Design And Optimization Of Cooling System Of Permanent Magnet Synchronous Motor For Vehicle

Permanent Magnet Synchronous Motors have been widely used in electric vehicles due to its advantages of high power density,high efficiency and strong anti-overload capacity.The temperature of the motor is easily risen to be beyond the limited values under tough or long operaing conditions,due to the small size,high speed and airtight installation space of motors,which will lead to the insulation failure of the insulation material,demagnetization of permanent magnet,structural deformation,etc.,so that,the working efficiency,service life and operation safety of the motor are seriously affected.In order to insure the motor works stably and reliably for a long time with high efficiency,it is necessary to keep the motor temperature within a allowable range through the reasonable design of the motor cooling system.In this paper,To solve the cooling problem of new developed Permanent Magnet Synchronous Motor,the loss of motor is simulated numerically,the structural type of cooling channel is determined according to the structural characteristics of motor,cooling performances and operation and manufacturing costs of the channel.Finally,the structural and flow parameters of cooling system are optimized.The research contents and main conclusions are as follows:(1)Simulation of motor losses.Based on ANSYS Maxwell software,combining the structural characteristics and relevant parameters of the motor,the two-dimensional simulation model of the motor electromagnetic is established and carried out to obtain the loss data of the motor under typical operating conditions,laying a foundation for the design of the motor cooling system.(2)Determination of cooling channel structure of motor.Based on the loss of motor under rated working condition,the total heat exchange area of cooling channel is determined according to the theoretical formula of heat transfer,and three different types of cooling channel structures are designed while the total heat exchange area and channel area are kept the same.On this basis,the temperature field and flow field of the motor are simulated by Fluent software.Comparing the maximum temperature of the motor,the flow loss of the channel and considering the manufacturing and operation costs,the axial Z-shaped channel is determined as the structure of the motor cooling channel.(3)Establishment and verification of Back Propagation Neural Network agent model.On the basis of Newton cooling formula,analysing the influence of structure and operation parameters on the cooling system’s capacity,the width and number of channel,flow of cooling water are determined as design variables,the maximum temperature of the motor and the flow loss of the channel are determined as response variables.Then an agent model based on Back Propagation Neural Network is established to describe the relationship between the width and number of channel,the flow of cooling water and the maximum temperature of motor,the flow loss of channel,as well as the fitting accuracy of the agent model is also verified by test samples.(4)Optimization of structure parameters of channel and flow parameter of cooling water.The second generation fast Non-dominated Sorting Genetic Algorithm combined with Back Propagation Neural Network model is applied to the multi-objective optimization design of channel structure and flow parameters of cooling system.According to Pareto optimal solution set,the optimal scheme is selected based on the principle of low motor maximum temperature and small flow loss.And the response predicted results of the optimal scheme were verified by the three-dimensional simulation of the motor temperature field and flow field,it’s show that the three-dimensional simulation results of the optimal scheme’s response values are in agreement with the results of the prediction,and the motor maximum temperature and the flow loss absolute errors are 0.05 K and 43.24 Pa,respectively.(5)Determination of flow parameters under peak conditions.Based on the loss of the motor under the peak speed and peak torque conditions,the influence laws of different cooling water flow on thermal characteristics of motor and flow characteristics of channel are studied by the three-dimensional simulation of temperature field and flow field,and the cooling water flow required for motor under the two conditions is determined.The results show that under the peak speed condition,when the cooling water flow is 9～10L/min,the cooling effect of the motor is better and the power loss of the pump is lower;under the peak torque condition,when the cooling water flow is20L/min,the temperature of the motor winding and the insulation material are within the allowable range.