Design And Research Of Synchronous Motors Based On Spliced Type Permanent Magnet Rotors

The air gap magnetic fields of permanent magnet synchronous motors are created by permanent magnets,hence permanent magnet synchronous motors have the advantages of high efficiency and high power density.The permanent magnets of interior permanent magnet synchronous motors are embedded in rotors,therefore the magnetic circuits of the rotors have no symmetry,the consequent reluctance torques are beneficial to improving the overload capacities and power densities of the motors.The two most commonly used measures for constraining the leakage fluxes in interior permanent magnet synchronous motors are adopting bridges and adopting block cores.In rotors with bridges,the bridges are generally very thin,hence the mechanical strengths of the bridges are relatively low,and the flux leakage coefficients of the rotors with bridges are still relatively high.In order to constrain the leakage fluxes in interior permanent magnet synchronous motors and improve the mechanical strengths of the rotors,block cores are adopted in the rotors of some interior permanent magnet synchronous motors.Currently retaining sleeve type rotors and wedge type rotors are the most common block core rotors,these two kinds of rotors can effectively constrain the leakage fluxes,but the equivalent air gap thicknesses corresponding to the retaining sleeve type rotors are relatively large,hence the corresponding magnet consumptions are relatively high,and the mechanical reliabilities of the wedge type rotors are relatively low,hence the wedge type rotors can only be used in low speed applications.Another disadvantage of conventional interior permanent magnet synchronous motors is that their air gap flux density waveforms are generally rectangular waveforms,these air gap flux density waveforms contain a lot of harmonic contents,therefore near-sinusoidal back electromotive force waveforms are not easy to achieve,this can easily lead to high output torque ripples.This dissertation analyzes the characteristics of conventional interior permanent magnet synchronous motors,on this basis,novel permanent magnet rotors with excellent characteristics are proposed to improve the performances of interior permanent magnet synchronous motors.This work relates specifically to two spliced type permanent magnet rotor structures,one of them is the tangential permanent magnet rotor structure,and another is the radial permanent magnet rotor structure,both of them adopt block cores made up of laminated silicon steel sheets.There are several flux barriers(air slots)in the block cores of each rotor structure,the air gap magnetic field can be optimized by designing the flux barriers properly.The high strength nonmagnetic components and the block cores are spliced together by using dove tail slots,they can constitute a solid whole and resist the centrifugal force due to rotation well,and the spliced type permanent magnet rotors are named from this.The two kinds of spliced type permanent magnet rotors do not require bridges,hence the flux leakage coefficients of them are much lower than those of conventional interior permanent magnet rotors.The main parameters of two 3kW synchronous motors were designed on the basis of the two proposed spliced type permanent magnet rotor structures.The initial parameters of the flux barriers of the two motors were designed by using equivalent magnetic circuit models.The flux barrier parameters of the two motors were optimized by using the Taguchi method.Then a comparative analysis of the conventional structure,the initial structure and the optimal structure was performed for each motor,the comparative analyses relate to air gap flux density waveforms,back electromotive force waveforms,flux leakage coefficients under no load condition,output torque waveforms and mechanical stresses.The comparative analysis results reveal that the optimal structure of each motor has outperformed the corresponding conventional structure and initial structure in terms of air gap flux density waveforms,back electromotive force waveforms,flux leakage coefficients under no load condition and output torque waveforms,and the key components of the respective initial structure and optimal structure of the two spliced type permanent magnet rotors can fulfill the strength requirements,the maximum stresses in all these components are lower than that in the key component of the corresponding conventional structure.Finally,the temperature fields of the two optimized motors were analyzed,the respective steady state temperature distributions and maximum temperatures of the main components of the two motors under different air velocity conditions were obtained,and the results of the analyses provided the basis for choosing the motor cooling systems.