No abstract

No abstract

Due to poor heat dissipation of rotor, especially in flywheel energy storage system (FESS) for uninterruptible power supply (UPS), there is a higher risk of irreversible demagnetization by rotor temperature rising. Irreversible demagnetization of permanent magnets by rotor loss always is a critical problem of high-speed permanent magnet synchronous machine (PMSM). The stabilization and efficiency can be increased by reduction of rotor loss. By Finite Element Method simulations with experiment date, the rotor temperature rising of the prototype PMSM mainly comes from rotor loss induced by time harmonic. The distribution and components of prototype rotor loss are given. Rotor loss is analyzed by equivalent magnetic circuit with considering time harmonic magnetomotive force in this paper. According to analysis of rotor loss, this paper presents a method to reduce rotor loss without changing stator structure and winding current. This rotor structure optimization will not affect output performance of PMSM. The method has been proved to be available by the no-load experiment finally. It can greatly reduce the rotor loss in no-load operation when PMSM is driven in high-speed operation zone. INDEX TERMS Permanent magnet synchronous machine, rotor loss, magnetic field harmonic, permanent magnet eddy current loss.

The ways to reduce rotor loss of a permanent magnet (PM) motor with 200kW/9000r/min for flywheel energy storage system (FESS) is discussed in this paper. Several methods are proposed to reduce the rotor loss by optimizing the structure of rotor. The air friction loss on the surface of rotor can be decreased rapidly when pressure in the sleeve is very small. So the rotor mostly works in a vacuum in high speed FESS. Due to the effect of time harmonics of stator current and space harmonics of air gap magnetic field, the loss in permanent magnets is considerable and leads to partial over-temperature. Thus the irreversible demagnetization of permanent magnets is occurred with poor cooling condition. The impact of rotor structure and silicon steel sheet thickness of rotor to the rotor loss are analyzed in the paper. The analysis and experimental results illustrate that there is the least rotor loss with the proposed rotor structures.

According to the structure size of automobile wheel hub, two types of outer rotor permanent magnet In-wheel motors which meet the performance requirements of electric vehicles are designed in this paper. The analysis of the electromagnetic in the motor with finite element method proves that the new Halbach array can optimize the back-electromotive force(EMF) waveform and raise the average electromagnetic torque of the motor. It can also effectively weaken the cogging torque and the torque ripple. Key words: In-wheel motor；Halbach；finite element analysis I. INSTRODUCTION In-wheel motor is also called hub built-in motor. The mechanical device integrates motor, transmission system and brake system was invented by an American named Robert in the 1950s[1]. Compared with the traditionally electric vehicle drive system, the transmission, clutch, suspension, gearbox and other related parts can be eliminated on vehicles equipped with in-wheel motors. The structure of the vehicle can be sampled. The drive mode can be the front-wheel drive, the rear-wheel-drive or the four-wheel drive. More and more researchers and electric vehicle manufacturers around the world focus on the In-wheel motors. The DC motor, the switch reluctance motor, the brushless permanent magnet DC motor, the induction motor and the permanent magnet synchronous motor can be selected as the motor of in-wheel drive system for electric vehicles. The permanent magnet synchronous motor becomes an ideal choice presently for a number of reasons: smaller size, higher efficiency, power density and power factor. Two 8.5 kW in-wheel motor models with the traditional and the new Halbach permanent magnets array are established in this paper. The air gap magnetic flux density waveform, electromagnetic torque and cogging torque of the motors with different permanent magnet arrays are compared by the Finite Element Analysis (FEA). The analysis shows that the Halbach permanent magnet array has the addition benefit of optimizing the EMF waveform. The electromagnetic torque is improved. The cogging torque and the torque ripple are reduced too.