PWM Voltage Rise Time and Pulse Width Control to Minimize Partial Discharge Exposure

Paper i proceeding, 2021

Pulse width modulated (PWM) shaped voltages provides a flexible approach to control electrical motorsefficiently. The downside is that the voltage stress imposed on insulation systems increases considerably, which often results in reduced efficiency and lifetime. One approach to reduce the stress on the insulation system is to increase the inverter level beyond two. The advantages of employing three level PWM waveforms with adjustable rise times to utilize the recent advantages of modern semiconductor technology are presented in this paper. To demonstrate this approach, a circuit solution is
introduced and utilized to investigate what influence the pulse width and rise time has on the partial discharge (PD) characteristics in the test object. Specifically, it is demonstrated that the presence of PDs can be reduced by adjusting the rise times at some of the voltage flanks only. Further the influence of pulse width and peak amplitude on these filtered flanks are explored. This to enable the use of higher carrier frequency and to reduce the inverter level otherwise required. It is confirmed that when applying a sufficiently wide pulse with increased rise time at the critical voltage flanks only, the PD exposure drops considerably. The demonstrated approach presents a promising principle to reduce the stress appearing in motor windings when applying ultra-short rise times.