Multifunctional static synchronous compensator system and method of operation thereof

Abstract

The application provides a multifunctional static synchronous compensator system, comprising: a plurality of three-phase converter valves, input ends of each three-phase converter valve being connected to a common DC bus; an energy storage valve, being connected in parallel with the three-phase converter valve, and the plurality of three-phase converter valves sharing the energy storage valve through the common DC bus; a switch breaker device, being arranged between the three-phase converter valve and the energy storage valve; and a control unit, being connected with the plurality of three-phase converter valves, the energy storage valve and the switch breaker device respectively. The application also provides a method for operating the multifunctional static synchronous compensator system. The multifunctional static synchronous compensator system provided by the application adopts back-to-back converter valves, shares energy storage elements through a common DC bus, and connects two AC buses to the two sides of the converter valve, so that the system can support the two AC power grids, greatly save the installation capacity of the energy storage elements in the energy storage valve, and provide power interconnection between the two AC power grids and play a role in tidal flow control.

Description

Technical Field

[0001] This application relates to the field of static var compensation technology, specifically to a multifunctional static synchronous condenser system and its operation method. Background Technology

[0002] With the accelerated construction of the national new energy system, the "dual high" characteristics of the power system—high proportion of new energy and high proportion of power electronic equipment—are becoming increasingly prominent. The control-driven external characteristics of power electronic equipment such as those used in new energy sources have a significant impact on the stability of the power grid under a weak grid structure, leading to a complex interplay of voltage stability issues, power angle stability issues, and dynamic frequency stability issues caused by insufficient inertia. In addition to providing voltage and reactive power support for AC systems, static synchronous condensers also possess the capability to provide inertia support for AC systems, resolving transient frequency stability issues caused by insufficient inertia during AC system faults.

[0003] Conventional static synchronous condensers use energy storage units such as supercapacitors and lithium batteries as energy carriers. The output side is connected to the AC power grid at one end and adopts grid control. Under the transient fault of the power grid, they can respond naturally and quickly provide voltage and frequency support. However, when the power grid is running stably, they mainly rely on reactive power regulation and the utilization rate of energy storage components is low. Therefore, the overall cost-effectiveness of installing one static synchronous condenser on each AC bus section is not high. Summary of the Invention

[0004] This application provides a multifunctional static synchronous condenser system and its operation method to solve the problem of low utilization rate of energy storage components of static synchronous condensers when the power grid is running stably.

[0005] To address the aforementioned technical problems, this application provides a multifunctional static synchronous conversion system, comprising:

[0006] Multiple three-phase converter valves, with the input terminal of each three-phase converter valve connected to a common DC bus;

[0007] An energy storage valve is connected in parallel with the three-phase converter valve, and the multiple three-phase converter valves share the energy storage valve through the common DC bus;

[0008] A switchgear is installed between the three-phase converter valve and the energy storage valve;

[0009] The control unit is connected to the plurality of three-phase converter valves, the energy storage valve, and the switchgear, respectively.

[0010] Furthermore, the three-phase converter valve adopts a three-phase six-bridge arm structure, with each phase consisting of upper and lower bridge arms, and each bridge arm adopts a full-bridge submodule series structure or a full-half-bridge submodule hybrid series structure.

[0011] Furthermore, the AC side of the multi-functional static synchronous condenser system includes a start-up circuit, and the multi-functional static synchronous condenser system also includes a smoothing reactor, which is connected between each phase arm and the start-up circuit.

[0012] Furthermore, the energy storage valve adopts a single-branch structure or a multi-branch parallel structure.

[0013] Furthermore, each submodule of the energy storage valve includes an energy storage unit, which is connected in parallel with a supporting capacitor via a fuse, a circuit breaker, and a capacitor.

[0014] Furthermore, the energy storage valve employs a lithium battery, a supercapacitor, and / or a lithium battery.

[0015] The present invention also provides a method for operating a multifunctional static synchronous condenser system. The control unit detects the DC voltage in real time. When the voltage of the common DC bus is lower than a set threshold, the control unit locks the energy storage valve and simultaneously controls the multiple three-phase converter valves to make the output active power zero. The control unit then switches to the charging mode for the energy storage valve.

