• Proceedings of the KIEE Conference
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• 1998.11a
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• pp.46-48
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• 1998

In this paper, axial type double rotor brushless DC motor is designed where the rotor is located at the both sides of stator. The rotor uses rare-earth magnets of 16 poles and the stator has 12 coils. The genetic algorithm is used to optimize the efficiency of the designed motor. The characteristics of the design parameters are estimated by varying them for the maximum efficiency.

• 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 KIEE Conference
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• 2003.07b
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• pp.714-716
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• 2003

This paper deals with the characteristic analysis of a brushless DC motor (BLDC) and taking into consideration the freewheeling diodes and DC link voltage ripple using a time-stepped voltage source finite element method. By comparing with the experimental results, we show that the proposed computational method is useful for the analysis and design of a BLDC motor. We also examine the influence of freewheeling diodes and DC link voltage ripples on the performance of a BLDC motor such as torque ripples and radial force on the surface of the teeth.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.36T no.3
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• pp.50-55
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• 1999

Brushless DC Motor(BLDCM) has high efficiency. But this type of motor needs a rotor sensor which complicates the motor configuration. Rotor position sensor degrades system reliability in the severe environmental condition. In this paper, we study a controller which permits the determination of the rotor position by the back EMF to eliminate the rotor position sensor Also, since the back EMF is zero at standstill, a starting technique which permits the starting of an asynchronous motor without a sensor is described. The controller is implemented using microcontroller for minimal external component.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.5
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• pp.416-422
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• 2001

The BLDC(Brushless DC) Motor is characterized by linear torque to current and speed to voltage. It has low acoustic noise and fast dynamic response. Moreover, it has high power density with high proportion of torque to inertia in spite of small size drive. However, when armature current is commutated, the current ripple is generated by the motor inductance components in stator windings and back-EMF. This current ripple caused to torque ripple. Therefore, it is difficult to apply the BLDC motor to a precision servo drive system. In this paper, a new current control algorithm using fourier series coefficients is proposed. This proposed algorithm can minimize torque ripple due to the phase current commutation of BLDC motor. Simulation and Experimental results prove the effectiveness at the Proposed algorithm through comparison with the conventional unipolar PWM method.

• The Transactions of the Korean Institute of Power Electronics
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• v.3 no.3
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• pp.199-205
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• 1998

Brushless DC motors have trapezoidal back-EMF waveform. Theoretically it should be fed with rectangular phase current in order to produce torque ripple free. Because it is drived by a voltage source inverter, perfect rectangular phase current can not available and therefore produce torque ripple. In this paper, the torque ripple due to commutation is analyzed and the practical method that can reduce the torque ripple is proposed. Experimental and simulation results show the effectiveness of the proposed method.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.2
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• pp.63-68
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• 1999

This pper describes a digital sensorless drive of permanent magnet brushless DC motors. In order to detect in real time the rotor positions of which Emf becomes zero, terminal voltages are sampled during PWM duty cycle. This method generates detection error in indirect sensed position, which is the harmonic component of PWM frequency. In this paper, the drive adopted Butterworth low pass filter for rejection of the sensing error and for accurate estimation of commutation time. Analytical design process of the digital filter is proposed and the experimental results show that the performance of the proposed sensorless drive is superior to that of the sensorless drives without filterint.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1094-1095
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• 2007

현재 산업분야에서는 보편적으로 방경방향 자속(Radial Flux)형 전동기가 사용되고 있다. 때문에 대용량의 경우 축방향 길이가 길어지게 되고 구조적 제약이 있는 곳에서의 적용이 어렵다. 이와 달리 축방향 자속(Axial Flux)형 전동기의 응용 범위는 광범위하며 기구적, 구조적으로 많은 이점을 지니고 있다. 본 논문에서는 7.5kW급 축방향 자속형 Brushless DC(BLDC) 전동기의 구동회로 및 속도제어 알고리즘을 구성하고 시뮬레이션과 실험을 통하여 그 결과를 검토하였다.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.9
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• pp.476-483
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• 1999

In this paper, electromagnetic forces acting on the rotor surface of a BLDC motor for hard disk drive are calculated by the finite element field analysis. The frequency characteristics of torque ripple, local force and unbalanced magnetic force as a source of mechanical vibration area analyzed. Ring-type permanent magnets for the brushless DC motor are apt to have different magnetization levels at each pole because of the unbalanced air gap between the magnet surface and the magnetizer fixture during the multi-poles magnetizing process. This paper discusses the effect of the unsymmetric magnetization distribution in the permanent magnet on the brushless DC motor performances. As a result, the unbalanced magnetic force acting on the rotor surface and the torque ripple are examined for the motor with an unsymmetric magnetization distribution, and compared with those of an ideally symmetric motor.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.12
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• pp.1169-1176
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• 2005

In this paper, thermal reliability of a closed type BLDC (Brushless DC) motor for high speed axial fan was analyzed by the accelerated life test. The closed type BLDC (Model No. MB1-8855-J01) motor was controlled by PCB module, which was composed of various electrical components. The failure of the closed type BLDC motor happened in PCB module due to high temperature. Failure mechanism of the closed type BLDC motor appears to be electrolyte dry out of capacitor. The accelerate life test was performed in temperature stress of $85^{\circ}C\;and\;105^{\circ}C$, respectively The failure data from the accelerated life test were analyzed and the life in each stress level was estimated with 960h and 261 h. At last, both life expression according to operating temperature of PCB module and life of the closed type BLBC motor in normal condition $(50^{\circ}C)$ were suggested.