Overvoltage protection test method, device and flexible direct current back-to-back transmission system

Abstract

The present invention discloses an overvoltage protection test method, device and flexible direct current back-to-back power transmission system. The method comprises: establishing a simulation model of a flexible direct current back-to-back power transmission system; obtaining the three-phase AC voltage output by the flexible direct current converter on the DC power side according to the simulation model of the flexible direct current back-to-back power transmission system; obtaining the simulated measured abnormal quantity of the three-phase AC voltage; and testing whether the valve-controlled bridge arm capacitor voltage average value overvoltage protection of the flexible direct current converter on the DC voltage side is activated according to the measured abnormal quantity. The technical solution provided by the present invention realizes direct simulation detection of the overvoltage protection of the valve-controlled bridge arm capacitor voltage average value of the flexible direct current converter, thereby improving the detection efficiency.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of bridge arm capacitor voltage protection, and in particular to an overvoltage protection test method, device and flexible direct current back-to-back power transmission system. Background Art

[0002] As a voltage source converter, in order to prevent the overall bridge arm overvoltage or DC voltage control instability, the bridge arm capacitor voltage average overvoltage protection is set in the flexible DC converter valve control. This protection is a slow protection. When it is detected that the capacitor voltage average value exceeds the set value, the DC converter issues a blocking command and the outlet trips. In order to reliably evaluate and verify the rationality of the bridge arm capacitor voltage average overvoltage protection criterion and set value, this protection needs to be tested.

[0003] Since the power system has extremely high requirements for safety and stability, it is impossible to carry out bridge arm capacitor voltage average value overvoltage protection related tests in the actual system, and the traditional dynamic model test has the disadvantages of poor simulation scale scalability and limited testing capabilities. On the other hand, since the bridge arm capacitor voltage average value overvoltage protection is used as a backup protection, even if various short-circuit faults are simulated in the simulation, it is difficult to trigger the protection action, and the protection cannot be tested. Summary of the invention

[0004] The present invention provides an overvoltage protection test method, device and flexible direct current back-to-back power transmission system, which realize the test of overvoltage protection of the average value of the capacitor voltage of the valve-controlled bridge arm of the flexible direct current converter and improve the detection efficiency.

[0005] In a first aspect, an embodiment of the present invention provides an overvoltage protection test method, comprising:

[0006] Establish a simulation model of flexible direct current back-to-back transmission system;

[0007] According to the flexible DC back-to-back power transmission system simulation model, the three-phase AC voltage output by the flexible DC converter on the DC power side is obtained;

[0008] Obtaining a simulated measurement abnormality of the three-phase AC voltage;

[0009] Whether the overvoltage protection of the average value of the capacitor voltage of the valve-controlled bridge arm of the flexible DC converter on the DC voltage side is actuated is tested based on the measured abnormal quantity.

[0010] Optionally, after establishing the flexible direct current back-to-back transmission system simulation model, it also includes:

[0011] The simulation model of the flexible direct current back-to-back power transmission system is initialized, wherein the initialization setting includes setting an adjustment coefficient.

[0012] Optionally, after initializing the simulation model of the flexible direct current back-to-back power transmission system, the method further includes:

[0013] The power transmission mode of the flexible direct current back-to-back power transmission system simulation model is set; wherein the power transmission mode includes a forward transmission mode and a reverse transmission mode.

[0014] Optionally, obtaining the simulated measured abnormal amount of the three-phase AC voltage includes:

[0015] The three-phase AC voltage is multiplied by the adjustment coefficient to obtain the measurement abnormality.

[0016] Optionally, after testing whether the average value overvoltage protection of the valve-controlled bridge arm capacitor voltage of the flexible DC converter on the DC voltage side is actuated according to the measured abnormal quantity, the method further includes:

[0017] If no protection action is generated, the adjustment coefficient is updated, wherein the adjustment coefficient is updated according to the step value;

[0018] Multiplying the three-phase AC voltage by the updated adjustment coefficient to obtain an updated measurement abnormality;

[0019] According to the updated measurement abnormality test, the overvoltage protection of the average value of the valve-controlled bridge arm capacitor voltage of the flexible DC converter on the DC voltage side is activated.

[0020] In a second aspect, the present invention provides an overvoltage protection detection device according to an embodiment, comprising:

[0021] Model building module, used to build a simulation model of flexible direct current back-to-back transmission system;

[0022] A voltage acquisition module, used for acquiring the three-phase AC voltage output by the flexible DC converter on the DC power side according to the flexible DC back-to-back transmission system simulation model;

[0023] A regulating module, used for obtaining a measured abnormal amount of the simulated three-phase AC voltage;

[0024] The test module is used to test whether the valve-controlled bridge arm capacitor voltage average value overvoltage protection of the flexible DC converter on the DC voltage side is activated according to the measured abnormal quantity.

