Optimization And Research Of Rotor Eddy-Current Loss In Electric Vehicles

Permanent magnet motor has the advantage of small volume, big power, high efficiency, high integration, large range of speed, etc. Meanwhile, magnet will produce eddy current when the magnetic field changes. As a result, the temperature of the rotor will increase due to its closed structure, and high conductivity and poor heat resistance of permanent magnet made of Nd FeB rare earth. High temperature is fatal to permanent magnet motor, so it is indispensable to do research and analysis on the eddy-current loss to find ways to reduce it.Firstly, this paper mainly analyses the mechanism of the magnet eddy current loss and briefly introduces the basic principle of electromagnetic field and the main method used in this article, 2D and 3D finite element method. Factors that influence the magnet eddy current loss, including pole-slot coordination, rotor structure(magnet position and rotor surface shape), the air gap length, PWM time harmonic current, the stator slot width, the stator chute Angle, segmenting number of permanent magnet blocks, etc were also analyzed. A conclusion was gotten that appropriate pole-slot coordination, “V” type magnet, asymmetry air gap, the increasement of air gap length, inclined slot angle, segmenting number of magnet and reducement of width of slot could reduce the eddy current loss. Current harmonics of PWM will cause more eddy current loss.Then, magnet segmenting was used to reduce eddy-current loss. Magnet segmenting can reduce the eddy-current loss with the increasement of eddy-current circuit resistance. Based on this, a new segmenting way of magnet, inclined segmenting, was introduced in this paper. In this way, more eddy-current loss can be reduced at the same circumstance of magnet segmenting number. And experiments with different axial segmenting way were done to demonstrate that more eddy current loss could be reduced with more segmenting of magnet.Finally, Taguchi method was used in this paper to optimize the motor on four factors, air gap length, stator slot width, stator chute angle and groove depth of rotor surface with the magnet segmented and got a good result in a short time.