Yubo Yang

The optimization of pole arc coefficient to reduce cogging torque in surface-mounted permanent magnet motors

In this paper, the optimization method of improved domain elimination algorithm (DEA), finite-element method (FEM), and analytical method are combined to optimize the pole arc coefficient of a permanent magnet (PM) to minimize the cogging torque of a permanent magnet motor. Since the cogging torque is very sensitive to the changing of the pole arc coefficient of a PM, the changing of the pole arc coefficient should be very small in optimization. The cogging torque corresponding to many relative positions between magnet and armature must be calculated by FEM to find the peak value for every pole arc coefficient, so in order to reduce the computing time, the feasible region of the pole arc coefficient should be set to as small as possible. In this paper, the analytical method is first used to reduce the feasible region of pole arc coefficient in which the cogging torque is small. Then, improved DEA and FEM are used to find the best pole arc coefficient. After optimization, the cogging torque is greatly reduced, and the computing time decreases notably

Optimization of Magnetic Pole Shifting to Reduce Cogging Torque in Solid-Rotor Permanent-Magnet Synchronous Motors

In this paper, the method of magnetic poles shifting was combined with optimization method to reduce cogging torque in solid-rotor permanent-magnet synchronous motors. Although the finite-element method (FEM) can calculate the cogging torque accurately, to find the peak value of cogging torque, the cogging torque for different relative positions between permanent magnets and slots must be calculated; thus, the optimization will take a long time. To reduce optimization time, a novel analytical method was proposed to determine the initial value and feasible range of the shifting angles. Then the optimization method and FEM were used to minimize the cogging torque. Two prototype motors were analyzed and optimized, respectively. It was proved that the cogging torque can be greatly reduced by the proposed method.

Research of cogging torque reduction by different slot width pairing permanent magnet motors

Cogging torque is one of the main concerns of permanent magnet motor. In this paper, analytical analysis is used to analyze the cogging torque when different slot width pairing method is adopted. The effect of slot width pairing on cogging torque is studied, and some conclusions are drawn. If the least integer n, which makes (nz/2)/(2p) be an integer, is an even number, the cogging torque can be greatly reduced by different slot width pairing, and the method to calculate the width of slot is deduced in this paper. On the contrary, if the least n is an odd number, different slot width pairing method is not effective in reducing cogging torque. The correctness of the above conclusions is verified by finite element analysis of cogging torque.

Study of a Novel Energy Efficient Single-Phase Induction Motor With Three Series-Connected Windings and Two Capacitors

This paper presents a novel energy efficient single-phase induction motor with three series-connected windings and two capacitors. By suitable selection of capacitors, the currents in three windings are approximately symmetrical, and thus, the motor can operate approximately symmetrically from single-phase supply. Based on the symmetrical components method, the condition for balanced operation is studied, and the method for determining capacitances is proposed. The performance analysis method is put forward to calculate the steady performances. Performance tests are performed on the proposed motor and three-phase induction motor. It is proved that their rated efficiency is approximately the same, while the power factor of the former is higher than that of the latter. In comparison with the ordinary single-phase induction motor, it has the advantages of higher efficiency and smaller volume, thus can take the place of the latter in some applications.

Study of magnet asymmetry for reduction of cogging torque in permanent magnet motors

In order to reduce cogging torque of permanent magnet(PM) motor, the lower harmonics of cogging torque should be reduced. It is found that if the slot number per pole is not an integer, new lower harmonics of cogging torque may be introduced when the method of asymmetry magnet is adopted. To reduce cogging torque, both the lower original and newly introduced harmonics of cogging torque should be reduced. In this paper, the analytical expression of cogging torque with asymmetry magnet is got. Based on the distribution of the square of residual flux density of PM, the analytical expression of its Fourier coefficient can be got. If the Fourier coefficient of the square of residual flux density of PM is reduced by asymmetry magnet, the corresponding harmonics of cogging torque can be reduced. So in order to eliminate the lower harmonics of cogging torque, we can let Fourier coefficient(which is corresponding to the lower harmonics of cogging torque) to be zero. By solving the system of equations, we can get the shifting angles of magnets. It is verified at last that the cogging torque can be greatly reduced by the shifting angles got in this paper.

Reducing cogging torque by adopting isodiametric permanent magnet

In this paper, being based on Fourier expansion and energy method, the analytical expression of cogging torque of permanent magnet(PM) motor is derived, which can be used to analyze the effects of design parameters on cogging torque. Then a new method for reducing cogging torque by adopting isodiametric magnetic pole is proposed. Finite element analysis is used to calculate the cogging torque and flux per pole for different shapes of magnetic pole. It is proved that the cogging torque could be greatly reduced by adopting isodiametric magnetic pole, while the flux per pole changes little, which verifies the effectiveness of the proposed method.

Study of Magnet Shifting for Reduction of Cogging Torque in Permanent Magnet Motors

It is found that if the slot number per pole is not an integer, new lower harmonics of cogging torque may be introduced when permanent magnet (PM) shifting is adopted. To reduce cogging torque, both the original and newly introduced lower harmonics of cogging torque should be reduced. In this paper, the effect of PM shifting on Bnz(B nz is the Fourier coefficient of the square of magnetic flux density B2 in the center of airgap without the effect of slot and tooth) is studied. The finite element method (FEM) and evolution strategies are combined to find the best shifting angles to reduce the original and new lower harmonics of cogging torque. It is verified cogging torque can be greatly reduced by the shifting angles calculated in this paper

Analytical Prediction of Electromagnetic Performance of Vernier Machine with Rotor Eccentricity

Abstract In this article, an analytical model is developed for the magnetic field calculation of the vernier machine with a normal or an eccentric rotor. The electromagnetic performance considering the armature reaction can be taken into consideration and calculated since the magnetic vector potential is adopted. In the analytical model, the whole working domain is divided into several subdomains, and the partial differential equations of the magnetic field can be built in all subdomains. The magnetic vector potential expressions can be obtained in all subdomains through applying boundary conditions to general solutions. The perturbation method is used to describe the rotor eccentricity. The effect of static or dynamic eccentricity on the flux density, flux linkage, cogging torque, electromagnetic torque, unbalanced magnetic pull, and winding inductances is calculated and validated by the finite-element method.

A novel rotor structure design of single-phase flux switching motor

A novel rotor structure is present in this paper, it make single-phase flux switching motor (FSM) have the ability of starting itself. The rotor is asymmetrical along its pole axis, so 2D finite element analysis (FEA) is incapable to analyze it directly. With the help of 2D FEA results of normal rotor FSM, an inductance modeling method is introduced in this paper also. Finally, 3D FEA is carried out, the result proves that the motor with novel rotor can start itself. The comparison of the result of 3D FEA and the result of inductance model calculation demonstrates that the inductance model is correct and available.

Suppression of sub-synchronous oscillation caused by HVDC using supplementary excitation damping controller

Two kinds of mechanism that cause Sub-synchronous Oscillation (SSO) by High Voltage Direct Current (HVDC) are introduced in this paper. The Unit Interaction Factor (UIF) and the test signal method are used to analyze SSO that caused by HVDC. The results show that when UIF>0.1, the simulation model takes the risk of SSO. Then, supplementary excitation damping controller (SEDC) is used to suppress the HVDC-SSO. The simulation results show that the SEDC designed has good damping effect on HVDC-SSO.