Loss Calculation And Temperature Rise Analysis Of Self Cooled Switched Reluctance Motor

Because of its unique advantages,SRM is widely used in aerospace industry,textile industry,coal mining machinery,new energy vehicles and other fields.SRM has the advantages of simple structure,high fault tolerance,small starting current,large starting torque,flexible control mode,long time and low speed operation.Self fan cooling is a commonly used cooling method for small and medium-sized motors.This cooling method relies on the wind cooling motor generated by the rotation of the coaxial self fan cooling fan of the motor,without additional power source.In the design of self cooled switched reluctance motor,its heat dissipation capacity is generally designed according to the rated working condition.Under the rated working condition,the self fan cooling fan of the coaxial fan has high speed,good cooling conditions,and the heat loss and heat dissipation capacity of the motor reach the heat balance within the allowable temperature rise range.SRM has the characteristics of small current and large torque when running at low speed.It can work at low speed and large load for a long time.When the motor speed is low and with rated load,the copper loss of the motor is close to the rated working condition,but the cooling capacity of the self fan will decrease due to the low speed.When running at low speed for a long time,the temperature rise of the motor will be too large due to the variation of the heat dissipation conditions,which will shorten the service life and even damage the motor.Therefore,it has a clear practical significance to analyze the loss and temperature rise of SRM.In this paper,a 7.5k W,12/8 pole self fan cooled switched reluctance motor is taken as an example.Based on the phase current waveform data verified by experiments,the loss of the motor when it runs on the maximum load capacity curve is calculated accurately.The cooling capacity of the motor in the self fan cooling cooling mode of each speed is calculated by the coupling simulation method of fluid field and temperature field.By comparing the loss and heat dissipation capacity of the motor at each speed,the speed range of the motor temperature rise which may be too large due to the lack of heat dissipation capacity is obtained,and the allowable output torque within the speed range under the temperature rise constraint is calculated.The specific research contents are as follows:According to the electromagnetic design of SRM,the electromagnetic finite element simulation model of SRM is built,and the static parameters such as flux characteristics,torque angle characteristics are calculated accurately.The time-step finite element analysis of SRM is carried out,and the analysis results are compared with the measured current waveform.According to the experimental platform of SRM drive system,the Simulink simulation model of SRM drive system is built.The control algorithm adopted is consistent with the control algorithm of the experimental platform.The current waveform of SRM phase winding calculated by the simulation model is highly consistent with the experimental measurement waveform.By using the simulation model,the motor phase current wave under different speed and load conditions can be calculated quickly and accurately Shape.The Simulink simulation model of SRM drive system verified by experiment is used to calculate the maximum load capacity curve of the motor and the phase current waveform when the motor is running on the maximum load capacity curve.Based on the phase current waveform,the formula method is used to accurately calculate the copper loss of the motor,and the time stepping finite element method is used to accurately calculate the iron loss of the motor.The variation of copper loss and iron loss with rotating speed is analyzed when running on the curve of maximum load capacity,and the conclusion that the total loss increases with decreasing rotating speed is obtained.Under the condition of low speed and constant speed,the change rule of the ratio of iron loss with the load is analyzed,and the conclusion that the ratio of iron loss increases with the load decreasing is obtained.According to the geometric parameters of the motor,the three-dimensional fluid field and temperature field coupling simulation model of the motor body and surrounding air area is established.The fluid field distribution around the motor and the temperature rise distribution of the motor body and surrounding air are calculated.The results show that the distribution of the fluid field and temperature field around the self cooling heat dissipation on-off reluctance motor is very uneven,and the fluid field and temperature field are adopted The coupling simulation method is more reasonable to analyze the temperature rise distribution of the motor.The maximum temperature rise point in the motor usually appears on the winding on the leeward side.Taking the allowable temperature rise stipulated by the national standard as the constraint condition,the coupling simulation method of fluid field and temperature field is used to calculate the heat dissipation capacity of the motor at each speed.The results show that the heat dissipation capacity of SRM decreases with the decrease of speed.When the motor speed is lower than 418r/min,the heat dissipation capacity of SRM will be less than the total loss of motor,and the allowable output torque of SRM will be limited by the heat dissipation capacity of motor.In this paper,when the speed of motor is lower than 418r/min,the total loss at each speed is exactly equal to the corresponding motor load torque when the motor has heat dissipation capacity,which is the allowable output torque of the motor at low speed.When the motor speed is higher than 418r/min,the heat dissipation capacity of the motor is enough,and the allowable output torque of the motor depends on the maximum load capacity of the motor.