Calculation Of Eddy Current Loss And Thermal Analysis Of The Permanent Magnet Spherical Motor

With the rapid development of robotics and other high-technology,the permanent magnet spherical motor(PMSM)has become a hot topic,and it can achieve three-degree-of-freedom(3-DOF)motion.Among them,the eddy current loss calculation and thermal analysis are the key problems in the design stage of the PMSM.At present,NdFeB is widely used in permanent magnet materials,and it has high coercivity and remanence.However,it also has high conductivity,and the resultant eddy current loss can be significant.This may cause a substantial temperature rise and result in partial irreversible demagnetization of the magnets.So,the problem of temperature rise is likely to affect the operation performance and even the life of the motor,and the thermal analysis of the PMSM is considered necessary.This paper shows the study of the eddy current loss calculation and thermal analysis of the PMSM.The rotor magnets of the PMSM have a structure of spherical cone,and all of the stator coils are distributed on the inner surface of the stator shell independently of each other.In view of these characteristics,a 3-D analytical model is presented to study the eddy current loss of magnets in the PMSM.This model combines the double Fourier series decomposition and the magnetic vector potential method.First,the current density distribution at the inner diameter of the stator is described by employing the double Fourier series decomposition.With the current density distribution and other boundary conditions,the unique solution of magnetic vector potential is obtained by solving 3-D Laplace equation.Further,the analytic expression of permanent magnet eddy current loss in the PMSM is derived.This model considers the effect of harmonics,and the influence of different motor parameters on the eddy current loss has been analyzed.Based on the calculation of the eddy current loss of magnets,the heat sources such as hysteresis loss and copper loss are also discussed.With these heat sources,a 3-D equivalent thermal network model is established,and the thermal resistances are calculated.By applying the thermal network model,the influence of different speed and load on temperature rise is analyzed,and a steady state thermal analysis of the motor is performed by using finite element method(FEM).At last,the structure of stator is improved and good heat dissipation effect is achieved.This paper provides the theoretical basis for the design of ventilation and cooling system of the PMSM.