• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.5
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• pp.503-510
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• 2011

This paper presents a method of optimizing the blade pitch and generator torque controllers which have been already designed for an existing wind turbine generator system. Since the highly nonlinear and uncertain characteristics of the wind turbine generator can not be fully considered in the controller design phase, some parameters such as control gains must be tuned during the field implementation phase. In this paper, nonlinear simulation software, which is based high fidelity wind turbine model, and optimization technique are effectively combined and used to tune a set of gains for the blade pitch and the generator torque controllers. Simulation results show that the baseline controllers can be effectively optimized to reduce the errors in wind turbine rotor speed and generator power output controls as well as twisting of the high and low speed shafts.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.2
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• pp.143-149
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• 2021

BLDC motors are getting better performance due to the improvement of material technology including high performance of permanent magnets, advancement of driving IC technology with high integration and high functionality, and improvement of assembly technology such as high point ratio. While having the advantage of such a square wave driven BLDC motor, interest in the design and development of a square wave driven BLDC permanent magnet motor and development of a position detection circuit and driver is increasing in order to more meet the needs of users. However, in spite of the cost and functional advantages due to reduced efficiency, switching loss and vibration, noise, etc., the application is somewhat limited. Therefore, in this paper, we study a position detection circuit that generates a sinusoidal signal in proportion to the magnetic flux of a BLDC motor rotor using a Hall Effect Sensor that generates a sinusoidal wave to increase the efficiency of the motor, reduce ripple, and drive a sinusoidal current with excellent speed and torque characteristics.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1832-1837
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• 2011

This paper presents the optimal permanent magnet shape on the rotor of an interior permanent magnet motor to reduce the core losses and improve the performance. As permanent magnet has conductivity inherently, it causes huge amount of eddy current losses by the slot harmonics with concentrated winding. This loss is roughly 100 times larger than that of distributed winding in high speed operation and it cannot be ignored, especially on traction motors. Each eddy current loss on permanent magnet has been investigated in detail by using FEM(Finite Element Method) instead of EMCNM(Equivalent Magnetic Circuit Network Method) in order to consider saturation and non-linear magnetic property. Simulation-based DOE(Design Of Experiment) is also applied to avoid large number of analyses according to each design parameter and consider expected interactions among parameters. Consequently, the optimal design to reduce the core loss on the permanent magnet while maintaining or improving motor performance is proposed by an optimization algorithm using regression equation derived and lastly, the core loss reduction on the proposed shape of the permanent magnet is verified by FEM.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.1
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• pp.57-65
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• 2007

Along with the development of power electronics and magnetic materials, permanent magnet (PM) brushless direct current (BLDC) motors are now widely used in many fields of modern industry BLDC motors have many advantages such as high efficiency, large peak torque, easy control of speed, and reliable working characteristics. However, Compared with the other electric motors without a PM, BLDC motors with a PM have inherent cogging torque. It is often a principle source of vibration, noise and difficulty of control in BLDC motors. Cogging torque which is produced by the interaction of the rotor magnetic flux and angular variation in the stator magnetic reluctance can be reduced by sinusoidal air-gap flux density waveform due to reduction of variation of magnetic reluctance. Therefore, this paper will present a design method of magnetizing system for reduction of cogging torque and low manufacturing cost of BLDC motor with isotropic bonded neodynium-iron-boron (Nd-Fe-B) magnets in ring type by sinusoidal air-gap flux density distribution. An analytical technique of magnetization makes use of two-dimensional finite element method (2-D FEM) and Preisach model that expresses the hysteresis phenomenon of magnetic materials in order for accurate calculation. In addition, For optimum design of magnetizing fixture, Factorial design which is one of the design of experiments (DOE) is used.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.2194-2200
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• 2014

This paper presents a design of novel 2-phase 6/5 switched reluctance motor (SRM) for an air-blower application. This type of motor is suitable for the applications that require high speed and only one directional rotation as air-blower. The desired air-blower is unidirectional application, and requires a wide positive torque region without torque dead-zone. In order to get a wide positive torque region without torque dead-zone during phase commutation, asymmetric inductance characteristic with non-uniform air-gap is considered. The proposed motor can be operated at any rotor position. The proposed 6/5 SRM uses short flux path technique that achieved by means of winding configuration and lamination geometry. The purpose of short flux path is to reduce the core loss and the absorption MMF in the stator. The proposed 2-phase 6/5 SRM is verified by finite element method (FEM) analysis and Matlab-Simulink. In order to verify the design, a prototype of the proposed motor was manufactured for practical system.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.81-90
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• 1985

