Discontinuous PWM Technique for the Asymmetrical Dual Inverter Configuration to Eliminate the Overcharging of DC-Link Capacitor

Abstract

To improve the quality of output voltage in the dual inverter fed open end winding induction motor drive, the dc voltages should be maintained in the ratio of 2:1. In such a configuration with a continuous modulating signal-based pulse width modulation (CPWM) technique, overcharging of the dc-link capacitor of inverter with low input dc voltage is observed (ratio of 2:1 is not maintained). Hence, wide range of speed control is not possible with the CPWM technique. The existing decoupled PWM methods and nested rectifier configuration may generate output voltage with poor quality and increase the cost of the drive system. This paper presents a discontinuous modulating signal-based PWM (DPWM) technique for asymmetrical dual inverter configuration, which eliminates the problem of overcharging of the dc-link. Hence, wide range of speed control is possible with better quality of output voltage. In the operating range, when compared to the CPWM technique, the DPWM technique reduces zero sequence voltage. The proposed PWM technique is easy to implement and does not require any reference voltage vector magnitude calculation, sector identification, and switching state selection as in space vector based PWM techniques. To show the effectiveness of the DPWM technique, experimental studies have been carried out, and results are presented and compared.