电压源换流器高压直流输电不平衡控制策略研究

Sliding-mode Control Based VSC-HVDC Under Unbalanced Input Voltage Condition

针对常规控制下电压源换流器(voltage source converter,VSC)对交流系统电压不平衡敏感特性,避免电网不平衡引起的直流侧电压二次脉动通过直流线路传播到相邻换流站,该文对VSC进行功率分析并研究其不平衡控制策略。在对换流站进行功率特性分析的基础上,采用了网侧与VSC侧复合功率控制策略,推导了不平衡条件下功率外环指令电流模型,设计了αβ静止坐标下离散滑模内环控制器。基于电磁暂态仿真软件PSCAD/EMTDC建立了VSC-HVDC模型及其离散化内环滑模控制器,两侧换流站分别发生电网不平衡故障,仿真结论验证了该控制策略的有效性。

According to the sensitive character of voltage source converter （VSC） to the AC unbalanced input voltage under traditional control strategy, the power character of VSC station and the control strategy under unbalanced conditions are analyzed in this paper, so as to supress the spread of 2^nd order fluctuation in DC voltage fluctuation from one station to the other through the DC cables during AC voltage unbalance occured. On this basis, the outer-loop current reference signals are deduced which take both the system side and VSC side power into account. In order to trace the reference signals, sliding-mode controller is adopted and the discrete model is derived in αβ reference frame. The correctness of discrete model and the validities of proposed strategies are verified by PSCAD/EMTDC simulation.