WO2022193709A1 - 一种柔性直流输电系统桥臂电抗器短路保护方法及装置 - Google Patents

一种柔性直流输电系统桥臂电抗器短路保护方法及装置 Download PDF

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WO2022193709A1
WO2022193709A1 PCT/CN2021/131708 CN2021131708W WO2022193709A1 WO 2022193709 A1 WO2022193709 A1 WO 2022193709A1 CN 2021131708 W CN2021131708 W CN 2021131708W WO 2022193709 A1 WO2022193709 A1 WO 2022193709A1
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current
bridge arm
short
satisfied
transmission system
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PCT/CN2021/131708
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English (en)
French (fr)
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蔡东晓
黄伟煌
曹润彬
李桂源
郭铸
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南方电网科学研究院有限责任公司
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/52—Testing for short-circuits, leakage current or ground faults
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • the invention relates to the field of flexible direct current transmission systems, in particular to a method and a device for short circuit protection of bridge arm reactors of a flexible direct current transmission system.
  • the bridge arm reactor is one of the important equipments of the flexible DC transmission system, which has the function of restraining the rising rate of the fault current.
  • the bridge arm reactors are respectively arranged in the three-phase upper and lower bridge arms of the Modular Multilevel Converter (MMC), and are generally located between the AC connection point and the converter valve. between the DC pole line and the converter valve to reduce the impact of the short-circuit fault of the two-phase bridge arm through the wall bushing on the system.
  • MMC Modular Multilevel Converter
  • the inside of the bridge arm reactor is composed of multi-turn coils. When an inter-turn short-circuit fault or an inter-terminal short-circuit fault occurs inside the bridge arm reactor, the three-phase bridge arm parameters of the converter are no longer symmetrical, and harmonic currents appear in the bridge arms. Time running will bring harm to bridge arm reactor and converter valve.
  • the existing technical solution generally monitors the bridge arm reactor in operation by observing the temperature rise and noise of the bridge arm reactor, or evaluates the deterioration state of the bridge arm reactor during outage for maintenance. This method cannot be used. Find out the internal fault of the bridge arm reactor in time.
  • the valve control When the HVDC flexible transmission system is in the operation mode without DC power transmission such as Static Synchronous Compensator (STATCOM) or Open Line Test (OLT), the valve control will actively inject circulating current to the bridge arm to ensure The accuracy of the bridge arm current detection.
  • STATCOM Static Synchronous Compensator
  • OHT Open Line Test
  • the flexible DC transmission system When the flexible DC transmission system is in the single-pole operation mode, the DC current flowing into the neutral point of the transformer through the ground may cause the transformer to saturate and generate harmonic voltage and current.
  • the existing technical solutions are in these operating conditions. Misjudgment may occur below.
  • the prior art solution needs to collect a plurality of electrical quantities to perform a large number of operations, and the efficiency is low.
  • the technical problem to be solved by the present invention is: to provide a short-circuit protection method for bridge arm reactors of a flexible direct current transmission system, which has a small amount of calculation, can improve efficiency, and has high reliability, and can fully consider the influence of complex operating conditions of the flexible direct current transmission system. Effectively identify the short-circuit fault of the bridge arm reactor, so as to protect the bridge arm reactor and converter valve and other equipment.
  • an embodiment of the present invention provides a short-circuit protection method for bridge arm reactors in a flexible DC transmission system, including:
  • the extraction of the second harmonic component of the bridge arm current and the DC component of the neutral point current of the grid-side transformer is specifically:
  • the bridge arm reactor has a short-circuit fault
  • the preset conditions are specifically:
  • IbP 100Hz is the second harmonic component amplitude of the three-phase upper arm current
  • IbN 100Hz is the second harmonic component amplitude of the three-phase lower arm current
  • I dc is the DC side current
  • I N is The DC components of the neutral point current of the grid-side transformer
  • I set1 , I set2 and I set3 are respectively the first protection setting, the second protection setting and the third protection setting.
  • the setting methods of the I set1 , I set2 and I set3 are specifically:
  • I set1 is set according to the manufacturing tolerance of the bridge arm reactor and the measurement error of the bridge arm current
  • I set2 is set according to the DC current during the minimum power operation of the flexible DC transmission system
  • I set3 is set according to the critical value of the neutral point DC current when the grid-side transformer is saturated.
  • the preset condition (4) is satisfied, specifically:
  • the preset condition (4) is satisfied, it is determined that the bridge arm reactor has a short-circuit fault.