[0025] Optionally, the model building module includes:

[0026] A mode setting unit is used to set the power transmission mode of the flexible direct current back-to-back power transmission system simulation model; wherein the power transmission mode includes a forward transmission mode and a reverse transmission mode.

[0027] Optionally, the adjustment module includes a multiplier;

[0028] The multiplier is used for multiplying the three-phase AC voltage by the adjustment coefficient to obtain the measurement abnormality.

[0029] Optionally, the test module includes a selector;

[0030] The selector is used to output the measured abnormal amount to the flexible DC converter on the DC power control side for a preset time, and then resume outputting the three-phase AC voltage.

[0031] In a third aspect, an embodiment of the present invention provides a flexible DC back-to-back power transmission system, comprising any overvoltage protection detection device described in any embodiment of the present invention.

[0032] The technical solution provided by the embodiment of the present invention is to establish a simulation model of a flexible direct current back-to-back transmission system, wherein the simulation model adopts a typical control strategy of a flexible direct current back-to-back, wherein the simulation model can be established using a non-real-time simulation tool or a real-time simulation tool, thereby improving the versatility of simulation applications. When the model outputs normally, the three-phase AC voltage output by the flexible direct current converter on the DC power side is obtained, and the measured abnormal amount of the simulated three-phase AC voltage is obtained, and the measured abnormal amount is used as the simulated fault amount of the model. By changing the input measured abnormal amount, it is possible to detect one by one whether the overvoltage protection action of the average value of the bridge arm capacitor voltage of the valve-controlled bridge arm capacitor of the flexible direct current converter is triggered, thereby realizing direct testing of the overvoltage protection, which solves the problem that it is difficult to trigger the overvoltage protection action of the average value of the bridge arm capacitor voltage by simulating various short-circuit faults in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic flow chart of an overvoltage protection test method provided by an embodiment of the present invention.

[0034] Figure 2 A schematic structural diagram of a flexible direct current back-to-back power transmission system provided in an embodiment of the present invention.

[0035] Figure 3 A flowchart of another overvoltage protection test method provided by an embodiment of the present invention.

[0036] Figure 4 A flowchart of another overvoltage protection test method provided by an embodiment of the present invention.

[0037] Figure 5 A flowchart of another overvoltage protection test method provided by an embodiment of the present invention.

[0038] Figure 6 A schematic diagram of testing the three-phase AC voltage on the second flexible DC converter side in the forward transmission mode provided in an embodiment of the present invention.

[0039] Figure 7 A schematic diagram of testing the average value of the capacitor voltage of the bridge arm of the first flexible DC converter in the forward transmission mode provided by an embodiment of the present invention.

[0040] Figure 8 A schematic structural diagram of an overvoltage protection detection device provided in an embodiment of the present invention.

[0041] Fig. 9 Schematic diagram of the simulation for measuring anomaly for a forward feed mode.

[0042] Fig.10 Schematic diagram of a simulation for measuring anomalies for a backfeed mode. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] The embodiment of the present invention provides an overvoltage protection test method. Figure 1 A flow chart of an overvoltage protection test method provided by an embodiment of the present invention is shown in FIG. Figure 1 This embodiment is applicable to the overvoltage protection detection scenario of the average value of the valve-controlled bridge arm capacitor voltage of the flexible DC converter of the flexible DC back-to-back power transmission system. The method can be executed by an overvoltage protection detection device, which can be implemented in hardware and / or software. The method specifically includes the following steps:

[0045] S110. Establish a simulation model of a flexible direct current back-to-back transmission system.

[0046] Specifically, Figure 2 A schematic diagram of a flexible direct current back-to-back power transmission system provided by an embodiment of the present invention is shown in FIG. Figure 2 , a simulation model of a flexible DC back-to-back transmission system is established in a simulation tool, wherein the simulation model at least includes: a first flexible DC converter MMC1, a second flexible DC converter MMC2, a first flexible DC transformer 210, a second flexible DC transformer 220, a first AC system AC1, and a second AC system AC2. The flexible DC back-to-back transmission system adopts a flexible DC back-to-back typical control strategy. The flexible DC back-to-back typical control strategy at least includes a flexible DC back-to-back typical protection including an overvoltage protection of the average value of the valve-controlled bridge arm capacitor voltage of the flexible DC converter. The simulation tool can adopt a non-real-time simulation tool or a real-time simulation tool, thereby improving the versatility of the simulation application.

[0047] S120. Obtain the three-phase AC voltage output by the flexible DC converter on the DC power side according to the flexible DC back-to-back transmission system simulation model.

