中文摘要：

在并网电压不平衡或补偿无功电流不平衡的工况下,需采用控制策略以保证链式静止同步补偿器（STATCOM）各个链节单元的直流电压基本恒定。常用的方法是将三角形接线的STATCOM叠加零序电流或星形接线的STATCOM叠加零序电压。基于零序分量叠加的方法,分析了在不平衡工况下保证链式STATCOM正常运行的条件。综合考虑并网电压不平衡与补偿无功电流不平衡的情况,分析了并网电压不平衡度、补偿无功电流不平衡度与装置额定电流、额定电压之间的关系。据此定量给出了三角形接线与星形接线的STATCOM装置不平衡运行的极限。通过比较发现,三角形接线的STATCOM更适用于补偿无功电流不平衡度较高的场合,而星形接线的STATCOM更适用于并网电压不平衡度较高的场合。最后在MATLAB/Simulink环境中搭建了仿真系统,仿真结果验证了上述分析的正确性和有效性。

英文摘要：

In the operating conditions of unbalanced grid voltage or unbalanced compensating reactive current,it is necessary to maintain the DC-link voltage of cascaded STATCOM by additional control. The widely-used method is to superpose the zero-sequence current to the delta-connected STATCOM or the zerosequence voltage to the star-connected STATCOM,based on which,the requirements for maintaining the normal operation of cascaded STATCOM in unbalanced operating conditions are analyzed. The relationship between the unbalance factor of grid voltage or compensating reactive current and the rated current or voltage of device is analyzed. Accordingly,the operational limits of delta-connected and star-connected STATCOMs are given quantitatively. Comparison shows that,the delta-connected STATCOM is more suitable for the operating conditions with higher unbalance factor of compensating reactive current while the starconnected STATCOM for those with higher unbalance factor of grid voltage. The results of simulation in MATLAB / Simulink environment demonstrate the correctness and effectiveness of analysis.