DC capacitor voltage stability analysis for cascade multilevel STATCOM

XIE Tiancai1, ZHANG Yujuan1, ZHANG Junquan2, WANG Zhongquan2

(1.State Grid Liaoning Electric Power Co.,Ltd. Chaoyang Power Supply Company, Chaoyang 122000, China;
2.Integrated Electronic System Lab Co.,Ltd., Jinan 250100, China)

Abstract: Aiming at the problem of the imbalance among each independent DC capacitor voltage of cascade multilevel STATCOM, a DC capacitor voltage detection and control method is proposed to guarantee the DC capacitor voltage stability of cascade multilevel STATCOM. Firstly, the influence caused by grid reactive power exchange on DC capacitor voltage is analyzed. Then, a cascade multilevel STATCOM energy balance model is established based on energy balance principle. At the same time, a PI closedloop control method is adopted to solve the problem of filter circuit timedelay, and a stability analysis is also carried out. Finally, the multilevel cascade STATCOM experimental prototype is set up and relevant experiments are conducted. The results indicate that this control system and method can guarantee the stability of DC side capacitor voltage and the stability is mainly influenced by the integral time constant Tdi, consistent with the theoretical analysis results.

Key words: static synchronous compensator; cascade multilevel inverter; DC capacitor; voltage stability control