A new sub-module based commutation failure mitigation method

Abstract

The application provides a commutation failure inhibition method based on a novel submodule, and the method comprises the following steps: S101, collecting grid commutation converter system data based on an LCC novel submodule in real time; S102, implementing a capacitor voltage balancing strategy based on the grid commutation converter system data; S103, based on the capacitor voltage balancing strategy, the LCC novel submodule is put into standby at a rated capacitor voltage; S104, implementing an auxiliary commutation strategy based on the grid commutation converter system data, and putting the LCC novel submodule into auxiliary commutation; S105, based on steps S101-S104, establishing a simulation analysis model. The application can be used for the modification of an existing high-voltage direct-current power transmission project based on a grid commutation converter, is simple and easy to implement, and has high engineering applicability.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a method for suppressing commutation failure based on a novel submodule. Background Technology

[0002] AC system failure is the main cause of commutation failure. In existing research, the solutions to commutation failure revolve around adding reactive power compensation equipment on the AC side, changing the system control, and modifying the system topology. Among these, the invention and use of new topologies are the main research directions.

[0003] Regarding the topology modification of LCC-HVDC systems, controllable commutated converters (CLCCs) have been applied in the Gezhouba-Shanghai renovation project, but the modification cost is relatively high. Connecting RC submodules in series within the thyristor valve arms can compensate for AC voltage dips and impede the development of fault currents. Research on topology modification schemes indicates that the key to resisting commutation failure in LCC-HVDC systems lies in suppressing the first commutation failure. While domestic and international scholars have conducted relevant research on the current approach of modifying converter station topologies, the ability to resist commutation failure still needs improvement, and the investment cost of new topologies can be reduced. Therefore, it is necessary to research new topologies with better overall performance and improve related control strategies. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a commutation failure suppression method based on a novel submodule to solve the problem that AC side faults can easily lead to commutation failures.

[0005] To achieve the above objectives, the first aspect of the present invention provides a commutation failure suppression method based on a novel submodule, the method comprising the following steps:

[0006] S101. Real-time acquisition of power grid phase-commutator system data based on LCC new sub-module;

[0007] S102. Implement a capacitor voltage balancing strategy based on grid commutator system data.

[0008] S103. Based on the capacitor voltage balancing strategy, the new LCC sub-module is ready to be put into operation with the rated capacitor voltage.

[0009] S104. Implement an auxiliary commutation strategy based on grid commutator system data, and deploy a new LCC sub-module to assist commutation;

[0010] S105. Based on steps S101-S104, establish a simulation analysis model.

[0011] Furthermore, the grid-connected converter system data includes the capacitor voltage and arm current of the LCC novel submodule.

[0012] Furthermore, the implementation of the capacitor voltage balancing strategy includes:

[0013] For the j-th capacitor voltage u of the new LCC submodule Cj , if u Cj <k1U CN Then, the control LCC new submodule will switch from bypass mode to charging mode when u Cj =U CN The control module of the LCC is switched from charging mode to bypass mode.

[0014] If u Cj >k2U CN Then, the control LCC new submodule will switch from bypass mode to discharge mode when u Cj =U CN The control LCC new submodule returns from discharge mode to bypass mode;

[0015] Where k1 is the charging control coefficient of the LCC novel submodule capacitor voltage balancing strategy, k2 is the discharging control coefficient of the LCC novel submodule capacitor voltage balancing strategy, and U CN This refers to the rated capacitor voltage value of the new LCC submodule.

[0016] Furthermore, the novel LCC submodule is ready to be engaged at its rated capacitor voltage, including:

[0017] When the LCC novel submodule terminates the capacitor voltage equalization control strategy, the capacitor voltage is maintained at U. CN It is ready for use and awaits deployment.

[0018] Furthermore, the deployment of the novel LCC submodule to assist commutation includes:

[0019] When the bridge arm current begins to increase, i. arm If / dt > 0, it means that the bridge arm needs to be turned on in the next moment, then the control is U CN The standby LCC new submodule enters the auxiliary conduction mode from the bypass mode when i arm =I d When the bridge arm is determined to be conducting, the control LCC new sub-module is switched from auxiliary conduction mode back to bypass mode.

