Optimization And Design On Vernier Pseudo-Direct-Drive Permanent-Magnet Machine

With the rise of new developing industries such as renewable sources power generation,electric vehicles,high-speed rail transportation and electrical propulsion ships,there is a growing demand for low-speed and high-torque machines in modem industry.The traditional solution is the combination of a motor and a mechanical gearbox which can match the speed and torque between the motor and the loads.However,the mechanical gears are driven by mechanical contact to achieve energy transmission.Mechanical gears,which are present in the transmission system,inevitably introduce many problems such as friction,mechanical vibration and noise,while requiring lubrication,regular maintenance and lack of overload protection.In order to solve these problems caused by mechanical gears,the research of low-speed and high-torque motors that can directly drive the load has both engineering and practical significance.This dissertation studies a motor that can achieve low speed and high torque,namely the Vernier pseudo-direct-drive permanent-magnet machine.The Vernier pseudo-direct-drive permanent-magnet motor has a high-torque output capability based on the principle of magnetic field modulation,and does not require mechanical gearboxs to drive the load.In this thesis,the Vernier pseudo-direct-drive permanent-magnet machine is taken as the research object,aiming at improving its output torque capability and enhancing the mechanical strength of its output components.Different motor topologies are proposed,using finite element simulations.The electromagnetic performance and the mechanical performance of the motor are both taken into account.The main work and contributions of this thesis are summarized as following:1.The principle of magnetic field modulation is introduced,and the development process and working principle of the Vernier pseudo-direct-drive permanent-magnet motor are introduced in detail.The calculation process of the working point of this kind of motor is also introduced.2.The effects of different magnetization of permanent magnets on the radial magnetic flux distribution of the air gap of the Vernier pseudo-direct-drive permanent-magnet motor are studied.The influence of different permanent-magnets arrangements on the electromagnetic performance of the motor is considered.Different topologies of the Vernier pseudo-direct-drive permanent-magnet motor are proposed.The output torque capability and the limit current density are compared.The Vernier pseudo-direct-drive permanent-magnet machine with Halbach rotor can reach the output torque density of 137.4 Nm/L,increased by 52.4%compared to the initial design.Meanwhile,the RMS current density is 2.6 A/mm2,a simple 2D thermal modeling shows that the temperature rise of the motor is 57? and the demagnetization on the permanent magnets is negligible.3.According to the previous design,the Vernier pseudo-direct-drive permanent-magnet machine is further improved with a stainless steel sleeve to enhance the mechanical strength of the output rotor.Using the finite element analysis,the position and the thickness of the stainless steel sleeve are studied.The stainless steel is added on the inner side of the low-speed rotor.The thickness affects the output torque of the Vernier pseudo-direct drive permanent-magnet motor.With a thickness of the sleeve from 0 to 6.0 mm,the motor output torque is greater than that of the initial design.When the output torque is the maximal,the mechanical state of the stainless steel sleeve is studied,including mechanical stress and mechanical strain.According to the results of electromagnetic finite element analysis and mechanical finite element analysis,we choose a 2 mm stainless steel sleeve.4.According to the finite element analysis results,the final design is a Vernier pseudo-direct-drive permanent-magnet machine with a Halbach permanent-magnet rotor,which has a 2 mm stainless steel sleeve.When the Vernier pseudo-direct-drive machine works normally,the output torque density is 120.81 Nm/L,increased by 33.9%compared to the original design,and the output torque ripple rate is 0.83%.The RMS value of the limiting current density is 2.6 A/mm2 and the temperature rise is 57? using a simple 2D thermal model.The irreversible demagnetization of the permanent magnet is negligible.According to the Mises yield criterion,the maximal stress of sleeve is 35.72 MPa,which is lower than that of yield stress of M304 stainless steel.