Research On Rotor Magnet Loss And Thermal Field In Fractional-Slot Concentrated-Windings Permanent Magnet Synchronous Motor

Fractional-Slot Concentrated-Windings (FSCW) Permanent Magnet Synchronous Motor (PMSM) has become the driving motor in new energy vehicles domain because the lower copper loss, high power density, lower vibration and lower noise. But the magnetic field distortion is serious inside the motor, so there are many harmonics that rotate with rotor in different speed that can produce a large number of eddy-current loss in the permanent magnets and core of stator and rotor. High temperature will shorten the life of motor due to the poor heat dissipation in new energy automobiles. The raise of temperature will lead to the magnet demagnetized and even burned down.The rotor magnet loss and temperature field of FSCW PMSM for electrical vehicle which has 24 slots and 16 poles are researched in this paper. The main work of this paper is as follow:Firstly, the flux density in air-gap which is generated by the existence of teethes and slots of stator, the non-uniform distribution of stator windings in slots of stator and the non-sinusoidal of excitation current in stator windings are analyzed. The harmonics of flux density in air-gap which generates the magnet loss is much. The rotor magnet loss is calculated by fast-calculated analytical method and precise electromagnetic Finite Element Analysis (FEA) method, the calculation results are approximately the same. The methods include widening air-gap, widening width of slot-opening, shortening the depth of the slot-opening, circumferential and radial PM segmentation are also validated to reduce the magnet loss. The relation curves of rotor magnet loss and these factors are obtained by FEM.Secondly, the losses of the prototype which contain the copper loss, the core loss and the mechanical loss are analyzed. The influences on core loss with speed, load, thickness of silicon-steel sheets, air-gap size, width and depth of slot-opening are analyzed. The temperature field calculation model is built in a series of equivalent in the FEA software which used the results of the loss. The temperature distribution is obtained when the motor runs 2 seconds in infinite insulation and when the temperature of stator windings reaches 150℃. The temperature distribution diagrams of stator, rotor, windings and permanent magnets are also obtained in different working conditions. The temperature distribution of permanent magnets is analyzed with methods that reduce PM eddy-current loss. The simulation results show that the methods can reduce the temperature of the PM.