• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.611-614
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• 1991

In variable speed driving system of three phase induction motor controlled by an inverter, because of the switching of semiconductor devices in inverter, an appreciable amount of harmonic components of voltage waveform can cause the motor to generate losses, torque ripple, acoustic noise and oscillation of semiconductor devices. In this paper a new PAM type PWM inverter using IGBT is described. The output waveforms in the proposed PAM type PWM inverter are investigated both theoretiically and experimentally. The line-voltage waveform is composed of fundamental component and the sidebands of carrier frequency. The lower order harmonics are not included in the output wave form. As each inverter arm does not operate during two-thirds period, the heats, generated in the devices are reduced. That is, the size of the inverter system can he minimized because of the reduction in the heat dissipating equipment.

• Journal of the Korea Computer Industry Society
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• v.5 no.9
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• pp.993-1004
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• 2004

We propose the method for kinematic and dynamic modeling and Path-tracking of four-wheeled mobile robots with 2 d.o.f having the limited drive-torques. Controllability of wheeled-mobile robots is revealed by using the kinematic model. Instantaneously coincident coordinate system, force/torque propagation and Newton's equilibrium law are used to induce the dynamic model. When drive-torques generated by inverse dynamics exceed the limitation, we make wheeled-mobile robots follow the reference path by modifying the planned reference trajectory with time-scaling. The controller is introduced to compensate for error owing to modeling uncertainty and measurement noise. And simulation results prove that the method proposed by this paper is efficient.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.1 s.94
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• pp.265-271
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• 1999

In the feed drive systems or the spindle systems of machine tools that consist of many mechanical components, a torsional vibration is often generated because of its elastic elements in torque transmission-Generally, the accuracy of motion control system is strongly influenced by the dynamic behavior of coupled transmission components Especially, a torsional vibration caused by the elasticity of mechanical elements might deteriorate the quick movement of system and lead to shorten the life time of the mechanical transmission elements. So, it is necessary to analyze the electromechanical system mathematically to optimize the dynamic characteristics of the feed m1d spindle system. In this paper, based on the DC motor model, a model of electro-drive system with motor has been developed and an optimal criterion for tuning the gain of speed controller is discussed. The frequency bandwidth of the system and the damping ratio in time domain are optimal design specifications for the gain adjustment speed controller. The gains of PI speed controller are then derived from the bandwidth and damping ratio, and those relationships have been classified.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.11
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• pp.1130-1136
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• 2009

A new control algorithm for the yaw motion control of a unicycle robot has been proposed in this paper. With the increase of life quality, there are various transportation systems such as segway and unicycle robot which provide not only transportation but also amusement. In most of the unicycle robots share the same technology in that the directions of roll and pitch are controlled by the balance controllers, allowing the robots to maintain balance for a long period by continuously moving forward and backward. However, one disadvantage of this technology is that it cannot provide the capability to the robots to avoid obstacles in their path way. This research focuses to provide the yawing function to the unicycle robot and to control the yaw motion to avoid the obstacles as desired. For the control of yawing motion, the yaw angle is adjusted to the inertia generated by the velocity and torque of a yawing motor which is installed in the center axes of the unicycle robot to keep the lateral control simple. Through the real experiments, the effective and robustness of the yawing control algorithm has been demonstrated.

• Journal of Power System Engineering
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• v.19 no.1
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• pp.24-30
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• 2015

Geothermal energy is used in various types, such as power generation, direct use, and geothermal heat pumps. Geothermal energy with high temperature have been used for power generation for more than a century. The purpose of the study is to investigate flow and electricity power characteristics of hydraulic turbine for power generation of geothermal heat pump type with closed-system. The differences between the four types of hydraulic turbine, are different from the blade shape, volume, angle and etc. In case of prototype(1), pressure at blade was reduced to 2.1 bar, the kinetic energy of blade increased by increasing flow velocity(4.1 m/s). The increase of flow velocity at the blade edge markedly appeared, to increase the kinetic energy of the rotating shaft. In case that gateway in hydraulic turbine was installed, operating torque and RPM(1,080) of the rotating shaft increased respectively. Although rotational speed of prototype(2) compared to prototype(1) was reduced, the power generation capacity was greater about 3.4 times to 97 W. The most power of 255W was generated from prototype (4).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.04c
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• pp.10-14
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• 2008