  • the embodiments of the present invention also provide a short circuit protection device for bridge arm reactors of a flexible DC transmission system, including:
  • the acquisition unit is used to collect the bridge arm current, the DC side current and the neutral point current of the grid side transformer of the flexible DC converter;
  • a data processing unit configured to extract the second harmonic component of the bridge arm current and the DC component of the neutral point current of the grid-side transformer
  • the logic judging unit is used for judging whether the bridge arm reactor has a short-circuit fault according to a preset condition, and if so, sending an alarm signal and locating the converter with the bridge-arm reactor short-circuit fault.
  • the data processing unit is specifically:
  • It is used to perform Fourier decomposition on the bridge arm current and the grid-side transformer neutral point current, and extract the second harmonic component of the bridge arm current and the DC component of the grid-side transformer neutral point current.
  • the logic judgment unit when the preset conditions are satisfied at the same time, it is judged that the bridge arm reactor has a short-circuit fault
  • the preset conditions are specifically:
  • IbP 100Hz is the second harmonic component amplitude of the three-phase upper arm current
  • IbN 100Hz is the second harmonic component amplitude of the three-phase lower arm current
  • I dc is the DC side current
  • I N is The DC components of the neutral point current of the grid-side transformer
  • I set1 , I set2 and I set3 are respectively the first protection setting, the second protection setting and the third protection setting.
  • the setting methods of the I set1 , I set2 and I set3 are specifically:
  • I set1 is set according to the manufacturing tolerance of the bridge arm reactor and the measurement error of the bridge arm current
  • I set2 is set according to the DC current during the minimum power operation of the flexible DC transmission system
  • I set3 is set according to the critical value of the neutral point DC current when the grid-side transformer is saturated.
  • the preset condition (4) is satisfied, specifically:
  • the preset condition (4) is satisfied, it is determined that the bridge arm reactor has a short-circuit fault.
  • the method and device for short-circuit protection of bridge arm reactors in a flexible DC power transmission system collect the bridge arm current, DC side current, and grid-side transformer neutral point current of the flexible DC converter, and extract the bridge arm current.
  • the second harmonic component of the current and the DC component of the neutral point current of the grid-side transformer determine whether the bridge arm reactor has a short-circuit fault, if so, send an alarm signal and locate the bridge arm reactor short-circuit faulty converter.
  • the invention has small calculation amount, can improve efficiency, and has high reliability, can fully consider the influence of complex operating conditions of the flexible direct current transmission system, and effectively identify the short-circuit fault of the bridge arm reactor, thereby protecting the bridge arm reactor and the converter valve and other equipment. .
  • FIG. 1 is a schematic structural diagram of an MMC provided by an embodiment of the present invention.
  • FIG. 2 is a schematic structural diagram of a pseudo-bipolar flexible DC power transmission system provided by an embodiment of the present invention
  • FIG. 3 is a schematic structural diagram of a bipolar flexible DC power transmission system provided by an embodiment of the present invention.
  • FIG. 4 is a schematic flowchart of a short-circuit protection method for a bridge arm reactor of a flexible DC transmission system provided by an embodiment of the present invention
  • FIG. 5 is a schematic structural diagram of a short-circuit protection device for bridge arm reactors of a flexible DC power transmission system provided by an embodiment of the present invention.
  • FIG. 4 it is a schematic flowchart of a short-circuit protection method for bridge arm reactors of a flexible DC power transmission system provided by an embodiment of the present invention.
  • S101 collect the bridge arm current, the DC side current and the neutral point current of the grid side transformer of the flexible DC converter
  • S103 determine whether the bridge arm reactor has a short-circuit fault, if so, send an alarm signal and locate the converter with the bridge arm reactor short-circuit fault.
  • Step S103 will be described in detail below with reference to the basic structure of the MMC.
  • an MMC is composed of three phase units, each phase is composed of two upper and lower bridge arms, and each bridge arm contains N sub-modules (Sub-Module, SM) and a series-connected bridge arm reactor.
  • SM Sub-Module
  • the circulating current suppression control function will be put into operation when the MMC is in normal operation, and the second harmonic component will not appear in the bridge arm current. If a turn-to-turn short-circuit fault (fault F 1 as shown in Figure 1 ) or an end-to-end short-circuit fault (fault F 2 as shown in Figure 1 ) occurs inside the bridge arm reactor of a certain phase arm, the parameters of the three-phase bridge arm will not be changed. Symmetric again, the second harmonic current will appear in the bridge arm.
  • the bridge arm reactor has a short-circuit fault.
  • more conditions are preset to avoid the influence of complex operating conditions of the HVDC flexible transmission system;
  • the flexible DC transmission system is equipped with a circulating current injection function.
  • the valve control detects that the bridge arm current is too small, and will actively enable the circulating current injection function.
