| Permanent magnet synchronous motor is widely used as a driving motor for new energy vehicles.However,due to its high power density and limited heat dissipation space,the internal temperature rise of the motor will be too high.In severe cases,winding insulation failure and high temperature demagnetization of permanent magnets will occur,which will affect the operating performance of the motor.Therefore,it is necessary to accurately calculate the temperature field distribution of the motor and design a reasonable cooling system to control the temperature rise of the motor.In view of the above problems,based on the extensive reading and analysis of the cooling literature of permanent magnet motor at home and abroad,the calculation method of motor loss and temperature field is determined,and a new type of casing series-parallel mixed flow channel structure is proposed.The cooling characteristics of the motor are analyzed by theoretical analysis and simulation calculation,and the cooling parameters and flow channel structure parameters of the motor are optimized.Firstly,because of the internal heat of the motor comes from the operating loss of each component of the motor,the loss of each component of the motor needs to be calculated before calculating the temperature field of the motor.Therefore,a twodimensional electromagnetic field simulation model of the motor is built.The accuracy of the electromagnetic field simulation model is verified by the simulation analysis of the electromagnetic characteristics of the no-load electromagnetic field of the motor.The electromagnetic field characteristics of the motor under rated load conditions are simulated and analyzed,and the operating losses of the motor components under rated operating conditions are calculated.Among them,the stator core loss is 390 W,the winding copper loss is 466 W,the rotor core loss is 44 W,and the permanent magnet eddy current loss is 19 W.The loss of stator and winding parts is much larger than that of rotor and permanent magnet.Secondly,a three-dimensional physical model of the motor is constructed.The finite element method and the lumped parameter thermal network method are used to calculate the steady-state temperature field distribution of the motor under rated operating conditions and natural convection heat dissipation conditions.The two methods calculate that the temperature of each component of the motor is similar,and the maximum error is only 3.5 %.However,the lumped parameter thermal complex method can only obtain the average temperature of the node,while the finite element method can more accurately calculate the temperature field distribution of the motor and the flow field distribution of the liquid cooling structure studied in the subsequent research.Therefore,the finite element method is used to solve the temperature field of the motor in the subsequent research.The maximum temperature of the winding insulation is calculated to be 120.6 ℃ by the finite element method,which exceeds the heat resistance limit of 120 ℃ of the E-level insulation material used.In order to effectively control the temperature rise of the motor,a new type of casing series-parallel mixed flow channel structure is proposed.The finite element method is used to simulate the temperature field distribution of the motor under the heat dissipation condition of the casing liquid cooling channel.The maximum temperature of the winding insulation layer is reduced to 87.6 ℃.Then,the cooling performance of the casing series-parallel mixed flow channel structure is compared with the traditional series flow channel and parallel flow channel structure.The results show that the series-parallel mixed flow channel structure can greatly reduce the pressure drop of the coolant inlet and outlet while ensuring better cooling performance.Thirdly,the effects of the structure combination type,the number of flow channels,the inlet flow rate of coolant and different cooling media on the cooling performance of the series-parallel hybrid flow channel of the casing were studied.The results show that the comprehensive cooling performance of the 2-1-2-1-2 series-parallel mixed flow channel is the best.Increasing the number of flow channels and coolant flow rate can improve the cooling performance,but it will increase the pressure drop of coolant inlet and outlet.When pure water is used as the coolant,the cooling effect is the best.When transformer oil is used as the cooling medium,the maximum temperature of the motor is the largest,and the pressure drop of the inlet and outlet of the coolant is the smallest.As the concentration of ethylene glycol solution increases,the maximum temperature of the motor gradually increases,and the pressure drop at the inlet and outlet of the coolant gradually increases.Considering that pure water as coolant is easy to affect the cooling effect due to low temperature icing,it is more appropriate to use ethylene glycol solution with lower freezing point as coolant.In order to further improve the heat dissipation performance of the permanent magnet synchronous motor,the orthogonal test was established on the number of annular flow channels,the inlet flow rate of coolant and the concentration of ethylene glycol solution with the maximum temperature of the motor and the pressure drop at the inlet and outlet of the coolant as the evaluation indexes.The primary and secondary order of the influence of the three factors(coolant inlet flow rate > annular flow channel number > ethylene glycol solution concentration)was determined.When the coolant inlet flow rate,the number of annular flow channels and the concentration of ethylene glycol solution were 10 L /min,8 and 50 %,the comprehensive cooling effect of the motor was the best.Finally,the Kriging surrogate model is constructed with the maximum temperature of the casing and the cooling hydraulic pressure drop as the objective function,and the section size parameters of the flow channel are optimized based on the MOGA genetic algorithm.The optimized results show that the pressure drop of the inlet and outlet of the coolant is not much different from the initial model,and the maximum temperature of the motor decreases by 2.8 ℃. |
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