VSC-HVDC互联系统电压稳定控制策略

柔性直流输电系统具有有功无功可独立解耦控制的特点，使其不仅可以实现直流系统内有功的合理分配，还可以通过对无功的控制辅助所连接的交流系统以维持电压稳定。为充分挖掘电压源型换流站无功输出潜力，提高与之连接的交流系统的电压稳定性，作者提出一种基于VSC-HVDC互联系统的电压稳定控制策略。在两端柔性直流系统中，对整流站采用直流电压偏差斜率控制，逆变站采用定直流电压控制，按照无功优先模式设置电流限幅即以无功电流的大小决定有功电流的限幅值，分别针对整流站和逆变站设计有功电流动态限幅控制器，扩大无功电流限幅值。在不需要站间通信的情况下，将VSC-HVDC输电系统部分有功转换为无功，提高了换流站的无功输出能力，以此减轻扰动或事故端系统调整无功的负担。通过仿真软件PSCAD/EMTDC进行仿真验证，结果表明所提控制策略充分利用了VSC-HVDC互联系统的功率调整能力，提高了VSC-HVDC互联系统的交流电压稳定性。该控制策略为通过VSC-HVDC系统连接的交流系统的电压稳定问题提供了一种新的解决方案。

Voltage Stability Control Strategy for Interconnected Systems Through VSC-HVDC

Due to the independent control of active and reactive power,voltage source converter (VSC) base on HVDC system can not only distribute power in DC system,but also improve the stability of AC system connected by VSC-HVDC.In order to fully excavate the reactive power potential of VSC,and to improve the voltage stability of AC system,a voltage stability control strategy based on VSC-HVDC interconnected system was proposed.In VSC-HVDC system,rectifier station was controlled by DC voltage margin and droop,and the inverter station was controlled by constant DC voltage.The limit value of active current was calculated based on reactive current.Then,the dynamic limiter controllers of the active current were respectively designed for rectifier and inverter stations to expand the limit value of reactive current.Without interstation communications,apart of active capacity of VSC-HVDC system was converted to reactive capacity,which increased the reactive output of the VSC stations and reduced the reactive adjustment burden of AC system in the case of disturbance or fault.Finally,simulations with PSCAD/EMTDC verified that the control strategy proposed in the paper took full use of the power adjustment ability and enhanced the voltage stability of AC system connected by VSC-HVDC.The strategy provides a new solution for voltage stability of AC system connected by VSC-HVDC.