A 6.6-kV transformerless motor drive using a five-level diode-clamped PWM inverter for energy savings of pumps and blowers

This paper describes a 6.6-kV adjustable-speed motor drive for pumps and blowers without transformer. The power conversion system consists of a front-end diode rectifier, a five-level diode-clamped PWM inverter with a voltage-balancing circuit, and a hybrid active filer for harmonic-current mitigation of the diode rectifier. A 200-V 5.5-kW downscale model is designed, constructed and tested with focus on the five-level PWM inverter. Experimental results obtained from the 200-V downscale model verify the viability and effectiveness of the 6.6-kV adjustable- speed motor drive, showing that the four split dc capacitors are well balanced in all the operating conditions with improvements of operating performance at low inverter modulation indices.