Method and device for preventing differential protection maloperation of converter transformer and electronic equipment

Abstract

The invention provides a method for preventing differential protection maloperation of a converter transformer, and the method comprises the steps: locking a bipolar transistor after the current of any bridge arm in a modular multilevel converter reaches a preset current protection value; obtaining a first waveform of the differential current of the internal fault of the converter transformer and a second waveform of the differential current of the external fault of the converter transformer; according to the first waveform and the second waveform, whether fault inrush current occurs or not is judged, and differential protection is locked according to the judgment result, so that whether fault inrush current occurs or not can be accurately judged based on the first waveform and the second waveform, differential protection action refusal or action delay caused by harmonic braking is avoided, and the reliability of differential protection is improved. The problem of differential protection maloperation of the converter transformer is effectively prevented, and the safety and reliability of a power system are further guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method, a device and electronic equipment for preventing malfunction of differential protection of a converter transformer. Background Art

[0002] In recent years, my country's offshore wind power has developed rapidly. Offshore wind power will become an important choice for my country to vigorously develop new energy and play a vital role in the transformation of energy structure.

[0003] The transmission system refers to the high-voltage electrical network connecting the offshore boost converter platform and the onshore main grid connection point. For example, the offshore wind power transmission system topology includes high voltage alternating current (HVAC) and conventional direct current, such as line commutated converter based high voltage direct current (LCC-HVDC), modular multi-level converter high voltage direct current (MMC-HVDC), etc. Compared with LCC-HVDC, MMC-HVDC has the advantages of flexible control, no commutation failure risk, and compact modular design. However, when a fault surge occurs in the inverter side converter, when an out-of-zone fault occurs on the converter valve side, it will malfunction, and when an out-of-zone to in-zone grounding fault occurs, the converter differential protection may fail to operate. Therefore, how to prevent the differential protection from failing to operate or delaying the operation to ensure the normal operation of the power system has become an urgent problem to be solved. Summary of the invention

[0004] The present application provides a method for preventing false operation of differential protection of converter transformers, which is used to accurately determine whether a fault surge occurs through a first waveform and a second waveform, thereby avoiding the failure of differential protection to operate or delayed operation due to harmonic braking, effectively preventing the problem of false operation of differential protection of converter transformers, and further ensuring the safety and reliability of the power system.

[0005] According to the first aspect of the present application, there is provided a method for preventing misoperation of differential protection of a converter transformer, comprising: in response to the current of any bridge arm in a modular multilevel converter reaching a preset current protection value, locking a bipolar transistor; obtaining a first waveform of the differential current of an intra-zone fault and a second waveform of the differential current of an extra-zone fault of the converter transformer; judging whether it is a fault surge current based on the first waveform and the second waveform, and locking the differential protection based on the judgment result.

[0006] According to the second aspect of the present application, there is provided a device for preventing misoperation of differential protection of a converter transformer, comprising: a locking module for locking the bipolar transistor in response to the current of any bridge arm in a modular multilevel converter reaching a preset current protection value; an acquisition module for acquiring a first waveform of the differential current of an intra-zone fault and a second waveform of the differential current of an extra-zone fault of the converter transformer; and a judgment module for judging whether it is a fault surge current based on the first waveform and the second waveform, and locking the differential protection based on the judgment result.

[0007] In order to achieve the above-mentioned purpose, the third aspect of the present application proposes an electronic device, characterized in that it includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, and when the processor executes the program, it implements the method for preventing false operation of the converter transformer differential protection as described in the first aspect.

[0008] In order to achieve the above-mentioned purpose, the fourth aspect of the present application proposes a non-transitory computer-readable storage medium storing computer instructions, wherein the computer instructions are used to enable the computer to execute the method for preventing false operation of converter transformer differential protection as described in the first aspect.

[0009] In order to achieve the above-mentioned purpose, the fifth aspect of the present application proposes a computer program product, including a computer program, which, when executed by a processor, implements the method for preventing false operation of converter transformer differential protection according to the first aspect.

