Optimal Design of Permanent Magnetic Coupling with High Torque Transmission and Low Eddy-current Loss

This study presents an optimal design of permanent magnetic coupling (PMC) for dynamic sealing in pressurized vessel considering non-leakage of harmful working medium. An improved partial swarm optimization method was designed to perform a multi-objective design optimization of the structure of PMC, in order to increase the torque transmission with limited magnetic material cost and decrease the eddy-current loss of the magnetic coupling caused by the metal isolation cover. After accurate computation, the optimal structure parameters of PMC were obtained. Then, a 3-D finite element model of PMC with the optimal structure was constructed to analyze the transmitted torque and eddy current loss, and verified the validity of the proposed design method. Introduction With the progress of industry and development of advanced manufacture, higher requirements of sealing are put forward, particularly to the heavy-pressure and high-speed dynamic sealing, which often affects the security, reliability and durability of the mechanical equipment. The appearance of permanent magnetic coupling (PMC), which transmits torque between two rotors without any mechanical contact, solves thoroughly the leak problems existed in dynamic sealing of mechanical equipment and has been widely applied to the zero-leakage applications. However, the non-contacted magnetic torque transmission requires a large amount of permanent materials, which causes a high active material cost. Thus, how to design a PMC with higher torque transmission and lower structural mass is worthy of study. By the increasing application of PMCs in the heavy-pressure and high-speed hermetic situation, the analysis of their structural design and optimization methods has been an active field of recent researches. Sethian and Wiegmann [1] introduced level set based optimization for the structural design in 2000. After that, Seungmin et al. [2] proposed a new level-set-based topology optimization method for magnetic coupling design using remeshing techniques that can generate meshes on the exact structural boundaries to improve the accuracy of finite-element analysis. To obtain weight reduction and high performance, Sang-In and Seungjae [3] addressed a novel scheme based on level set function to design the optimal configuration of a magnetic coupling for maximizing the actuating force. Besides, some other optimization methods were also used for PMC design. Mahmoudi et al. [4] evaluated an optimized PM motor using the GA for maximum power density and low cogging torque. Nevertheless, reports on the particle swarm optimization (PSO) adopted to structural design of PMC with the objectives of high torque transmission and low eddy-current loss have not been described. PMC consists of two concentric sets of radial-shaped magnets assembled by tile permanent magnets, and one isolation set made of metal to withstand a certain load between them. The drive set combines with drive motor, and the load set is connected to the rotating load, seen in Fig. 1. To obtain high torque transmission, the maximum torque characteristics is the main factor, which directly affects the transmission performance, and the eddy current caused by the metal isolation set is another factor, which blocks torque transfer.