Feedforward Control of an Active Front End in Cascaded Medium Voltage Frequency Converter

Abstract

The frequency converters with the cascaded low-voltage multi-cell topology are the most common solution for the medium voltage drives. The considered topology contains active front end in each cell of the converter, which improves harmonic composition at the input, provides unity power factor and bidirectional power flow. However, each cell of the converter works with the periodical load due to the fact that it feeds only a single phase of the medium voltage motor. This periodical load causes the undesired voltage ripple in the DC link. This paper proposes voltage-oriented control system for the active front end of the low-voltage cell utilizing feedforward control. The proposed control system balances the input currents and minimizes the DC link voltage ripples. The simulation results show operation of voltage-oriented control system and the positive impact of the feedforward control.