• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.5
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• pp.437-442
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• 2013

For open-end permanent magnet synchronous machine(PMSM) with dual inverter system, where one inverter is connected to the source and the other is flying, the dc link voltage of the flying inverter can be boosted through the machine. For this reason, when compared with single inverter drive system, higher voltage can be applied to PMSM, and higher torque can be generated in the flux weakening region. In this case, however, active and reactive powers are separately supplied by each inverter to maintain the dc link voltage of flying inverter. Therefore, the required flux weakening control is different from the conventional method for a single inverter drive system. This paper proposes the novel flux weakening control method which maximizes the active voltage component in a dual inverter PMSM drive system. The proposed method was demonstrated and verified through experimental results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.4
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• pp.36-44
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• 2003

In the industrial motor drive system which is composed of a motor and load connected with a flexible shaft, a torsional vibration is often generated because of the elastic elements in torque transmission. To solve this problem, the two degrees of freedom H$_{\infty}$ controller was designed. But it is difficult to realize that controller. In this paper, H$_{\infty}$ control of 2-mass system using partial state feedback and resonance ratio control is proposed. Proposed controller has simple structure but satisfies the attenuation of disturbances and vibrations.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.1
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• pp.57-68
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• 2014

This paper propose a development of squirrel-cage induction motor(IM) for 5-phase 1.5kW, 220V, 60Hz in order to study a polyphase ac machinery that keep hold of advantages more than traditional three-phase a IM, such as reducing a amplitude of torque pulsation, decreasing electric noises, and increasing the reliability. Designed methods of the motor use a development tools with Maxwell 2D and Simplorer program. There are designed drawing of manufactured frames of the IM. amplitude and waveform of the generated electromotive force, FFT analysis of harmonics within output voltages and current, and reviewing a experiment results are shown by variable output. We are presenting a design and manufacture methods for the 5-phase squirrel-cage IM.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.7
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• pp.525-529
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• 2010

In this paper, the characteristics of a thin-type ultrasonic motor generating elliptical displacements analyzed by FEM are presented, and then fabrication of the motor is then described. The structure of the motor consists of sixteen ceramic pieces attached to the upper and bottom surfaces of an elastic body. The principle of the motor is to apply alternating voltages which have a 90 phase difference to the attached ceramics, and then elliptical displacements are generated at four edges of the elastic body. Then the rotor is moved by the elliptical displacements. In the case of a ceramic thickness of 1.5, the highest speed was obtained at 79 kHz. In the case of a ceramic thickness of 2 mm, the highest speed was obtained at 77.5 kHz. Consequently, the speed and torque of the ultrasonic motor (USM) increased linearly with increasing applied voltage.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.296-296
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• 2015

The aim of this paper is to numerically explore the feasibility of designing a Mini-Hydro turbine. The interest for this kind of horizontal axis turbine relies on its versatility. For instance, in the field of renewable energy, this kind of turbine may be considered for different applications, such as: tidal power, run-of-the-river hydroelectricity, wave energy conversion. It is fundamental to improve the turbine performance and to decrease the equipment costs for achievement of "environmental friendly" solutions and maximization of the "cost-advantage". In the present work, the commercial CFD code ANSYS is used to perform 3D simulations, solving the incompressible Unsteady Reynolds-Averaged Navier-Stokes (U-RANS) equations discretized by means of a finite volume approach. The implicit segregated version of the solver is employed. The pressure-velocity coupling is achieved by means of the SIMPLE algorithm. The convective terms are discretized using a second order accurate upwind scheme, and pressure and viscous terms are discretized by a second-order-accurate centered scheme. A second order implicit time formulation is also used. Turbulence closure is provided by the realizable k - turbulence model. In this study, a mini hydro turbine (3kW) has been considered for utilization of horizontal axis impeller. The turbine performance and flow behavior have been evaluated by means of numerical simulations. Moreover, the performance of the impeller varied in the pressure distribution, torque, rotational speed and power generated by the different number of blades and angles. The model has been validated, comparing numerical results with available experimental data.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.68 no.2
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• pp.262-268
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• 2019

Previous dynamic models of hysteresis motor use an extended induction machine equivalent circuit or somewhat different equivalent circuit with conventional one, which makes unsatisfiable results. In this paper, the hysteresis dynamic characteristics of the motor rotor are analyzed using the inverse Preisach model and the hysteresis motor equivalent circuit considering eddy current effect. The hysteresis loop for the rotor ring is analyzed under full-load voltage source static state. The calculated hysteresis loop is then approximated to an ellipse for simplicity of dynamic computation. The permeability and delay angle of the elliptic loop apply to the dynamic analysis model. As a result, it is possible to dynamically analyze the hysteresis motor according to the applied voltage and the rotor material. With this method, the motor speed, generated torque, load angle, rotor current as well as synchronous entry time, hunting effect can be calculated.

