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Description
Drive motors for hybrid electric vehicles (EVs) have often been studied to increase their efficiency and improve the total driving distance on a single charge. The motors are required to operate over a wide operating speed range according to operating characteristics of HEVs, which should improve the efficiency in the frequent operating range. To achieve this improvement, this paper presents optimal design of interior permanent magnet synchronous motor (IPMSM) with electrical winding changeover technic (EWCT) to maximize the efficiency of hybrid EV based on finite-element analysis. Since IPMSM has outstanding performance in terms of wide operating speed range, high efficiency and power density, IPMSM has often been used in EV applications. However, because a back-electromagnetic force (EMF) of the IPMSM increases linearly with speed, the motor can be damaged by an excess voltage at an overspeed. The EWCT is a method to switch the number of turns to decrease the back-EMF at high speed, which can extend the operating speed range under a limited maximum voltage. For this motor, two switching steps of EWCT were adopted, where the turn number of the first switching step is twice that of the other switching step. According to two switching steps, the performance of the IPMSG changes greatly in terms of field weakening control, winding resistance, magnitude and phase shift of current, etc. These characteristics also affect the efficiency including copper loss and iron loss. As a result, the two efficiency maps are presented, which can be operated for better efficiency.
In optimal design, maximizing the efficiency is applied at frequent operating points of HEV, and a differing extent mesh adaptive direct search is used as the optimization algorithm. Finally, the performance and the optimization method of IPMSM are validated from experimental test results. This work is funded by the Korea Automotive Technology Institute.
