Fault isolation and restart method and system for multi-terminal flexible direct current power transmission system

Abstract

The invention provides a fault isolation and restart method and system for a multi-terminal flexible DC power transmission system, and relates to the technical field of flexible DC power transmission. The fault isolation and restart method comprises the steps of determining a station grounding current first effective value of each converter in the multi-terminal direct current power transmission system under the condition that a single-phase grounding fault exists on a valve side or a bridge arm side of the multi-terminal direct current power transmission system; according to the first effective value of the station grounding current and the second effective value of the station grounding current of each current converter, determining a faulty current converter; the current converter with the fault is isolated; and unlocking a fault-free converter in the multi-terminal direct current power transmission system, and increasing the power of the fault-free converter to a set value. According to the method and the system, the problem of simultaneous locking of the whole multi-end flexible direct current power transmission system caused by single-phase grounding fault of a single converter valve side or a bridge arm side of the multi-end flexible direct current power transmission system can be solved, and the operation reliability of the multi-end flexible direct current power transmission system is improved.

Description

Technical Field

[0001] The present application relates to the technical field of flexible direct current transmission, and in particular to a fault isolation and restart method and system for a multi-terminal flexible direct current transmission system. Background Art

[0002] Flexible DC transmission has the characteristics of flexible control, rapid dynamic response, low harmonic content, etc. It can quickly and independently adjust active power and reactive power, and has flexible control and coordination capabilities. It is widely regarded as one of the technical means for island power transmission, grid interconnection, reliable access and effective utilization of new energy, and has broad application prospects. Especially in the field of urban grid interconnection, it can realize reliable grid zoning, reduce short-circuit current, and realize rapid active power support in various regions.

[0003] After the urban power grid deploys multi-terminal flexible direct current transmission, since the connection method between the converter and the AC system is mostly Y / Y transformer, and the valve side of the transformer is grounded through a resistor, at this time, if a single-phase grounding fault occurs on the valve side or bridge arm side of a single converter, other non-fault converters can also feel the fault characteristics at the same time, eventually causing the overall locking of the multi-terminal flexible direct current.

[0004] Therefore, it is necessary to find a multi-terminal flexible DC back-to-back fault isolation and restart method that can distinguish and isolate the faulty converter and ensure the normal operation of other non-faulty converters. Summary of the invention

[0005] In order to solve at least one of the above problems, the present application proposes a fault isolation and restart method and system for a multi-terminal flexible direct current transmission system.

[0006] According to the first aspect of the present application, at least one embodiment of the present application provides a fault isolation and restart method for a multi-terminal flexible direct current transmission system, comprising: in the event that a single-phase grounding fault exists on the valve side or the bridge arm side of the multi-terminal direct current transmission system, determining a first effective value of a station grounding current of each converter in the multi-terminal direct current transmission system; determining a faulty converter according to the first effective value of the station grounding current and the second effective value of the station grounding current of each converter; isolating the faulty converter; unlocking a fault-free converter in the multi-terminal direct current transmission system, and increasing the power of the fault-free converter to a set value.

[0007] For example, in some embodiments of the present application, when a single-phase grounding fault exists on the valve side or the bridge arm side of the multi-terminal DC transmission system, determining the first effective value of the station grounding current of each converter in the multi-terminal DC transmission system includes: when a single-phase grounding fault exists on the valve side or the bridge arm side of the multi-terminal DC transmission system, locking each converter; determining the first effective value of the station grounding current, the active power value and the reactive power value of each converter before locking; and outputting a first AC incoming line switch instruction, wherein the first AC incoming line switch instruction is used to delay disconnecting the AC incoming line switch of each converter for a first time.

[0008] For example, in some embodiments of the present application, determining the faulty converter according to the first effective value of the station grounding current and the second effective value of the station grounding current of each converter includes: determining the second effective value of the station grounding current after each converter is locked for a second time, wherein the second time is less than or equal to the first time; determining that any converter has a fault when the ratio of the second effective value of the station grounding current to the first effective value of the station grounding current of any converter in the multi-terminal direct current transmission system is less than a first set threshold; determining that any converter has not a fault when the ratio of the second effective value of the station grounding current to the first effective value of the station grounding current of any converter in the multi-terminal direct current transmission system is not less than the first set threshold.