  • the preset condition (2) that is, the DC side current I dc is greater than or equal to the second protection
  • the fixed value I set2 can avoid misjudgment under this operating condition;
  • the preset conditions are specifically:
  • IbP 100Hz is the second harmonic component amplitude of the three-phase upper arm current
  • IbN 100Hz is the second harmonic component amplitude of the three-phase lower arm current
  • I dc is the DC side current
  • I N is The DC components of the neutral point current of the grid-side transformer
  • I set1 , I set2 and I set3 are respectively the first protection setting, the second protection setting and the third protection setting.
  • the setting methods of the I set1 , I set2 and I set3 are as follows:
  • I set1 is set according to the manufacturing tolerance of the bridge arm reactor and the measurement error of the bridge arm current
  • I set2 is set according to the DC current during the minimum power operation of the flexible DC transmission system
  • I set3 is set according to the critical value of the neutral point DC current when the grid-side transformer is saturated.
  • the preset condition (4) is satisfied. Specifically, when the preset conditions (1) to (3) are all satisfied, start timing, and determine whether the preset condition (4) is satisfied; if during the timing process, the preset conditions (1) to (3) ) is not satisfied, then reset the timing time and return to judge whether the preset conditions (1) to (3) are satisfied; if in the timing process, the preset condition (4) is satisfied, then judge The bridge arm reactor has a short circuit fault. Preferably, it is judged whether the preset conditions (1) to (3) are satisfied at the same time, and if so, the timer is started to start timing; and then it is judged whether the condition (4) is satisfied.
  • the preset conditions (1) to ( 3) If any one of them is not satisfied, reset the timer and return to determine whether the preset conditions (1) to (3) are satisfied at the same time; if the preset condition (4) is satisfied, an alarm signal will be issued and the bridge arm reactor short circuit will be located. faulty converter.
  • the present invention also provides a short circuit protection device for bridge arm reactors of a flexible DC transmission system, which can implement all steps of the short circuit protection method for bridge arm reactors of a flexible DC transmission system in the above embodiments.
  • FIG. 5 it is a schematic structural diagram of a short circuit protection device for bridge arm reactors of a flexible DC power transmission system provided by an embodiment of the present invention.
  • the collection unit 201 is used to collect the bridge arm current, the DC side current and the grid side transformer neutral point current of the flexible DC converter;
  • a data processing unit 202 configured to extract the second harmonic component of the bridge arm current and the DC component of the neutral point current of the grid-side transformer;
  • the logic judging unit 203 is configured to judge whether the bridge arm reactor has a short-circuit fault according to a preset condition, and if so, send an alarm signal and locate the converter with the bridge-arm reactor short-circuit fault.
  • the data processing unit 202 is specifically:
  • It is used to perform Fourier decomposition on the bridge arm current and the grid-side transformer neutral point current, and extract the second harmonic component of the bridge arm current and the DC component of the grid-side transformer neutral point current.
  • the logic judgment unit 203 when the preset conditions are satisfied at the same time, it is judged that the bridge arm reactor has a short-circuit fault
  • the preset conditions are specifically:
  • IbP 100Hz is the second harmonic component amplitude of the three-phase upper arm current
  • IbN 100Hz is the second harmonic component amplitude of the three-phase lower arm current
  • I dc is the DC side current
  • I N is The DC components of the neutral point current of the grid-side transformer
  • I set1 , I set2 and I set3 are respectively the first protection setting, the second protection setting and the third protection setting.
  • the setting methods of the I set1 , I set2 and I set3 are as follows:
  • I set1 is set according to the manufacturing tolerance of the bridge arm reactor and the measurement error of the bridge arm current
  • I set2 is set according to the DC current during the minimum power operation of the flexible DC transmission system
  • I set3 is set according to the critical value of the neutral point DC current when the grid-side transformer is saturated.
  • the preset conditions (1) to (3) determine whether the preset conditions (4) are satisfied, specifically: when the preset conditions (1) to (3) are all satisfied, start time, and determine whether the preset condition (4) is satisfied; if any one of the preset conditions (1) to (3) is not satisfied during the timing process, reset the timing time and return to judging the preset condition ( Whether 1) to (3) are all satisfied; if the preset condition (4) is satisfied in the timing process, it is determined that the bridge arm reactor has a short-circuit fault.
  • the method and device for short-circuit protection of bridge arm reactors in a flexible DC power transmission system are individually configured according to the converters. If there are multiple converters in a flexible DC power transmission system, each converter is configured with a bridge arm Reactor short circuit protection. If a short-circuit fault of the bridge arm reactor is detected, an alarm signal is issued and the faulty converter is located.
