Design And Analysis Of Less-Rare-Earth Spoke-type Hybrid Permanent Magnet Motor

Permanent magnet synchronous motors(PMSMs) that employ rare-earth permanent magnets(PMs) have distinct advantages such as compact structure, light weight, high power density, and high efficiency. However, as a kind of strategic resource, recently, the price of the rare-earth PM material is increasing with the continuous exploitation of rare-earth resources and the implementation of related protection policies. This will pose potential risks for further wide application of rare-earth PMSMs in the fields of industries and national defense.To reduce the usage of rare-earth material, the study on non-rare-earth or less-rare-earth PM motors has attracted more and more attention in motor research field. Because of the low cost and stable resource of the non-rare-earth material, such as the ferrite PMs, they have earned much research attention from relevant researchers. However, due to the magnetic energy product of ferrite PMs is merely one fourth of that of rare-earth PMs, it is of great challenge for non-rare-earth or less-rare-earth PM motors to realize the similar torque density with rare-earth PM motors. Moreover, the coercive force of the ferrite PMs is rather lower than that of rare-earth PMs, the anti-demagnetization ability is also a great concern of the non-rare-earth PM motors.Firstly, the current development of the non-rare-earth motor and less-rare-earth motor as well as their topology classification is introduced in this paper. Then, the Hybrid Permanent Magnet Motor(HPMM) is proposed to solve some existing problems of the Ferrite Permanent Magnet Motor(FPMM) such as relatively low power density, narrow speed range and poor anti-demagnetization ability. The NdFeB PMs and the ferrite PMs are both applied as the magnetic source in the HPMM. Thus, on the one hand, the power density of HPMM is assured; on the other hand, due to the coercive force of the NdFeB PMs is much higher than the ferrite PMs, the HPMM has better anti-demagnetization ability than the FPMM, making up the defect of FPMM.Secondly, due to there exist two kinds of PMs with great difference in magnetic performance in the HPMM, the working points of the NdFeB PMs and the ferrite PMs will affect on each other, which will in turn has influence on the performance of the motor. In this paper, the motor design section focuses on the design method of the two types of PMs. At first, through the analysis of the magnetic circuit model, the proper size combination of the two kinds of PMs is deduced. Then, the real working points, the output torque ability, the speed range and the magnets cost are considered in PM size design to assure the power density and the speed range as well as to reduce the PM cost.Then, the performance of the HPMM is compared with that of the rare-earth PM motor(RPMM). The analysis results show that on the basis of reducing the PM cost, the torque density of the HPMM is similar with that of the RPMM and the speed range of the HPMM is wider than that of the RPMM. Besides, the performance of the HPMM is also compared with that of the FPMM. The comparison results show that the HPMM has wider speed range and higher efficiency in the high speed region. Furthermore, the anti-demagnetization ability of HPMM is superior to that of the FPMM.Finally, the prototype motors of the HPMM and FPMM are manufactured and the test plate is built to do preliminary experimental analysis. The experimental results have verified the rationality and feasibility of the proposed motor.