Postfault operation strategy with minimum harmonic injection for cascaded H-bridge inverters driving a multiphase motor

Abstract

Multiphase motor drives based on cascaded H-bridge (CHB) voltage source inverters (VSIs) offer enhanced reliability by accommodating both motor and VSI faults. The VSI faults, the most prevalent type, can be addressed by bypassing damaged H-Bridges. However, operating the VSI in this condition without an appropriate postfault strategy can increase the torque ripple and losses, and reduce the maximum motor speed. While conventional postfault strategies for three-phase CHB VSIs can be extended to more phases, they often result in a suboptimal performance because the extra degrees of freedom available in multiphase motors are ignored. Recently, these degrees of freedom have been exploited for the postfault operation of n -phase CHB VSIs to maximize the drive speed range without field weakening or torque ripple. However, excessive low-order xy harmonics arose in the stator current, producing a significant increase in its copper losses, which were limited by the use of a bulky filter. This article proposes a novel postfault operation strategy for n -phase CHB VSIs that dramatically reduces the stator copper losses by minimizing the injection of low-order xy harmonics in the stator voltage, effectively eliminating the filter requirement, while maintaining a wide speed range without field weakening or torque ripple. Experimental results obtained with a five-level five-phase motor drive corroborate the theoretical findings. This article is accompanied by a MATLAB script with the proposed strategy coded for the five-phase cas