  • the solution provided by the present invention is suitable for the flexible direct current transmission system of pseudo-bipolar structure as shown in FIG. 2 and the flexible direct current transmission system of bipolar structure as shown in FIG. 3 .
  • the solution provided by the present invention is not only applicable to the two-terminal flexible direct current transmission system shown in FIG. 2 and FIG. 3 , but also applicable to the multi-terminal flexible direct current transmission system.
  • the method and device for short-circuit protection of bridge arm reactors in a flexible DC transmission system extract the bridge arm current by collecting the bridge arm current, the DC side current and the neutral point current of the grid side transformer of the flexible DC converter.
  • the second harmonic component and the DC component of the neutral point current of the grid-side transformer reduce the amount of calculation and improve the efficiency.
  • the criterion is simple, and the complex operation of the flexible DC transmission system is fully considered.
  • the fixed value I set3 ensures that there will be no misjudgment when the flexible DC transmission system operates in STATCOM, OLT or unipolar pole, through the preset condition (4), that is, the preset conditions (1) to (3) are all satisfied and the duration exceeds
  • the set time value can avoid misjudgment during transient processes such as unlocking and AC fault ride-through, and effectively identify the short-circuit fault of the bridge arm reactor, thereby protecting the bridge arm reactor and converter valve and other equipment. higher.

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Abstract

一种柔性直流输电系统桥臂电抗器短路保护方法及装置，所述方法通过采集柔性直流换流器的桥臂电流、直流侧电流和网侧变压器中性点电流(S101)，并提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量(S102)，根据预设条件，判断桥臂电抗器是否发生短路故障，若是，则发出告警信号并定位发生桥臂电抗器短路故障的换流器(S103)。计算量小，可以提高效率，可靠性高，能充分考虑柔性直流输电系统复杂运行工况的影响，有效识别桥臂电抗器的短路故障，从而保护桥臂电抗器和换流阀等设备。

Description

一种柔性直流输电系统桥臂电抗器短路保护方法及装置 技术领域
本发明涉及柔性直流输电系统领域，尤其涉及一种柔性直流输电系统桥臂电抗器短路保护方法及装置。
背景技术
桥臂电抗器是柔性直流输电系统的重要设备之一，具有抑制故障电流上升率的作用。桥臂电抗器在模块化多电平换流器(Modular Multilevel Converter,MMC)三相上下桥臂中分别配置，一般位于交流连接点和换流阀之间，也有工程将桥臂电抗器安置在直流极线和换流阀之间，以减轻两相桥臂穿墙套管短路故障对系统造成的影响。桥臂电抗器内部由多匝线圈构成，当桥臂电抗器内部发生匝间短路故障或端间短路故障时，换流器三相桥臂参数不再对称，桥臂中出现谐波电流，长时间运行会对桥臂电抗器和换流阀带来危害。
