Novel Generic Fault Model Considering Fundamental and PWM Current Components of PM Machines With Interturn Short-Circuit

This article proposes a novel analytical fault model for permanent magnet machines with interturn short-circuits that considers the influence of various factors on the fault current. These factors include mutual inductances between the faulted turns and the remaining healthy windings (faulted and healthy phases), load current, and pulsewidth modulation (PWM) harmonics introduced by the drives. These three factors have been largely neglected by the published methods in literatures but could have significant influence on fault current depending on operating conditions. The investigation in this article shows that, without using the proposed fault model, the conventional fault model that only considers the back-electromotive force in the short-circuited loop and the self-impedance of the short-circuited turns, would underestimate the fundamental fault current by more than 45%. In addition, the proposed model establishes the relationship between the PWM ripple current in the short-circuited turns and that in the faulted phase. By doing so, the fault current including both the fundamental and PWM ripple components can be accurately predicted. The accuracy of the proposed method has been fully validated by a series of experiments.