[0020] When the bridge arm current begins to decrease, i. arm If / dt < 0, it means that the bridge arm needs to be turned off in the next moment, and the control is U. CN The standby LCC new submodule enters auxiliary shutdown mode from bypass mode when i arm When the value is 0, it is determined that the bridge arm has been shut down, and the control LCC new sub-module is switched back from auxiliary shutdown mode to bypass mode.

[0021] Among them, I d This refers to the DC-side current of the grid-commutated converter.

[0022] Furthermore, the method is applied to a computer-readable storage medium and a processor, wherein a computer program and computer instructions are stored on the computer-readable storage medium, and the processor executes the computer program by executing the computer instructions, wherein the computer program, when executed by the processor, implements the steps of the method as described in any one of claims 1-5.

[0023] A second aspect of the present invention provides a computer-readable storage medium comprising:

[0024] A computer-readable storage medium storing a computer program and computer instructions, characterized in that the processor executes the computer program by executing the computer instructions, and the computer program, when executed by the processor, implements the steps of the method as described in any one of claims 1-5.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This invention proposes a commutation failure suppression method based on a novel submodule. By collecting data from a grid-based phase-commutation converter system using the novel LCC submodule, a capacitor voltage balancing strategy and an auxiliary commutation strategy are implemented. Based on the capacitor voltage balancing strategy, the novel LCC submodule is ready to be put into operation with its rated capacitor voltage. Based on the auxiliary commutation strategy, the novel LCC submodule is put into operation to assist in commutation, thereby suppressing commutation failure. This method can be used to upgrade existing high-voltage direct current transmission projects based on grid-based phase-commutation converters. It is simple to implement and has high engineering applicability. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only preferred embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A schematic diagram of the commutation failure suppression method based on a novel submodule provided in an embodiment of the present invention;

[0029] Figure 2 A schematic diagram of a grid phase-commutation converter topology based on a novel submodule provided in an embodiment of the present invention;

[0030] Figure 3 Eight operating modes of the novel submodule provided in the embodiments of the present invention;

[0031] Figure 4 A schematic diagram of the current flow path of the novel submodule provided in this embodiment of the invention under eight operating modes;

[0032] Figure 5 This is a schematic diagram of the DC current waveform during an AC side fault, provided in an embodiment of the present invention.

[0033] Figure 6 This is a schematic diagram of the DC voltage waveform during an AC-side fault, provided as an embodiment of the present invention.

[0034] Figure 7 This is a schematic diagram of the active power waveform during an AC side fault, provided as an embodiment of the present invention.

[0035] Figure 8 This is a schematic diagram of the system arm current waveform during an AC side fault, provided as an embodiment of the present invention.

[0036] Figure 9 This is a schematic diagram of the system shutdown angle waveform during an AC side fault, provided as an embodiment of the present invention. Detailed Implementation

[0037] The principles and features of the present invention are described below with reference to the accompanying drawings. The listed embodiments are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0038] like Figure 1 As shown, this invention provides a schematic flowchart of a commutation failure suppression method based on a novel submodule.

[0039] Reference Figure 1 This embodiment provides a commutation failure suppression method based on a novel submodule, the method comprising the following steps:

[0040] S101. Real-time acquisition of power grid phase-commutator system data based on the new sub-module, specifically including:

[0041] The grid commutator system data includes the capacitor voltage u of the LCC new submodule. Cj (j∈{1,2}), bridge arm current i arm .