现有技术方案一般通过观察桥臂电抗器温升和噪音情况来对在运行的桥臂电抗器进行监测，又或者在停运检修时对桥臂电抗器的劣化状态进行评估，这种方法无法及时发现桥臂电抗器的内部故障。也有技术方案提出通过检测桥臂环流、子模块电容电压、直流电压和直流电流的谐波量来判别桥臂电抗器短路故障，但该方案没有充分考虑柔性直流输电系统复杂运行工况的影响。当柔性直流输电系统处于静止同步补偿器(Static Synchronous Compensator,STATCOM)或空载加压试验(Open Line Test,OLT)等无直流功率传输运行模式时，阀控会主动向桥臂注入环流以保证桥臂电流检测的准确性，当柔性直流输电系统处于单极大地运行模式时，直流电流经过大地流入变压器中性点可能会导致变压器饱和产生谐波电压电流，现有技术方案在这些运行工况下可能会出现误判。此外，现有技术方案需要采集多个电气量进行大量运算，效率较低。
发明内容
本发明要解决的技术问题是：提供一种柔性直流输电系统桥臂电抗器短路保护方法，计算量小，可以提高效率，可靠性高，能充分考虑柔性直流输电系统复杂运行工况的影响，有效识别桥臂电抗器的短路故障，从而保护桥臂电抗器和换流阀等设备。
为解决以上的技术问题，本发明实施例提供一种柔性直流输电系统桥臂电抗器短路保护方法，包括：
采集柔性直流换流器的桥臂电流、直流侧电流和网侧变压器中性点电流；
提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量；
根据预设条件，判断桥臂电抗器是否发生短路故障，若是，则发出告警信号并定位发生桥臂电抗器短路故障的换流器。
优选地，所述提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量，具体为：
对所述桥臂电流和网侧变压器中性点电流进行傅里叶分解，提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量。
优选地，当预设条件同时满足时，则判断桥臂电抗器发生短路故障；
所述预设条件具体为：
(1)max(IbP 100Hz，IbN 100Hz)＞I set1；
(2)I dc≥I set2；
(3)I N＜I set3；
(4)预设条件(1)～(3)均满足，且持续时间超过预设时间定值；
其中，IbP 100Hz为三相上桥臂电流的二次谐波分量幅值，IbN 100Hz为三相下桥臂电流的二次谐波分量幅值，I dc为所述直流侧电流，I N为所述网侧变压器中性点电流的直流分量，I set1、I set2和I set3分别为第一保护定值、第二保护定值和第三保护定值。
优选地，所述I set1、I set2和I set3的整定方法具体为：
I set1按躲过所述桥臂电抗器的制造公差和桥臂电流的测量误差整定；
I set2按所述柔性直流输电系统最小功率运行时的直流电流整定；
I set3按所述网侧变压器饱和时中性点直流电流的临界值整定。
优选地，在所述预设条件(1)～(3)均满足时，判断所述预设条件(4)是否满足，具体为：
当所述预设条件(1)～(3)均满足时，开始计时，并判断预设条件(4)是否满足；
若在计时过程中，所述预设条件(1)～(3)任意一条没有满足，则重置计时时间并返回判断所述预设条件(1)～(3)是否均满足；
若在所述计时过程中，所述预设条件(4)满足，则判断桥臂电抗器发生短路故障。
相应地，本发明实施例还提供了一种柔性直流输电系统桥臂电抗器短路保护装置，包括：
采集单元，用于采集柔性直流换流器的桥臂电流、直流侧电流和网侧变压器中性点电流；
数据处理单元，用于提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量；
逻辑判断单元，用于根据预设条件，判断桥臂电抗器是否发生短路故障，若是，则发出告警信号并定位发生桥臂电抗器短路故障的换流器。
优选地，所述数据处理单元具体为：
用于对所述桥臂电流和网侧变压器中性点电流进行傅里叶分解，提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量。
优选地，所述逻辑判断单元中当预设条件同时满足时，则判断桥臂电抗器发生短路故障；
所述预设条件具体为：
(1)max(IbP 100Hz，IbN 100Hz)＞I set1；
(2)I dc≥I set2；
(3)I N＜I set3；
(4)预设条件(1)～(3)均满足，且持续时间超过预设时间定值；
其中，IbP 100Hz为三相上桥臂电流的二次谐波分量幅值，IbN 100Hz为三相下桥臂电流的二次谐波分量幅值，I dc为所述直流侧电流，I N为所述网侧变压器中性点电流的直流分量，I set1、I set2和I set3分别为第一保护定值、第二保护定值和第三保护定值。
优选地，所述I set1、I set2和I set3的整定方法具体为：
I set1按躲过所述桥臂电抗器的制造公差和桥臂电流的测量误差整定；
I set2按所述柔性直流输电系统最小功率运行时的直流电流整定；
I set3按所述网侧变压器饱和时中性点直流电流的临界值整定。
