Thermal Analysis And Cooling Structure Optimization Of High Speed And High Power Motors Supported By Active Magnetic Bearings

The high-speed and high-power motor realizes direct drive because it eliminates the intermediate speed-increasing link such as complex gear transmission box.And it has obvious technical advantages such as compact structure,high power density,high transmission efficiency and small vibration noise.The motor 1s widely used in centrifugal blowers and compressors,new energy vehicles,aerospace and other fields.As one of the main supporting methods of high-speed and high-power motors,magnetic suspension bearings use electromagnetic force to overcome the weight of the rotor and make the rotor in floating state.It has the advantages of frictionless wear,long service life and high reliability.It can work in special environments,for instance,no air and no oil.However,the high speed and high power motors supported by active magnetic bearings has the problems of high power density,small volume,limited heat dissipation space,and effective dissipation heat.The higher the power,the higher rotational speed,the problem is particularly prominent,which seriously affects the reliability of the motor operation,and needs to be solved.The main work of the paper is as follows.(1)The flow-solid-thermal coupled temperature field calculation model of high speed and high power motors supported by active magnetic bearings established.The CFD and finite element model solving method based on unidirectional flow-solid-thermal coupling 1s proposed to realize the quantitative simulation of the steady temperature field of the motor.The research shows that under rated conditions,the temperature difference of the stators of high speed and high power motors supported by active magnetic bearings 1s small from left to right along the axial direction,and the temperature difference of the rotor components is large.From the inside to the outside,the stator winding temperature 1s basically no change,the temperature of the stator core gradually decreases,the temperature of the permanent magnet gradually increases and the temperature difference is large.(2)Based on the proposed model and algorithm,the influence of cooling structure and cooling parameters on the steady-state temperature field distribution of magnetic suspension high-speed high-power asynchronous motor under different working conditions is revealed.The results show that the maximum temperature of the motor at full load is nearly 30 ? higher than that at no-load;the reduction and expansion of the forced air-cooled air outlet area is beneficial to heat dissipation;increasing the forced air-cooled inlet speed within a certain range will be beneficial to the heat dissipation of the motor and lower the temperature rise of the motor.(3)An air gap three-dimensional incompressible steady-state turbulence model with carbon fiber sheath roundness error is established.The research reveals the influence law of surface air-friction loss of the magnetic suspension high-speed and high-power permanent magnet synchronous motor rotor caused by the permanent magnet sheath roundness error,cooling system parameters,rotating speed and boundary temperature.The results show that the roundness error amplitude,the rotational speed and the air outlet area have a great influence on the rotor surface air-friction loss,while the roundness error type,forced air cooling inlet speed and boundary temperature have little effect on the rotor surface air-friction loss.(4)A high speed and high power motors supported by active magnetic bearings test bench was built to test the temperature of the stator winding,rotor,bearing end cover and case at rated speed from no-load operation to thermal equilibrium.The theoretical and experimental comparisons were carried out to verify the effectiveness of the established model and the proposed algorithm and the correctness of the theoretical research results.The research shows that the relative error of the temperature of the stator winding of the motor and the rotor of the motor are both within 5%.So the degree of coincidence is good.The research work in this paper provides an engineering reference for temperature field analysis,cooling system design and heat dissipation efficiency optimization of high speed and high power motors.