[0048] Specifically, the simulation model is run to enable the first AC system AC1 to transmit power to the second AC system AC2. The first flexible DC converter MMC1 adopts fixed DC voltage control, and the second flexible DC converter MMC2 adopts fixed DC power control. The DC output of the back-to-back transmission system is set to the rated operating condition. For example, the DC power is 1000MW and the DC voltage is 700kV. The flexible DC converter on the DC power control side refers to a flexible DC converter that adopts fixed DC power control. Exemplarily, in this embodiment, the first AC system AC1 transmits power to the second AC system AC2, and the flexible DC converter on the DC power control side is the second flexible DC converter MMC2. The three-phase AC voltage output by the second flexible DC converter MMC2 through the second flexible DC transformer 220 is collected. In other words, the three-phase AC voltage of the second three-phase AC voltage measuring point US2 is collected, and the three-phase AC voltage of the second three-phase AC voltage measuring point US2 at this time is the true value of the three-phase AC voltage.

[0049] S130: Obtain the measured abnormal amount of the simulated three-phase AC voltage.

[0050] The measured abnormal amount is the amount that is different from the true value of the three-phase AC voltage due to the measurement abnormality. Exemplarily, the measured abnormal amount in this embodiment is the three-phase AC voltage after the three-phase AC voltage simulation measurement abnormality of the second three-phase AC voltage measuring point US2. The measured abnormal amount will be input into the model as the abnormal fault amount.

[0051] S140, testing whether the average value overvoltage protection of the valve-controlled bridge arm capacitor voltage of the flexible DC converter on the DC voltage side is actuated according to the measured abnormal quantity.

[0052] Specifically, the flexible DC converter on the DC voltage side refers to a flexible DC converter controlled by DC voltage. In this embodiment, the first AC system AC1 transmits power to the second AC system AC2, and the flexible DC converter on the DC voltage side is the first flexible DC converter MMC1. The measured abnormal amount is continuously output for a preset time, for example, the preset time can be set to 20ms. After the preset time is continuously output, the true value of the output three-phase AC voltage is restored, that is, the three-phase AC voltage of the second three-phase AC voltage measuring point US2 collected is restored. If the valve control of the flexible DC converter on the DC voltage side detects that the average value of the bridge arm capacitor voltage exceeds the set value, the flexible DC converter on the DC voltage side issues a locking command and trips at the outlet, then the valve-controlled bridge arm capacitor voltage average value of the flexible DC converter on the DC voltage side is judged to be overvoltage protection action. When the three-phase AC voltage is different from the actual three-phase AC voltage due to measurement abnormality, the measured abnormal amount is input, and the average value of the bridge arm capacitor voltage of the valve-controlled flexible DC converter on the DC voltage side will increase. When the protection set value and protection delay are met, the protection action is taken.

[0053] The technical solution provided by the embodiment of the present invention is to establish a simulation model of a flexible direct current back-to-back transmission system, wherein the simulation model adopts a typical control strategy of a flexible direct current back-to-back, wherein the simulation model can be established using a non-real-time simulation tool or a real-time simulation tool, thereby improving the versatility of simulation applications. When the model outputs normally, the three-phase AC voltage output by the flexible direct current converter on the DC power side is obtained, and the measured abnormal amount of the simulated three-phase AC voltage is obtained, and the measured abnormal amount is used as the simulated fault amount of the model. By changing the input measured abnormal amount, it is possible to detect one by one whether the overvoltage protection action of the average value of the bridge arm capacitor voltage of the valve-controlled bridge arm capacitor of the flexible direct current converter is triggered, thereby realizing direct testing of the overvoltage protection, which solves the problem that it is difficult to trigger the overvoltage protection action of the average value of the bridge arm capacitor voltage by simulating various short-circuit faults in the prior art.

[0054] Based on the above embodiments, Figure 3 A flow chart of another overvoltage protection test method provided by an embodiment of the present invention, combined with Figure 2 See also Figure 3 The method steps include:

[0055] S310. Establish a simulation model of a flexible direct current back-to-back transmission system.

[0056] S320, initializing the simulation model of the flexible direct current back-to-back transmission system, wherein the initialization includes setting an adjustment coefficient.

[0057] The adjustment coefficient is a variable parameter. Different measurement anomalies are obtained by simulating the adjustment coefficient. The adjustment coefficient VP is set in the initialization setting. The adjustment coefficient is a percentage coefficient.

[0058] S330. Obtain the three-phase AC voltage output by the flexible DC converter on the DC power side according to the flexible DC back-to-back transmission system simulation model.

[0059] S340: Obtain the measured abnormal amount of the simulated three-phase AC voltage.