优选地，在所述预设条件(1)～(3)均满足时，判断所述预设条件(4)是否满足，具体为：
当所述预设条件(1)～(3)均满足时，开始计时，并判断预设条件(4)是否满足；
若在计时过程中，所述预设条件(1)～(3)任意一条没有满足，则重置计时时间并返回判断所述预设条件(1)～(3)是否均满足；
若在所述计时过程中，所述预设条件(4)满足，则判断桥臂电抗器发生短路故障。
本发明实施例提供的柔性直流输电系统桥臂电抗器短路保护方法及装置，通过采集柔性直流换流器的桥臂电流、直流侧电流和网侧变压器中性点电流，并提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量，根据预设条件，判断桥臂电抗器是否发生短路故障，若是，则发出告警信号并定位发生桥臂电抗器短路故障的换流器。本发明计算量小，可以提高效率，可靠性高，能充分考虑柔性直流输电系统复杂运行工况的影响，有效识别桥臂 电抗器的短路故障，从而保护桥臂电抗器和换流阀等设备。
附图说明
图1是本发明实施例提供的MMC结构示意图；
图2是本发明实施例提供的伪双极柔性直流输电系统的结构示意图；
图3是本发明实施例提供的双极柔性直流输电系统的结构示意图；
图4是本发明实施例提供的柔性直流输电系统桥臂电抗器短路保护方法的流程示意图；
图5是本发明实施例提供的柔性直流输电系统桥臂电抗器短路保护装置的结构示意图。
具体实施方式
下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
参见图4，是本发明实施例提供的柔性直流输电系统桥臂电抗器短路保护方法的流程示意图。
本发明实施例提供的柔性直流输电系统桥臂电抗器短路保护方法，包括以下步骤：
S101，采集柔性直流换流器的桥臂电流、直流侧电流和网侧变压器中性点电流；
S102，提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量；
具体的，对所述桥臂电流和网侧变压器中性点电流进行傅里叶分解，提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量。
S103，根据预设条件，判断桥臂电抗器是否发生短路故障，若是，则发出 告警信号并定位发生桥臂电抗器短路故障的换流器。
下面结合MMC的基本结构，对步骤S103进行详细的描述。
如图1所示，一个MMC由三个相单元构成，每相由上下两个桥臂构成，每个桥臂包含N个子模块(Sub-Module,SM)和一个串联的桥臂电抗器。
MMC正常运行时上下桥臂会流过内部环流，内部环流主要由直流电流和负序的二次谐波电流构成。在实际工程中，MMC正常运行时会投入环流抑制控制功能，桥臂电流中不会出现二次谐波分量。若某相桥臂的桥臂电抗器内部发生匝间短路故障(如图1所述的故障F 1)或端间短路故障(如图1所述的故障F 2)，三相桥臂参数不再对称，桥臂中将出现二次谐波电流。因此，通过预设条件(1)即六个桥臂的桥臂电流二次谐波分量幅值中的最大值超过第一保护定值I set1，判断桥臂电抗器发生短路故障。为了进一步避免误判，因此预设更多的条件来规避柔性直流输电系统复杂运行工况的影响；
在实际工程中，为保证桥臂电流检测准确性，避免桥臂电流方向检测错误或出现频繁的桥臂电流正负变化，柔性直流输电系统设置有环流注入功能。当柔性直流输电系统处于STATCOM或OLT运行方式时，阀控检测到桥臂电流过小，会主动使能环流注入功能，通过预设条件(2)即直流侧电流I dc大于或等于第二保护定值I set2，可避免在此运行工况下出现误判；
柔性直流输电系统有多种运行方式，以单极大地方式运行时，直流电流流经大地对地表的电位分布造成影响，会有直流电流从变压器中性点流入变压器绕组，造成变压器发生直流偏磁，变压器饱和后激励产生谐波，通过预设条件(3)即网侧变压器中性点电流的直流分量I N小于第三保护定值I set3，可避免在此情形下出现误判。
通过预设条件(4)即预设条件(1)～(3)均满足且持续时间超过设定的时间定值，可避免在解闭锁、交流故障穿越等暂态过程中出现误判。即，
当预设条件同时满足时，则判断桥臂电抗器发生短路故障；
所述预设条件具体为：
(1)max(IbP 100Hz，IbN 100Hz)＞I set1；
(2)I dc≥I set2；
(3)I N＜I set3；
(4)预设条件(1)～(3)均满足，且持续时间超过预设时间定值；
其中，IbP 100Hz为三相上桥臂电流的二次谐波分量幅值，IbN 100Hz为三相下桥臂电流的二次谐波分量幅值，I dc为所述直流侧电流，I N为所述网侧变压器中性点电流的直流分量，I set1、I set2和I set3分别为第一保护定值、第二保护定值和第三保护定值。
具体的，所述I set1、I set2和I set3的整定方法具体为：
I set1按躲过所述桥臂电抗器的制造公差和桥臂电流的测量误差整定；
I set2按所述柔性直流输电系统最小功率运行时的直流电流整定；
I set3按所述网侧变压器饱和时中性点直流电流的临界值整定。