For the prediction of the real vibration and stability behaviour of rotor-beaing systems, various additional effects were considered, which are simplified or neglected by conventional modeling of real rotors. These are specially coupled spring and damping coefficients of journal bearings, spring and damping coefficients of external supporting elements for bearings, static load exerting on gears or pulleys by power transmissions, excitation through the gear tolerance or failure, and positive or negative spring and damping characteristics of magnetic or sealing friction force. Considering these effects, a computer program for the calculation of free and forced vibration of rotating shafts supported by two or more bearings is developed, based on the transfer matrixed method. The reliability of the calculated resutls were ascertianed by comparing with the measured data on high speed rotors supported by two journal bearings.

• International Journal of Fluid Machinery and Systems
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• v.7 no.1
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• pp.28-33
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• 2014

In order to research the relationship between the tip clearance and leakage flow of centrifugal compressor, a high speed centrifugal compressor was investigated by using CFD. A numerical study on the effect of four different rotor tip clearance sizes of centrifugal compressor, which were 0.5times, 1 times, 1.5times and 2.0times of the design tip clearance, was carried out. Efficiency and pressure ratio curves were obtained under different mass flow. The reasons of the clearance vortex and the factors of vortex size were analyzed. The result indicated that with the increase of tip clearance size, the performance of the compressor changed obviously, the performance parameters such as efficiency and pressure ratio tended to decrease obviously. While, the leakage flow does not always lead to leak vortex. The strength of the vortex increased with the tip clearance. The size of leak vortex was affected by the pressure difference between the suction side and the pressure side of blade tip.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.95-99
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• 2004

The developing Smart UAV in KARI supposes high speed flight as like a conventional plane, as well as vertical takeoff and landing as like a helicopter. Therefore, the air intake system should be designed to provide the sufficient air flow to the engine and the maximum possible total pressure recovery at the engine intake screen over a wide range of flight conditions. For this purpose, we designed the intake system using a pilot type intake model and plenum chamber In this paper, we designed the intake model and analyzed the performance of designed intake system using the general-purpose commercial CFD code, CFD-ACE+ For 3-D calculation, we generated mesh using the unstructured gird and used $\kappa-\epsilon$ turbulence model. The analysis results of the total pressure variation and the velocity distribution was illustrated in this paper. The pressure recovery and distortion coefficient at a plane coincident with the compressor inlet were calculated and streamline variation through the intake system was investigated at the worst condition as well as the standard flight condition.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.12
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• pp.608-616
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• 2006

Recently, a switched reluctance motor is widely used in various industries because it has many advantages such as a simple structure, robustness, less maintenance, high torque/weight ratio, and easy speed control over other types of motors. However, a switched reluctance motor inherently produces acoustic noise and vibration caused by torque ripple. Applications of these motors where silent operation is desirable have thus been limited. In this paper, a new stator pole face having a non-uniform air-gap and a pole shoe attached to the lateral face of the rotor pole are suggested in order to minimize torque ripple. The effects of each design parameter are validated using a time-stepping finite element method. The parameters are optimized by utilizing response surface method (RSM) combined with (1+1) evolution strategy. The result shows that the optimized shape gives higher average torque and drastically reduced torque ripple.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.26-33
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• 2005

Smart UAV, which adopting tiltrotor aircraft concept, requires vertical take-off and landing, long endurance and high speed capability. These contradictable flight performances are hard to meet unless the operation of flap system which should reveal optimal performance for each flight mode. In order to design SUAV flaperon satisfying the three performance requirements, various configurations are generated and their aerodynamic performances are analyzed using numerical flow computations around flap systems. Considering aerodynamic performance and structural simplicity, a final flap configuration is selected and the performance is validated through the wind tunnel testing for 40% scale model.