[0060] Specifically, the measurement abnormality is calculated according to the adjustment coefficient VP, that is, the three-phase AC voltage of the second three-phase AC voltage measuring point US2 is adjusted according to the adjustment coefficient VP to obtain the simulated measurement abnormality. For example, if the adjustment coefficient VP is 100, it means that there is no measurement abnormality, that is, the measurement abnormality is equal to the true value of the three-phase AC voltage. If the adjustment coefficient VP is 80, the measurement abnormality is 80% of the true value of the three-phase AC voltage.

[0061] S350, testing whether the average value overvoltage protection of the valve-controlled bridge arm capacitor voltage of the flexible DC converter on the DC voltage side is actuated according to the measured abnormal quantity.

[0062] Specifically, the measured abnormal amount is output to the flexible DC converter on the DC power side, and the output is continuously output for a preset time, for example, the preset time can be set to 20ms. After the preset time is continuously output, the true value of the output three-phase AC voltage is restored. If the valve control of the flexible DC converter on the DC voltage side detects that the average value of the bridge arm capacitor voltage exceeds the set value, the flexible DC converter on the DC voltage side issues a locking command and the outlet trips, and it is judged that the overvoltage protection of the average value of the bridge arm capacitor voltage of the valve-controlled flexible DC converter on the DC voltage side is activated. When the three-phase AC voltage differs from the actual three-phase AC voltage due to measurement abnormality, the measured abnormal amount is input, and the average value of the bridge arm capacitor voltage of the valve-controlled flexible DC converter on the DC voltage side will increase. When the protection set value and protection delay are met, the protection is activated.

[0063] Based on the above embodiments, Figure 4 A flow chart of another overvoltage protection test method provided by an embodiment of the present invention, combined with Figure 2 See also Figure 4 The method steps include:

[0064] S410. Establish a simulation model of a flexible direct current back-to-back transmission system.

[0065] S420, initializing the simulation model of the flexible direct current back-to-back transmission system, wherein the initialization includes setting an adjustment coefficient.

[0066] S430, setting a power transmission mode of the flexible direct current back-to-back transmission system simulation model, wherein the power transmission mode includes a forward transmission mode and a reverse transmission mode.

[0067] For details, please refer to Figure 2For the flexible direct current back-to-back transmission system, the system is a pseudo-bipolar structure, and the two ends respectively include a first flexible direct current converter MMC1 and a second flexible direct current converter MMC2. The first three-phase AC voltage measuring point US1 and the second three-phase AC voltage measuring point US2. In normal operation, the flexible direct current back-to-back transmission system adopts constant DC power control at one end and constant DC voltage control at the other end. That is to say, when the power mode is the positive transmission mode, that is, the first AC system AC1 transmits power to the second AC system AC2, at this time, the first flexible direct current converter MMC1 on the rectifier side of the sending end, that is, the first AC system AC1 side, adopts constant DC voltage control, and the second flexible direct current converter MMC2 on the inverter side of the receiving end, that is, the second AC system AC2 side, adopts constant DC power control. When the power mode is the reverse transmission mode, that is, the second AC system AC2 transmits power to the first AC system AC1, at this time, the second flexible DC converter MMC2 on the rectifier side of the sending end, that is, the second AC system AC2 side, adopts constant DC voltage control, and the first flexible DC converter MMC1 on the inverter side of the receiving end, that is, the first AC system AC1 side, adopts constant DC power control. Since the flexible DC back-to-back transmission system is a symmetrical structure, the same test method is used in subsequent tests to set the forward transmission mode to test the first flexible DC converter MMC1, or to set the reverse transmission mode to test the second flexible DC converter MMC2. Optionally, in the forward or reverse power transmission mode, the DC output of the back-to-back transmission system is set to the rated operating condition to improve the consistency of the three-phase AC voltage output by the flexible DC converter on the DC power side in the forward or reverse power transmission mode.

[0068] S440. Obtain the three-phase AC voltage output by the flexible DC converter on the DC power side according to the flexible DC back-to-back transmission system simulation model.

[0069] Specifically, in the forward transmission mode, the three-phase AC voltage output by the flexible DC converter on the DC power side through the second flexible DC transformer is collected. In other words, the three-phase AC voltage of the second three-phase AC voltage measuring point US2 is collected, and the three-phase AC voltage of the second three-phase AC voltage measuring point US2 at this time is the true value of the three-phase AC voltage. Or in the reverse transmission mode, the three-phase AC voltage output by the flexible DC converter on the DC power side through the first flexible DC transformer is collected. In other words, the three-phase AC voltage of the first three-phase AC voltage measuring point US1 is collected, and the three-phase AC voltage of the first three-phase AC voltage measuring point US1 at this time is the true value of the three-phase AC voltage.

[0070] S460: Obtain the measured abnormal amount of the simulated three-phase AC voltage.