具体的，在所述预设条件(1)～(3)均满足时，判断所述预设条件(4)是否满足。具体为当所述预设条件(1)～(3)均满足时，开始计时，并判断预设条件(4)是否满足；若在计时过程中，所述预设条件(1)～(3)任意一条没有满足，则重置计时时间并返回判断所述预设条件(1)～(3)是否均满足；若在所述计时过程中，所述预设条件(4)满足，则判断桥臂电抗器发生短路故障。优选的，判断预设条件(1)～(3)是否同时满足，若是，则启动计时器开始计时；再判断条件(4)是否满足，若在计时过程中，预设条件(1)～(3)任意一条没有满足，则重置计时器并返回判断预设条件(1)～(3)是否同时满足；若预设条件(4)满足，则发出告警信号并定位发生桥臂电抗器短路故障的换流器。
具体的，当判断桥臂电抗器发生短路故障，则发出告警信号并定位发生桥臂电抗器短路故障的换流器。
相应地，本发明还提供了柔性直流输电系统桥臂电抗器短路保护装置，能够实现上述实施例中的柔性直流输电系统桥臂电抗器短路保护方法的所有步 骤。
参见图5，是本发明实施例提供的柔性直流输电系统桥臂电抗器短路保护装置结构示意图。
本发明实施例提供的柔性直流输电系统桥臂电抗器短路保护装置，包括：
采集单元201，用于采集柔性直流换流器的桥臂电流、直流侧电流和网侧变压器中性点电流；
数据处理单元202，用于提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量；
逻辑判断单元203，用于根据预设条件，判断桥臂电抗器是否发生短路故障，若是，则发出告警信号并定位发生桥臂电抗器短路故障的换流器。
具体的，所述数据处理单元202具体为：
用于对所述桥臂电流和网侧变压器中性点电流进行傅里叶分解，提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量。
具体的，所述逻辑判断单元203中当预设条件同时满足时，则判断桥臂电抗器发生短路故障；
所述预设条件具体为：
(1)max(IbP 100Hz，IbN 100Hz)＞I set1；
(2)I dc≥I set2；
(3)I N＜I set3；
(4)预设条件(1)～(3)均满足，且持续时间超过预设时间定值；
其中，IbP 100Hz为三相上桥臂电流的二次谐波分量幅值，IbN 100Hz为三相下桥臂电流的二次谐波分量幅值，I dc为所述直流侧电流，I N为所述网侧变压器中性点电流的直流分量，I set1、I set2和I set3分别为第一保护定值、第二保护定值和第三保护定值。
具体的，所述I set1、I set2和I set3的整定方法具体为：
I set1按躲过所述桥臂电抗器的制造公差和桥臂电流的测量误差整定；
I set2按所述柔性直流输电系统最小功率运行时的直流电流整定；
I set3按所述网侧变压器饱和时中性点直流电流的临界值整定。
在所述预设条件(1)～(3)均满足时，判断所述预设条件(4)是否满足，具体为：当所述预设条件(1)～(3)均满足时，开始计时，并判断预设条件(4)是否满足；若在计时过程中，所述预设条件(1)～(3)任意一条没有满足，则重置计时时间并返回判断所述预设条件(1)～(3)是否均满足；若在所述计时过程中，所述预设条件(4)满足，则判断桥臂电抗器发生短路故障。
具体的，当判断桥臂电抗器发生短路故障，则发出告警信号并定位发生桥臂电抗器短路故障的换流器。
本发明提供的柔性直流输电系统桥臂电抗器短路保护方法及装置，按照换流器单独进行配置，如一个柔性直流输电系统中有多个换流器，则每个换流器分别配置桥臂电抗器短路保护。若检测出桥臂电抗器短路故障，则发出告警信号并定位发生故障的换流器。
本发明提供的方案适用于如图2所示的伪双极结构的柔性直流输电系统和如图3所示的双极结构的柔性直流输电系统。但本发明提供的方案不仅适用于图2和图3所示的两端柔性直流输电系统，也适用于多端柔性直流输电系统。
本发明实施例提供的柔性直流输电系统桥臂电抗器短路保护方法及装置，通过采集柔性直流换流器的桥臂电流、直流侧电流和网侧变压器中性点电流，提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量，减少了计算量，提高效率。同时根据预设条件，判断桥臂电抗器是否发生短路故障，若是，则发出告警信号并定位发生桥臂电抗器短路故障的换流器，判据简单，充分考虑了柔性直流输电系统复杂运行工况的影响，通过预设条件(2)即直流侧电流I dc大于或等于第二保护定值I set2和预设条件(3)即网侧变压器中性点的直流分量I N小于第三保护定值I set3，保证柔性直流输电系统在STATCOM、OLT或单极大地运行时不会出现误判，通过预设条件(4)即预设条件(1)～(3)均满足且持续时间超过设定的时间定值，可避免在解闭锁、交流故障穿越等暂态过程中出现误判，有效识别桥臂电抗器的短路故障，从而保护桥臂电抗器和 换流阀等设备，可靠性更高。
以上所述是本发明的优选实施方式，应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也视为本发明的保护范围。

Claims (10)

  1. 一种柔性直流输电系统桥臂电抗器短路保护方法，其特征在于，包括：
    采集柔性直流换流器的桥臂电流、直流侧电流和网侧变压器中性点电流；
    提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量；
