Back-to-Back Connected Five-Level Diode-Clamped PWM Converters for Motor Drives

This paper addresses a medium-voltage adjustable-speed motor drive consisting of two five-level diode-clamped PWM converters connected back-to-back. It is followed by designing, constructing and testing a 200-V down-scaled model to verify the validity and effectiveness of the medium-voltage motor drive. This down-scaled model has four split dc capacitors equipped with a voltage-balancing circuit using two bidirectional buck-boost choppers. The two five-level converters are based on sinusoidal PWM (SPWM) with a carrier frequency of 3 kHz. The motor tested in this paper is a three-phase four-pole induction motor rated at 200 V, 5.5 kW and 60 Hz. Experimental waveforms show that the four split dc-capacitor voltages are well balanced in any operating conditions, and that the total harmonic distortion (THD) values of the input line current and the output motor current are 3.9% and 3.35%, respectively.