基于VSC的多端直流环网系统故障分析与定位研究

摘要

Compared with the two-terminal DC system, the multi-terminal DC ring system is more reliable and flexible.However, the multi-terminal DC ring system brings more challenges in terms of DC fault analysis and isolation due to the increasing of the fault current loops.This paper firstly provides background on the topology and control method of the DC grid, analyzes the fault characteristics of the DC bus and line, and deduces the mathematical expressions of fault current and voltage.According to the above analysis and with the use of various equipments (current limiting inductor, DC breaker, and DC direction switch), this paper investigates a new fault location and protection strategy based on the fault feather di/dt without using communication between converters.Finally, a three-terminal structure of DC ring network simulation model is established in Matlab/Simulink.The simulation results show that the proposed strategy can quickly identify and isolate fault and ensure the rapid recovery of multi-terminal DC ring system after fault.%与两端系统相比,多端直流环网系统具有更好的供电可靠性和灵活性,但由于故障后电流回路的增多,给故障的分析与定位带来更大挑战.本文首先对直流电网的拓扑和控制方式进行介绍,并对环网中直流侧母线及线路的故障暂态特性进行分析,推导出故障电压和电流的数学表达式.在此基础上配合线路出口限流器、直流断路器及直流方向开关的使用,提出一种基于故障特征量di/dt的无需换流站间通信的故障定位保护策略.最后在Matlab/Simulink上搭建了三端直流环网系统仿真模型,仿真结果表明所提故障定位与保护策略能快速识别并切除故障,保证故障后多端直流环网系统的快速恢复.