• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.847-852
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• 2007

This paper investigates the characteristics of cogging torque and magnetic force of a brushless DC (BLDC) motor due to imperfect magnetization of permanent magnet (PM) numerically and experimentally which results in the magnetically induced vibration. A predicted magnetization pattern of the PM of the BLDC motor, which is derived from the measured surface magnetic flux density along the PM, is applied to the finite element analysis in order to calculate the cogging torque and the unbalanced magnetic force. This research also develops the experimental setup to measure the unbalanced magnetic force as well as the cogging torque. It shows numerically and experimentally that the imperfect magnetization of permanent magnet generates the driving frequencies of cogging torque with integer multiple of slot number in addition to the least common multiple of pole and slot. It also shows that the driving frequencies of unbalanced magnetic force are integer multiple of slot number ${\pm}1$ due to imperfect magnetization of PM even in the rotationally symmetric design.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.202-205
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• 2008

This paper presents an optimization of permanent magnet (PM) in a brushless dc (BLDC) motor using the response surface methodology (RSM). Size and angle of the PM are optimized to minimize the cogging torque, while reducing the magnitude of harmonic at a dominant frequency and maintaining the operating torque. A fitted RS model is constructed by verifying the high reliability of the total variation and the variation of estimated error. The optimized design is validated by carrying out the reanalysis and comparing to the initial model using the nonlinear transient finite element analysis.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.5
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• pp.325-331
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• 2004

The multiobjective optimization (MO) problem usually includes the conflicting objectives and the use of conventional optimization algorithms for MO problem does not so good approach to obtain an effective optimal solution. In this paper, genetic algorithm (GA) as an effective method is used to solve such MO problem of brushless DC motor (BLDCM). 3D equivalent magnetic circuit network (EMCN) method which enables us to reduce the computational burden is also used to consider the 3D structure of BLDCM. In order to effectively obtain a set of Pareto optimal solutions in MO problem, ranking method proposed by Fonseca is applied. The objective functions are decrease of cogging torque and increase of torque respectively. The airgap length, teeth width and magnetization angle of PM are selected for the design variables. The experimental results are also shown to confirm the validity of the optimization results.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.4
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• pp.39-46
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• 1998

For permanent magnet brushless DC motors used for high speed fuel pumps, torque ripple is an important origin of vibration, acoustic noise and speed fluctuation. In this paper, the output torque profile of a PM motor with one phase energized is decomposed into the commutation torque, the reluctance torque and the armature reaction torque according to their source origins. It verifies that the output torque profile is qualitatively equivalent to the BEMF profile for low reluctance motors. This paper discusses the effect of magnet pole shaping and magnet arc length on the output torque and torque ripple. A magnet edge shaping is proposed to design a trapezoidal BEMF motor without torque ripple, with minimal sacrifice of the maximum output torque.

• Proceedings of the KIEE Conference
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• 2003.04a
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• pp.170-172
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• 2003

Among low power servo applications, classical DC motors are very popular because they are reasonably cheap and easy to control. The main disadvantage is the mechanical collector which has only a limited life period. Also, brush sparking can destroy the rotor coil, generate EMC problems. So permanent magnet brushless do motors and drives are being used increasingly in a wide range of applications. This has been made possible with the advantages of high performance permanent magnets with high coercively and residual magnetic, which make it possible for the PM to have superior power density, torque to inertia ratio and efficiency, when compared to an induction or conventional dc machine. This paper presents the design of a PM brushless dc motor drive simplistically operates as a classical dc motor. The BLDC motor drive system for this paper composes to the power integrated circuits, the one chip device. And several simple semiconductors add to drive system for a motor drive system simplistically operates as a conventional dc motor. Test results confirmed the feasibility of the proposed motor drive system design.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.12
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• pp.1661-1667
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• 2013

This paper studies the dynamic irreversible demagnetization characteristics of an interior permanent magnet (PM) brushless DC motor with a stator turn fault. A new algorithm, which is a finite element method (FEM) combined with a line voltage equation of the motor, is developed to analyze irreversible demagnetization under dynamic and transient states and considers a stator turn fault. The input current, circulating current, magnetic distribution characteristics, and operating property of the PM, including the irreversible demagnetization in the fault state, are analyzed using this algorithm by considering the magnetic saturation effect. The feasibility of the proposed method confirmed from the analysis results is verified via an experiment. Through this fault analysis, we can accurately check the fault phenomena of a PM motor against the demagnetization fault for fault prevention.

• Journal of Magnetics
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• v.6 no.3
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• pp.101-107
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• 2001

A model to describe the effect of stator slotting in the airgap region of a linear brushless permanent magnet motor (LBLPMM) is proposed for analytical prediction of magnetic field distribution. It is a two-dimensional model based on superposition of the effect of stator slotting and main field due to permanent magnet (PM) without stator slotting. The effect of stator slotting is expressed in form of a generalized equation, which is obtained by numerical analysis and is a function of motor geometric parameters, so the proposed model effectively accounts for the effect of stator slotting in the airgap field distribution according to change of motor geometry or relative motion of stator and armature. Results of prediction from the proposed model are compared with corresponding finite element analysis.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.7
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• pp.315-322
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• 2001

High speed brushless permanent magnet(PM) machines need a key technology to minimize the iron core losses in stator and the eddy current losses in the retained sleeve and magnets caused by slotting harmonics. Thus, slotless or iron-coreless brushless PM machines have been applied for a very high rotational speed and/or the ripple-free torque. Unfortunately, slotless or coreless PM machines have lower open-circuit field than slotted and/or iron-cored types, which cause to reduce power density. Fortunately, Halbach array can generate the strong magnetic field systems without additional magnetic materials. In this paper, the 4-pole Halbach array is applied to the high speed machine and is compared with the radial magnetized PM array in field system. The iron-/air-cored stator of PM machine is constructed with/without winding slots. Open circuit magnetic fields of each type are presented from the analytical method and finite element method. Consequently, it is confirmed that the Halbach array field system with slotless stator is more suitable to the high speed motor because it has high flux density, sinusoidal flux distribution than others.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.4
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• pp.495-501
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• 2013

In the present study, a BLDC motor for a pump in which a neodymium PM is replaced with a Ferrite PM has been developed in preparation for the cost increase and to ensure the stability of the resource supply. One of the currently used motors for pumps is a BLDC motor having an interior PM wherein a rare-earth PM is adopted. However, a BLDC motor for a pump is designed to have large airgap because of the use of a waterproof insulator according to its structural characteristics, and therefore, a SPM structure is suitable. Hence, an SPM BLDC motor in which a Ferrite PM is used is designed. Nevertheless, the use of Ferrite instead of rare-earth materials causes a deterioration in the performance of the electric motor, such as a decrease in the BEMF and the maximum power of the motor and the irreversible demagnetization of the PM. In order to mitigate such disadvantages, an optimized design of the BLDC motor is developed by changing each design parameter and by improving the electromagnetism structure.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.27-29
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• 2005

This paper studies particularly applicable method for sensorless Permanent Magnet Brushless DC(PMBLDC) Motor drive system. The waveform of the motor internal voltages (or back emf) contains a fundamental and higher order frequency harmonics. Therefore the third harmonics. component is extracted from the stator phase voltage. The resulting third harmonic signal keeps a constant phase relationship with the rotor flux for any motor speed and load condition. In addition, a simple starting method and a speed estimation approach are also proposed.