Research On Magnetic Steel Eddy Current Loss Of Interior Permanent Magnet Synchronous Machine In High-speed Flywheel Energy Storage Application

With the characteristics of high-speed and high-frequency, the interior permanent magnet synchronous machine used for flywheel energy storage makes the low order harmonics'frequency of the air-gap magnetic field be higher, and the interior magnetic steel's cooling is poor, the NdFeB magnetic steel's conductivity is high, loss of field is easy at high temperature, so the problems of magnetic steel eddy current are more prominent. In this paper, magnetic steel eddy current loss of the interior permanent magnet synchronous machine used for high-speed flywheel energy storage is researched deeply and comprehensively.Firstly, the design characteristics of high-speed permanent magnet synchronous machine was analyzed and reasonable motor parameters were chosen according to the characteristics. Meanwhile, a two-dimensional finite element model of high-speed permanent magnet synchronous machine was developed based on the basic theory of electromagnetic field. Secondly, a two-dimensional finite element model use to calculated magnetic steel eddy current loss of permanent magnet synchronous motor was developed in the transient field by adopting air-gap magnetic potential distribution function as boundary condition, taking into account the magnetic saturation and the slot effect magnetic steel eddy current loss caused by harmonic magnetic field of a interior permanent magnet synchronous machine can be calculated using the model. Thirdly, magnetic steel eddy current loss taking into account the magnetic saturation or not were calculated and compared by using established model. Fourthly, the principles and characteristics of the slot harmonics caused by the slot effect, the space harmonics caused by stator winding, time harmonics caused by the stator non-sinusoidal current were analyzed. Meanwhile, law of distribution of the magnetic steel eddy current loss produced by all the harmonics was analyzed and computed. Finally, magnetic steel eddy current loss under different load conditions, such as different speed and acceleration, were analyzed and contrasted, according to the operation characteristics of high-speed motor used for flywheel energy storage. Meanwhile, the magnetic steel eddy current loss effect of notch width and segmentation of the magnetic steels were analyzed. And then some solutions were proposed for decreasing the magnetic steel eddy current loss.The results indicate that magnetic saturation has great impact on eddy current loss, mainly because high saturation of the magnetic circuit near the magnetic bridge changed the magnetic distribution of the area around the magnetic steel. As for the interior permanent magnet synchronous machine, those harmonic magnetic field having same order as 1th slot harmonic are the key factors to induce magnetic steel eddy current loss. The eddy current can be reduced by decreasing the notch width and dividing the magnetic steels.This paper obtain the law of distribution of magnetic steel eddy current loss of high-speed interior permanent magnet synchronous machine and someother related conclusions by useing the finite element model, of which the eddy current loss caused by various harmonics magnetic field can be calculated alone. That can be a basic for optimizing the design of high-speed permanent magnet synchronous machine used for flywheel energy storage.