Determination of D and Q Axes Inductances for Steady State Model Analysis of PM Motor with Non-Ideal Machine Parameters

Abstract

The permanent magnet (PM) motors are widely used in electric vehicle (EV) application due to their high power density. Since EVs have wide operating speed range, it is necessary that the motors used in EVs satisfy this condition. One way to achieve the wide speed range operation in PM motors is by using field weakening. The field weakening capacity of the PM motors depends on the ratio of direct axis and quadrature axis inductances $(L_{d}, L_{q})$ . The analytical models of PM motor assumes constant values of $L_{d}$ and $L_{q}$ . 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. This results in erroneous prediction of motor's behavior, especially in field weakening region. To overcome this, an improved analytical model is proposed in this work. Here, the inductances are made a function of current and the results obtained by the proposed model are compared with results obtained from FEA.