Analysis Of Cooling Performance Of Low Speed High Torque Permanent Magnet Motor

With the increasing requirement of high efficiency and energy saving,permanent magnet motor has been widely used in various fields due to its high efficiency.Therefore,it is imperative to research and develop permanent magnet motor with higher efficiency and better performance in the field of motor design.The permanent magnet motor is characterized by small size,light weight,simple structure and high power density.However,a large amount of heat will be generated in the working process.Therefore,the cooling performance analysis has become one of the main research issue of the permanent magnet motor.In this paper,the three-dimensional steady flow field and temperature field of water-cooled permanent magnet motor with low speed and large torque are analyzed and studied,which provides valuable reference for the development of more efficient permanent magnet motor.The main research contents of this paper are as follows:Firstly,the common cooling methods of permanent magnet motors are analyzed,and the differences between axial and circumferential cooling structures are compared and analyzed.The cooling structure of low speed and high torque permanent magnet motor is designed.The pump loss caused by fluid flowing in the cooling water channel is calculated by theoretical formula.Based on the theoretical knowledge of heat transfer,the heat transfer mode and heat dissipation mode of the permanent magnet motor are analyzed,and the calculation formula of heat exchange coefficient between fluid and solid is deduced based on the theoretical knowledge of fluid mechanics.Secondly,the heating power of the low-speed and high-torque permanent magnet motor is analyzed.By analyzing the structure and working principle of the permanent magnet motor,the heating source of the permanent magnet motor is understood.The main heat source of the permanent magnet motor is the copper consumption,and the skin effect of the copper wire should be considered in the calculation of the copper consumption.The other main heat source of the permanent magnet motor is iron loss,which is divided into stator tooth loss and stator yoke loss.After analyzing the calculation method of iron consumption,it is found that it is difficult to accurately calculate the iron consumption,so the method of no-load test is adopted to calculate the iron consumption.According to the rated parameters of the low-speed and high-torque permanent magnet motor,the losses of the permanent magnet motor are obtained by combining the calculation formula.Then,according to the dimension parameters of the low-speed high-torque permanent magnet motor,the three-dimensional domain model of the motor is established to simulate the fluid field and temperature field.The Flow Simulation software was used to simulate the cooling medium in the motor,and the temperature field of the parts in the motor was analyzed.At the same time,the influence of different water flow rates on the temperature rise of internal windings of the motor and the influence of changing the initial cooling medium temperature on the temperature change of internal windings of the motor are analyzed.Finally,according to the test method of national standard,the temperature rise test of the permanent magnet motor with low speed and high torque is carried out to analyze and study the cooling performance of the permanent magnet motor.Two sets of schemes were developed for the temperature rise test.The test data were analyzed,the winding temperature rise was calculated by using the resistance method to measure the temperature rise,and the influence of water flow on the motor temperature rise and motor efficiency was studied.By comparing the simulation results and experimental data of the permanent magnet motor with low speed and large torque,the distribution of the temperature field in the permanent magnet motor is analyzed.It is found that the error between the simulation results and the experimental data is very small.The simulation results have certain guiding significance for the cooling performance analysis of the permanent magnet motor with low speed and large torque.