Analysis on DC Voltage Balance Control Between Three Phases for STATCOM

Maintaining the DC voltage balance between three phases is one of the keys to cascaded STATCOM. Due to the difference in parallel loss, switching loss, modulation ratio and pulse delay of the H-bridge unit, there is a problem of DC voltage imbalance between the three phases of cascaded STATCOM. To solve this problem, a simple zero-sequence voltage calculation method is proposed by deriving the output power relationship of cascaded STATCOM based on the existing zero-sequence voltage injection method. Meanwhile, considering the asymmetry of the power grid, the negative sequence component in the voltage will cause DC voltage unbalanced fluctuation of the phases, a power feedforward control method is proposed. The method calculates the unbalanced power generated by the negative sequence voltage in real time and feeds it forward, effectively suppressing the unbalanced power between the three phases during asymmetry. Simulation and experimental results verify the effectiveness of the proposed control method.