[0010] The technical solution provided by the embodiments of the present application includes at least the following beneficial effects:

[0011] The present application provides a method for preventing false operation of differential protection of converter transformers. Whether a fault surge current occurs can be accurately determined through a first waveform and a second waveform, thereby avoiding the failure of differential protection to operate or delayed operation due to harmonic braking, effectively preventing the problem of false operation of differential protection of converter transformers, and further ensuring the safety and reliability of the power system.

[0012] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present application, nor is it intended to limit the scope of the present application. Other features of the present application will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings are used to better understand the present solution and do not constitute a limitation of the present application.

[0014] Figure 1 A flow chart of a method for preventing malfunction of differential protection of a converter transformer provided in an embodiment of the present application;

[0015] Figure 2 A schematic diagram of the structure of an MMC-HVDC system provided in an embodiment of the present application;

[0016] Figure 3 A schematic diagram of the charging current of the upper bridge arm before locking provided in an embodiment of the present application;

[0017] Figure 4 A schematic diagram of a charging current of an upper bridge arm after locking provided in an embodiment of the present application;

[0018] Figure 5 A flow chart of another method for preventing malfunction of converter transformer differential protection provided by an embodiment of the present application;

[0019] Figure 6 A schematic diagram of the structure of a device for preventing malfunction of differential protection of a converter transformer provided in an embodiment of the application;

[0020] Figure 7 A schematic structural diagram of an electronic device provided in an application embodiment. DETAILED DESCRIPTION

[0021] The following is a description of exemplary embodiments of the present application in conjunction with the accompanying drawings, including various details of the embodiments of the present application to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those of ordinary skill in the art that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present application. Similarly, for the sake of clarity and conciseness, the description of well-known functions and structures is omitted in the following description.

[0022] The following uses an embodiment to explain in detail the method for preventing malfunction of the converter transformer differential protection of the present application.

[0023] Figure 1 A flow chart of a method for preventing malfunction of converter transformer differential protection provided in an embodiment of the present application.

[0024] like Figure 1 As shown, the method for preventing malfunction of converter transformer differential protection proposed in this embodiment specifically includes the following steps:

[0025] S101 . In response to a current in any bridge arm of a modular multilevel converter reaching a preset current protection value, locking a bipolar transistor.

[0026] It should be noted that the system structure diagram of MMC-HVDC, such as Figure 2 As shown, the system topology is symmetrical, each pole can be controlled independently, and the characteristics of a valve-side single-phase grounding fault on any pole are similar.

[0027] For example, taking the positive pole of the receiving end as an example, a modular multi-level converter (MMC) is a three-phase MMC composed of 6 bridge arms, each bridge arm is composed of N sub-modules and a bridge arm current limiting reactor, and the upper and lower bridge arms of each phase are combined into a phase unit. The MMC supports the voltage of the DC bus through the capacitor voltage of each sub-module, and meets the requirements of different power and voltage levels by putting in and removing sub-modules.

[0028] It should be noted that after a single-phase grounding fault occurs on the converter transformer side, the fault grounding point will form a fault loop with the grounding electrodes of the converter station on the opposite side and on this side through the upper and lower bridge arms respectively. When the current in any bridge arm reaches the preset current protection value, the insulated gate bipolar transistor (IGBT) will be locked.

[0029] Furthermore, since the time from the fault occurrence to the IGBT lockout of the MMC is very short (3-5 ms), and the charging current of the upper bridge arm after lockout is small, the valve side current is mainly the fault current flowing from the ground electrode through the lower bridge arm.

[0030] S102: Obtain a first waveform of a differential current of an intra-zone fault and a second waveform of a differential current of an extra-zone fault of a converter transformer.

[0031] It should be noted that the present application does not limit the specific method for obtaining the first waveform of the differential current of the intra-zone fault and the second waveform of the differential current of the extra-zone fault of the converter transformer, which can be selected according to actual conditions.

[0032] Optionally, the differential current of the fault within the zone may be extracted to obtain the first waveform, and the differential current of the fault outside the zone may be extracted to obtain the second waveform.

[0033] S103: Determine whether it is a fault surge current according to the first waveform and the second waveform, and lock the differential protection according to the determination result.

