Bidirectional Power Flow of Grid Connected Single to Three Phase Multilevel Converter with Reduced Switch Count for Traction

Abstract

In this paper, an independent control of a single-phase half bridge active front end converter and three-level T-type inverter for traction has been proposed. The mid-point of dc-link capacitor is the point of common coupling (PCC) for single-phase AFEC as well as three-level T-type inverter. The control strategy implemented on single-phase half bridge active front end converter effectively works and unity power factor (UPF) is achieved at the utility grid side under different loading conditions of induction motor. The application of resonant controller in the inner current loop selectively eliminates the lower order harmonics (i.e. 3rd, 5th, 7th, 9th, and 11th) from the grid current and thereby enhances the THD profile of the grid current. The bidirectional power flow capability of single-phase active front end converter has been shown. The grid voltage and current are in opposite phase when the dc-link voltage exceeds the set reference voltage $(\mathrm{V}_{\mathrm{d}\mathrm{c}}^{\star})$ during transient operation. The modified space vector PWM technique implemented on three-level T-type inverter balances the individual capacitor voltages. The voltage vectors of each subsector are selected in such a way that the capacitor error voltage $(\mathrm{V}_{\mathrm{c}1}-\mathrm{V}_{\mathrm{c}2})$ is 5-S% and 2-4%, when the reference dc-link voltage is 700 V and 600 V respectively. The effectiveness of control technique implemented on single phase half bridge active front end converter and three-level T-type inverter is verified with simulation results.