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Low Inertia Motor Design with Halbach PM Array

Title
Low Inertia Motor Design with Halbach PM Array
Authors
구본길
Date Issued
2021
Publisher
포항공과대학교
Abstract
As the electric vehicle market is revitalized, there is an increasing need for an electric motor design capable of high speed operation while having a high power density. In particular, the motor used in the dynamo system for the load test must be capable of high acceleration/deceleration operation. For low inertia, the outer diameter and weight of the rotor are limited. Since the Halbach structure forms a magnetic flux path only with magnets, a back iron is not required for the rotor, thus reducing the weight and inertia of the rotor. This feature of the Halbach motor is also suitable for aircraft applications such as urban air mobility (UAM). This is because the Halbach structure can reduce motor weight while maintaining high power density. It is very important to find an optimal motor design method in situations where high speed operation, light weight, and high output are required at the same time. However, despite the many advantages of Halbach motor, research on optimal design is insufficient. According to previous research, the 2-segment Halbach motor maintains the same arc length of radial and circumferential magnets. Also, a back iron is not used. However, in high speed applications, optimal ratios exist for the arc length of radial and circumferential magnets when the motor is designed with low poles or when the height of the rotor is extremely limited for weight reduction. In this case, it is more advantageous to use a back iron. In this thesis, we propose a design method for a Halbach array PM motor with high speed operating range and high power density. For optimization, we analyze the Halbach structure through a magnetic equivalent circuit (MEC). The saturation of the core is considered through iterations of the permeability calculation. The cost function that combines the use of magnets with the airgap flux density was determined and the values of the design variables were found with the minimum cost function. The optimal radial magnet arc ratio and the optimal magnet height ratio are obtained through the Levenberg-Marquardt algorithm (LMA). As an alternative method, subdomain analysis was introduced, which allows finding optimal design parameters through torque under load conditions. The subdomain analysis is combined with the MEC to reflect the saturation of the core. For multi-objective optimization, design variables and constraints were determined, and surface curve fitting was performed using least squares method (LSM). The optimal design was derived from the LSM results, and the validity of the proposed algorithm was verified through finite element analysis (FEA) simulation. Finally, a motor designed through the proposed method was produced and the experimental results were presented.
URI
http://postech.dcollection.net/common/orgView/200000368398
https://oasis.postech.ac.kr/handle/2014.oak/111024
Article Type
Thesis
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