Modelling and experimental studies of effects of steep fronted inverter waveforms on motor and supply cabling and their remedies

Due to the widespread adoption of IGBT power switches in motor drives, the detrimental effect of steep fronted waveforms on the supply leads to the motor and the motor itself has recently become a matter of concern. IGBT switches have many desirable properties; however, their fast switching edges can easily cause a total reflection of the inverter output voltage waveforms from the motor terminals, when the motor is at the end of a cable more than about 20 m long. This may lead to a doubling of the supply voltage to the motor and to the cable. This paper models IGBT inverters which supply induction motors via cables longer than this length and predicts the voltage stress at the motor terminals and along the length of the cable. Remedial measures are also modelled. Experimental results are included which confirm the accuracy of the model and the suitability of the remedial measures suggested.