Research On Combined-pole Straight-shape Interior Permanent-magnet Synchronous Machine

Owing to the advantages of high power density and excellent field-weakening performance, interior permanent-magnet synchronous machines(IPMSM) are widely applied in electric drive system of electric vehicles(EVs). This paper proposes a Combined-pole Straight-shape Interior Permanent-Magnet Synchronous Machine(CPS-IPMSM). By adopting the combination of rare earth permanent magnet material with ferrite permanent magnet material, the air-gap flux density is improved, the harmonic of the air-gap flux density is reduced and the efficiency is improved. Ferrite permanent magnet material with high demagnetization withstand capability is set in the irritable demagnetization region, which improves the demagnetization withstand capability of IPMSM and reduces the amount of rare earth permanent magnet materials, further reduces the cost of the machines. CPS-IPMSM gains the advantages of high efficiency, high demagnetization withstand capability and low cost. Several aspects of CPS-IPMSM are studied in this paper, including the analysis of operation principle, scheme design, optimization of structure and parameters, the analysis of temperature distribution, and the analysis of the demagnetization.First of all, a scheme of CPS-IPMSM is designed and achieved by focusing on motor design principle and combing with the operation principle of combined pole. An equivalent model of the combined pole is established to analyze the air-gap flux density. The finite-element simulation model of CPS-IPMSM is established according to the design scheme. The inductance of CPS-IPMSM is calculated considering the influence of cross coupling. And the influence rule of cross coupling inductance distribution is investigated.Secondly, CPS-IPMSM is optimized from magnetic bridge size and magnetic pole size respectively. The influence of the motor structural parameters on the electromagnetic properties is determined. Among them, the sinusoidal air-gap flux density distribution is set as the optimization goal, and the optimal ratio of the width of Nd Fe B magnet to the width of combined pole is obtained to provide a theoretical basis for design of CPS-IPMSM. Finally, an optimization scheme which meets the electromagnetic and mechanical properties is achieved. Compared with the conventional-pole machine, CPS-IPMSM has several advantages such as sinusoidal air-gap magnetic flux density distribution, no-load sinusoidal back EMF, torque ripple, cost of Nd Fe B and so on.Thirdly, combined with the loss of each part in the motor and the thermal conductivity calculated with the equivalent method, the CPS-IPMSM thermal field model is established by using the commercial software ANSYS in this paper. The steady thermal field distribution under different conditions is analyzed. The transient thermal field is analyzed to verify the rationality of the motor cooling scheme. Meanwhile, the simulation results are compared with the ones o f the conventional straight-shape poles.Finally, the mechanism of demagnetization of permanent material is introduced. Combined with thermal field results of the permanent magnet, the demagnetization withstand capability of combined pole under the normal operating station is checked. According to the results, the permanent magnets have the demagnetization problem under the station of high temperature or large demagnetization current. As a result, this paper applies varying amounts of current oriented in D-Q axis to check the demagnetization in a static finite-element simulation and compare the demagnetization withstand capability of two machines.In conclusion, this paper proposes a combined-pole IPMSM, which is an ideal choice of low-cost high-performance machine.