基于电流控制电压源的并联三相变流器环流抑制控制方法

Circulation Current Suppressing for Parallel Three-phase Inverters Based on CCVS

三相变流器并联运行能提高系统可靠性和传输容量,然而并联结构为环流提供了流通路径,可能导致供电质量降低,运行损耗增加,为此必须采取措施抑制环流。本文以变流器作为电流控制电压源,通过增加环路等值阻抗的方法抑制环流。经分析可知,变流器输出电压不对称及线路参数不对称引起的零序环流和谐波环流流经相同的路径,采集并联变流器系统环流,经转移阻抗计算得到输出电压,并与正常运行时的控制系统输出电压叠加,环流回路相当于增加了该转移阻抗。仿真结果表明,采用该方法且转移阻抗选择纯电阻时,零序环流和谐波环流均能进行有效抑制。

Parallel three-phase inverters can improve operation reliability and increase transmission capacity,while the parallel structure provides path for circulating current,which worsen the power quality and increase energy losses.So it is necessary to suppress such circulating current.By transferring inverters into current-controlled voltage sources（CCVS）,the circulating current is suppressed through adding equivalent impedance in the circulating path in this paper.It can be seen from analysis that the zero-sequence circulating current and harmonic circulating current that are caused by the unbalance of voltage output of inverter and line parameters flow through same path.Through multiplying detected circulating current of parallel inverter system and transfer impedance,the output voltage can be obtained.When it is added to the output voltage of control system in normal conditions,the circulating path is equivalent to add this transfer impedance.Analysis and simulation results show that both zero-sequence and harmonic circulating current can be effectively suppressed when a pure resistance is chosen as the transfer impedance by using proposed method.