[0016] Furthermore, when the power grid is in steady state, the multiple three-phase converter valves inject reactive power into the system in real time.

[0017] Furthermore, when a grid fault occurs, the multiple three-phase converter valves under grid control inject active and reactive currents into their respective systems to support the voltage and frequency of their respective systems.

[0018] Furthermore, when a fault occurs in one of the power grids on the non-faulty side, the three-phase converter valves on the non-faulty side switch their operating modes to charge the energy storage valves.

[0019] The multifunctional static synchronous condenser system provided by this invention adopts a back-to-back converter valve and shares energy storage elements through a common DC bus. Two AC bus sections are connected to both sides of the converter valve, which can not only support the AC grids on both sides, but also greatly save the installation capacity of the energy storage elements in the energy storage valve. At the same time, it can provide power mutual assistance between the two AC grids and play a role in power flow control.

[0020] The multifunctional static synchronous condenser system operation method provided by this invention allows the interconnection device to continue supporting the substation voltage as a grid-type energy storage system when both grids are in synchronous operation. When the N-1 fault of the interconnected transmission channel interrupts, the static synchronous condenser can maintain the frequency and voltage stability of the regional power grid, avoiding the risk of regional power grid disconnection and large-scale power outages after the interconnected transmission channel fault. By isolating the impact of faults on the main grid side on the regional power grid through the static synchronous condenser, the main grid fault no longer causes angle of attack and voltage instability in the regional power grid, further increasing the transmission power limit of the interconnected channel. It changes the way the end of the power grid relies on the main grid for power supply, increases the output of new energy sources within the regional power grid, and can also transmit power externally when new energy generation is high, meeting the power balance needs of the regional power grid. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of a multifunctional static synchronous condenser system provided in an embodiment of the present invention;

[0023] Figure 2a This is a schematic diagram of the full-bridge electrical main circuit structure of the submodule of the three-phase converter valve provided in an embodiment of the present invention;

[0024] Figure 2b This is a schematic diagram of the half-bridge electrical main circuit structure of the submodule of the three-phase converter valve provided in an embodiment of the present invention;

[0025] Figure 3a A schematic diagram of the half-bridge electrical main circuit structure of the energy storage valve neutron module provided in an embodiment of the present invention;

[0026] Figure 3b A schematic diagram of the full-bridge electrical main circuit structure of the energy storage valve neutron module provided in an embodiment of the present invention. Detailed Implementation

[0027] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] In the description of this application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0029] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0030] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0031] This application provides a multifunctional static synchronous condenser system, comprising: multiple three-phase converter valves, each three-phase converter valve having its input terminal connected to a common DC bus; an energy storage valve connected in parallel with the three-phase converter valves, the multiple three-phase converter valves sharing the energy storage valve via the common DC bus; a switchgear device disposed between the three-phase converter valves and the energy storage valve; and a control unit connected to the multiple three-phase converter valves, the energy storage valve, and the switchgear device, respectively.

[0032] Figure 1 This is a schematic diagram of the structure of a multifunctional static synchronous condenser system provided in an embodiment of the present invention. (Refer to...) Figure 1 The multifunctional static synchronous condenser system includes, on its AC side, an AC switch 101, an AC side switch knife switch device 102, and a starting circuit 103 connected in series. The starting circuit 103 includes a starting resistor 103a and a bypass switch 103b connected in parallel. In this embodiment of the invention, the multifunctional static synchronous condenser system also includes two three-phase converter valves 104, with the input terminal of each three-phase converter valve 104 connected to a common DC bus.

[0033] An energy storage valve 105 is connected in parallel with the three-phase converter valve 104, and the two three-phase converter valves 104 share the energy storage valve 105 through the common DC bus; a switch device 106 is disposed between the three-phase converter valve 104 and the energy storage valve 105; and a control unit is connected to the two three-phase converter valves 104, the energy storage valve 105, and the switch device 106 respectively.

