Research On Rotor Eddy Current Loss Of High Speed Permanent Magnet Synchronous Motor

With the fast development of China’s economy and the rapid expansion of industrial scale,the motor is developing toward high speed,high efficiency and power density.Due to the advantages of small size,low noise,fast dynamic response,high power denstiy and high transmission efficiency,the high speed motor has been widely used in aerospace,electric vehicles,flywheel storage,and other fields.The higher frequency working condition makes the loss in unit volume of the high speed motor higher than the ordinary motor.The rotor eddy current loss for high-speed motor is not negligible because sheath structure is added,making it hard for heat dissipation.The value and rotor temperature is related to the reliable operation of high-speed motor,Therefore,it is necessary and practical to deeply analyze the eddy current loss of the rotor of high speed motor.A 250 kW,2-pole high speed permanent magnet synchronous motor is analyzed in this dissertation to study the causes of eddy current loss in detail.And the finite element mathematical model of two-dimensional eddy current field is established according to the basic theory of electromagnetic field.The motor under rated condition is calculated and the calculation result of finite element is analyzed.All electrical quantities have met the requirements of motor design.A new type of rotor structure with coating on the surface of rotor permanent magnet is put forward.Respectively,the rotor permanent magnet surface coating with different coating material and thickness,the rotor permanent magnet external surface coating with different coating thickness,and the internal and the rotor permanent magnet external surface coating with different coating thickness are analyzed.The law of the rotor eddy current loss with the change of the coating position,the distribution law of the eddy current loss density in the coating and the permanent magnet is analyzed under three different cases above.The variation of the total eddy current loss of the rotor is further analyzed when the material and thickness of the coating change.The influence of the sheath with different composite structure on the eddy current loss of the rotor is studied.The composite structure of copper coating outside and inside the steel sheath.The changing law of the total eddy current loss and the distribution characteristics of the eddy current density on the permanent magnet and the composite sheath are analyzed under two conditions.It is proved that the composite structure of copper coating outside the steel sheath has better effect on the eddy current loss of the rotor than the composite structure in the steel sheath by comparison.Finally,the sheath structure of the copper coating is further analyzed.And according to the changing law of the maximum value of the internal eddy current loss density,the reasonable thickness of the copper coating is obtained.