[0009] For example, in some embodiments of the present application, isolating the faulty converter includes: when the faulty converter is determined, outputting a second AC incoming line switch instruction, wherein the second AC incoming line switch instruction is used to immediately disconnect the AC incoming line switch of the faulty converter; when the AC incoming line switch of the faulty converter is disconnected, outputting an instruction to disconnect the DC side switch and the isolating knife of the faulty converter.

[0010] For example, in some embodiments of the present application, the multi-terminal flexible direct current transmission system includes n converters, one converter among the n converters is determined as a DC voltage-controlled operating converter, and n-1 converters among the n converters are determined as active power-controlled operating converters, where n is an integer greater than or equal to 3.

[0011] For example, in some embodiments of the present application, unlocking the fault-free converter in the multi-terminal direct current transmission system and increasing the power of the fault-free converter to a set value includes: when the faulty converter is determined, outputting a cancellation instruction, wherein the cancellation instruction is used to cancel the first AC incoming line switch instruction; when the DC side switch of the faulty converter is disconnected, judging the type of the faulty converter; when the faulty converter is an active power control operation converter, unlocking the DC voltage control operation converter; delaying a third time to unlock the fault-free active power control operation converter; restoring the active power value of the fault-free active power control operation converter to a first set value according to a first set rate; and restoring the reactive power value of the fault-free active power control operation converter to a second set value according to a second set rate.

[0012] For example, in some embodiments of the present application, the unlocking of the fault-free converter in the multi-terminal DC transmission system and increasing the power of the fault-free converter to a set value also includes: when the faulty converter is the DC voltage-controlled operating converter, according to the set DC voltage station takeover order, the active power control operating converter with the highest takeover priority among the fault-free active power control operating converters is set as a DC voltage-controlled operating converter and unlocked; delaying a fourth time to unlock the fault-free active power control operating converter; restoring the active power value of the fault-free active power control operating converter to a third set value according to a third set rate; and restoring the reactive power value of the fault-free active power control operating converter to a fourth set value according to a fourth set rate.

[0013] For example, in some embodiments of the present application, the first set value and the third set value include: the active power value determined before locking and / or the active power value determined according to the active power demand; the second set value and the fourth set value include: the reactive power value determined before locking and / or the reactive power value determined according to the reactive power demand.

[0014] For example, in some embodiments of the present application, the converter in the multi-terminal flexible direct current transmission system is connected to the alternating current system through a Y / Y transformer, and the valve side of the transformer is grounded through a resistor.

[0015] According to the second aspect of the present application, at least one embodiment of the present application provides a fault isolation and restart system for a multi-terminal flexible direct current transmission system, which is used to execute the fault isolation and restart method as described in any one of the first aspects, and the fault isolation and restart system includes: a fault detection module, which is used to determine the first effective value of the station grounding current of each converter in the multi-terminal direct current transmission system when a single-phase grounding fault exists on the valve side or the bridge arm side of the multi-terminal direct current transmission system; a fault converter judgment module, which is used to determine the faulty converter according to the first effective value of the station grounding current and the second effective value of the station grounding current of each converter; a fault converter isolation module, which is used to isolate the faulty converter; a non-fault converter restart module, which is used to unlock the fault-free converter in the multi-terminal direct current transmission system and increase the power of the fault-free converter to a set value.

[0016] Through the above-mentioned example embodiments, the present application provides a fault isolation and restart method and system for a multi-terminal flexible direct current transmission system. By detecting and comparing the magnitude of the station grounding current values ​​before and after the lockout, and recording the active power, reactive power, and operating mode before the lockout, the faulty converter is judged and isolated, and the non-faulty converter is restarted, thereby avoiding a single converter fault from causing the overall operation of the multi-terminal flexible direct current, solving the problem of the entire multi-terminal flexible direct current transmission system being locked simultaneously when a single-phase grounding fault occurs on the valve side or the bridge arm side of a single converter in the multi-terminal flexible direct current transmission system, and improving the operating reliability of the multi-terminal flexible direct current transmission system.

