Novel hybrid modulation based isolated high-frequency bidirectional inverter for microgrid application

Abstract

This paper presents a novel hybrid modulation method based isolated high frequency (HF) bidirectional inverter for AC microgrid application. Bidirectional current-fed converter has been employed to interface the energy storage and intermediate fluctuating dc bus. A new hybrid modulation techniques consisting of fluctuating-dc-modulation (FDM) at low frequency (LF) scale and secondary modulation (SM) at HF scale has been proposed for the current-fed converter. The zero current soft switching (ZCS) of primary side devices and zero voltage soft switching (ZVS) of secondary side devices of front-end current-fed full-bridge converter is realized. The back-end full bridge inverter has been utilized to interface the fluctuating dc bus and AC microgrid. A rotating partial hybrid pulsewidth modulation (RP-HPWM) has been introduced. One leg of inverter is commutated at low switching frequency while the other leg is operated at high switching frequency for partial period of line frequency cycle. Besides the high switching frequency operated switches are only commutated at low value of current flowing through them. Thus, switching losses of the back-end inverter can be considerably reduced. Rotating mechanism is used to equalize the switching losses of four switches of the inverter. The low frequency (LF) fluctuating dc bus allows the reduction of dc-link electrolytic capacitor. This paper presents operation and analysis of the complete inverter topology implementing the proposed hybrid modulation scheme. Simulation results using PSIM9.0.4 and experimental results from a lab prototype clearly validate effectiveness of the proposed modulation scheme.