Design And Thermal Study Of Internal Water Cooling Permanent Magnet Synchronous Motor

Permanent magnet synchronous motor(PMSM)has become mainstream choices in many fields due to its high efficiency,high power density,and low noise,especially in drive systems.With the gradual improvement of the performance index of the drive system,the power density requirement of the permanent magnet synchronous motor is also increasing.On the one hand,the improvement of the power density of PMSM can be realized through electromagnetic design.At the present stage,a great deal of research on the electromagnetic design of high power density PMSM are conducted and fruitful results have been achieved.On the other hand,improving the power density of PMSM needs to start from the perspective of motor cooling.In other word,it can be implement by enhancing the cooling capacity of the motor.However,with the gradual increase of the power density of PMSM,the existing heat dissipation schemes are increasingly difficult to meet the heat dissipation requirements of high power density PMSM.First,with reference to the general method of electromagnetic design of PMSM,under the premise of reserving a certain space for the cooling water channel in the stator slot,the electromagnetic design and loss analysis of an external rotor PMSM is performed.Results of the electromagnetic field simulation show that the motor designed can meet the design requirements of the motor.The loss analysis calculation shows that the power loss generated by the inverter in actual drive system is obviously higher than that with sine power supply.The loss result lays the foundation for the subsequent thermal calculations.Secondly,this paper studies the design of the water cooling tube in slot and the eddy current loss of the tube wall.Areasonable connection scheme has been studied and selected.Based on this,the eddy current loss of the copper pipe wall is studied to determine the location of the copper tube put in slot.Results show that the asymmetrical parallel waterway connection scheme proposed in this paper can eliminate the circulation between copper tubes,and the copper tube placed at the bottom of the slot can minimize the eddy current loss in the copper tube,as a result,the water cooling system has little effect on the electromagnetic performance of the motor.The feasibility of applying IWC scheme on PMSM is guaranted.Then,combined with the finite volume method(FVM)and the lumped parameter thermal network(LPTN),thermal circuit calculation model of the prototype is built and the model validation and temperature rise analysis were performed.First,the air-gap fluid field of the prototype and the water fluid field in the copper tube are simulated and analyzed by using the computational fluid dynamics(CFD)software Fluent.The equation of convective heat transfer coefficient are amended in order to be suitable for the prototype.Then,based on the basic theories of heat transfer,the LPTN of the prototype was established.Thermal steady state and thermal transient state are analyzed by using the LPTN that is able to indicate the radial,axial and circumferential temperature distributions.Results are compared with the result of water jacket cooling.The results show that the stator-side losses are almost entirely dissipated from the cooling channel during thermal steady state.IWC system not only guarantees long-term operation under the rated operating conditions of the motor,but also meet the heat dissipation requirements of the motor for longer overload operation.Compared with water jacket cooling,IWC scheme not only has better cooling effect on the windings,but also has a much lower demand for water pressure and is easier to be implemented,which proves that IWC scheme has irreplaceable advantages.Finally,based on verifying the accuracy of the LPTN constructed in this paper,by using LPTN,the design of the waterway size is quickly optimized and the effect of the addition of heat-dissipating fins on the temperature rise of the end-winding is studied.The results show that the diameter of copper tube has an optimal value.The temperature rise of the end winding can be minimized,which is beneficial to balance the heat dissipation and the electromagnetic performance of the motor.The addition of heat-dissipating fins at the end of the water channel can further reduce the temperature rise of end winding and has a significant heat dissipation effect on the rotor side,making the heat dissipation capability of the IWC system fully utilized.Thermal transient analysis shows that the addition of heat-dissipating fins can further extend the time of continuous overload operation.Both the two optimizations designs are based on the rapid calculation of LPTN,showing that the LPTN established in this paper has great application value to the thermal analysis of IWC-PMSM.At the same time,the two optimizations designs provide guidance for the design of IWC system and are of great significance to further increase the power density of PMSM.