[0071] Specifically, the measurement abnormality is calculated according to the adjustment coefficient VP. In the forward transmission mode, the simulated measurement abnormality is obtained according to the three-phase AC voltage of the second three-phase AC voltage measuring point US2 according to the adjustment coefficient VP. Or in the reverse transmission mode, the simulated measurement abnormality is obtained according to the three-phase AC voltage of the first three-phase AC voltage measuring point US1 according to the adjustment coefficient VP.

[0072] S470, testing whether the average value overvoltage protection of the valve-controlled bridge arm capacitor voltage of the flexible DC converter on the DC voltage side is actuated according to the measured abnormal quantity.

[0073] Specifically, since the flexible direct current back-to-back transmission system belongs to a symmetrical system, by setting the forward transmission mode, the overvoltage protection of the average value of the valve-controlled bridge arm capacitor voltage of the flexible direct current converter on the controlled direct current voltage side, i.e., the first flexible direct current converter MMC1, can be tested, or by setting the reverse transmission mode, the overvoltage protection of the average value of the valve-controlled bridge arm capacitor voltage of the flexible direct current converter on the controlled direct current voltage side, i.e., the second flexible direct current converter MMC2, can be tested. When the valve control of the flexible direct current converter on the controlled direct current voltage side detects that the average value of the bridge arm capacitor voltage exceeds a set value, the flexible direct current converter on the controlled direct current voltage side issues a locking command, and the output is tripped to cut off the output, so that the overvoltage protection action of the average value of the valve-controlled bridge arm capacitor voltage of the flexible direct current converter on the controlled direct current voltage side can be judged. By adjusting the three-phase AC voltage to obtain a simulated measurement abnormality, the overvoltage protection test of the average value of the valve-controlled bridge arm capacitor voltage of different transmission conditions and different converters can be realized.

[0074] Based on the above embodiment, optionally, obtaining the measured abnormal amount of the simulated three-phase AC voltage includes: multiplying the three-phase AC voltage by the adjustment coefficient to obtain the measured abnormal amount.

[0075] Specifically, if the adjustment coefficient VP is 100, it means there is no measurement abnormality, that is, the measurement abnormality is equal to the true value of the three-phase AC voltage*100%. If the adjustment coefficient VP is 80, the measurement abnormality is 80% of the true value of the three-phase AC voltage.

[0076] Based on the above embodiments, Figure 5 A flow chart of another overvoltage protection detection method provided by an embodiment of the present invention is shown in FIG. Figure 5 The method steps include:

[0077] S510. Establish a simulation model of a flexible direct current back-to-back transmission system.

[0078] S520, initializing the simulation model of the flexible direct current back-to-back transmission system, wherein the initialization includes setting an adjustment coefficient.

[0079] S530, setting a power transmission mode of the flexible direct current back-to-back transmission system simulation model, wherein the power transmission mode includes a forward transmission mode and a reverse transmission mode.

[0080] S540. Obtain the three-phase AC voltage output by the flexible DC converter on the DC power side according to the flexible DC back-to-back transmission system simulation model.

[0081] S550: Multiply the three-phase AC voltage by the adjustment coefficient to obtain an abnormal amount.

[0082] S560, testing whether the average value overvoltage protection of the valve-controlled bridge arm capacitor voltage of the flexible DC converter on the DC voltage side is actuated according to the abnormal quantity.

[0083] If no action is generated, the process returns to step S570 and updates the adjustment coefficient, wherein the adjustment coefficient is updated according to the step value. Specifically, in order to avoid the influence of too large data changes on the measurement accuracy when the three-phase AC voltage is adjusted according to the adjustment coefficient, a step value ΔVP of the adjustment coefficient is also set, that is, the amount of change that the adjustment coefficient VP can adjust each time is the step value ΔVP, thereby avoiding the irregular change of the measured abnormal amount and affecting the detection efficiency. The adjustment coefficient is updated according to the current adjustment coefficient and the step value, and the updated adjustment coefficient is the current adjustment coefficient minus the step value. The three-phase AC voltage is multiplied by the updated adjustment coefficient. For example, if the current adjustment coefficient is 100 and the step value ΔVP is 10, the updated adjustment coefficient is 90. The adjustment coefficient updated next time is the previous adjustment coefficient, i.e., 90 minus the step value ΔVP, i.e., 80. The measured abnormal amount is now the three-phase AC voltage multiplied by 80%. The updated adjustment coefficient obtained in the next execution is the last updated adjustment coefficient as the adjustment coefficient, that is, 80 minus the step value ΔVP, and the updated adjustment coefficient is 70. Each time this step is executed, the value of the last adjustment coefficient minus the step value is used as the new adjustment coefficient to calculate the measurement abnormality, and the automatic cyclic update of the adjustment coefficient can be realized for testing.