[0034] In the embodiment of the present application, after the first waveform and the second waveform are obtained, it can be determined whether it is a fault surge current based on the first waveform and the second waveform, and then the differential protection is locked based on the determination result.

[0035] The method for preventing misoperation of differential protection of a converter transformer provided in the present application, in response to the current of any bridge arm in a modular multilevel converter reaching a preset current protection value, locks the bipolar transistor, obtains a first waveform of the differential current of an intra-zone fault and a second waveform of the differential current of an extra-zone fault of the converter transformer, determines whether it is a fault surge based on the first waveform and the second waveform, and locks the differential protection based on the judgment result. The present application can accurately determine whether a fault surge occurs based on the first waveform and the second waveform, avoids the refusal or delay of differential protection due to harmonic braking, effectively prevents the problem of misoperation of differential protection of the converter transformer, and further ensures the safety and reliability of the power system.

[0036] The following is an explanation of the process of locking the bipolar transistor after the current of any bridge arm in the modular multilevel converter reaches a preset current protection value.

[0037] It should be noted that the lower bridge arm current after the IGBT is locked flows through the path, such as Figure 3 As shown in FIG. 1 , at the moment of phase A fault, the phase A voltage Ua becomes zero, and the non-fault phase voltages Ub and Uc become line voltages. The sending-end converter station charges the upper bridge arm submodule capacitor through the DC line. Since there are submodules in the switched-on state and the switched-off state in the same bridge arm, the current flow paths inside the submodules in different states are different. The current of the switched-on submodule flows through D′ to charge the capacitor, and the submodule in the switched-off state short-circuits the submodule through VT2. The current flow path is as follows: Figure 3 The submodule shown in the figure is shown by the dotted line. Therefore, when the fault occurs before the lockout, the upper bridge arm submodule will undergo a charging process, and the valve side current is mainly the capacitor charging current, and the direction is to flow into the converter transformer valve side.

[0038] Optionally, if it is determined that a ground fault occurs in the converter transformer, a DC grounding electrode and the fault grounding point form a loop, the bridge arm current increases, and in response to any bridge arm current in the modular multilevel converter reaching a preset current protection value, the bipolar transistor is locked.

[0039] It should be noted that when a grounding fault occurs on the converter transformer side, a loop is formed between the DC grounding electrode and the fault grounding point, and the bridge arm current will increase rapidly. Due to the weak current-carrying capacity of the IGBT, when the current of any bridge arm in the modular multilevel converter reaches the preset current protection value, the bipolar transistor will be locked.

[0040] It should be noted that after the bipolar transistor is locked, the fault characteristics of the upper bridge arm are mainly related to the conduction state of the diode. The current flow path of the upper bridge arm is as follows: Figure 4As shown by the middle dotted line, the voltage drop on the inductance and resistance of the bridge arm can be ignored. After locking, the voltage across D1, D3, and D5 is udc-xu' (x=a, b, c). Since the DC voltage udc is always greater than the midpoint voltage xu' (valve side line voltage) after the fault, the diodes D1, D3, and D5 of the upper bridge arm will be in the cut-off state.

[0041] Optionally, if the equivalent capacitor voltage of the upper bridge arm before the fault is udc, and the DC voltage remains unchanged at the moment of the fault, the voltage across 1D', 3D', and 5D' is x-u'. Therefore, 1D', 3D', and 5D' will be turned on in the negative half cycle of xu', and the fault current flowing through the DC line will charge the equivalent capacitor C0 in the negative half cycle of xu' until 1D', 3D', and 5D' are turned off due to reverse pressure. The DC voltage udc will gradually increase as the capacitor is charged. Due to the presence of the diode, the submodule will only be charged when the difference between the AC and DC voltages is greater than the bridge arm voltage.

[0042] Therefore, after the fault, there are multiple stable values ​​of the submodule capacitor voltage, and the maximum value reached is dc||xu-u', the xu' fault phase voltage is zero, and the non-fault phase voltage is the line voltage. Therefore, the maximum value of the fault phase submodule capacitor charging voltage is udc, and the maximum value of the non-fault submodule capacitor charging voltage is udc+max(|ux|)(x=b,c), among which the maximum value of the capacitor charging voltage of the non-fault phase is higher than that of the fault phase.

