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

TLDR

The study presents a transformerless medium‑voltage adjustable‑speed motor drive composed of two five‑level diode‑clamped PWM converters connected back‑to‑back. The authors designed, built, and tested a 200‑V downscaled prototype to validate the drive’s effectiveness. The prototype uses split DC capacitors with a voltage‑balancing circuit of two bidirectional buck‑boost choppers, and the converters employ sinusoidal PWM at 3 kHz to drive a 3‑phase, 4‑pole, 200 V, 5.5 kW induction motor. Measurements show the split capacitor voltages remain balanced under all conditions, with input and output current THD of 3.9 % and 3.5 %.

Abstract

This paper addresses a transformerless 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 downscaled model to verify the validity and effectiveness of the medium-voltage motor drive. This downscaled 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 pulsewidth modulation 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 values of the input line current and the output motor current are 3.9% and 3.5%, respectively.