Two-pulse magnetization process of the NdFeB multi-pole ring magnet for BLDC motors
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ORIGINAL PAPER
Two-pulse magnetization process of the NdFeB multi-pole ring magnet for BLDC motors Miroslav Novák1
· Želmíra Ferková2
Received: 12 August 2019 / Accepted: 17 April 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The magnetization of rare earth ring magnets forming the rotor of a BLDC or a synchronous motor requires a high level of magnetization field to achieve the desired magnetization pattern. The design of the magnetizing yoke is a compromise between the field strength requirements, the yoke temperature balance and the winding forces. The two-pulse magnetization allows reaching a higher steepness of magnetization at the pole edges and thus higher overall rotor magnetization under these difficult conditions. The magnetization fixture for the double-pulse method was designed and verified by finite element method simulations. A small series (100 pcs) of produced magnets are compared with simulations using external magnetic 3D field scanning. The artifacts (asymmetry of pole magnetization) after the two-pulse magnetization are recalculated onto unbalanced magnetic pull and torque ripple. It is shown that these artifacts do not adversely affect unbalanced magnetic pull and torque ripple, unlike the asymmetries caused by the geometric inaccuracy of the magnetizer, whose impact is crucial. Keywords Magnetizer · Magnetizing process · Permanent magnet motors · Unbalanced magnetic pull · Magnetic field measurement
1 Introduction Small brushless DC (BLDC) motors are usually designed with a rotor based on a permanent magnet ring with multipole magnetic polarization [1,2]. The high power density of the motor requires the use of NdFeB magnets. Creating radially polarized ring magnets with maximum material utilization is a challenge of modern technology. This is possible with sintered or bonded magnets. However, these materials need field strength for a full magnetization higher than 2500 The result was obtained through the financial support of the European Union within the framework of the project “Modular platform for autonomous chassis of specialized electric vehicles for freight and equipment transportation,” Reg. No. CZ.02.1.01/0.0/0.0/16_025/ 0007293 and project Slovak Research and Development Agency APVV-18-0436.
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Miroslav Novák [email protected] Želmíra Ferková [email protected]
1
Institute of Mechatronics and Computer Engineering, Technical University of Liberec, Liberec, Czech Republic
2
Faculty of Electrical Engineering and Informatics, Technical University of Košice, Kosice, Slovak Republic
kAm−1 [3–5]. Therefore, a capacitor discharge magnetizer is most commonly used as a source of the large enough current pulse for winding of the magnetizing yoke [6–8]. Nevertheless, it is difficult to achieve full magnetization especially at the space between neighboring poles of multi-pole magnets where not completely remagnetized regions remain. This leads to a reduction in motor torque and its efficiency. The imperfectly magnetized areas between the poles can b
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