[0042] S102. Implement a capacitor voltage balancing strategy based on grid commutator system data, specifically including:

[0043] For the first capacitor voltage u of the new LCC submodule C1 , if u C1 <k1U CN Then the control of the new LCC submodule is handled by Figure 3 Entering mode 2 from mode 3, i.e., from Figure 4(c) enters (b); when u C1 =U CN The control LCC new submodule is composed of Figure 3 Returning from Mode 2 to Mode 3, i.e., from Figure 4 (b) Return to (c);

[0044] For the second capacitor voltage u of the new LCC submodule C2 , if u C2 <k1U CN Then the control of the new LCC submodule is handled by Figure 3 Entering mode 5 from mode 3, i.e., from Figure 4 (c) enters (e); when u C2 =U CN The control LCC new submodule is composed of Figure 3 In the middle mode, it returns to mode 3, that is, from mode 5. Figure 4 (e) returns to (c);

[0045] For the first capacitor voltage u of the new LCC submodule C1 , if u C1 >k2U CN Then the control of the new LCC submodule is handled by Figure 3 Entering mode 7 from mode 3, i.e., from Figure 4 (c) enters (g); when u C1 =U CN The control LCC new submodule is composed of Figure 3 In the middle mode, it returns to mode 3, that is, from mode 7. Figure 4 (g) returns to (c);

[0046] For the second capacitor voltage u of the new LCC submodule C2 , if u C2 >k2U CN Then the control of the new LCC submodule is handled by Figure 3 Entering mode 4 from mode 3, i.e., from Figure 4 (c) enters (d); when u C2 =U CN The control LCC new submodule is composed of Figure 3 Returning from Mode 4 to Mode 3, i.e. from Figure 4 (d) Return to (c);

[0047] Where k1 is the charging control coefficient of the LCC new submodule capacitor voltage balancing strategy, with a value of 0.95; k2 is the discharging control coefficient of the LCC new submodule capacitor voltage balancing strategy, with a value of 1.05; U CN The rated capacitor voltage for the new LCC submodule is 25kV.

[0048] Of the eight operating modes, modes 3 and 6 are two equivalent bypass modes. Since mode 6 requires two IGBT trigger pulses (T1 and T3), while mode 3 only requires one IGBT trigger pulse (T2), mode 3 is selected as the rated bypass mode, and mode 6 as the standby bypass mode. During normal system operation, the LCC new submodule capacitor should be in a bypass state. At this time, the LCC new submodule operates in mode 3, such as... Figure 4 (c)

[0049] S103. Based on the capacitor voltage balancing strategy, the new LCC submodule is ready for deployment at the rated capacitor voltage, specifically including:

[0050] When the LCC novel submodule terminates the capacitor voltage equalization control strategy, the capacitor voltage is maintained at the rated value U. CN =25kV level and awaiting commissioning.

[0051] S104. Implement an auxiliary commutation strategy based on grid-connected converter system data, and deploy a new LCC submodule to assist commutation, specifically including:

[0052] When the bridge arm current begins to increase, i. arm If / dt > 0, it means that the bridge arm needs to be turned on in the next moment, then the control is U CN The new LCC submodule is ready to be deployed from Figure 3 Enter mode 8 from mode 3, that is, from Figure 4 (c) enters (h), assisting the bridge arm in completing the conduction; i arm =I d When the bridge arm is determined to be conducting, the control LCC new submodule is then activated. Figure 3 In the middle mode, you return to mode 3, that is, from mode 8. Figure 4 (h) returns to (c).

[0053] When the bridge arm current begins to decrease, i. arm If / dt < 0, it means that the bridge arm needs to be turned off in the next moment, and the control is U. CN The new LCC submodule is ready to be deployed from Figure 3 Entering Mode 1 from Mode 3, i.e., from Figure 4 (c) enters (a), assisting the bridge arm in completing the shutdown; when i arm When the value is 0, the bridge arm is determined to be conducting, and the control LCC new submodule is then activated. Figure 3 Returning from Mode 1 to Mode 3, i.e., from Figure 4 (a) Return to (c).

[0054] Among them, I d This is the DC side current of the grid-connected phase converter, with a value of 2000A.

