Xiuhe Wang

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

Design and Analysis of Different Line-Start PM Synchronous Motors for Oil-Pump Applications

This paper presents a comparison between three architectures of line-start PM motors for oil-pump application. This paper is focused on the performances in synchronous operation as well as the self-starting operations. Effects of electrical parameters on the starting and steady performance characteristics are demonstrated to find a satisfying design to meet required performances, it seems that the interior permanent magnet motor yields an impressive starting performance.

Reducing Cogging Torque in Surface-Mounted Permanent-Magnet Motors by Nonuniformly Distributed Teeth Method

This paper proposed a novel method for reducing cogging torque in surface-mounted permanent-magnet (PM) motors with nonuniformly distributed teeth. In this method, the width of one tooth tip is different from that of the others while all slot openings are the same. By suitable selection of the teeth width ratio, i.e., the width ratio of the one tooth tip to others, the cogging torque can be greatly reduced. First, the analytical expression of cogging torque was deduced and used to analyze the cogging torque qualitatively. Based on the above, analytical method was proposed to determine the teeth width ratio. To determine the teeth width ratio accurately, numerical method was proposed. Calculation of cogging torque by finite element method (FEM) shows that cogging torque can be greatly reduced by teeth width ratio determined by analytical method, and the teeth width ratio determined by numerical method can reduce the cogging torque further, which proved the effectiveness of the proposed methods. At last, the influences of the stator asymmetry resulted by this method on PM motors were discussed.

Reduction on Cogging Torque in Flux-Switching Permanent Magnet Machine by Teeth Notching Schemes

The cogging torque in flux-switching permanent magnet machines (FSPMs) is high due to its unique structure and high air-gap flux density. The cogging torque principle in FSPM is different from that in traditional PM machines, which can not be correctly predicted by analytical consideration. The aim of paper is to present the investigation on cogging torque principle in FSPM by analyzing the flux density distribution and a simple cogging torque reduction technique, i.e., teeth notching. Various kinds of notching schemes and their influence on cogging torque are examined along with instantaneous torque and average output torque at different load conditions. Numerical optimization process combined with finite-element analysis, which gives more preciseness to calculations, is performed to minimize cogging torque. The results show that the cogging torque circle depends on the real flux density distribution in the machine rather than the number of stator/rotor poles and the presented method can greatly reduce the torque ripple at only slight cost of average output torque.

Cogging Torque Minimization and Torque Ripple Suppression in Surface-Mounted Permanent Magnet Synchronous Machines Using Different Magnet Widths

Permanent magnet synchronous machines are vulnerable to significant amounts of torque ripple if they are not carefully designed. Even though minimizing cogging torque can help reduce the torque ripple, but can not definitely give rise to a low level torque ripple. This paper presents a simple solution for minimizing the cogging torque and suppressing operation torque ripple simultaneously. The principle of that simple solution is illustrated, where a magnet with different width is used so that the flux density distribution in the machine is substantially changed. The magnet widths for minimizing cogging torque are obtained by using an analytical model. The influence of magnet widths on operation torque ripple and average operation torque is examined by using Finite Element Analysis (FEA) which gives more preciseness to calculations. It is found that the cogging torque and operation torque ripple can be greatly reduced, but with slight average output torque reduction. At last, the Unbalance Magnetic Pull (UMP) is examined, indicating that the presented method can substantially increase the UMP due to the asymmetric distribution of magnets.

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.

Integrated Optimization of Two Design Techniques for Cogging Torque Reduction Combined With Analytical Method by a Simple Gradient Descent Method

This paper presents an integrated optimization process to minimize cogging torque in permanent-magnet (PM) machines by a simple Gradient Descent method. The presented optimization method can be easily achieved in machine design. The design techniques of nonuniformly distributed magnets and teeth are presented to illustrate the optimization process. First, with the assistance of an analytical model deduced, the initial solution and feasible domain of the optimization can be easily identified. Then a simple Gradient Descent method is combined with finite element analysis to perform the optimization within the identified feasible domain. Four representative PM machines-including surface-mounted permanent-magnet synchronous machine (SPMSM), brushless DC machine (BLDC), and interior permanent-magnet synchronous machine (IPMSM)-are designed and optimized by the presented method, respectively. The results verify that the presented optimization process can greatly reduce the cogging torque in PM machines. In addition, it is easily achieved and very time-saving. At last, the influence of the nonuniformly distributed magnets method on load torque is examined.

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.

Performance analysis of single-phase induction motor based on voltage source complex finite-element analysis

In this paper, to make a compromise between accuracy and efficiency in the design of single-phase induction motors, voltage source complex finite-element model, which is combined with the equivalent circuit method to carry out the performance analysis, is presented. The voltage source complex finite-element method is used to determine equivalent circuit parameters by simulating the no-load tests and locked-rotor tests, while the conventional method is adopted to calculate the performances. Good agreement is achieved between the calculated results and test results, which verifies the effectiveness of the presented method

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.