• Journal of the Korean Society of Visualization
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• v.8 no.2
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• pp.23-30
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• 2010

Regarding the aircrafts with a rotor blade system, the miniaturization of them is limited due to the rotor blade length and the tail rotor system. To miniaturize an aircraft, an equipment is required that increases thrust and also shortens the length of the rotor blade. The present study will conduct the flow analysis for miniaturizing the aircraft by applying a duct to the coaxial rotor blade system without tail rotor. First, the verification on the calculated results was conducted through the computational flow analysis on the coaxial rotor blade system without a duct. Then, the flow analysis for the coaxial rotor blade systems was performed including Ka-60 duct, Single duct, Twin duct, and Double duct, respectively. From the numerical results, the thrust coefficient appeared higher with the duct than without a duct for the coaxial rotor blade system. Especially, in the case of Double duct, the thrust was improved due to the increase of incoming flow and the extension of the wake area. These results will be used as the basic concepts for miniaturizing the aircraft with the rotor blade system. The flow analysis on the coaxial rotor blade system including the fuselage remains as a future work.

• Proceedings of the KIEE Conference
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• 1998.11a
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• pp.168-170
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• 1998

In this paper a driving method using the microcomputer in safe driving the axial type double rotor brushless DC motor without shaft position sensor is studied. The rotor position is determined from the back-EMF passed though special filter. Starting technique which uses the motor as a synchronous motor at standstill are explained. The motor speed is controlled by changing the duty cycle of PWM. The test motor has Y-connected three-phase stator and 8-pole axial type double rotor. From the experiments, we got good performences of the proposed control system.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.812-821
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• 2018

An electromagnetic excitation force is caused by the air-gap flux density, which greatly influences the noise and vibration of the motor. In many real projects, skewed slot technology is widely used to reduce the harmonic components of the air-gap flux density to reduce the noise and vibration of the motor. However, a skewed slot has several side effects such as a transverse current and axial drifting. Thus, a double skewed slot rotor is selected with the aim of eliminating these side effects. This paper presents the exact structure of the double skewed slot rotor and the mechanism whereby the electromagnetic excitation force can be reduced. A multi-slice method is adopted to model the special structure. Finite element simulation is used to verify the theory.

• Journal of Power Electronics
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• v.9 no.4
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• pp.575-581
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• 2009

In this paper two modes of operating a wound rotor induction machine as a generator at sub-and super-synchronous speeds in wind energy conversion systems are investigated. In the first mode, known as double fed induction generator (DFIG), the rotor circuit is fed from the ac mains via a controlled rectifier and a forced commutated inverter. Adjusting the applied rotor voltage magnitude and phase leads to machine operation as a generator at sub-synchronous speeds. In the second mode, the machine is operated in a slip recovery scheme where the slip energy is fed back to the ac mains via a rectifier and line commutated inverter. This mode is described as double output induction generator (DOIG) leading to increase the efficiency of the wind-to electrical energy conversion system. Simulated results of both modes are presented. Experimental verification of the simulated results are presented for the DOIG mode of operation, showing larger amount of power captured and better power factor when compared to conventional induction generators.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.3
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• pp.272-276
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• 2005

This paper deals with the method to calculate the rotor eddy current losses of permanent magnet high-speed machines considering the effects of time/space flux harmonics. The flux harmonics caused by the slot geometry in the stator is calculated from the time variation of the magnetic field distribution obtained by the magneto-static finite element analysis and double Fast Fourier Transform. And, using the analytical approach considering the multiple flux harmonics and the Poynting vector, the rotor losses is evaluated in each rotor composite. Using this method is simple and workable for any kind of stator slot shape for rotor loss analysis.

• Journal of Electrical Engineering and Technology
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• v.12 no.1
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• pp.256-261
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• 2017

This paper deals with the experimental evaluation on power loss of a double-side permanent magnet synchronous motor/generator (DPMSM/G) applied to a flywheel energy storage system (FESS). Power loss is one of the most important problems in the FESS, which supplies the electrical energy from the mechanical rotation energy, because the power loss decreases the efficiency of energy storage and conversion of capability FESS. In this paper, the power losses of coreless DPMSM/G are separated by the mechanical and rotor eddy current losses in each operating mode. Moreover, the rotor eddy current loss is calculated by the 3-D finite element analysis (FEA) method. The analysis result is validated by separating the power loss as electromagnetic loss and mechanical loss by a spin up/down test.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.6
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• pp.123-130
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• 2010

In general, a design method based on the equivalent magnetic circuit has been used for basic design of Interior Permanent Magnet Synchronous Motor(IPMSM). However, the equivalent magnetic circuit method has difficulty in considering the arrangement of PM. IPMSM has high degree of freedom for PM rotor design. In this paper, we proposed the multiobjective optimal design method considering the arrangement of PM for the double-layer PM rotor structure that minimizes the torque ripple as well as maximizes the torque of IPMSM. The design variables of double-layer PM rotor structure are obtained from the Response Surface Method. Torque and torque ripple were calculated by Finite Element Method.

• International Journal of Fluid Machinery and Systems
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• v.7 no.1
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• pp.16-27
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• 2014

Double-blade vertical axis wind turbines (DB-VAWTs) can improve the self-starting performance of lift-driven VAWTs. We here propose the quadruple-multiple streamtube model (QMS), based on the blade element momentum (BEM) theory, for simulating DB-VAWT performance. Model validity is investigated by comparison to computational fluid dynamics (CFD) prediction for two kinds of two-dimensional DB-VAWT rotors for two rotor scales with three inner-outer radius ratios: 0.25, 0.5, and 0.75. The BEM-QMS model does not consider the effects of an inner rotor on the flow speed in the upwind half of the rotor, so we introduce a correction factor for this flow speed. The maximum power coefficient predicted by the modified BEM-QMS model for a DB-VAWT is thus closer to the CFD prediction.

• Journal of Magnetics
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• v.21 no.3
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• pp.356-363
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• 2016

To improve the sensing accuracy of the newly developed magnetically suspended sensitive gyroscope (MSSG), it is necessary to analyze the causes of drift error. This paper build the models of disturbing torques generated by stator assembly errors based on the geometric construction of the MSSG with double spherical envelope surfaces, and further reveals the generation mechanism of the drift error. Then the drift error from a single stator magnetic pole is calculated quantitatively with the established model, and the key factors producing the drift error are further discussed. It is proposed that the main approaches in reducing the drift error are guaranteeing the rotor envelope surface to be an ideal spherical and improving the controlling precision of rotor displacement. The common problems associated in a gyroscope with a spherical rotor can be effectively resolved by the proposed method.

• 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.