[0055] S105. Based on steps S101-S104, establish a simulation analysis model, specifically including:

[0056] According to such Figure 2-4 The novel submodule topology and control strategy shown are implemented based on the Simulink simulation platform. The inverter-side valve arm is improved on the basis of the CIGRE standard test model to realize the application of the LCC-HVDC system and its control strategy based on the novel submodule and establish a simulation analysis model.

[0057] The novel LCC submodule proposed in this invention exhibits higher device utilization and reduced costs when outputting a unit level; the current stress of the switching devices remains unchanged, and only the voltage stress T2 doubles, while the others remain constant; under AC fault conditions, the reasonable switching of the novel LCC submodule assists in successful commutation of the converter station, successfully avoiding large fluctuations in DC current and DC voltage (e.g., Figure 5 , Figure 6 ) and active power transmission interruption or even power backfeed (such as Figure 7 ), while reducing the commutation overlap angle μ (e.g. Figure 8 Increase the shut-off angle γ (e.g.) Figure 9 This increases system stability.

[0058] Another embodiment of the present invention provides a computer-readable storage medium, comprising:

[0059] The computer-readable storage medium stores a computer program and computer instructions, characterized in that the processor executes the computer program by executing the computer instructions, and the computer program, when executed by the processor, implements the steps of the method as described in any one of claims 1-5.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A commutation failure suppression method based on a novel submodule, characterized in that, The method includes the following steps: S101. Real-time acquisition of power grid phase-commutator system data based on LCC new sub-module; S102. Implement a capacitor voltage balancing strategy based on grid commutator system data, including: For the j-th capacitor voltage u of the new LCC submodule Cj , if u Cj <k1U CN Then, the control LCC new submodule will switch from bypass mode to charging mode when u Cj =U CN The control module of the LCC is switched from charging mode to bypass mode. If u Cj k2U CN Then, the control LCC new submodule will switch from bypass mode to discharge mode when u Cj =U CN The control LCC new submodule returns from discharge mode to bypass mode; Where k1 is the charging control coefficient of the LCC novel submodule capacitor voltage balancing strategy, k2 is the discharging control coefficient of the LCC novel submodule capacitor voltage balancing strategy, and U CN This refers to the rated capacitor voltage value of the new LCC submodule; S103. Based on the capacitor voltage balancing strategy, the new LCC sub-module is ready to be put into operation with the rated capacitor voltage. S104. Implement an auxiliary commutation strategy based on grid-connected converter system data, and deploy a new LCC submodule to assist commutation, including: When the bridge arm current begins to increase, i. arm If / dt>0, it means that the bridge arm needs to be turned on in the next moment, and the control is U CN The standby LCC new submodule enters auxiliary conduction mode from bypass mode when i arm =I d When the bridge arm is determined to be conducting, the control LCC new sub-module is switched from auxiliary conduction mode back to bypass mode. When the bridge arm current begins to decrease, i. arm If / dt<0, it means that the bridge arm needs to be turned off in the next moment, and the control is U. CN The standby LCC new submodule enters auxiliary shutdown mode from bypass mode when i arm When the value is 0, it is determined that the bridge arm has been shut down, and the control LCC new sub-module is switched back from auxiliary shutdown mode to bypass mode. Among them, I d This refers to the DC-side current of the grid-commutated converter. S105. Based on steps S101-S104, establish a simulation analysis model.

2. The commutation failure suppression method based on a novel submodule according to claim 1, characterized in that, The data of the grid-connected phase converter system includes the capacitor voltage and bridge arm current of the LCC new submodule.

3. The commutation failure suppression method based on a novel submodule according to claim 1, characterized in that, The new LCC submodule is ready to be put into operation with the rated capacitor voltage, including: When the LCC novel submodule terminates the capacitor voltage equalization control strategy, the capacitor voltage is maintained at U. CN It is ready for use and awaits deployment.

4. A computer-readable storage medium storing a computer program and computer instructions thereon, characterized in that, The processor executes a computer program by executing computer instructions, which, when executed by the processor, implements the steps of the method as described in any one of claims 1-3.

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