Research On Vernier Permanent Magnet Machine With Dual-Rotor Toroidal-Winding System

Vernier motors based on the principle of magnetic field modulation have higher torque density than those of conventional permanent magnet synchronous motors and have the capability to generate high torque at low speeds,making this type of motors enjoy broad application prospects in the fields of electric vehicles and new energy power generation.In this paper,the dual PM Vernier machine is resached and the single-rotor and double-rotor structures are studied in depth in terms of topology structure,working mechanism,magnetic field analysis,performance calculation,etc.The research contents are summarized as follows:First,the analytical expressions of air gap flux density with respect to rotor-PM Vernier motor,stator-PM Vernier motor and dual PM Vernier motor are derived based on the principle of magnetic field modulation and the relationships among pole-pair number,rotation speed and rotating direction of air-gap harmonics are analyzed.It is found that when the dual PM Vernier machine is used,increasing the amplitude of rotating magnetic field with pole pair number equal to |Pr±Qs| permits significant increments of winding electromotive force and electromagnetic torque.The calculation formula of the fundamental wave electromotive force is derived,and the fundamental wave electromotive force generated by the main rotating harmonics in the air gap magnetic field is calculated.The influence of rotor-slot number on the amplitude of the fundamental wave of electromotive force is studied.Furthermore,the electromotive force of rotor permanent magnet Vernier motor and stator permanent magnet Vernier motor with different permanent magnet pole pair Pr are compared with each other.The influence of rotor-slot number on the harmonic content of the electromotive force is studied.It was found that when Pr is a multiple of 4,the even harmonics in the electromotive force have a large waveform harmonic distortion rate and suffer poor sine quality.Second,a dual-rotor toroidal-winding Vernier machine(DTVM)is proposed.The low-cost ferrite is utilized in the DTVM.The performance deficiency of ferrite can be neutralized through double-rotor and dual-PM structures.The operation principle of DTVM is analyzed,and the electromotive force generated by the main harmonics of the internal and external air gaps in the windings is calculated.The reason why the electromotive forces generated by the harmonics of the internal and external air gap magnetic fields in the double rotor structure can be superimposed on each other is explained.The motor electromotive forces,torques,losses,power factors and efficiencies corresponding to different permanent magnet arrangements and different winding structures are compared.The quadrature axis inductance and torque-speed curves with respect to different rotor winding structures are calculated.The effect of changing Pr on DTVM performance is analyzed.The DTVMs containing ferrites and NdFeB permanent magnets are compared in terms of motor performances.The comparison results show that both the permanent-magnet loss and the permanent-magnet cost per unit torque become decreased when the ferrite is used.The performances of motors with different sizes are calculated.The mathematical model of the motor is studied and simulated.Finally,a single-rotor Vernier motor prototype and a dual-rotor toroidal-winding Vernier motor prototype are designed and manufactured respectively.The prototypes are tested to verify the correctness of the above theoretical analyses.