星形级联静止无功补偿发生器在三相不平衡工况下的控制方法研究

Research on the Control Strategy of Star Cascaded SVG under Three-phase Unbalanced Conditions

星形级联静止无功补偿发生器(SVG)在三相电压不平衡工况下若不进行相间功率调节,会造成三相直流侧电压严重失衡,甚至会因过压、欠压而退出运行。为此,文章提出一种电压外环-电流内环的双环控制策略,其内环采用状态反馈解耦PI控制,通过负序电压前馈控制抑制SVG过流;再结合零序电压注入法调节直流电压,实现有功功率在三相间的再分配。文中对该控制策略的数学模型进行了分析,并开展了仿真与试验验证。结果表明,在单相电压跌至0.8p.u.和0.5p.u.的前提下,该控制策略能够控制三相直流侧电压的均衡;且随着输出电流的增大,SVG输出电流质量逐渐得到改善。

Star cascaded static var compensator(SVG)does not regulate power among phases under the condition of unbalanced voltage.It will cause serious imbalance of three-phase DC voltages,and made device withdraw from operation because of over-voltage or under-voltage.This paper proposes a two-loop control strategy with voltage outer loop and current inner loop,which adopts a method of state feedback decoupling PI control.Over-current of SVG is suppressed by negative sequence voltage feed-forward control,and DC voltage is adjusted by zero sequence voltage injection method to reallocate the active power in three phases.Mathematical model of the control strategy is analyzed and verified by simulation and experiment.The results show that under the condition that single phase voltage drops to 0.8p.u.and 0.5p.u.,the control strategy can control equalization of the three-phase voltage in DC side.With the increase of output current,waveform quality of SVG output current is improved.