A DC capacitor voltages balancing control strategy for cascade D-STATCOM

Power quality problem often cause serious accidents. Nowadays, with the fast development of power system, reactive power control through cascade D-STATCOM has become a hot topic because of its outstanding compensation performance. However, due to the series loss, shunt loss, switching loss and pulse delay, the DC capacitor voltage of each module can´t maintain balanced, which would influence its normal operation. A DC capacitor voltages balancing control strategy based on PI controller is proposed in this paper. The math model was built. The absorbed active current in each phase of STATCOM is controlled so that the sum of DC capacitors voltage of that phase can be controlled as expected. Then the balance of DC capacitors voltage in each phase is realized by distributing the active power of each H-bridge unit. Simulation and experiment of D-STATCOM is done, The results show the correctness of this method.