Voltage balancing of the four split DC capacitors for a five-level diode-clamped PWM inverter with a front-end diode rectifier

This paper describes voltage balancing of all the four split dc capacitors for a five-level diode-clamped PWM inverter intended for a transformerless mediumvoltage motor drive with a three-phase diode rectifier used as the front end. A dc-voltage-balancing circuit is installed on the dc link, and introduces a new midpoint-voltage-balancing method based on phase-shift control. As a result, the dc mean voltages of the four split dc capacitors can be balanced, independent of the inverter control. Experimental results obtained from the 200-V 5.5-kW downscale model verify that the dc mean voltage of the four split capacitors are balanced well under all the operating conditions.