Starting topological structure of network construction type SVG device and two-stage starting method of starting topological structure

Abstract

The invention relates to the technical field of power system energy storage, in particular to a network construction type SVG (static var generator) device starting topological structure and a two-stage starting method thereof, comprising a starting loop and an energy storage type static var generator; the energy storage type static var generator comprises a modularized multi-level converter valve circuit and a super capacitor circuit. The modular multi-level converter valve circuit comprises an upper bridge arm and a lower bridge arm, and each of the upper bridge arm and the lower bridge arm comprises a plurality of half-bridge sub-modules which are connected in series; the modularized multi-level converter valve circuit is used for controlling energy conversion between an alternating current system and a direct current system and adjusting the voltage of a power grid by controlling a half-bridge sub-module. Each super-capacitor branch of the super-capacitor circuit comprises a plurality of super-capacitor sub-modules which are connected in series; and the super capacitor sub-module is used for storing energy and discharging. According to the two-stage starting method for starting the topological structure by the network-building type SVG device, stable starting and efficient charging of the network-building type SVG device containing the super capacitor are realized.

Description

Technical Field

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

[0002] With the rapid development of renewable energy power generation technology, large-scale wind power, photovoltaic 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 power systems. Compared with traditional synchronous generators, renewable energy power generation is usually connected to the grid through power electronic converters, but 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 power grid face short-term power fluctuations. The frequency changes faster and the regulation becomes more difficult. At the same time, the short-circuit ratio of the power grid is reduced, further limiting the absorption capacity of new 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 to the power grid, the introduction of grid-type energy storage devices has become the focus of industry attention. Such grid-type energy storage devices can effectively supplement the inertia and damping of the power system and enhance the stability and transmission capacity of the system. Supercapacitors, as a type of energy storage element, have shown 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 adjustment functions such as reactive power rapid 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, how to achieve reliable startup in a meshed SVG device containing supercapacitors has become a technical problem that needs to be solved urgently. As an important reactive compensation device in the power system, the stability and reliability of the startup process of the SVG device (static VAR generator) are directly related to the safe operation of the entire system. Traditional startup methods often ignore the characteristics of supercapacitors, which may lead to current shocks, voltage fluctuations and other problems during the startup process, affecting the performance and life of the SVG device. Therefore, for a meshed SVG device containing supercapacitors, it is urgent to provide a meshed SVG device startup method to improve the startup performance and operation stability of the SVG device, and provide strong support for the safe and stable operation of the power system. Summary of the invention

[0005] The object of the present invention is to provide a meshed SVG device startup topology structure and a two-stage startup method thereof, which realizes smooth startup and efficient charging of a meshed SVG device based on a supercapacitor through the two-stage startup method, thereby improving the instantaneous frequency and voltage support capabilities of the system.

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

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

[0008] The modular multilevel converter valve circuit comprises a plurality of modular multilevel converter valve branches connected in parallel, each of the modular multilevel converter valve branches comprises an upper bridge arm and a lower bridge arm connected in series, and the upper bridge arm and the lower bridge arm each comprise 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 adjust a grid voltage by controlling a switching state of the half-bridge sub-module;

[0009] The supercapacitor circuit comprises a plurality of supercapacitor branches, each of which comprises 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 stage in response to the start signal by controlling the switching action of the main circuit breaker and the energy storage type static reactive power generating device;

[0011] Furthermore, the half-bridge submodules are unlocked in order by controlling the start of an active charging strategy, so that the modular multi-level converter valve circuit charges the supercapacitor branch and enters 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 turn-on 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 super capacitor 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 anti-parallel connected to the second switch tube.

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

[0019] The fourth switch module includes a fourth switch tube and a fourth diode anti-parallel connected to 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 startup circuit includes a startup resistor, a startup isolation 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 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.

[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 comprises 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;

[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 of a meshed SVG device startup topology structure, using the meshed SVG device startup topology structure as described above, 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, the main circuit breaker is controlled 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, and the modular multi-level converter valve circuit charging phase is entered;

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

[0031] The first DC side switch and the second DC side switch are closed to charge the supercapacitor branch through the modular multi-level converter valve circuit, and the DC voltage is raised to the rated voltage, thus entering the supercapacitor charging stage;

[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 fully charged, and the AC system is switched from the charging mode to the network control operation mode.

