Investigation of inter-turn short-circuit fault of PM machines using PWM voltage-based modeling

This paper aims to develop an analytical fault model based on PWM voltages for permanent magnet (PM) machines with inter-turn short-circuit fault. Using PWM voltage-based modelling is mainly because the PM machines are commonly driven by PWM inverters. This model is more accurate compared to the ones that use sinewave voltages as inputs as the latter neglect the PWM harmonics in the fault current. However, the investigation in this paper showed that, depending on the DC bus voltage and switching frequency, the PWM harmonic component could be more than 50% of the fundamental component in the fault current, therefore, cannot be neglected. Based on this developed fault model, the characteristics of the fault current have been explored first, which revealed that the back-EMFs mainly contribute to the fundamental component of the fault current, whilst the PWM voltages not only affect its fundamental component but also the PWM harmonics. Secondly, the factors such as DC bus voltage, switching frequency, number of short-circuited turns and different coil connections affecting the PWM ripple components in the phase current and the fault current have also been investigated. Finally, the MATLAB/Simulink simulations based on the developed fault model have been fully validated by a series of tests.