A Transformerless Hybrid Active Filter Using a Three-Level PWM Converter for a Medium-Voltage Motor Drive

This paper presents a transformerless hybrid active filter integrated into a medium-voltage motor drive for energy savings. This hybrid filter is intended for harmonic-current mitigation of the three-phase diode rectifier used as the front end of the motor drive. It consists of a passive filter tuned to the seventh-harmonic frequency and an active filter using a three-level PWM converter. This paper makes a theoretical discussion on voltage-balancing control of two split dc capacitors of the active filter. An experimental system rated at 400 V and 15 kW is designed and constructed, which is scaled down from a 6.6-kV motor drive without regenerative braking. Experimental results verify that the hybrid filter has the capability of satisfactory harmonic filtering and stable voltage balancing in all the operating conditions.