链式星形STATCOM补偿不平衡负载的控制策略

A Control Strategy of Star-connected Cascade Circuit STATCOM for Unbalanced Load Compensation

星形结构的链式静止同步补偿器(static synchronous compensator,STATCOM)受限于三相输出电流之和等于零的约束条件,因此,在补偿不平衡负载时,必须注入零序电压,以强迫输出电流的相位与STATCOM相电压的相位相差90。首先推导在补偿不平衡负载工况下所要添加的零序电压的数学公式,证明该工况下零序电压添加的必要性与唯一性;然后改进适用于补偿不平衡负载工况的目标电流提取方法,该方法能有效减少参考电流的二倍频分量。而且,提出的零序电压计算方法,无需对参考电流锁相,参考电流提取完毕后,即可计算出零序电压。给出基于经典控制理论在静止坐标系下的参考电流跟踪控制策略。最后,仿真与实验结果验证了所提出方法的正确性。

The star-connected cascade circuit static synchronous compensator （STATCOM） is subjected to the restriction that the sum of three phase output currents is zero. Consequently, in order to compensate the unbalanced load currents, zero-sequence voltage must be added to the phase-to-neutral voltage of the converter, to force the improved phase-to-neutral voltage to be orthogonal to the output current for every phase. This paper firstly deduced the zero-sequence voltage in condition of unbalanced load compensation, the expression of which is unique and the adding is necessary in this working condition. Secondly, the improved reference current detection method was also presented, which can reduce the 2na ripple effectively. Besides, the zero-sequence voltage calculation presented in this paper depends on reference currents detection completely, without detecting the phases of reference currents in advance. Finally, the precise reference current tracking strategy was also presented based on classical control theory under αβ stationary frame. Simulation and experiment results verify the feasibility and effectiveness of the control strategy.