[0034] In this embodiment of the invention, the three-phase converter valve adopts a three-phase six-bridge arm structure, with each phase consisting of two bridge arms, one above the other. Each bridge arm adopts a full-bridge submodule series structure or a hybrid full-half-bridge submodule series structure. By employing the nearest level approximation or carrier phase shift control algorithm, the switching of the bridge arm submodules is controlled. Figure 2a This is a schematic diagram of the full-bridge electrical main circuit structure of the submodule of the three-phase converter valve provided in an embodiment of the present invention; Figure 2b This is a schematic diagram of the half-bridge electrical main circuit structure of the submodule of the three-phase converter valve provided in an embodiment of the present invention. (Refer to...) Figure 2a The full-bridge electrical main circuit of the converter valve neutron module includes bridge arms composed of T1 and T2, and bridge arms composed of T3 and T4. Energy-dissipating resistors and supporting capacitors are connected in parallel with the bridge arms, respectively. A transition thyristor is connected between the two bridge arms, and the transition thyristor is connected in parallel with the bypass switch. (Refer to...) Figure 2b The half-bridge electrical main circuit of the converter valve neutron module includes a bridge arm composed of T1 and T2, a power-consuming resistor and a supporting capacitor connected in parallel with the bridge arm, a turnaround thyristor connected in parallel with the semiconductor device T2, and the turnaround thyristor connected in parallel with the bypass switch.

[0035] In this embodiment of the invention, the grid-side static synchronous condenser system further includes a smoothing reactor 107, which is connected between each phase arm of the converter valve and the starting circuit, as well as in each branch of the overcapacity valve, to suppress harmonic circuits and fault currents.

[0036] Each submodule of the energy storage valve includes an energy storage unit, which is connected in parallel with a supporting capacitor via a fuse and a circuit breaker. The energy storage valve adopts a single-branch structure or a multi-branch parallel structure connected in parallel with multiple three-phase converter valves. In this embodiment of the invention, the energy storage valve adopts a dual-branch parallel structure connected in parallel with two three-phase converter valves. The energy storage valve can use a lithium battery, a supercapacitor, or a hybrid structure of a supercapacitor and a lithium battery.

[0037] Figure 3a A schematic diagram of the half-bridge electrical main circuit structure of the energy storage valve neutron module provided in an embodiment of the present invention; Figure 3b This is a schematic diagram of the full-bridge electrical main circuit structure of the energy storage valve neutron module provided in an embodiment of the present invention. (Refer to...) Figure 3a The energy storage valve neutron module includes an overcapacity module and a half-bridge arm connected in parallel with the overcapacity module; refer to Figure 3b The energy storage valve submodule includes an overcapacitance module and a full-bridge arm connected in parallel with the supercapacitance module. The DC-side voltage is controlled by switching on / off or charging / discharging the overcapacitance valve submodule. Furthermore, the overcapacitance valve adopts a single-branch structure or a multi-branch parallel structure, and its online on / off function is achieved by controlling the DC-side switchgear.

[0038] The multifunctional static synchronous condenser system provided by this invention adopts a back-to-back converter valve and shares energy storage elements through a common DC bus. Two AC bus sections are connected to both sides of the converter valve, which can not only support the AC grids on both sides, but also greatly save the installation capacity of the energy storage elements in the energy storage valve. At the same time, it can provide power mutual assistance between the two AC grids and play a role in power flow control.

[0039] The present invention also provides a method for operating a multifunctional static synchronous condenser system. The control unit detects the DC voltage in real time. When the voltage of the common DC bus is lower than a set threshold, the control unit locks the energy storage valve and simultaneously controls the multiple three-phase converter valves to make the output active power zero. The control unit then switches to the charging mode for the energy storage valve.

[0040] When the power grid is in steady state, the multiple three-phase converter valves inject reactive power into the system in real time and adjust it accordingly. When the power grid fails, the multiple three-phase converter valves under grid control inject active and reactive current into their respective systems to support the voltage and frequency of their respective systems. When the power grid on one side where the multiple three-phase converter valves are located fails, the three-phase converter valves on the non-faulty side of the power grid switch their operating modes to charge the energy storage valves.

