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Protection and Fault Isolation Scheme Based on Active Current-limiting Control for DC Distribution Network
Author:
Affiliation:

1.State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources;(North China Electric Power University), Beijing 102206, China;2.Department of Electronic and Electrical Engineering, University of Strathclyde, Glasgow G1 1XW, UK

Fund Project:

This work is supported by Key Project of Smart Grid Technology and Equipment of National Key R&D Program of China (No. 2016YFB0900600)and State Grid Corporation of China (No. 521104180002).

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    Abstract:

    DC faults in flexible DC distribution network could easily lead to overcurrent, which seriously threatens the safe operation of power grid. Modular multilevel converter (MMC) blocking is mostly used to cut off the fault current in FBSM-MMC based distribution network, but the blocking will cause power outage of the whole network for a moment, which reduces the reliability of the power supply. To solve the problem, a protection and fault isolation scheme based on active current-limiting control of FBSM-MMC for flexible DC distribution network is proposed, which consists of three stages. After a short-circuit fault occurs, the output DC current of the inverter will be limited to 1.2 times of the rated current by the control of MMC (stage 1). The faulty line is identified according to the synchronous zero-crossing characteristic at both ends of each line (stage 2). A fault isolation scheme which contains the cooperation of DC circuit breakers and high-speed switches is proposed (stage 3). By disconnecting the DC breaker associated with the fault and controlling the output DC current of the corresponding converter station to be reduced to 0, the mechanical switch on the fault line can also be quickly turned off, thereby achieving fault isolation. Finally, a four-terminal flexible DC distribution network model is built in PSCAD/EMTDC, and the feasibility of the proposed protection and fault isolation scheme are verified through a large number of simulations.

    表 1 Table 1
    图1 柔性直流配电网拓扑结构Fig.1 Topology of flexible DC distribution network
    图2 FBSM-MMC结构示意图Fig.2 Schematic diagram of FBSM-MMC structure
    图3 不同故障点处线路L 1故障电流流向Fig.3 Flow direction of fault current with different fault locations on line L 1
    图4 保护及故障隔离方案流程图Fig.4 Flow chart of protection and fault isolation scheme
    图5 f 1处故障时L 1~L 4线路电流波形Fig.5 Fault current waveforms of L 1~L 4 when a fault occurs at f 1
    图 MMC控制结构图Fig. Structure of MMC control
    图 CCSC控制原理图Fig. Principle of CCSC control
    图 MMC子模块电压参考值计算逻辑图Fig. Calculation of the reference value of MMC sub-module voltage
    图 MMC主动限流控制策略示意图Fig. Diagram of the current limited control strategy of MMC
    图 F 1处故障下故障电流示意图Fig. Fault current when a fault occur at F 1
    图 增加电流偏差量后区内故障示意图Fig. Diagram of in-zone fault when ΔI added
    图 线路L 1两端保护装置动作示意图Fig. The action of protection device at both ends of line L 1
    图 换流站控制切换示意图Fig. Switching of the converter’s control
    图 主动限流控制投入前后换流站输出直流电流Fig. DC current of MMC output i dc1 with and without MMC current limited control
    图 CB 1处电流 i 12波形Fig. Fault current of i 12
    图 换流站T 2中换流站输出直流电流 i MMC2及CB 2处电流i 24波形Fig. Fault current of i MMC2 and i 24
    图 开关S 2处电流 i 21波形Fig. Fault current of i 21
    图 线路L 1首端(0%)处双极短路故障电流波形Fig. Current waveform of the bipolar short-circuit fault at the beginning (0%) of line L 1
    图 线路L 1中点(50%)处双极短路故障电流波形Fig. Current waveform of the bipolar short-circuit fault at the middle (50%) of line L 1
    图 线路L 1末端(100%)处双极短路故障电流波形Fig. Current waveform of the bipolar short-circuit fault at the end (100%) of line L 1
    图 线路L 1中点单极接地故障电流波形Fig. Current waveform of the single-pole grounded fault at the middle of line L 1
    图 线路L 2中点单极接地故障电流波形Fig. Current waveform of the single-pole grounded fault at the middle of line L 2
    图 线路L 3中点单极接地故障电流波形Fig. Current waveform of the single-pole grounded fault at the middle of line L 3
    图 线路L 4中点单极接地故障电流波形Fig. Current waveform of the single-pole grounded fault at the middle of line L 4
    图 线路L 1中点双极短路故障电流波形Fig. Current waveform of the bipolar short-circuit fault at the middle of line L 1
    图 线路L 2中点双极短路故障电流波形Fig. Current waveform of the bipolar short-circuit fault at the middle of line L 2
    图 线路L 3中点双极短路故障电流波形Fig. Current waveform of the bipolar short-circuit fault at the middle of line L 3
    图 线路L 4中点双极短路故障电流波形Fig. Current waveform of the bipolar short-circuit fault at the middle of line L 4
    图 过渡电阻分别为10Ω、20Ω、50Ω时的双极短路故障电流波形Fig. Current waveform of bipolar short-circuit fault with 10Ω, 20Ω, and 50Ω transition resistances
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Get Citation

ZHENG Tao,WU Qiong,LYU Wenxuan,et al.Protection and Fault Isolation Scheme Based on Active Current-limiting Control for DC Distribution Network[J].Automation of Electric Power Systems,2020,44(5):114-121.DOI:10.7500/AEPS20191114003

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History
  • Received:November 14,2019
  • Revised:December 08,2019
  • Adopted:
  • Online: March 08,2020
  • Published: