| Squirrel Cage Induction Motor(SC-IM)has the advantages of simple structure,low cost,reliable operation and easy maintenance.It has become the preferred driving motor for low-speed and low-power electric vehicles(such as golf carts,police patrol cars,etc.).However,the frequent start-stop and speed change in the operation of electric vehicles require that the motor has a high instantaneous power density and a large overload capacity,which makes the loss and temperature of the motor rise rapidly,resulting in the decline of operational reliability and shortening of service life.Therefore,studying how to reduce the operating loss and temperature of SC-IM is crucial for the optimal design of the motor.In this paper,a 4kW SC-IM is used as a prototype to analyze and study the loss and temperature rise of the motor under power-supply voltage operating conditions.The influence of the main dimensions of stator slot on the loss and temperature is also discussed.On this basis,an optimization scheme for the main size parameters of stator slot is proposed.The correctness of the optimization scheme is verified by simulation and experiment,which provides theoretical and engineering references for the optimization design of electromagnetic and temperature fields of SC-IM for electric vehicles.Firstly,according to the basic size parameters of the prototype,a two-dimensional electromagnetic field model is established to analyze all kinds of losses caused by temperature rise in the motor.The copper and iron losses of stator and rotor are mainly considered.Based on the electromagnetic field theory and loss generation mechanism,the loss distribution of the motor under power-supply voltage operating conditions is calculated,and the distribution of magnetic lines and the variation of magnetic density with time in the motor are analyzed,to ensure the correctness of model establishment and loss calculation.Secondly,based on the basic theory of heat transfer and fluid mechanics,a three-dimensional finite element temperature field calculation model is established,and the complex flow field and temperature field coupling problem between the inner rotor and air gap of the motor is equivalently processed.At the same time,load is applied according to the loss calculated by electromagnetic calculation and boundary conditions are set to simulate the steady-state temperature field of the motor under power-supply voltage working conditions,and the temperature distribution law of each part of the motor is obtained,which lays a foundation for the performance optimization of the motor.Next,slot width,slot height,slot width,slot shoulder angle,slot radius and slot height of motor stator slot,the effects of each parameter on various losses and overall temperature rise are studied respectively.Taguchi experiment method is used to calculate and analyze the influence of various parameters on loss and temperature rise.A set of optimization parameters are determined without affecting the groove filling rate and structural stiffness.The distribution of magnetic field,loss and temperature field of the motor before and after optimization is simulated and compared.The results show that all performance indexes are improved after optimization.Finally,a prototype is made according to the optimized scheme and no-load and load experiments are carried out.The experimental value of iron loss was measured by no-load loss separation experiment.Then the temperature of the motor in steady state is obtained by load experiment.The loss and temperature rise of the motor under the simulated experimental conditions are compared with the simulation values.The error between the two values is within a reasonable range,which verifies the correctness of the calculation method and the optimization process of SC-IM temperature field. |
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