Comparison of HF losses and vibration of an automotive PM motor with Si and SiC inverter supply

Abstract:
Permanent magnet synchronous motors (PMSM) are usually operated with a pulse width modulated (PWM) voltage supplied by a voltage source inverter (VSI). In addition to Si inverters, SiC inverters are increasingly being used, particularly in the automotive sector, which are characterized by faster switching and steeper voltage slopes by a factor of 10...100 in addition to higher possible switching frequencies. A key aspect in determining losses and electromagnetic force excitation is knowledge of the current harmonics resulting from the pulsed voltage. Being mainly determined by the winding inductance, in PMSMs as sum of main and leakage inductance, the harmonic current depends on the saturation of the magnetic circuit and thus is working point dependent. As the d- and q-inductance of (interior permanent magnet) IPM motors vary greatly depending on the operating point and therefore the saturation, the same PWM signal results in different current harmonics depending on the operating point. Based on measurement results, the current harmonics, the resulting additional losses in a IPM test machine and the vibration amplitudes for operation with a Si inverter and a SiC inverter are compared.