An Experimental Assessment of the Impact of High dv/dt SiC Converters on Insulation Lifetime of Electrical Machines

SiC MOSFETs, capable of operating at higher dc link voltages with faster rise times and higher switching frequency, are becoming more prominent in converter-fed drives. While they offer higher power density and high efficiency with improved performance, they also result in significantly increased voltage stresses to the insulation of machine windings. In this paper, the impact of SiC based converters on the insulation lifetime of a commercially available 2.8kW permanent magnet machine is assessed experimentally at elevated temperatures under a range of dc link voltages, rise times and switching frequencies. The lifetime of these samples and samples fed by a Si based inverter are compared, allowing the impact of SiC inverters to be studied. Specific focus is given to the quantity of partial discharge (PD) activity within the machine windings monitored throughout the experiments. It is shown that presence of PD during tests lead to very significant reduction in insulation lifetime.