[0043] The following explains how to determine whether it is a fault surge current based on the first waveform and the second waveform, and how to lock the differential protection process based on the determination result.

[0044] As a possible implementation, Figure 5 As shown, based on the above steps, in the above step S103, judging whether it is a fault surge current according to the first waveform and the second waveform, and locking the differential protection according to the judgment result, the specific process includes the following steps:

[0045] S501 , judging whether the second waveform is offset and distorted based on the first waveform.

[0046] S502: Determine that the second waveform is offset and distorted, determine that it is a fault surge, and lock the differential protection.

[0047] For example, after the converter transformer core in MMC-HVDC reaches deep saturation, the fault surge current is a sine wave with DC bias, the amplitude increases and the second harmonic content will be significantly reduced, which is likely to cause the differential protection to malfunction during an out-of-zone fault. In the scenario of an in-zone fault, due to the large amplitude of the fault current, the fundamental amplitude in the differential current is very high, and the second harmonic content is lower than the set value, the differential protection can operate correctly. In other words, the differential current is basically a sine wave during an in-zone fault of the converter transformer, while there are a large number of harmonic components in the differential current during an out-of-zone fault, and the waveform is offset and distorted. The fault surge current can be identified through the waveform distortion, effectively preventing the differential protection from malfunctioning.

[0048] The present application provides a method for preventing false operation of differential protection of converter transformers. Based on a first waveform and a second waveform, it can accurately determine whether a fault surge occurs, thereby avoiding the failure of differential protection to operate or delayed operation due to harmonic braking, effectively preventing the problem of false operation of differential protection of converter transformers, and further ensuring the safety and reliability of the power system.

[0049] In order to implement the above embodiment, this embodiment provides a device for preventing malfunction of differential protection of converter transformer. Figure 6 A schematic diagram of the structure of a device for preventing malfunction of differential protection of a converter transformer provided in an embodiment of the present application.

[0050] like Figure 6 As shown, the device 1000 for preventing malfunction of differential protection of converter transformer includes: a locking module 110 , an acquisition module 120 and a judgment module 130 .

[0051] The locking module 110 is used to lock the bipolar transistor in response to the current of any bridge arm in the modular multi-level converter reaching a preset current protection value;

[0052] An acquisition module 120, configured to acquire a first waveform of a differential current of an intra-zone fault and a second waveform of a differential current of an extra-zone fault of a converter transformer;

[0053] The judgment module 130 is used to judge whether it is a fault surge current according to the first waveform and the second waveform, and lock the differential protection according to the judgment result.

[0054] According to one embodiment of the present application, the locking module 120 is used to: determine that a ground fault occurs in the converter transformer, then a DC grounding electrode and the fault grounding point form a loop, the bridge arm current increases, and in response to any bridge arm current in the modular multi-level converter reaching a preset current protection value, the bipolar transistor is locked.

[0055] According to an embodiment of the present application, the device 1000 is further used to obtain the maximum value of the capacitor charging voltage of the faulty phase submodule and the maximum value of the capacitor voltage of the non-faulty submodule.

[0056] According to an embodiment of the present application, the device 1000 is used to: obtain the difference between AC and DC voltages; and determine whether to charge the submodule according to the difference between AC and DC voltages and the bridge arm voltage.

[0057] According to an embodiment of the present application, the judgment module 130 is further used to: judge whether the second waveform is offset and distorted based on the first waveform; determine that the second waveform is offset and distorted, determine that it is a fault surge, and lock the differential protection.

[0058] The device for preventing misoperation of differential protection of converter transformers provided in the present application, in response to the current of any bridge arm in the modular multilevel converter reaching a preset current protection value, locks the bipolar transistor, obtains the first waveform of the differential current of the intra-zone fault and the second waveform of the differential current of the extra-zone fault of the converter transformer, judges whether it is a fault surge based on the first waveform and the second waveform, and locks the differential protection based on the judgment result. The present application can accurately judge whether a fault surge occurs based on the first waveform and the second waveform, avoids the refusal or delay of differential protection due to harmonic braking, effectively prevents the problem of misoperation of differential protection of converter transformers, and further ensures the safety and reliability of the power system.