[0041] In coordination with power grid planning, a static synchronous condenser composed of multiple three-phase converter valves can switch the power grids on both sides to synchronous operation by switching the operating mode. At this time, the interconnection device, as a grid-type energy storage, continues to play a role in supporting the voltage of the substation and flexibly integrates into the power grid planning. When the AC switch is open, multiple three-phase converter valves operate in series, and the power grid is asynchronous. When the AC switch is closed, multiple three-phase converter valves operate in parallel, and the power grid is synchronous.

[0042] The multifunctional static synchronous condenser system operation method provided by this invention allows the interconnection device to continue supporting the substation voltage as a grid-type energy storage system when both grids are in synchronous operation. When the N-1 fault of the interconnected transmission channel interrupts, the static synchronous condenser can maintain the frequency and voltage stability of the regional power grid, avoiding the risk of regional power grid disconnection and large-scale power outages after the interconnected transmission channel fault. By isolating the impact of faults on the main grid side on the regional power grid through the static synchronous condenser, the main grid fault no longer causes angle of attack and voltage instability in the regional power grid, further increasing the transmission power limit of the interconnected channel. It changes the way the end of the power grid relies on the main grid for power supply, increases the output of new energy sources within the regional power grid, and can also transmit power externally when new energy generation is high, meeting the power balance needs of the regional power grid.

[0043] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for operating a multi-functional static synchronous compensator system, characterized by, The multi-functional static synchronous compensator system comprises: a plurality of three-phase converter valves, the input end of each three-phase converter valve being connected to a common DC bus, and the output end being connected to an AC bus through an AC switch; an energy storage valve connected in parallel with the three-phase converter valves, the plurality of three-phase converter valves sharing the energy storage valve through the common DC bus; a switch breaker device arranged between the three-phase converter valves and the energy storage valve; and a control unit connected with the plurality of three-phase converter valves, the energy storage valve and the switch breaker device respectively; the control unit detects the DC voltage in real time, and when the voltage of the common DC bus is lower than a set threshold, the control unit locks the energy storage valve, controls the plurality of three-phase converter valves to output zero active power, and switches the static synchronous compensator composed of the plurality of three-phase converter valves to synchronous operation of the two sides of the power grid through the operation mode, when the AC switch is opened, the plurality of three-phase converter valves are operated in series, and the power grid is asynchronous, and when the AC switch is closed, the plurality of three-phase converter valves are operated in parallel, and the power grid is synchronous.

2. The method of operating a multi-functional static synchronous compensator system according to claim 1, wherein, When the power grid is in steady state operation, the plurality of three-phase converter valves inject real-time regulated reactive power into the system.

3. The method of operating a multi-functional static synchronous compensator system of claim 1, wherein, When the power grid fails, the plurality of three-phase converter valves under grid control inject active and reactive currents into the respective systems to support the voltage and frequency of the respective systems.

4. The method of operating a multi-functional static synchronous compensator system of claim 1, wherein, When one of the power grids in which the plurality of three-phase converter valves is located fails, the three-phase converter valves on the non-fault side of the power grid switch the working mode to charge the energy storage valve.

5. The method of operating a multi-functional static synchronous compensator system of claim 1, wherein, The three-phase converter valve adopts a three-phase six-bridge-arm structure, each phase being composed of an upper bridge arm and a lower bridge arm, and each bridge arm adopting a full-bridge sub-module series structure or a full-half-bridge sub-module hybrid series structure.

6. The method of operating a multi-functional static synchronous compensator system of claim 1, wherein, The AC side of the multi-functional static synchronous compensator system comprises a starting loop, and is characterized in that it further comprises a smoothing reactor connected between each phase bridge arm and the starting loop.

7. The method of operating a multi-functional static synchronous compensator system of claim 1, wherein, The energy storage valve adopts a single-branch structure or a multi-branch parallel structure.

8. The method of operating a multi-functional static synchronous compensator system of claim 1, wherein, Each sub-module in the energy storage valve comprises an energy storage unit connected in parallel with a support capacitor through a fuse and a circuit breaker.

9. The method of operating a multi-functional static synchronous compensator system of claim 1, wherein, The energy storage valve adopts a lithium battery, a super capacitor and / or a lithium battery.

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