新型可控电网换相换流器拓扑及其控制方法

A Novel Controllable Line Commutated Converter Topology and Control Strategy

为保持传统电网换相换流器(line commutated converter,LCC)低损耗、高可靠性和经济性等优点的同时,又避免换相失败故障风险,提出一种新型具有可控关断能力的电网换相换流器(controllable line commutated converter,CLCC)拓扑结构。该拓扑基于全控和半控器件混联的设计思路,首先通过全控型器件转移电流,等待晶闸管关断能力恢复后,再利用全控器件关断电流以快速完成桥臂间换相。可控电网换相换流器主要包括常规换流和可控换流2种运行模式,研究不同运行模式下换流器的工作原理及换流器内部控制策略。通过搭建特高压直流输电系统仿真模型,分析可控电网换相换流器的暂、稳态和典型故障态运行特性。仿真结果表明,在发生交流故障时,可控电网换相换流器可以主动关断桥臂电流实现强迫换相,同时提供一定的无功支撑,解决多馈入直流系统换相失败问题,有利于提高电网安全稳定运行水平,提升多直流馈入受端电网电力接纳能力。

In order to maintain the advantages of low loss,high reliability and efficiency of traditional line commutated converter(LCC)and avoid the risk of commutation failure,a novel topology of controllable line commutated converter(CLCC)with controllable turn-off capability was proposed.The topology is based on a serial-parallel of fully-controlled and semi-controlled devices.During the commutation process,current through the thyristor valve transfers to the auxiliary branch at first by the fully controlled devices,then after the forward blocking capability is restored,the current is shut off by the auxiliary branch which also contained fully controlled devices,completing commutation between bridge arms.The CLCC can work in two operation modes,one is natural commutation and the other is controllable commutation.The working principle of the two operation modes and the internal control strategy of the converter are investigated.A UHVDC transmission system simulation model is built to analysis the performance of CLCC converter under various conditions,including steady state,transient state and fault conditions.The simulation results show that CLCC converter not only had the same system operation performance with LCC converter,but also completely solved the commutation failure problem,which was conducive to improve the safety and stability of power grid and improve the power acceptance capacity in multi-infeed HVDC systems.