    根据预设条件，判断桥臂电抗器是否发生短路故障，若是，则发出告警信号并定位发生桥臂电抗器短路故障的换流器。
  2. 如权利要求1所述的柔性直流输电系统桥臂电抗器短路保护方法，其特征在于，所述提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量，具体为：
    对所述桥臂电流和网侧变压器中性点电流进行傅里叶分解，提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量。
  3. 如权利要求1所述的柔性直流输电系统桥臂电抗器短路保护方法，其特征在于，当预设条件同时满足时，则判断桥臂电抗器发生短路故障；
    所述预设条件具体为：
    (1)max(IbP 100Hz，IbN 100Hz)＞I set1；
    (2)I dc≥I set2；
    (3)I N＜I set3；
    (4)预设条件(1)～(3)均满足，且持续时间超过预设时间定值；
    其中，IbP 100Hz为三相上桥臂电流的二次谐波分量幅值，IbN 100Hz为三相下桥臂电流的二次谐波分量幅值，I dc为所述直流侧电流，I N为所述网侧变压器中性点电流的直流分量，I set1、I set2和I set3分别为第一保护定值、第二保护定值和第三保护定值。
  4. 如权利要求3所述的柔性直流输电系统桥臂电抗器短路保护方法，其特征在于，所述I set1、I set2和I set3的整定方法具体为：
    I set1按躲过所述桥臂电抗器的制造公差和桥臂电流的测量误差整定；
    I set2按所述柔性直流输电系统最小功率运行时的直流电流整定；
    I set3按所述网侧变压器饱和时中性点直流电流的临界值整定。
  5. 如权利要求3所述的柔性直流输电系统桥臂电抗器短路保护方法，其特征在于，在所述预设条件(1)～(3)均满足时，判断所述预设条件(4)是否满足，具体为：
    当所述预设条件(1)～(3)均满足时，开始计时，并判断预设条件(4)是否满足；
    若在计时过程中，所述预设条件(1)～(3)任意一条没有满足，则重置计时时间并返回判断所述预设条件(1)～(3)是否均满足；
    若在所述计时过程中，所述预设条件(4)满足，则判断桥臂电抗器发生短路故障。
  6. 一种柔性直流输电系统桥臂电抗器短路保护装置，其特征在于，包括：
    采集单元，用于采集柔性直流换流器的桥臂电流、直流侧电流和网侧变压器中性点电流；
    数据处理单元，用于提取所述桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量；
    逻辑判断单元，用于根据预设条件，判断桥臂电抗器是否发生短路故障，若是，则发出告警信号并定位发生桥臂电抗器短路故障的换流器。
  7. 如权利要求6所述的柔性直流输电系统桥臂电抗器短路保护装置，其特征在于，所述数据处理单元具体为：
    用于对所述桥臂电流和网侧变压器中性点电流进行傅里叶分解，提取所述 桥臂电流的二次谐波分量及所述网侧变压器中性点电流的直流分量。
  8. 如权利要求6所述的柔性直流输电系统桥臂电抗器短路保护装置，其特征在于，所述逻辑判断单元中当预设条件同时满足时，则判断桥臂电抗器发生短路故障；
    所述预设条件具体为：
    (1)max(IbP 100Hz，IbN 100Hz)＞I set1；
    (2)I dc≥I set2；
    (3)I N＜I set3；
    (4)预设条件(1)～(3)均满足，且持续时间超过预设时间定值；
    其中，IbP 100Hz为三相上桥臂电流的二次谐波分量幅值，IbN 100Hz为三相下桥臂电流的二次谐波分量幅值，I dc为所述直流侧电流，I N为所述网侧变压器中性点电流的直流分量，I set1、I set2和I set3分别为第一保护定值、第二保护定值和第三保护定值。
  9. 如权利要求8所述的柔性直流输电系统桥臂电抗器短路保护装置，其特征在于，所述I set1、I set2和I set3的整定方法具体为：
    I set1按躲过所述桥臂电抗器的制造公差和桥臂电流的测量误差整定；
    I set2按所述柔性直流输电系统最小功率运行时的直流电流整定；
    I set3按所述网侧变压器饱和时中性点直流电流的临界值整定。
  10. 如权利要求8所述的柔性直流输电系统桥臂电抗器短路保护装置，其特征在于，在所述预设条件(1)～(3)均满足时，判断所述预设条件(4)是否满足，具体为：
    当所述预设条件(1)～(3)均满足时，开始计时，并判断预设条件(4)是否满足；
    若在计时过程中，所述预设条件(1)～(3)任意一条没有满足，则重置计 时时间并返回判断所述预设条件(1)～(3)是否均满足；
    若在所述计时过程中，所述预设条件(4)满足，则判断桥臂电抗器发生短路故障。
PCT/CN2021/131708 2021-03-15 2021-11-19 一种柔性直流输电系统桥臂电抗器短路保护方法及装置 WO2022193709A1 (zh)

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