A Second-order Voltage Ripple Suppression Strategy of Five-Level Flying Capacitor Rectifiers under Unbalanced AC Voltages

Unbalanced ac voltages drastically deteriorate the performance of five-level flying capacitor (5L-FC) rectifiers. Without introducing an extra buffering circuit to absorb the second-order oscillating power, it is an incompatible contradiction for realizing both negative-sequence current reduction and second-order voltage ripple suppression. In this paper, based on the idea of using FCs in the rectifier to absorb the oscillating power, a second-order voltage ripple suppression strategy for unbalanced ac voltage conditions is proposed. Reducing the negative-sequence currents and suppressing the dc voltage ripples can be simultaneously realized. Simulations and experimental results verified the effectiveness and performance of the proposed scheme well.