[0059] In order to implement the above embodiment, the present application also proposes an electronic device 2000, such as Figure 7 As shown, it includes: a memory 210, a processor 220, and a computer program stored in the memory 210 and executable on the processor 220. When the processor executes the program, the method for preventing misoperation of the converter transformer differential protection as described in the first aspect is implemented.

[0060] In order to implement the above embodiment, the present application proposes a non-transitory computer-readable storage medium storing computer instructions, wherein the computer instructions are used to enable the computer to execute the method for preventing misoperation of converter transformer differential protection as described in the first aspect.

[0061] In order to implement the above embodiments, the present application also proposes a computer program product, including a computer program, which, when executed by a processor, implements the method for preventing malfunction of converter transformer differential protection as described in the first aspect.

[0062] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps recorded in this application can be executed in parallel, sequentially or in different orders, as long as the expected results of the technical solution disclosed in this application can be achieved, and this document is not limited here.

[0063] The above specific implementations do not constitute a limitation on the protection scope of this application. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principles of this application should be included in the protection scope of this application.

Claims

1. A method for preventing malfunction of differential protection of a converter transformer, characterized in that: The method comprises: In response to the current of any bridge arm in the modular multilevel converter reaching a preset current protection value, the bipolar transistor is locked; Acquire a first waveform of a differential current of an intra-zone fault and a second waveform of a differential current of an extra-zone fault of a converter transformer; It is determined whether it is a fault surge current according to the first waveform and the second waveform, and the differential protection is locked according to the determination result.

2. The method according to claim 1, characterized in that The method of locking the bipolar transistor in response to the current of any bridge arm in the modular multilevel converter reaching a preset current protection value comprises: If it is determined that a ground fault occurs in the converter transformer, a loop is formed between the DC grounding electrode and the fault grounding point, and the bridge arm current increases. In response to any bridge arm current in the modular multilevel converter reaching a preset current protection value, the bipolar transistor is locked.

3. The method according to claim 2, characterized in that After the bipolar transistor is locked, the method comprises: The maximum value of the capacitor charging voltage of the faulty phase submodule and the maximum value of the capacitor voltage of the non-faulty submodule are obtained.

4. The method according to claim 3, characterized in that The method comprises: Get the difference between AC and DC voltages; Whether to charge the submodule is determined according to the difference between the AC and DC voltages and the bridge arm voltage.

5. The method according to claim 1, characterized in that The step of judging whether it is a fault surge current according to the first waveform and the second waveform, and locking the differential protection according to the judging result, comprises: Determining whether the second waveform is offset and distorted based on the first waveform; It is determined that the second waveform is offset and distorted, which is determined to be a fault surge current, and the differential protection is locked.

6. A device for preventing malfunction of differential protection of converter transformer, characterized in that: The device comprises: A locking module, used for locking the bipolar transistor in response to the current of any bridge arm in the modular multi-level converter reaching a preset current protection value; An acquisition module, used for acquiring a first waveform of a differential current of an intra-zone fault and a second waveform of a differential current of an extra-zone fault of a converter transformer; The judgment module is used to judge whether it is a fault surge current according to the first waveform and the second waveform, and lock the differential protection according to the judgment result.

7. The device according to claim 6, characterized in that The locking module is used for: If it is determined that a ground fault occurs in the converter transformer, a loop is formed between the DC grounding electrode and the fault grounding point, and the bridge arm current increases. In response to any bridge arm current in the modular multilevel converter reaching a preset current protection value, the bipolar transistor is locked.

8. The device according to claim 6, characterized in that The judging module is further used for: Determining whether the second waveform is offset and distorted based on the first waveform; It is determined that the second waveform is offset and distorted, which is determined to be a fault surge current, and the differential protection is locked.

9. An electronic device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, a method for preventing misoperation of differential protection of a converter transformer as described in any one of claims 1 to 5 is implemented.

10. A non-transitory computer-readable storage medium storing computer instructions, wherein: The computer instructions are used to enable the computer to execute the method for preventing malfunction of converter transformer differential protection according to any one of claims 1 to 5.

Images