[0017] It should be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] By describing in detail exemplary embodiments thereof with reference to the accompanying drawings, the above and other objects, features and advantages of the present application will become more apparent. The accompanying drawings described below are only some embodiments of the present application, and are not intended to limit the present application.

[0019] Figure 1 A schematic diagram of a multi-terminal flexible direct current transmission system of the present application is shown;

[0020] Figure 2 A schematic diagram showing the topological structure of a single converter of the present application is shown;

[0021] Figure 3 A flow chart showing a fault isolation and restart method for a multi-terminal flexible direct current transmission system according to an exemplary embodiment;

[0022] Figure 4 A schematic diagram of a fault isolation and restart system for a multi-terminal flexible direct current transmission system is shown according to an exemplary embodiment. DETAILED DESCRIPTION

[0023] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this application will be comprehensive and complete and will fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar parts, and thus their repeated description will be omitted.

[0024] The described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of these specific details, or other modes, components, materials, devices, etc. may be adopted. In these cases, known structures, methods, devices, implementations, materials or operations will not be shown or described in detail.

[0025] The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0026] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0027] Those skilled in the art will appreciate that the drawings are merely schematic diagrams of example embodiments, and the modules or processes in the drawings are not necessarily necessary for implementing the present application, and therefore cannot be used to limit the scope of protection of the present application.

[0028] Figure 1 A schematic diagram of a multi-terminal flexible direct current transmission system of the present application is shown.

[0029] like Figure 1As shown, the multi-terminal flexible DC transmission system includes n converters: one converter among the n converters is determined as a DC voltage controlled operating converter, and n-1 converters among the n converters are determined as active power controlled operating converters, where n is an integer greater than or equal to 3. Converter 1 is set as a DC voltage controlled operating converter, and the other converters are active power controlled operating converters. The operating converter refers to a converter that is in an unlocked state and connected on the DC side.

[0030] Figure 2 A schematic diagram of the topological structure of a single converter of the present application is shown.

[0031] like Figure 2 As shown, each converter includes an AC incoming line switch QF1, DC side switches Q1, Q91, Q2, Q92 and spacers Q51, Q52, Q53, Q54, Q55, Q56.

[0032] The converter in the multi-terminal flexible DC transmission system is connected to the AC system through a Y / Y transformer, and the valve side of the transformer is grounded through a resistor.

[0033] Figure 3 A flow chart of a fault isolation and restart method for a multi-terminal flexible direct current transmission system according to an exemplary embodiment is shown.

[0034] like Figure 3 As shown, the steps of the fault isolation and restart method for a multi-terminal flexible direct current transmission system include:

[0035] Step S101: when a single-phase grounding fault occurs on a valve side or a bridge arm side of a multi-terminal direct current transmission system, determining a first effective value of a station grounding current of each converter in the multi-terminal direct current transmission system.

[0036] According to an exemplary embodiment, the effective value of the station ground current of the operating converter is detected in real time. I rg . In the event of a single-phase grounding fault on the valve side or the bridge arm side of the multi-terminal DC transmission system, each converter in the multi-terminal DC transmission system is blocked. Determine the first effective value of the station grounding current of each converter in the multi-terminal DC transmission system before blocking I rg1 , active power value P and reactive power value Q, and output a first AC incoming line switch instruction, the first AC incoming line switch instruction is used to delay the first time t1 Disconnect the AC line switch of each converter in the multi-terminal DC transmission system.

[0037] For example, record the effective value of the station ground current before blocking I rg1 , the active power value P and reactive power value Q 50ms before blocking. You can set it yourself at the first time, for example,t1 >10ms.

