Square Shaped Waveform Pulse Control to minimize PD Exposure within Motor Insulation

Artikel i vetenskaplig tidskrift, 2023

Pulse width modulated (PWM) voltage supply is important for efficiently controlling the performance of electric motors. The downside brought up by its use is that the electric stress imposed on motor insulation considerably increases, compared to traditional 50 or 60 Hz sinusoidal supply, and it often result in reduction of insulation lifetime. In this paper the advantages arising from employing PWM waveforms with adjustable rise time and pulse height are verified by evaluating their influence on partial discharge (PD) characteristics of motor winding insulation, exemplified using twisted pair test object. A test set-up enabling control of the voltage pulse shape is introduced for demonstrating that intensity of PD activity can be reduced or even ceased by adjusting the slope of voltage flanks at which the electric stress reaches its maximum level, including application of ultra-short rise times imposed by modern semiconductor technology. It is also shown that proposed solution yields reduced PD activity without increasing switching losses and the influence of reflections becomes considerably limited. Quantitative guideline to reduce the PD activity is presented.