三相串联VSC的通用控制策略

Universal Control Strategy for Three-Phase Series-Connected Voltage Source Converters

三相串联VSC将三个单相VSC换流器在直流侧串联,相比传统的三相并联VSC,在承受相同直流电压的情况下,可以有效地减少开关元器件数目而降低直流换流器的造价。首先分析了利用交流侧有功功率调制实现三相串联VSC换流器交流故障穿越的基本原理,然后考虑换流器变压器的接线方式,针对交流故障下保持电网电流三相对称、抑制瞬时有功二次波动、抑制瞬时无功二次波动以及抑制零序电流4种不同的控制目标,分别提出了相应的电流控制方案,并给出了推导参考电流的通用方法和4种电流控制方案对应的参考电流公式。最后在PSCAD/EMTDC中进行了仿真验证,仿真结果证明了所提控制策略的有效性。

Three-phase series-connected VSCs are composed of three single-phase VSCs connected in series at the DC side. Compared with conventional three-phase parallel-connected VSCs,this topology reduces the number of swithing devices offectively to withstand the same DC voltage and therefore reduces the investment. Firstly,the basic principle of three-phase series- connected VSCs riding though AC faults by mean of AC power regulation are analyzed,and then considering the connections of transformer windings,the corresponding current control schemes are proposed to achieve four various control objectives under AC faults,i.e.,balancing AC current,suppressing ripples of instantaneous active power,suppressing ripples of instantaneous reactive power and suppressing zero-se-quence current. The approach to derive the reference currents is presented and the expressions of current references corresponding to four different control schemes are also derived. Finally,simulations are performed in PSCAD/EMTDC and the results validate the pro-posed control strategies.