[0084] Return to step S550, multiply the three-phase AC voltage by the adjustment coefficient to obtain the measurement abnormality.

[0085] S560, testing whether the overvoltage protection of the average value of the capacitor voltage of the valve-controlled bridge arm of the flexible DC converter on the DC voltage side generates a protective action according to the measured abnormal amount, until the overvoltage protection of the average value of the capacitor voltage of the valve-controlled bridge arm of the flexible DC converter on the DC voltage side generates a protective action.

[0086] Specifically, if no protection action is generated, step S570 is executed, and the updated measurement abnormality is obtained by updating the adjustment coefficient, and the updated adjustment coefficient is used. Through the cyclic test, it can be detected that the flexible DC converter on the DC voltage side issues a locking command and the outlet trips, that is, the protection action is generated and then stops. After multiple tests in the power forward mode, when the adjustment coefficient VP is 0, that is, under the rated working condition of the power forward mode, the measured abnormality becomes 0% of the real three-phase AC voltage, and it recovers after 20ms, and the flexible DC converter on the DC voltage side generates a protection action. Figure 6 A schematic diagram of a test of the three-phase AC voltage on the second flexible DC converter side in the forward transmission mode provided by an embodiment of the present invention, see Figure 6 , the three-phase AC voltage waveform on the second flexible DC converter MMC2 side is within the preset time of the output measurement abnormality, and the preset time is exemplarily set to 20ms. The three-phase AC voltage on the second flexible DC converter MMC2 side becomes 0, and the three-phase AC voltage returns to normal after the preset time of about 20ms. Figure 7 A test schematic diagram of the average value of the capacitor voltage of the first flexible DC converter bridge arm in the forward transmission mode provided by an embodiment of the present invention, see Figure 7 , the three-phase AC voltage on the second flexible DC converter MMC2 side lasts for about 20ms. After the three-phase AC voltage is restored, the average value of the bridge arm capacitor voltage of the first flexible DC converter MMC1 remains constant. The first flexible DC converter MMC1 issues a locking command and trips to cut off the output. It can be seen that when the average value of the bridge arm capacitor voltage overvoltage protection signal changes, the average value of each bridge arm capacitor voltage has exceeded 2.2kV. In other words, when the three-phase AC voltage differs from the actual three-phase AC voltage due to measurement anomalies, the input measurement abnormality will increase the average value of the bridge arm capacitor voltage of the flexible DC converter valve-controlled DC voltage side. When the protection setting value and protection delay are met, the protection action is taken.

[0087] Figure 8 A schematic diagram of the structure of an overvoltage protection detection device provided by an embodiment of the present invention is shown in FIG. Figure 8 ,include:

[0088] The model building module 810 is used to build a simulation model of a flexible direct current back-to-back transmission system.

[0089] The voltage acquisition module 820 is used to obtain the three-phase AC voltage output by the flexible DC converter on the DC power side according to the flexible DC back-to-back transmission system simulation model.

[0090] The regulating module 830 is used to regulate the three-phase AC voltage to obtain the measured abnormal amount.

[0091] The test module 840 is used to test whether the overvoltage protection of the average value of the capacitor voltage of the valve-controlled bridge arm of the flexible DC converter on the DC voltage side generates a protection action according to the measured abnormal quantity.

[0092] For details, see Figure 2 , the model building module 810 builds a simulation model of the flexible direct current back-to-back transmission system, wherein the simulation model at least includes: a first flexible direct current converter MMC1, a second flexible direct current converter MMC2, a first flexible direct current transformer, a second flexible direct current transformer, a first alternating current system AC1, and a second alternating current system AC2. The flexible direct current back-to-back transmission system adopts a flexible direct current back-to-back typical control strategy. Among them, the flexible direct current back-to-back typical control strategy at least includes a flexible direct current back-to-back typical protection including an overvoltage protection of the average value of the valve-controlled bridge arm capacitor voltage of the flexible direct current converter. The voltage acquisition module 820 collects the three-phase alternating current voltage output by the flexible direct current converter on the direct current power side through the second flexible direct current transformer according to the simulation model, and the collected three-phase alternating current voltage is the true value of the three-phase alternating current voltage. The adjustment module 830 collects the three-phase alternating current voltage and calculates and simulates it to obtain the measurement abnormality. The measurement abnormality is the amount that is different from the true value of the three-phase alternating current voltage due to the measurement abnormality. The test module 840 continuously outputs the measurement abnormality for a preset time, for example, the preset time can be set to 20ms. After the preset output time, the real value of the output three-phase AC voltage is restored. If the flexible DC converter valve control on the DC voltage side detects that the average value of the bridge arm capacitor voltage exceeds the set value, the flexible DC converter on the DC voltage side will issue a blocking command and trip to cut off the output, and the average value of the bridge arm capacitor voltage of the flexible DC converter valve control on the DC voltage side will be judged to be overvoltage protection action.

