The drive of an electric vehicle requires a small volume, a high power to weight ratio, a high efficiency, a wide speed range, reliability and low costs in manufacturing and maintenance. In this article is presented the comparison of induction motors (ASM's), permanent magnet synchronous motors (PMSM's) and a permanent magnet synchronous motor with auxiliary exciting windings (HYB).
Because of absence of maintenance and its large robustness the squirrel-cage ASM is absolutely suitable to equip an electric vehicle. To reach a wide speed range (over 7000 rpm) and a high efficiency the motor must be designed with low stray reactance's and coppercage rotor. This does not lead to a weight optimal solution.
The PMSM with high energy rare earth magnets has a higher efficiency than the ASM, because it does not need a magnitizing current, which produces additional losses. It also can reach speeds as high as the ASM, by feeding the stator windings with an additional negative winding current. But such properties are only possible with a small number of pole pairs.
The HYB has a high number of pole pairs, that is more intersting from the weight point of view, but it needs auxiliary exciting windings. By field-strengthening at low speed the motor can deliver a high torque if necessary. By field-weakening in the rotor and feeding the stator with a negative direct current the motor can also reach the maximal speed. Prototypes of each synchronous machine have been designed by FEM-analysis, built and measured on a test bench in the institute.
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