Voltage Propagation in Inverter-driven Machine Windings over Wide Operation Range

This paper studies the pulse voltage propagation inside machine windings driven by power inverters. The fast switching of devices in the inverter generates voltage pulses with high dv/dt and induces high overshoots at the machine winding terminals. Those high voltage overshoots can accelerate the degradation of the winding insulation system. This work analyzes how the steep-front voltage distributes along the windings during switching transients over a wide range of operation conditions. Circuit analysis is conducted for each transition of switching events over an entire fundamental cycle. An 8-pole interior permanent magnet synchronous machine for hybrid electric vehicle traction applications with a complex winding structure was used to verify the analysis. Tests were conducted to obtain the pulse voltage propagation along the machine winding at all the transition of switching events over an entire fundamental cycle when the machine was working at certain operating points. The effect of multiple factors on the pulse winding voltage propagation were tested and analyzed in this work, such as DC voltage level, current level, rotor speed, etc. Then, the voltage stress was mapped on each part of the winding insulation along the winding for various machine operating points, which quantifies the maximum voltage stress distribution on the winding insulation system. The understanding of the voltage stress distribution gained from this study will be applied to guide optimization of electric machine winding insulation in the future.