circuit is charged through the AC system, entering the modular multi-level converter valve circuit charging phase; Controlling the start isolation switch of the start loop to close, so as to initiate the active charging strategy to orderly unlock the half-bridge sub-module, and during the unlocking process, controlling the voltage on the modular multi-level converter valve circuit side to zero; Close the first DC side switch and the second DC side switch to charge the supercapacitor branch through the modular multi-level converter valve circuit, and raise the DC voltage to the rated voltage, entering the supercapacitor charging phase; After the DC voltage reaches the rated voltage, the supercapacitor branch is unlocked and charged with constant power current limiting until the supercapacitor branch is charged. The AC system is switched from the charging mode to the grid control operation mode.

Images