[0093] The technical solution provided by the embodiment of the present invention is that the model building module establishes a simulation model of the flexible direct current back-to-back transmission system, wherein the simulation model adopts a typical control strategy of the flexible direct current back-to-back, wherein the simulation model can be established by using a non-real-time simulation tool or a real-time simulation tool, thereby improving the versatility of the simulation application. When the model outputs normally, the voltage acquisition module obtains the three-phase AC voltage output by the flexible direct current converter on the DC power side, and adjusts the three-phase AC voltage through the adjustment module to obtain the measured abnormal quantity, and inputs the measured abnormal quantity into the model. The test module detects the overvoltage protection that triggers the average value of the bridge arm capacitor voltage of the valve-controlled bridge arm capacitor of the flexible direct current converter, thereby realizing direct testing of the overvoltage protection, which solves the problem that it is difficult to trigger the overvoltage protection action of the average value of the bridge arm capacitor voltage by simulating various short-circuit faults in the prior art.

[0094] Optionally, the model building module includes:

[0095] The mode setting unit is used to set the power transmission mode of the flexible direct current back-to-back transmission system simulation model, wherein the power transmission mode includes a forward transmission mode and a reverse transmission mode.

[0096] For details, please refer to Figure 2For the flexible direct current back-to-back transmission system, the system is a pseudo-bipolar structure, and the two ends respectively include a first flexible direct current converter MMC1, and a second flexible direct current converter MMC2. The first three-phase AC voltage measuring point US1 and the second three-phase AC voltage measuring point US2. In normal operation, the flexible direct current back-to-back transmission system adopts constant DC power control at one end and constant DC voltage control at the other end. That is to say, when the mode setting unit sets the power mode to the forward transmission mode, that is, the first AC system AC1 transmits power to the second AC system AC2, at this time, the first flexible direct current converter MMC1 on the rectifier side of the sending end, that is, the first AC system AC1 side, adopts constant DC voltage control, and the second flexible direct current converter MMC2 on the inverter side of the receiving end, that is, the second AC system AC2 side, adopts constant DC power control. When the mode setting unit sets the power mode to the reverse transmission mode, that is, the second AC system AC2 transmits power to the first AC system AC1, at this time, the second flexible DC converter MMC2 on the rectifier side of the sending end, that is, the second AC system AC2 side, adopts constant DC voltage control, and the first flexible DC converter MMC1 on the inverter side of the receiving end, that is, the first AC system AC1 side, adopts constant DC power control. Since the flexible DC back-to-back transmission system is a symmetrical structure, the same test method is used in subsequent tests to set the forward transmission mode to test the first flexible DC converter MMC1, or to set the reverse transmission mode to test the second flexible DC converter MMC2. Optionally, in the forward or reverse power transmission mode, the output adjustment unit sets the DC output of the back-to-back transmission system to the rated operating condition, thereby improving the consistency of the three-phase AC voltage output by the flexible DC converter on the DC power side of the controlled DC in the forward or reverse power transmission mode.

[0097] Based on the above embodiments, Fig. 9 This is a logical diagram of a simulation of abnormal quantity measurement in a forward delivery mode. Fig.10 Schematic diagram of the simulation of abnormal quantity measurement for a reverse transmission mode, see Fig. 9 and Fig.10 , the adjustment module includes a multiplier 910.

[0098] The multiplier 910 is used to multiply the three-phase AC voltage by the adjustment coefficient to obtain the measurement abnormality.

[0099] Specifically, in the forward transmission mode, the three-phase AC voltage VUS2 of the second three-phase AC voltage measuring point US2 is multiplied by the adjustment coefficient VP through the multiplier 910 to obtain the measured abnormal amount, wherein the adjustment coefficient VP is a percentage parameter. In the reverse transmission mode, the three-phase AC voltage VUS1 of the first three-phase AC voltage measuring point US1 is multiplied by the adjustment coefficient VP through the multiplier 910 to obtain the measured abnormal amount, wherein the adjustment coefficient VP is a percentage parameter.

[0100] Continue to see Fig. 9 and Fig.10 , the test module includes a selector 920:

[0101] The selector 920 is used to output the measured abnormal value to the flexible DC converter on the DC power side for a preset time, and then restore the output three-phase AC voltage.

