Analysis and Mitigation of Sector Transition Distortions for Unfolding-based Grid-tied AC-DC Converters

In this paper, a comprehensive analysis is performed of ac input current distortion in 3-phi unfolding-based ac-dc converters. The source of current distortion, which occurs at the mains voltage sector boundaries, is studied. An equivalent circuit model is presented to describe the problem and estimate the correlation between the magnitude of current distortion and system parameters. A control-based technique is proposed to realize power factor correction (PFC) and output power control while mitigating grid current distortion by emulating appropriate current sources/sinks. Simulation results are provided to illustrate the control approach, followed by experimental results on a 21 kW hardware prototype. A significant improvement in the grid current total harmonic distortion (THD) from 4.46% to 1.94% is achieved.