[0033] The present invention provides a grid-type SVG device startup topology structure and a two-stage startup method thereof. The grid-type SVG device startup topology structure comprises a main circuit breaker, a startup loop and a supercapacitor-based energy storage type static reactive power generator; the startup loop comprises a startup resistor, a startup isolating switch, a first DC side switch and a second DC side switch; the supercapacitor-based energy storage type static reactive power generator comprises a modular multi-level converter valve circuit and a supercapacitor circuit connected in parallel; the modular multi-level converter valve circuit comprises a plurality of modular multi-level converter valve branches connected in parallel, each of the modular multi-level converter valve branches comprises an upper bridge arm and a lower bridge arm connected in series, and the upper bridge arm and the lower bridge arm each comprise a plurality of half-bridge sub-modules connected in series; the modular multi-level converter valve circuit is used to control energy conversion between an AC system and a DC system, and to adjust a grid voltage by controlling the switch state of the half-bridge sub-module; the supercapacitor circuit comprises a plurality of supercapacitor branches, each of the supercapacitor branches comprises a plurality of supercapacitor sub-modules connected in series; the supercapacitor sub-module is used to store and discharge energy. Compared with the prior art, the grid-type SVG device startup topology structure realizes the smooth startup and efficient charging of the grid-type SVG device containing supercapacitors through an orderly two-stage startup method, effectively suppresses the current fluctuation during the startup process, reduces the power impact on the power grid, and improves the instantaneous frequency and voltage support capabilities of the system. It solves the problem of poor grid stability caused by volatility when new energy is connected to the grid and the problem of large power impact on the power grid caused by traditional startup methods during the startup of the SVG device, thereby improving the reliability and flexibility of the power grid operation. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0037] Figure 4 It is a flowchart of a two-stage startup method for starting a topology structure of a meshed SVG device provided by an embodiment of the present invention;

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

[0039] The following specifically illustrates the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood 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 patent protection of the present invention, because many changes can 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 starting topology of the meshed SVG device includes a control system and a main circuit breaker QF1 connected to the control system, a starting loop and a supercapacitor-based energy storage type static reactive power generator, wherein the main circuit breaker is connected to the energy storage type static reactive power generator through the starting loop; the control system is used to respond to the starting signal, enter the charging stage of the modular multi-level converter valve circuit by controlling the switching action of the main circuit breaker and the energy storage type static reactive power generator; and orderly unlock the half-bridge sub-module by controlling the starting active charging strategy, so that the modular multi-level converter valve circuit charges the supercapacitor branch and enters the supercapacitor charging stage.

[0041] In this embodiment, the supercapacitor-based energy storage type static reactive power generating device 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 startup topology structure of the meshed SVG device to the external power supply system, so as to cut off or connect the power supply through the main circuit breaker QF1 before the startup topology structure of the meshed SVG device is started. For example: during the startup process, this embodiment connects the startup topology structure of the meshed SVG device to the external power supply system by closing the main circuit breaker QF1, and prepares to enter the startup process to ensure the 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 limitation 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, thereby 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 started to orderly unlock the half-bridge submodule 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 to charge the supercapacitor branch as a power source to raise 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 isolating 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 isolating 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 to adjust the grid voltage by controlling the switching state of the half-bridge sub-modules; it should be noted that the number of half-bridge sub-modules of the upper bridge arm and the lower bridge arm may be the same or different, and those skilled in the art may adjust the number of half-bridge sub-modules of the upper bridge arm and the lower bridge arm according to specific implementation conditions, which is 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 connected in parallel with the first DC capacitor C1; the bypass switch KM, the turning thyristor T1 and the second switch module S2 are connected in parallel, wherein the first switch module S1 includes a first switch tube IGBT1 and a first diode VD1 anti-parallel to the first switch tube IGBT1; the second switch module S2 includes a second switch tube IGBT2 and a second diode VD2 anti-parallel to the second switch tube 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, and the startup circuit realizes the orderly unlocking of the half-bridge submodule during the startup process of the startup topology structure of the meshed SVG device, and controls the voltage on the MMC converter valve circuit side to be 0, thereby ensuring that the startup topology structure of the meshed SVG device 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, and 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, and 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] The 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 type static reactive power generator; the startup circuit includes a startup resistor, a startup isolating switch, a first DC side switch and a second DC side switch; the supercapacitor-based energy storage type static reactive power generator includes a modular multi-level converter valve circuit and a supercapacitor circuit connected in parallel; the modular multi-level converter valve circuit includes a plurality of modular multi-level converter valve branches connected in parallel, each of the multi-level 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 a plurality of half-bridge sub-modules connected in series; the modular multi-level converter valve circuit is used to control energy conversion between an AC system and a DC system, and adjust the grid voltage by controlling the switching state of the half-bridge sub-module; the supercapacitor circuit includes a plurality of supercapacitor branches, each of which includes a plurality of supercapacitor sub-modules connected in series; the supercapacitor sub-module is used to store and discharge energy. Compared with the prior art, the grid-type SVG device startup topology structure adopted in this embodiment can realize smooth startup and efficient charging of the grid-type SVG device based on supercapacitors through a modular multi-level converter valve circuit and a supercapacitor circuit, combined with a two-stage startup method, effectively suppress current fluctuations during startup, reduce power impact on the power grid, improve the instantaneous frequency and voltage support capabilities of the system, and provide the power grid with more stable and efficient dynamic adjustment 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, and the meshed SVG device startup topology structure described above is applied. The two-stage startup method includes the following steps:

