Research On Key Issues Of Permanent Magnet Synchronous Motor With Hairpin Winding For Electric Vehicle Driven By SiC Inverter

Traction machines for electric vehicles are developing towards high efficiency and high power density.SiC power devices have the characteristics of higher voltage,higher temperature,higher switching frequency and lower loss,which bring new opportunities for improving the efficiency and power density of electric drive systems.However,under the high frequency and high dv/dt excitation of SiC inverter,the insulation reliability of hairpin winding motor becomes more prominent.Therefore,in order to fully explore the performance improvement potential of the hairpin winding motor driven by SiC inverter and avoid the negative effects such as insulation damage,the AC loss,heat distribution in slot and insulation voltage stress of hairpin will be studied in this paper.The main work are as follows:In order to analyze the influence of excitation characteristics of SiC inverter on hairpin winding,this paper will first establish the fast analytical calculation model of current harmonic,and overvoltage simulation model considering dynamic characteristics of SiC MOSFET and cable distribution parameters.The effects of rising time of SiC MOSFET,cable length,switching frequency and inductance of motor on current harmonics and overvoltage of winding end will be analyzed.The results show that the amplitude of pulse overvoltage is related to the rise time and cable length,while the oscillation frequency of pulse voltage is independent of the rise time and negatively related to cable length.With the increase of switching frequency,the current harmonic content decreases,but the higher switching frequency may cause the occurrence of double pulse phenomenon,resulting in higher amplitude pulse overvoltage.Aiming at the problem of high frequency AC loss of hairpin windings,this paper will discusse the AC loss generation mechanism,calculation model and suppression method.Firstly,a hybrid calculation method of hairpin winding loss based on analytical and static magnetic finite element method will be proposed to solve the problem that the influence of magnetic field of interior permanent magnet rotor on AC loss of winding cannot be considered in existing analytical methods.In order to solve the serious problem of highest conductor loss near the slot opening,a hybrid transposed hairpin winding(HTHW)scheme,which combines hairpin and litz wire,is proposed.The simulation results show that the HTHW has good AC loss suppression effect when the frequency is greater than 200 Hz.The measurement platform of winding loss influenced by the rotor magnetic field is built,and the loss of traditional hairpin winding and HTHW are measured.The effectiveness of the proposed scheme in reducing high frequency AC loss is verified.Aiming at the possible difficulties in the processing and manufacturing process of HTHW winding,a HTHW winding structure based on 3D printing technology is proposed,which could solve the problems of stress rebound,insulation paint removal and welding of the litz wire winding.In view of the thermal challenge of hairpin winding motor under the high frequency excitation,the uneven temperature distribution in the slot and the local hot spot in the slot are studied.The thermal network model of hairpin winding motor will be established firstly,and the uneven loss distribution of each conductor layer and stator core on both sides is fully considered.The accuracy and validity of the proposed method are verified by experiments.From the perspective of loss suppression and cooling heat dissipation,a direct water cooling scheme for hairpin winding motor moving partial waterway of jacket into slot is proposed.The temperature rise suppression effects of different cooling schemes are compared and analyzed,and the influence of switching frequency,winding position and cooling parameters on local maximum temperature under high frequency excitation is analyzed.Based on the above research,the design concept and material selection principle of the modular inslot cooling waterway are given,which provides beneficial reference for further research and prototype manufacture.In order to accurately evaluate the interturn voltage stress of hairpin winding under the high dv/dt voltage pluse of SiC inverter,a high frequency equivalent circuit model for interlayer transposition hairpin windings is proposed.Then,the interturn voltage stress of hairpin winding is calculated based on this model.Aiming at the problem of high voltage stress between two turns of hairpin winding caused by traditional interlayer transposition,a new interlayer transposition scheme is proposed,and the general design principle of low voltage stress for different layers of hairpin winding will be presented.Finally,based on the heat distribution in the slot and the voltage stress distribution between turns of the hairpin winding driven by SiC inverter,the calculation model and analysis method of partial discharge of interturn insulation under electric and thermal coupling stress of hairpin winding are given.In this paper,the hairpin winding motor driven by SiC inverter is taken as the research object,aiming at the key problems such as the AC loss,temperature rise in the slot and the uneven distribution of interturn voltage stress under high frequency and high dv/dt excitation.The mechanism,calculation model,influencing factors and inhibition methods are comperhensively analyzed.It provides effective reference for the design and analysis of the next generation electric drive system based on hairpin motor driven by SiC inverter.