A new DC-voltage-balancing circuit including a single coupled inductor for a five-level diode-clamped PWM inverter

This paper proposes a new DC-voltage-balancing circuit for a five-level diode-clamped inverter intended for a medium-voltage motor drive. This circuit consists of two unidirectional choppers and a single coupled inductor with two galvanically-isolated windings. The inductor is prominent in producing no DC magnetic flux inside the magnetic core because the individual DC magnetic fluxes generated by the two windings are cancelled out with each other. This makes the inductor compact by a factor of six, compared to the previous balancing circuit including two non-coupled inductors. Experimental results obtained from a 200-V 5.5-kW downscaled model verify that the DC mean voltages of the four split dc capacitors are balanced well under all the operating conditions.