[0102] Specifically, in the forward mode, the measured abnormal amount output by the multiplier 910 is connected to the first input terminal 1 of the selector 920, and the selector 920 outputs the measured abnormal amount for a preset time, and then the output of the measured abnormal amount is cut off. At this time, the second input terminal 0 of the selector 920 resumes inputting and outputting the three-phase AC voltage VUS2 of the second three-phase AC voltage measuring point US2. In the reverse mode, the measured abnormal amount output by the multiplier 910 is connected to the first input terminal 1 of the selector 920, and the selector 920 outputs the measured abnormal amount for a preset time, and then the output of the measured abnormal amount is cut off. At this time, the second input terminal 0 of the selector 920 resumes inputting and outputting the three-phase AC voltage VUS1 of the first three-phase AC voltage measuring point US1.

[0103] The embodiment of the present invention provides a flexible direct current back-to-back power transmission system, including any overvoltage protection detection device of the embodiment of the present invention. Specifically, the flexible direct current back-to-back power transmission system is mainly used for interconnection or power transmission between two asynchronously operated AC power systems. Because it includes the overvoltage protection detection device provided by any embodiment of the embodiment of the present invention, it also has the same beneficial effects, which will not be described in detail here.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An overvoltage protection test method, characterized in that: include: Establish a simulation model of flexible direct current back-to-back transmission system; According to the flexible DC back-to-back power transmission system simulation model, the three-phase AC voltage output by the flexible DC converter on the DC power side is obtained; Obtaining a simulated measurement abnormality of the three-phase AC voltage; Test whether the average value overvoltage protection of the capacitor voltage of the valve-controlled bridge arm of the flexible DC converter on the DC voltage side is actuated according to the measured abnormal quantity; After establishing the flexible direct current back-to-back transmission system simulation model, it also includes: Initializing the simulation model of the flexible direct current back-to-back power transmission system, wherein the initialization setting includes setting an adjustment coefficient; After the simulation model of the flexible direct current back-to-back power transmission system is initialized, the method further includes: Setting a power transmission mode of the flexible direct current back-to-back power transmission system simulation model; wherein the power transmission mode includes a forward transmission mode and a reverse transmission mode; Acquiring the simulated measured abnormal amount of the three-phase AC voltage, including: Multiplying the three-phase AC voltage by the adjustment coefficient to obtain the measurement abnormality; After testing whether the average value overvoltage protection of the valve-controlled bridge arm capacitor voltage of the flexible DC converter on the DC voltage side is actuated according to the measured abnormal quantity, the method further includes: If no protection action is generated, the adjustment coefficient is updated, wherein the adjustment coefficient is updated according to the step value; Multiplying the three-phase AC voltage by the updated adjustment coefficient to obtain an updated measurement abnormality; According to the updated measurement abnormality test, the overvoltage protection of the average value of the valve-controlled bridge arm capacitor voltage of the flexible DC converter on the DC voltage side is activated.

2. An overvoltage protection detection device, characterized in that: include: Model building module, used to build a simulation model of flexible direct current back-to-back transmission system; A voltage acquisition module, used for acquiring the three-phase AC voltage output by the flexible DC converter on the DC power side according to the flexible DC back-to-back transmission system simulation model; A regulating module, used for obtaining a measured abnormal amount of the simulated three-phase AC voltage; A test module, used for testing whether the average value overvoltage protection of the valve-controlled bridge arm capacitor voltage of the flexible DC converter on the DC voltage side is activated according to the measured abnormal quantity; After establishing the flexible direct current back-to-back power transmission system simulation model, the method further includes: initializing the flexible direct current back-to-back power transmission system simulation model, wherein the initialization setting includes setting the adjustment coefficient; The model building module includes: A mode setting unit, used to set the power transmission mode of the flexible direct current back-to-back power transmission system simulation model; wherein the power transmission mode includes a forward transmission mode and a reverse transmission mode; The adjustment module includes a multiplier; The multiplier is used to multiply the three-phase AC voltage by the adjustment coefficient to obtain the measured abnormality; After testing whether the average value overvoltage protection of the valve-controlled bridge arm capacitor voltage of the flexible DC converter on the DC voltage side is actuated according to the measured abnormal quantity, the method further includes: If no protection action is generated, the adjustment coefficient is updated, wherein the adjustment coefficient is updated according to the step value; Multiplying the three-phase AC voltage by the updated adjustment coefficient to obtain an updated measurement abnormality; According to the updated measurement abnormality test, the overvoltage protection of the average value of the valve-controlled bridge arm capacitor voltage of the flexible DC converter on the DC voltage side is activated.

3. The overvoltage protection detection device according to claim 2, characterized in that: The test module includes a selector; The selector is used to output the measured abnormal amount to the flexible DC converter on the DC power control side for a preset time, and then resume outputting the three-phase AC voltage.

4. A flexible DC back-to-back power transmission system, comprising the overvoltage protection detection device according to any one of claims 2-3.

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