[0051] S1. In response to the start signal, the main circuit breaker is closed to enable the grid-type SVG device to start the topology structure and establish 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. Charging the half-bridge submodule in the modular multi-level converter valve circuit through the AC system, entering the modular multi-level converter valve circuit charging phase;

[0054] S4. Control the start-up isolation switch of the start-up circuit to close, so as 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, 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 stage;

[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, and switch the AC system from the charging mode to the network control operation mode.

[0057] Specifically, Figure 5As shown, in this embodiment, the main circuit breaker QF1 is closed to establish a connection between the starting topology of the meshed SVG device and the external power supply system, and the starting resistor is connected to the starting circuit to suppress the overcurrent phenomenon during the starting process. At the same time, the bypass switch KM of the half-bridge submodule is closed to make the bypass path of all the half-bridge submodules in the modular multi-level converter valve circuit in a non-blocking state, that is, the bypass paths of all the half-bridge submodules are opened to allow current to flow, and ensure that the supercapacitor branch (that is, the circuit path where the supercapacitor is located) is in a locked state to prevent the current from suddenly flowing into the supercapacitor before charging starts. Then, the AC system (or AC power supply) charges the first DC capacitor of the half-bridge submodule in the MMC converter valve circuit through the starting circuit to establish an initial voltage in the MMC converter valve circuit to avoid excessive current shock in the subsequent charging process. Then, the starting isolation switch QS1 of the starting circuit is closed to start the active charging stage. The half-bridge submodules in the MMC converter valve are unlocked in an orderly manner using an active charging strategy to ensure voltage stability. During the unlocking process, the voltage on the MMC converter valve side is controlled to be maintained at 0. V to prevent excessive voltage fluctuations during the unlocking process. At this point, the first startup stage is completed. In the startup topology of the grid-forming SVG device, the DC side switches QS2 and QS3 are used to control the on-off of the DC side circuit. In this embodiment, the first DC side switch QS2 and the second DC side switch QS3 are closed to charge the supercapacitor branch through the MMC converter valve circuit. As the charging progresses, the DC voltage gradually rises to the rated voltage and enters the supercapacitor charging stage. When the DC voltage reaches the rated value, the supercapacitor branch is unlocked. In this embodiment, constant power current limiting charging of the supercapacitor SC is started to ensure that the supercapacitor is not affected by overcurrent during the charging process and the charging efficiency is guaranteed. When the supercapacitor is fully charged, the startup topology of the grid-forming SVG device completes the startup process and converts the system from the charging mode to the grid-forming control operation mode. In the grid-forming control operation mode, the supercapacitor energy storage system will participate in the dynamic regulation of the power grid, provide reactive power support, frequency regulation, voltage support and other functions, so as to improve the stability and reliability of the power grid and provide the power grid with a more stable and efficient dynamic regulation capability.

[0058] It should be noted that unlocking refers to making the path of the circuit conductive through a control mechanism such as a relay or a switch, that is, allowing current to pass, so that the supercapacitor branch (composed of multiple supercapacitor submodules CM connected in series) changes from an initial locked or isolated state to an operable 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 is continued until the voltage of all supercapacitor submodules reaches the rated voltage. When the voltage of all supercapacitor submodules reaches the rated voltage, the system will switch from the charging mode to the network control operation mode. In summary, the two-stage startup method adopted in this embodiment realizes the 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 can start smoothly and gradually transition to a fully functional operation state, while effectively avoiding the overvoltage problem during the startup process, reducing the 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 embodiments of the present application.

