一种新的柔性直流输电系统远端启动策略

A New Remote Start-up Strategy for Flexible DC Transmission System

模块化多电平换流器(MMC)的启动是MMC柔性直流输电系统工程应用首先需要面临的问题,针对采用MMC结构的两端或者多端柔性直流输电系统,提出了一种新型的有序解锁启动方法,以减少传统充电方式下换流阀解锁瞬间的直流电压跌落和桥臂电流冲击。该方法在传统不控充电过程后,先解锁定直流电压换流站,再对其他换流站进行远端充电,期间其他换流站的桥臂按其子模块电容电压高低顺序逐步减少投入充电的子模块个数,以此不断抬高子模块电容电压,在电容电压到达一定数值后再解锁换流站。通过理论分析计算了本方法最大的电压跌落,并通过PSCAD/EMTDC仿真验证了该方法的有效性和优越性。此外,新的远端启动控制策略对多端柔性直流系统的定功率换流站启动顺序和启动时刻没有特殊要求,并针对单桥臂进行设计,可以重复应用于各桥臂,因此,其适用于实际工程中的多端柔性直流系统远端启动和交流系统故障造成无源端闭锁后的在线重启动。

Modular multilevel converter （MMC） start up is a primary problem confronted by MMC high voltage direct current （HVDC） engineering applications. Based on the modular multilevel converter HVDC, a new ordered charging method is proposed for the remote start-up of a project to decrease the DC voltage drop of the converter valve and bridge arm current impact the instant it＇ s unlocked the traditional way. After the process of traditional uncontrolled charging, the DC voltage station is unlocked, then other converter stations are uncontrollably charged by bypassing the sub-module according to the voltage level. Finally, the stations are unlocked until the voltage of the sub module is sufficiently high. The method has greatly reduced the DC voltage drop and bridge arm shock current for the passive converter station during start-up. Theoretical analysis has been made to obtain the largest voltage drop using this method, and simulation has been done to verify the feasibility of the method. The method can effectively reduce voltage drop, while making no particular requirements on the boot sequence and moment for unblocking. And single-arm design enables it to be reused for all arms, making it applicable to the multi terminal flexible DC system for remote start-up and post-locking restart online because of AC faults.