VSC-HVDC系统启动控制

合适的启动方式对减缓VSC-HVDC系统启动及重新启动时对自身和电网的冲击非常重要.如何把直流电容器电压快速提升到设定值,是后续控制策略正确工作的基础.针对目前应用较广泛的两电平和二极管钳位型三电平换流器拓扑结构,提出了一种简单、适用于VSC-HVDC系统的两阶段自励启动方法.在启动第一阶段,串接限流电阻器对直流侧电路充电;若在设定的时间内电容器电压不能达到设定值,启动转入第二阶段,即换流站在直流电压控制器的作用下对电容器继续充电,直至达到预设值,从而为换流器从启动控制模式切换到正常运行模式做好准备.另外,针对电网黑启动和无源网络的启动,设计了变压器和长线路启动控制策略,可以降低变压器充电过程中的励磁涌流及长距离线路合闸时引起的过电压水平.仿真表明提出的启动控制方式具有良好的控制效果.

Startup Procedures for the VSC-HVDC System

In order to reduce the undesired impacts and damages on the VSC-HVDC system and the connected AC system during the startup and re-startup procedures, appropriate startup control strategy should be dedicatedly designed. Charging the DC capacitor voltage to the preset value quickly is the fundamental of the subsequent control strategy. In this paper, a two-stage self startup procedure is proposed for VSC-HVDC system consisting of two-level and diode-clamped three-level converters. During the first stage, the resistors are inserted to limit the current during the charging. If the DC voltage can not reach the preset value after predetermined time, the startup procedure switches to the second stage and the capacitors will be further charged with a DC voltage controller. The startup procedure completes till the DC link voltage reaches the preset value and then the converters are ready to change from the startup mode to the normal operating mode. In addition, a new control strategy is proposed for the startup of the passive network and the AC system suffered from black out. With the proposed control strategy, the inrush currents during the energization of the transformers and the overvoltage during the closure of the long overhead transmission lines can be suppressed. Simulation results verify the feasibility of the proposed startup procedures.