[0060] For the specific definition of the two-stage startup method of 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 can 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 structure 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 startup topology structure of the meshed SVG device is connected to an external power supply 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 loop; charging the half-bridge submodules in the modular multilevel converter valve circuit through an AC system, and entering a charging phase of the modular multilevel converter valve circuit; controlling a startup isolation switch of the startup loop to close, so as to start an active charging strategy to orderly unlock the half-bridge submodules, and in the unlocking process, controlling the voltage on the side of the modular multilevel converter valve circuit to be zero; closing a first DC side switch and a second DC side switch, charging a supercapacitor branch through the modular multilevel converter valve circuit, and raising the DC voltage to a rated voltage, and entering a supercapacitor charging phase; after the DC voltage reaches the rated voltage, unlocking the supercapacitor branch, and performing constant power current limiting charging on the supercapacitor branch until the charging of the supercapacitor branch is completed, and switching the AC system from a charging mode to a meshed control operation mode. Compared with the prior art, this embodiment solves the grid stability problem caused by volatility when new energy is connected to the grid, and the problem of large power impact on the grid during the startup of the SVG device through an orderly two-stage startup method, and realizes smooth startup and efficient charging of the supercapacitor-based grid-forming SVG device, effectively suppresses current fluctuations during the startup process, reduces the power impact on the grid during the startup process, improves the system's instantaneous frequency and voltage support capabilities, and ensures the safe and stable operation of the power system.

[0062] The above-mentioned embodiments only express several preferred implementation modes of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in the technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be regarded as the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be based on the protection scope of the claims.

Claims

1. A mesh-type SVG device startup topology structure, characterized in that: It comprises a control system and a main circuit breaker connected to the control system, a starting circuit and an energy storage type static reactive power generator based on a supercapacitor; the main circuit breaker is connected to the energy storage type static reactive power generator through the starting circuit; the energy storage type static reactive power generator based on the supercapacitor comprises a modular multi-level converter valve circuit and a supercapacitor circuit connected in parallel; The modular multilevel converter valve circuit comprises a plurality of modular multilevel converter valve branches connected in parallel, each of the modular multilevel converter valve branches comprises an upper bridge arm and a lower bridge arm connected in series, and the upper bridge arm and the lower bridge arm each comprise 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 adjust the grid voltage by controlling the switching state of the half-bridge sub-module; The supercapacitor circuit comprises a plurality of supercapacitor branches, each of which comprises 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 stage in response to the start signal by controlling the switching action of the main circuit breaker and the energy storage type static reactive power generating device; Furthermore, the half-bridge submodules are unlocked in order by controlling the start of an active charging strategy, so that the modular multi-level converter valve circuit charges the supercapacitor branch and enters the supercapacitor charging phase.

2. A mesh-type SVG device startup topology structure as claimed in 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. A mesh-type SVG device startup topology structure as claimed in claim 2, characterized in that: 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 super capacitor is connected in parallel with the second DC capacitor.

4. A mesh-type SVG device startup topology structure as claimed in claim 2, characterized in that: 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 anti-parallel connected to the second switch tube.

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

6. A mesh-type SVG device startup topology structure as claimed in claim 3, characterized in that: 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. A mesh-type SVG device startup topology structure as claimed in 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 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.

8. A mesh-type SVG device startup topology structure as claimed in claim 7, characterized in that: 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.

9. A mesh-type SVG device startup topology structure as claimed in claim 8, characterized in that: Each of the supercapacitor branches also includes a second current limiting reactor; the second current limiting reactor is used to reduce the DC current fluctuation 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 network-type SVG device startup 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, the main circuit breaker is controlled 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, and the modular multi-level converter valve circuit charging phase is entered; Controlling the start-up isolation switch of the start-up loop to close, so as to start the active charging strategy to orderly unlock the half-bridge sub-module, and during the unlocking process, controlling the voltage on the side of the modular multi-level converter valve circuit to be zero; The first DC side switch and the second DC side switch are closed to charge the supercapacitor branch through the modular multi-level converter valve circuit, and the DC voltage is raised to the rated voltage, thus entering the supercapacitor charging stage; 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 fully charged, and the AC system is switched from the charging mode to the network control operation mode.

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