• Journal of the Korea Safety Management & Science
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• v.23 no.4
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• pp.93-104
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• 2021

In this paper, we propose a method for diagnosing overload and working load of collaborative robots through performance analysis of machine learning algorithms. To this end, an experiment was conducted to perform pick & place operation while changing the payload weight of a cooperative robot with a payload capacity of 10 kg. In this experiment, motor torque, position, and speed data generated from the robot controller were collected, and as a result of t-test and f-test, different characteristics were found for each weight based on a payload of 10 kg. In addition, to predict overload and working load from the collected data, machine learning algorithms such as Neural Network, Decision Tree, Random Forest, and Gradient Boosting models were used for experiments. As a result of the experiment, the neural network with more than 99.6% of explanatory power showed the best performance in prediction and classification. The practical contribution of the proposed study is that it suggests a method to collect data required for analysis from the robot without attaching additional sensors to the collaborative robot and the usefulness of a machine learning algorithm for diagnosing robot overload and working load.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.9
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• pp.21-27
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• 2022

The rotorcraft engine gearbox transmits the power generated by the turboshaft engine to the rotor by reducing the rotational speed and increasing the torque. The core of the rotorcraft engine gearbox is lightweight performance, which requires maximum weight reduction within the range that meets various requirements and constraints. Therefore, lightweight design through gear macro geometry optimization is necessary. In this study, gear macro geometry optimization was performed to reduce the weight of a rotorcraft engine gearbox. NSGA-III was used for the optimization, resulting in a combination of the gear ratio and macro geometry that minimizes the weight of the total gear. In addition, the safety factor of the gears satisfied the given conditions.

• Korean Journal of Acupuncture
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• v.29 no.1
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• pp.83-92
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• 2012

Objectives : The purpose of this research was to develop the magnetic acupuncture system which used solenoid coil for magnetizing acupuncture needle. The system could generate the meridian electric potential (MEP) similar to the potential by manual acupuncture. Thus, we tried to confirm the therapeutic effect that is caused by the MEP generation. Methods : To confirm the MEP, we stimulated the magnetic acupuncture with at 2Hz, $92.7{\pm}2mT$, PEMFs (Pulsed Electro-Magnetic Fields) at ST37 and measured the evoked potential between ST36 and ST41. Also, we conducted a fatigue recovery test using isokinetic exercise in order to identify the therapeutic effect on musculoskeletal disorders. We chose LR9 as a stimulation point. To observe the state of fatigue, we measured the EMG and analyzed median frequency and peak torque for 20minutes. Results : We observed that MEP which incurred from magnetic acupuncture was higher than he reported MEP induced by manual acupuncture. Moreover, its modes were divided into two types by the direction of magnetic flux. When generating magnetic flux in the direction of acupoint, the positive peak voltage of the MEP was generated. In contrast, negative peak voltage of the MEP was generated whenever meganetic flux generated in the outward direction. As a result of fatigue recovery, the median frequency (MF) of the magnetic acupuncture group were recovered faster than that of the non-stimulation group. However, the peak torques of both groups were not restored until after 20 minutes. Conclusions : We confirmed that the magnetic acupuncture system can lead to the MEP similar to manual acupuncture. Moreover, the MEP had a therapeutic effect on the musculoskeletal disorders.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.9
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• pp.150-155
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• 2019

Cavitation refers to a phenomenon in which empty spaces occur in a fluid due to changes in pressure and a velocity. When a liquid moves at a high speed, the pressure drops below the vapor pressure, and vapor bubbles are generated in the liquid. This study used CFD to analyze the flow of fluid machinery used in marine and offshore plants. The goals are to ensure the validity of the analysis method for marine propellers in an open water test, to increase the forward ratio, and to use FLUENT to understand the flow pattern due to cavitation. A three-dimensional analysis was performed and compared with experimental data from MOERI. The efficiency was highest at advance ratios of 0.7 - 0.8. Thrust was generated due to the difference between the pressure surface and the suction surface, and it was estimated that bubbles would be generated in the vicinity of the back side surface rather than the face side of the propeller, resulting in more cavitation. The cavitation decreased sharply as the advance ratio increased. The thrust and torque coefficients were comparable to those of the MOERI experimental data except at the advance ratio of 1, which showed a difference of less than 5%. Therefore, it was confirmed that CFD can evaluate an open water propeller test.