[0038] Step S102: determining a faulty converter according to a first effective value of a station grounding current and a second effective value of a station grounding current of each converter.

[0039] According to an exemplary embodiment, after the converter is locked, the effective value of the grounding current is detected. Determine the second locking time of each converter in the multi-terminal direct current transmission system t2 The second effective value of the station ground current after I rg2 Among them, the second time t2 Less than or equal to the first time t1 , t2≤t1.

[0040] When the ratio of the second effective value of the station grounding current of any converter in the multi-terminal DC power transmission system to the first effective value of the station grounding current is less than the first set threshold, it is determined that the current converter has failed. When the ratio of the second effective value of the station grounding current of any converter in the multi-terminal DC power transmission system to the first effective value of the station grounding current is not less than the first set threshold, it is determined that the current converter has not failed.

[0041] For example, after the converter is locked, the effective value of the ground current at the detection station is I rg2 , and delay t2 The station ground current locked at the time of locking I rg1 For comparison, if I rg2 >0.5I rg1 , then the converter is judged to be faulty and the fault flag VF is set to 1. I rg2 ≤0.5I rg1 , it is determined that the converter has not failed, and the fault flag VF is set to 0. The first set threshold can be set by itself, and this application only takes 0.5 as an example, but this application is not limited to this.

[0042] Step S103, isolating the faulty converter.

[0043] According to the exemplary embodiment, when a faulty converter is determined, a second AC line switch instruction is output, and the second AC line switch instruction is used to immediately disconnect the AC line switch of the faulty converter. When the AC line switch of the faulty converter is disconnected, an instruction to disconnect the DC side switch and the isolating knife of the faulty converter is output.

[0044] Step S104: unlocking the converter without fault in the multi-terminal direct current transmission system, and increasing the power of the converter without fault to a set value.

[0045] According to an exemplary embodiment, when a faulty converter is determined, a cancellation instruction is output, and the cancellation instruction is used to cancel the first AC incoming line switch instruction. When the DC side switch of the faulty converter is disconnected, the type of the faulty converter is determined:

[0046] In the case that the faulty converter is an active power control converter, unlock the DC voltage control converter; delay for a third time to unlock the active power control converter without faults; restore the active power value of the active power control converter without faults to a first set value according to a first set rate; restore the reactive power value of the active power control converter without faults to a second set value according to a second set rate.

[0047] In the case that the faulty converter is a DC voltage-controlled converter, according to the set DC voltage station takeover order, the active power control converter with the highest takeover priority among the fault-free active power control converters is set as the DC voltage-controlled converter and unlocked; the unlocking of the fault-free active power control converter is delayed for a fourth time; the active power value of the fault-free active power control converter is restored to the third set value according to the third set rate; the reactive power value of the fault-free active power control converter is restored to the fourth set value according to the fourth set rate.

[0048] For example, after determining that the current converter is not a faulty converter and receiving the fault flag VF=1 of other converters, a cancel instruction is immediately output to cancel the delay. t1 The command to disconnect the AC line switch command of each converter of the multi-terminal DC transmission system and wait for the DC side switch of the faulty converter to be separated.

[0049] After the DC side switch of the faulty converter is separated, if the faulty converter is an active power control converter, the DC voltage control converter in other converters with fault identification bit VF=0 will be unlocked first, and then other normal active power control converters will be unlocked after a delay of 50ms, and the active power value of the active power control converter will be restored to the set active power value at a certain rate, and the reactive power value of the active power control converter will be restored to the set reactive power value at a certain rate.

[0050] For example, when the faulty converter is a DC voltage-controlled converter, according to the set DC voltage station takeover order, the active power control converter with the highest priority in the DC voltage station takeover order among other converters with fault identification bit VF=0 is used as the DC voltage-controlled converter and unlocked, and other normal active power control converters are unlocked after a delay of 50ms, and the active power value of the active power control converter is restored to the set active power value at a certain rate, and the reactive power value of the active power control converter is restored to the set reactive power value at a certain rate.

