Zhang Yuejin

Design and study of a novel linear motor for Stirling Cryocooler

Based on the analysis of the two existing typical linear motors for Stirling Cryocoolers, a novel structure linear motor is developed, which adopts assembled stator core and has the characteristics of high air gap flux density, small volume, light weight and simple installation. Firstly, the size estimation formula is established in this paper, and then the motor parameters are optimized with the finite element method(FEM) considering the effect of changing its structure size. Analytical results show that the novel structure can significantly reduce the volume, which is specially important for the spaceflight application. The experiment verifies the feasibility and calculation accuracy of the design.

Semi-analytical method for air-gap main magnetic field computation of direct drive permanent magnet torque motors

This paper presents a semi-analytical method to computer the air gap magnetic field of direct drive permanent magnet (PM) torque motors for being evaluated slotting effects accurately. The field region is divided into the smooth air gap region and the extended slot sub-regions. The magnetic vector potentials in the air gap region are first solved by the analytical method, and those in the extended slot sub-regions solved secondly by the numerical method. Boundary values in the extended parts of slot sub-regions are obtained by the analytical solutions while permanent magnets are dealt with the equivalent surface current sheets. After combined the results of each slot sub-region the flux density distributions in air gap with slot opening are obtained. The magnetic field distribution and back-EMF computed with the proposed method are verified with those obtained from finite element method (FEM) and measurement.

Design of double-stator slotless permanent magnet machine for wind generator

A double-stator slotless permanent magnet (PM) machine for wind generator has been designed in this paper. This machine inherits the merits of double-stator PM machine, high torque density and high utilization rate of the space and material. At the same time, Because of having no cogs and slots the cogging torque has been eliminated and the starting drag torque has been reduced dramatically. The performance of this machine is analyzed by using finite element method (FEM). The experimental results verify the validity of the proposed machine.

A Practical Sensorless Permanent Magnet Brushless DC Motor Drive with New Start-up Scheme for Automotive Engine Cooling Applications

Abstract A practical sensorless permanent magnet brushless DC motor drive for automotive engine cooling application is presented in this article. A new method is proposed to identify the rotor position after running from standstill by the current response to back electromotive force variation. Compared to conventional methods, the positioning accuracy and acceleration performance are effectively improved. In addition, a practical detection method based on bipolar modulation is employed to improve the detection accuracy of zero crossing of back electromotive force and protect it from the interference of pulse-width modulation. The proposed method is verified by simulation and experiment results.

Analytical calculation of electromagnetic torque for surface mounted permanent magnet brushless motors

With the air gap magnetic field distribution of surface mounted permanent magnet (PM) motors obtained using an analytical technique, the instantaneous electromagnetic torque and its corresponding components are investigated with the Maxwell stress tensor method. Accurate results can easily be achieved using the proposed method without using the tedious finite element analysis (FEA). In this paper, the electromagnetic torque of a surface mounted PM motor with two phases energized is decomposed into four torque components. This technique is useful not only for the design and optimization of the permanent magnet motor, but also for the choice of control strategy.