Qualitative and Quantitative Analysis of Different Inductance Measurement Techniques for IPM Synchronous Machines.

The accurate estimation of equivalent circuit parameters (EEC) is necessary for performance analysis and control of electric drives using the analytical models of electrical machines. The analytical models of PM motor assume constant values of d and q axis inductances. Since the B vs. H curve of the lamination material is non-linear, the $L-{d}$ and $L-{q}$ inductances vary as the stator current increases. So, the assumption of constant inductances results in an erroneous prediction of the motor's behavior. Hence, an accurate estimation of nonlinear variation of inductances in PM motors is necessary. There are many techniques specified in standards and literature for the evaluation of IPM machine inductances. However, a reliable method to capture the nonlinear variation of inductances is not discussed. This work gives a comparative analysis of various inductance measurement techniques for the interior permanent magnet (IPM) machines to capture the nonlinear variation of inductances with current based on motor performance. Statistical and qualitative analysis of experimental and FEA results on an IPM motor design is done in this work to determine a reliable inductance measurement technique.