[0051] According to some embodiments, the first set value and the third set value include: an active power value determined before blocking and / or an active power value determined according to an active power demand. The second set value and the fourth set value include: a reactive power value determined before blocking and / or a reactive power value determined according to a reactive power demand.

[0052] The present application also provides a fault isolation and restart system for a multi-terminal flexible DC power transmission system, which is used to execute the fault isolation and restart method for a multi-terminal flexible DC power transmission system as described above. Figure 4 As shown, the fault isolation and restart system includes: a fault detection module, a fault converter judgment module, a fault converter isolation module and a non-fault converter restart module.

[0053] The fault detection module is used to determine the first effective value of the station grounding current of each converter in the multi-terminal DC power transmission system when a single-phase grounding fault exists on the valve side or the bridge arm side of the multi-terminal DC power transmission system.

[0054] The faulty converter judgment module is used to determine the faulty converter according to the first effective value of the station grounding current and the second effective value of the station grounding current of each converter.

[0055] The faulty converter isolation module is used to isolate the faulty converter.

[0056] The non-faulty converter restart module is used to unlock the non-faulty converter in the multi-terminal DC transmission system and increase the power of the non-faulty converter to a set value.

[0057] The fault isolation and restart system is used to execute the fault isolation and restart method as described above, so it will not be described again here.

[0058] The present application provides a fault isolation and restart method and system for a multi-terminal flexible direct current transmission system. By detecting and comparing the magnitude of the grounding current values ​​of the stations before and after the lockout, and recording the active power, reactive power, and operating mode before the lockout, the faulty converter is judged and isolated, and the non-faulty converter is restarted, so as to avoid the overall operation of the multi-terminal flexible direct current caused by a single converter fault, solve the problem of the simultaneous lockout of the entire multi-terminal flexible direct current transmission system caused by a single-phase grounding fault on the valve side or the bridge arm side of a single converter in the multi-terminal flexible direct current transmission system, and improve the operating reliability of the multi-terminal flexible direct current transmission system.

[0059] It should be clearly understood that the present application describes how to form and use specific examples, but the present application is not limited to any details of these examples. On the contrary, based on the teaching of the content disclosed in the present application, these principles can be applied to many other embodiments.

[0060] In addition, it should be noted that the above figures are only schematic illustrations of the processes included in the method according to the exemplary embodiments of the present application, and are not intended to be limiting. It is easy to understand that the processes shown in the above figures do not indicate or limit the time sequence of these processes. In addition, it is also easy to understand that these processes can be performed synchronously or asynchronously, for example, in multiple modules.

[0061] The exemplary embodiments of the present application are specifically shown and described above. It should be understood that the present application is not limited to the detailed structures, configurations or implementations described herein; on the contrary, the present application is intended to cover various modifications and equivalent configurations included within the objectives and scope of the appended claims.

Claims

1. A fault isolation and restart method for a multi-terminal flexible direct current transmission system, characterized in that: include: In the case where a single-phase grounding fault exists on the valve side or the bridge arm side of the multi-terminal direct current transmission system, determining a first effective value of a station grounding current of each converter in the multi-terminal direct current transmission system; Determining a faulty converter according to a first effective value of a station grounding current and a second effective value of a station grounding current of each converter; isolating the faulty converter; Unlock the converter without fault in the multi-terminal direct current transmission system, and increase the power of the converter without fault to a set value.

2. The fault isolation and restart method according to claim 1, characterized in that: The determining, when a single-phase grounding fault exists on a valve side or a bridge arm side of the multi-terminal direct current transmission system, a first effective value of a station grounding current of each converter in the multi-terminal direct current transmission system comprises: When a single-phase grounding fault occurs on a valve side or a bridge arm side of the multi-terminal direct current transmission system, locking each converter; Determining a first effective value of the station grounding current, an active power value, and a reactive power value of each converter before blocking; A first AC incoming line switch instruction is output, where the first AC incoming line switch instruction is used to delay disconnecting the AC incoming line switch of each converter for a first time.

