Comparative Study on Insulation Lifetime of Stator Winding of Dual Inverter Fed Open Winding IPMSM and Single Inverter Fed Star-Connected IPMSM for EV Application

In this paper, the turn-to-turn insulation lifetime of a dual inverter fed open winding interior permanent magnet synchronous motor (OWIPMSM) is compared with a conventional single inverter fed star-connected interior permanent magnet synchronous motor (SCIPMSM) for an EV traction application via an on-line experiment. A twisted pair coil (TP) is connected between the line-to-line terminal of windings of an OWIPMSM and a SCIPMSM without rotor and the effect of the line-to-line terminal surge voltage on the turn-to-turn insulation lifetime using the TP is investigated by generating PWM pulses at the inverter output identical to a variable load traction inverter drive. The turn-to-turn insulation life of the TP windings is approximately estimated by measuring the capacitance of the TP windings at regular time intervals during the on-line testing. Finally, experiment is carried out to detect the partial discharge in the TP windings and understand the physical relationship that exists between the total partial discharge count number and the decrease in capacitance of the TP windings after a specified time-period of insulation life testing. From the present preliminary insulation lifetime testing results using the TP, it is found that for motors with the same ratings, an OWIPMSM could be designed with a lower insulation level winding than the SCIPMSM for an EV traction application.