Study On Stator Loss And Temperature Rise Of High-Speed PM Machine

The high speed permanent magnet (PM) machine has been widely investigated since it has high speed, small size, high power density and high efficiency. The application areas for this machine include high-speed grinding machine, high-speed energy storage flywheel, and sewage treatment and so on. However, due to the high loss and small size, the heat dissipation difficulty becomes a serious problem. To ensure safe and reliable operation of high speed PM machine, it is necessary to study the methods to reduce the losses and improve the ventilation effect. This thesis is focused on the key problem in machine design. The problems of loss, temperature rise and ventilation are researched based on the analysis of electromagnetic field, equivalent heat circuit, fluid field and temperature field. The main contents are listed as follows:(1) The core loss increases along with the alternate frequency of the magnetic field. Therefore, the accurate calculation of core loss is more important to the high speed machines. In this thesis, the coefficients of hysteretic loss and eddy-current losses in core losses calculation model are determined by the loss experiments of oriented electrical sheet in different rolling direction for different frequency. Based on the finite element analysis of magnetic field in the stator core, considering the influence of alternating and rotating magnetic field, the core losses of a 60000r/min high speed PM machine are analyzed and compared with the tested result. The comparative study shows that the calculated core losses considering the influence of rotating magnetic field as well as the harmonic magnetic field are closer to the experimental results.(2) The additional winding losses produced by the high-frequency skin effect in high speed machine are investigated. The winding additional loss is calculated. The related factors affecting the additional winding losses are analyzed based on the theory of electromagnetic field. Through field-circuit coupled finite element analysis, the relationship between high-frequency loss and rotor speed is established and the additional winding losses are separated from the total losses. The comparison of the calculated value with the experimental result shows the validity and feasibility of the proposed copper loss calculation method for the high speed PM machine.(3) According to the characteristics of axial ventilation system, the calculation model of high speed PM machine is established on the basis of the fluid field analysis. The fluid velocity of cooling gas in the axial ventilation duct is computed. The temperature field is calculated by using the combination method of equivalent heat circuit and fluid field solution with fluid-solid field coupled analysis method respectively. The comparison of the calculated value with the experimental result shows that the combination method of equivalent heat circuit with fluid field analysis is not accurate enough, but it is simple and easily computed. Compared with the conventional equivalent heat circuit method, the combination method is more accurate. The calculated temperature rise by the fluid-solid coupled method is closer to the experimental result.(4) The ventilation system of 12-slot high speed PM machine is investigated. The three-dimensional fluid field models with oil cooling and mixture cooling of air and water are established. The temperature field of high speed PM machine with different cooling medium is calculated by using the fluid-solid coupling analysis.