Research On Coupled Magnetic-thermal Network Modeling Of Permanent Magnet Linear Machine

Because of its conversion ability between electrical and mechanical energy,Motors are widely used in industry and production.Double-sided Permanent-Magnet Tubular Machine(DSTM)is improving from ordinary linear motor.Considering its higher space utilization and power density,DSTM has well planning in wave energy generation or other fields.However,with the asymmetry of internal and external stator,it brings difficulties to performance analysis because heat dissipate difficultly.To improve the efficiency of performance analysis,this paper proposes an iterative bidirectional coupled magnetic-thermal network modeling method.Based on the multi parameter,nonlinear,and strong coupling characteristics of DSTM’s magnetic-thermal properties,the calculation results of DSTM’s performance are achieved through the proposed method.Major works are as follows:Firstly,the structural characteristics and operating principle of DSTM are introduced.An electromagnetic-thermal finite element model is established and the parameters of each physical field are iterated and corrected manually.The magnetic-thermal coupling iteration gets rid of the limitations of traditional temperature-correlated coefficients experience.This model is used to compare the electromagnetic,fluid,and temperature changes of DSTM under multiple operating conditions.The limited sustainable conditions of the motor are summarized.And it provides evidences for the grid division of the following magnetic-thermal analytical model.Secondly,an equivalent magnetic network model is established for DSTM.A segmented magnetic network is applied to the complex parts of the magnetic lines of flux.Adaptive connection magnetic circuit is built.Additional semi-arc paths are added to the circuit in order to simulate the leakage magnetic circuit.Introducing an iterative formula for magnetic permeability to accelerate the convergence of the calculation.The equivalent magnetic model is applied to solve the electromagnetic characteristics of the motor under no-load and rated operating conditions.Thirdly,an equivalent thermal network model is established for DSTM.The segmented magnetic network is applied to the stator tooth in order to improve the calculation precision of the junction between fluid and solid parts.The equivalent thermal conductivity is introduced to simplify the distribution of stator slots.Based on Nusselt number,the coefficient of convective heat transfer is calculated.Using the magnetic network loss as the heat source of the thermal network,the residual magnetism and resistivity of the motor are corrected according to the temperature which is obtained from the thermal network.Through coupling iteration between the two network models,the fast and accurate analytical results of the performance of DSTM are achieved.The influence of different armature current density ratios on DSTM temperature rise is analyzed according to the proposed elctromagnetic-thermal analytical model.Finally,the prototype experimental platform is built and the electromagnetic and thermal performance of DSTM is obtained.The experimental values of the back electromotive force are in good agreement with the analytical values.The experimental and analytical values of the cogging force show high consistency in both peak and periodicity.Only slight differences of the cogging force appear from the peaks and valleys due to the judgment error which is caused by the minimum grid width.The deviation between the experimental and analytical average temperature rise under long-term operation is about 5 ℃,which meets the engineering requirements.Rapidity and accuracy of the electromagnetic-thermal analytical method is verified by comparing with finite element method and experiment.