3. The fault isolation and restart method according to claim 2, characterized in that: The step of determining a faulty converter according to the first effective value of the station grounding current and the second effective value of the station grounding current of each converter comprises: Determine a second effective value of the station grounding current after each converter is locked for a second time, wherein the second time is less than or equal to the first time; When a ratio of a second effective value of a station grounding current to a first effective value of a station grounding current of any converter in the multi-terminal direct current transmission system is less than a first set threshold, determining that any converter has a fault; When the ratio of the second effective value of the station grounding current to the first effective value of the station grounding current of any converter in the multi-terminal direct current transmission system is not less than a first set threshold, it is determined that no fault occurs in any converter.

4. The fault isolation and restart method according to claim 3, characterized in that: The converter for isolating the fault comprises: When a faulty converter is determined, a second AC incoming line switch instruction is output, wherein the second AC incoming line switch instruction is used to immediately disconnect the AC incoming line switch of the faulty converter; When the AC incoming line switch of the faulty converter is disconnected, an instruction to disconnect the DC side switch and the isolating switch of the faulty converter is output.

5. The fault isolation and restart method according to claim 4, characterized in that: The multi-terminal flexible direct current transmission system includes n converters, one converter among the n converters is determined as a direct current voltage controlled operating converter, and n-1 converters among the n converters are determined as active power controlled operating converters, wherein n is an integer greater than or equal to 3.

6. The fault isolation and restart method according to claim 5, characterized in that: The unlocking of the converter without fault in the multi-terminal direct current transmission system and increasing the power of the converter without fault to a set value includes: When the faulty converter is determined, outputting a cancellation instruction, wherein the cancellation instruction is used to cancel the first AC incoming line switch instruction; When the DC side switch of the faulty converter is disconnected, determining the type of the faulty converter; In the case where the faulty converter is an active power control operation converter, unlocking the DC voltage control operation converter; Delaying the third time to unlock the fault-free active power control operation converter; Restoring the active power value of the fault-free active power control operating converter to a first set value according to a first set rate; The reactive power value of the active power control operating converter without fault is restored to a second set value according to a second set rate.

7. The fault isolation and restart method according to claim 6, characterized in that: The unlocking of the converter without fault in the multi-terminal direct current transmission system and increasing the power of the converter without fault to a set value further includes: In the case where the faulty converter is the DC voltage controlled operating converter, according to the set DC voltage station takeover order, the active power controlled operating converter with the highest takeover priority among the fault-free active power controlled operating converters is set as the DC voltage controlled operating converter and unlocked; Delaying the fourth time to unlock the fault-free active power control running converter; Restoring the active power value of the fault-free active power control operating converter to a third set value according to a third set rate; The reactive power value of the active power control operating converter without fault is restored to a fourth set value according to a fourth set rate.

8. The fault isolation and restart method according to claim 7, characterized in that: The first set value and the third set value include: an active power value determined before blocking and / or an active power value determined according to an active power demand; The second set value and the fourth set value include: a reactive power value determined before blocking and / or a reactive power value determined according to a reactive power demand.

9. The fault isolation and restart method according to claim 1, characterized in that: The converter in the multi-terminal flexible direct current power transmission system is connected to the alternating current system via a Y / Y transformer, and the valve side of the transformer is grounded via a resistor.

10. A fault isolation and restart system for a multi-terminal flexible direct current transmission system, characterized in that: Used to perform the fault isolation and restart method according to any one of claims 1 to 9, the fault isolation and restart system comprising: a fault detection module, configured to determine a first effective value of a station grounding current of each converter in the multi-terminal DC power transmission system when a single-phase grounding fault exists on a valve side or a bridge arm side of the multi-terminal DC power transmission system; A faulty converter judging module, used for determining a faulty converter according to a first effective value of a station grounding current and a second effective value of a station grounding current of each converter; A faulty converter isolation module, used to isolate the faulty converter; The non-fault converter restart module is used to unlock the non-fault converter in the multi-terminal direct current transmission system and increase the power of the non-fault converter to a set value.

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