VSC-HVDC离散模型及其不平衡控制策略

针对常规控制下电压源换流器(VSC)对交流电网电压不平衡的敏感特性,避免电网电压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VSC进行功率特性分析的基础上,采用了网侧功率节点控制并补偿换流电抗和损耗电阻二倍频功率的不平衡控制策略。同时针对工业现场微机控制器,推导了基于双序矢量电流控制器(DVCC)的离散化内环控制模型、Smith预估补偿器模型和外环控制模型。基于电磁暂态仿真软件PSCAD/EMTDC建立了电压源换流器高压直流输电(VSC-HVDC)离散模型,对外环功率指令阶跃以及两端换流站分别发生电网不平衡故障进行仿真,仿真结论验证了本文离散模型以及不平衡控制策略的有效性。

VSC-HVDC Discrete Model and Its Control Strategy Under Unbalanced Input Voltage

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 strategies under unbalanced conditions were analyzed in this paper, so as to cut off the spread of 2nd order DC voltage fluctuation from one station to the other through DC cables. On this basis, system side control was adopted which took the power on the L and R into account. In practical control system, digital discrete control is always adopted, so the discrete inner-loop controller consisted of dual vector current controller (DVCC) and Smith predictor was deduced in this paper, and later the outer-loop controller as well. Simulated model of voltage source converter based high voltage direct current transmission system (VSC-HVDC) is set up by PSCAD/EMTDC software, and the simulations for outer-loop power reference step and unbalanced input AC voltage conditions were carried out. The correctness of discrete model and the validity of proposed strategies are verified by simulated results.