Study of partial discharge detection in motors fed by SiC MOSFET and Si IGBT inverters

Voltage inverters based on the pulse width modulation are widely used for applications that require controlling rotation speed. The devices used today to create pulse width modulation are Silicon (Si) IGBTs. The use of IGBTs enables to generate rising edges of tens of kV /µs, and to reach switching frequencies around 20 kHz. These improvements have helped to reduce switching losses and motor torque ripple. On the other hand, the reliability of motors has declined dramatically. The causes of motor failures may be due to different phenomena, but one of the main ageing mechanisms is the erosion of the different insulation materials induced by Partial Discharges (PD). For high voltage, high power and/or high frequency applications, silicon carbide (SiC) based components will in most of the case replace the current silicon-based components. If some works have already been achieved for on-line PD detection in low voltage motors fed by inverters using Si-IGBT technology, works are now needed when SiC-based components are used. For motors fed by low voltage, PDs mainly occur during the voltage edge. It is therefore necessary to discriminate them from the noise induced by switchings. The use of high pass filters proved its effectiveness for IGBTs but the use of SiC MOSFET will result in an increase of switching speed and consequently an increase of the noise frequency. For such conditions, it may be difficult to differentiate partial discharges from noise. This paper presents a study on the partial discharge inception voltage, on the ability to detect partial discharges and on the voltage stresses in motors supplied by SiC-MOSFET and Si-IGBT inverters. These results are discussed and possible strategies are proposed.