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Abstract
This paper presents some aspects related to the performances of a high-speed induction motor used for the propulsion of an electric vehicle. For the construction of the rotor cage of a 20 kW machine operating at a rated speed of 26000 rpm, both aluminium and copper were used. A comparison among these structures both from the electromagnetic and mechanical point of view, based on an analytical, but mainly numerical analysis, was performed. The differences among these structures, underlining the advantages and shortcomings of the use of the two conductor materials, are discussed in detail in the paper. The performed numerical analysis validates the analytical choices from the electromagnetic point of view and shows the major differences between the two variants from the mechanical point of view.
Keywords: high speed, induction motors, electric vehicles, rotor bars, electromagnetics, mechanics, finite element method
Received: March, 10, 2016
1. Introduction
The application domain of the high-speed rotary motors is mainly related to compressors, pumps and machine tools [1, 2, 3]. The characteristic of the induction motor, of developing a practically constant torque while working most of the time in permanent regime at constant speed makes it suitable for the use in such cases. However, it must be considered that the high speed motors involve important problems related to the control dynamics and the limits of the power converter (switching frequency) and control unit (real-time computation).
On the other hand, our application, the electric vehicle (EV), requires high dynamic capabilities due to rapid acceleration and ramps [4]. The main candidates for such application are the DC brushless motor and the induction machine (IM). The advantages of the IM are related to the cost, the mechanical and control robustness (since no permanent magnet needed like for the case of an axial-flux permanent-magnet motor or a radial flux permanent magnet topology, and the control is more straightforward than for VRSM and SRM [5]). However, the only notable uses of induction drives have been the General Motors EV-1; the AC Propulsion vehicles, including the tzero and the Tesla Roadster. The progresses made in the control of the IM and in its operation at high frequencies by using special materials for the construction of the iron core made it attractive for...