Estimation of Magnet Temperature for Integer-slot Permanent Magnet Synchronous Machines via Extraction of First-order Slot Harmonic in Back-EMF

In this paper, a temperature estimation for rotor permanent magnets (PMs) of permanent magnet synchronous machines (PMSMs) with integer-slot winding is proposed, which is based on the extraction of first-order slot harmonic (FOSH) in back-EMF. It is based on the fact that due to the FOSH of back-EMF, the integer-slot PMSM with slot/pole number ratio of ν usually has non-negligible (2ν±1)th harmonics, of which the
q
-axis (quadrature-axis) component is found to be a good indicator for monitoring the rotor PM temperature and can be easily extracted by a synchronous filter. Besides, the frequency of FOSH in
q
-axis, being (2ν)th harmonic, is usually much higher than the 6th harmonic voltage generated by inverter nonlinearity. Thus, the extraction of FOSH can be irrespective of the influence of inverter nonlinearity in theory. The proposed method is experimentally verified on two prototype PMSMs with ν=9 and 6, respectively. It is found that under different speeds and load conditions, the maximum errors in temperature estimation of rotor permanent magnets are within the range of ±(3~4) °C.