Harmonic analysis and mitigation of low-frequency switching voltage source inverter with series LC filtered VSI

The output currents of high power Voltage Source Inverters (VSIs) are distorted by the switching harmonics and the backgroud harmonics in the grid voltage. In this paper, a hybrid power conversion system composed of a high power VSI with low switching frequency and an auxiliary series LC filtered VSI is proposed. The auxiliary VSI compensates both the switching harmonics of the high power VSI and the low order harmonics. The output current of the system remains sinusoidal when grid voltage is distorted. Impedance models of the system are built in different frequency ranges and harmonic interactions are analyzed within the system. Different control targets are obtained and the corresponding control strategies are proposed. Simulation and experimental results are provided to show the validity of the analysis and the performance of the proposed control strategy.