适用于直流电网的组合式高压直流断路器

An Assembled HVDC Breaker for HVDC Grid

模块化多电平换流器(modular multilevel converter,MMC)在直流电网中具有较大的应用潜力。当前各类MMC拓扑中,半桥型MMC具有最佳的经济效益,但缺乏直流故障清除能力。目前主要有两种直流故障清除方法:一种是采用具有直流故障清除能力的子模块,但会引入额外的功率损耗,同时,需要通过闭锁MMC来达到清除直流故障的目的;另一种是采用混合式高压直流断路器,它具有快速隔离直流故障的能力,但投资费用较大。为有效解决上述弊端,提出一种组合式高压直流断路器,并对其控制时序进行了研究。组合式直流断路器以混合式直流断路器为设计背景,对其主要设备进行重新配置并加以改进,更加适用于多端柔性直流输电系统及直流电网。在保证同等直流故障处理能力的前提下,相比混合式高压直流断路器,其投资成本大幅度降低。为验证组合式直流断路器的有效性,在PSCAD/EMTDC内建立了一个三端单极直流网络模型。仿真结果验证了组合式直流断路器在隔离直流线路故障方面的可行性和有效性。

Modular multilevel converter（MMC） with half-bridge sub-modules（SMs） is the most promising technology for high voltage direct current（HVDC） grids, but it lacks DC-fault clearance capability. There are two main methods to handle dc-side short-circuit fault. One is to employ SMs with dc-fault clearance capability and additional high power losses, and its converter has to be blocked during clearance. The other is to employ hybrid HVDC breakers with low cost-efficiency, especially in meshed HVDC grids. In this paper, an assembled HVDC breaker and corresponding control strategy are proposed to overcome these drawbacks. The assembled HVDC breaker consists of an active short-circuit breaker, a disconnecting circuit breaker, an ultra-fast mechanical disconnector, a load commutation switch and an accessory discharging switch. The proposed breaker can handle DC-side fault with competitively low cost, and its operating speed is fast enough. A model of a four-terminal monopolar HVDC grid is developed in PSCAD/EMTDC, and simulation result proves validity and feasibility of the proposed solution.