A Novel STATCOM Based on Cascaded Three-phases Voltage Source Inverter

A novel static synchronous compensator (STATCOM) for high-voltage, high-power is proposed in this paper. The STATCOM proposed is constructed by cascading several three-phases voltage source inverters (VSI) with individual DC capacitor. A control method for DC voltages regulation and equalization is developed to deal with VSI-parameter-difference which is prone to make DC voltage unbalanced. A so-called phase-shifted sinusoidal pulse-width-modulation (PS-SPWM) switching scheme is applied to control the switching device of each three-phases VSI, which can reduce the switch frequency without degrading the character of the output current. Single phase transformers are essential to make three-phases VSIs cascading possible. However, the capability of the transformers is far less than that of compensator. Compared to STATCOM based on single-phase VSI cascading, the proposed compensator has fewer DC capacitors, fewer switch-devices and lower DC voltage ripple. Moreover, fast response of the compensator is also achieved by applying dq decoupled currents control method in synchronous frame. Simulation results not only verify the validity and feasibility of the proposed STATCOM but also show that control method employed can maintain the DC voltages stable and equalizing