Calculation and Analysis on PM Thermal Characteristics Influence Performance of PMSM Based on FEM

The irreversible demagnetization of Nd-Fe-B permanent magnet (PM) material appears during the use of Nd-Fe-B permanent magnet synchronous motor (PMSM) has been blocking this kind of motor towards the direction of large-scale. Demagnetization of PM is mainly affected by the working temperature and the reverse magnetic field of stator armature, and the accurate calculation for the demagnetization characteristics of PMSM is usually difficult by using the analytical method. In this paper, we derive the calculation formula of the knee point under a working temperature for permanent magnets in PMSM firstly, then calculate and analyze the demagnetization characteristics of PMSM under different working temperatures and loads by using the Finite Element Method (FEM), Thereby more accurately reflect the working characteristics of PM and the overload capability of motor. This paper provides theoretical basis for the selection of PM materials and the calculation of PM thickness in the PMSM design.

THE DESIGN OF EDDY-CURRENT MAGNET BRAKES

The eddy-current is created by the relative motion between a magnet and a metal (or alloy) conductor. The current induces the reverse magnetic field and results in the deceleration of motion. The proposed mechanism implements this phenomenon in developing a braking system. The potential applications of the braking system can be a decelerating system to increase the safety of an elevator or any guided rail transportation system. To provide scientific investigation for industrial application of magnetic braking, this study presents four systematic engineering design scenarios to design a braking system. The constant magnetic field is the simplest and easiest design to implement. The optimal magnetic field distribution is obtained by minimizing the deceleration effort. The piecewise-constant magnetic field distribution offers a compromise between performance and magnetic field requirements. The advantages of the section-wise guide rail are tolerable deceleration; and simple design requirement and manufacturing processes. In the study, an experimental braking system using constant magnetic field is build to demonstrate the design procedure.

Study on Permanent Magnet Demagnetization Characteristics in Permanent Magnet Synchronous Machines

When Permanent Magnet Synchronous Machines (PMSM) working with rated load or overload, stator iron loss and copper loss, bearings friction loss, permanent magnet (PM) eddy-current all will cause PM temperature rise. In this condition, the PM is affected by the temperature and the stator of the reverse magnetic field generated prone to arouse demagnetization phenomenon, it will directly affect the performance of permanent magnet machines. Previous calculation method which used magnetic circuit method to analyze PM demagnetization characteristics cannot reflect the actual working condition of PM. Firstly, the calculation formula of PM thermal stability is deduced in this paper. Secondly, demagnetization characteristics are analyzed based on FEM, which can reflect the actual working condition of PM more accurately. This paper providing reference basis for optimum electromagnetic design, PM selection and optimum PM design.

Magnetostrictive Blocked-Force Clamping Mechanism for Secure and Heavy-Load Inchworm Motion

The capability of inchworm motor for long-displacement, heavy-load and precise positioning is greatly conditioned by the effectiveness of the clamping mechanism. A need exists in the art for clamping mechanism capable of delivering precise and heavy load motion. This paper presents a novel giant magnetostriction material (GMM) application to the development of such mechanism. GMM is advantageous over other smart materials in this particular aspect by its remarkable magnetostriction and especially the huge blocked stress. It can, e.g., display around 4000N at moderate magnetization with a φ25×100mm GMM rod. Most desirably, such large force could be used as clamping force in inchworm movement. However, the force can only be generated under blocked state, which is generally hard to reach, especially in a moving regime. Addressing this problem, the research utilizes GMM rod’s capacity to both positively stretch and negatively contract under permanent-magnet-biased condition and presents a specially designed clamping mechanism, a permanent-magnet-biased actuator fastened in a rigid guideway. Being applied reverse magnetic field, the formerly stretched actuator may contract to a suitable size to be put into the rigid guideway. Then, removal of the field will theoretically result in the restoration of the actuator. Practically, stretching of the actuator is blocked by the rigid guideway. This forms the so-called Pre-blocked-clamping-on state, where no-power fastening behavior exists. Moreover, the blocked force is adjustable. When being applied the same-direction field as the permanent one, the blocked force becomes greater (Blocked-clamping-on state). When being applied adequate reverse field, the blocked force is diminished with the shrinking of the actuator, till the actuator released from the rails (Blocked-clamping-off state). This process realizes the utilization of blocked force in clamping action, thus provides resolution for secure and heavy load inchworm motion. A clamping mechanism prototype (Size:φ32×130mm, with a φ10×100mm GMM rod) has been realized. The design and working process of the setup is presented. Through experiments, the prototype can be facilely manipulated by square-instant and sinusoid-continuing current and it can agilely perform to meet the proposed blocked force the proposed clamping principle.