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| Influence of PWM on Rotor Eddy-Current Losses in Brushless DC Motor |
| Xie En, Liu Weiguo, Luo Ling, Wang Pu |
| Northwestern Polytechnical University Xi’an 710072 China |
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Abstract The eddy-current losses in the rotor of brushless DC motor (BLDCM) under PWM modulation can mainly be divided into three parts. In terms of space, moving rotor cuts armature magnetic field, and electromotive force (EMF) is induced. In terms of time, variation of both armature magnetic potential caused by PWM and cogging flux density can induce EMF. In this paper, these three parts of EMF are defined as motional EMF, induced EMF and cogging EMF, respectively. Without considering eddy reaction, motional EMF and induced EMF of an 11kW BLDCM are calculated and analyzed by selecting maximum curved surface and closed curve at typical operating point. It can be found that the induced EMF is higher than motional EMF (cogging EMF is not considered), and the induced EMF is maximum when duty cycle equals to 50%. The rotor temperature rise caused by above three kinds of EMF is obtained respectively by pair-drive loading experiment. The experimental results verify the proposed method very well.
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Received: 11 October 2011
Published: 28 November 2013
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2013, Vol. 28 