In this paper, abnormal heating of circuit breaker in panel board by poor connection was studied. Firstly, calculation method of contact resistance shown in IEC 60943 was examined. Secondly, concerning abnormal heating of circuit breaker in panel board, field measurements were performed. Field measurements showed that locally abnormal heating by poor connection could be detected, therefore, in that case, immediate action was needed. Finally, experiments regarding abnormal heating between terminal of circuit breaker and electric wire were conducted. The results showed that abnormal heating above $180^{\circ}C$ was measured. Also, in the results of analysis of electrical waveforms according to load current, voltage drop occurred around poor connection, and the oxide was generated according to mechanical vibration. In order to prevent electrical disaster caused by poor connection, adequate torque should be applied to electrical connection, and periodic check-ups are needed.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.2 s.95
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• pp.218-224
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• 1999

In the feed drive systems of machine tools that consist of many mechanical components such as motor, coupling, ballscrew, nut or table, a torsional vibration is often generated because of its elastic elements in torque transmission. Generally, the accuracy of motion control system is strongly influenced by the dynamic behavior of coupled transmission components. Especially, a torsional vibration caused by the elasticity of mechanical elements might deteriorate the quick movement of system and lead to shorten the life time of the mechanical transmission elements. So, it is necessary to analyze the electromechanical system mathematically to optimize the dynamic characteristics of the feed system. In this paper, the mathematical model of a feed drive system was developed and its mechanical characteristics were analyzed on the basis of the proposed model. The design concepts of speed control loop to stabilize a feed drive system were also proposed.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.632-635
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• 2009

Nowadays renewable energy has undergone major development, however most renewable energy resources still have demerit which is under the influence of environmental factors that can not be set up the power plants or can not be generated the rated power. To wander from the point of environmental instability, the present paper looks at the tidal current energy which can supply regular electric power. It has an important merit which is more predictable than others, however the place which can be set up is limited and the turbine system must be optimized. The development of the optimized rotor blades design is urgent to obtain regular electric power using the tidal current energy. Therefore, the paper expands on this idea and presents a conceptual design of 100kW horizontal axis rotor blade for the tidal current turbine using blade element momentum (BEM) analysis. The compatibility of horizontal axis tidal turbine (HATT) is verified using a commercial computational fluid dynamics (CFD) code, ANSYS-CFX. This paper presents results of the numerical analysis, such as pressure, streak line and the performance curves with torque data for the inflow of the horizontal axis tidal current turbine (HATT).

• Earthquakes and Structures
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• v.9 no.1
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• pp.145-171
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• 2015

Due to earthquakes, many structures suffered extensive damages that were attributed to the torsional effect caused by mass, stiffness or strength eccentricity. Due to this type of asymmetry torsional moments are generated that are imposed by means of additional shear forces developed at the vertical resisting structural elements of the buildings. Although the torsional effect on the response of reinforced concrete buildings was the subject of extensive research over the last decades, a quantitative index measuring the amplification of the shear forces developed at the vertical resisting elements due to lateral-torsional coupling valid for both elastic and elastoplastic response states is still missing. In this study a reliable index capable of assessing the torsional effect is proposed. The performance of the proposed index is evaluated and its correlation with structural response quantities like displacements, interstorey drift, base torque, shear forces and upper diaphragm's rotation is presented. Torsionally stiff, mass eccentric single-story and multistory structures, subjected to bidirectional excitation, are considered and nonlinear dynamic analyses are performed using natural records selected for three hazard levels. It was found that the proposed index provides reliable prediction of the magnitude of torsional effect for all test examples considered.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.2
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• pp.66-71
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• 2011

This study analyzed the mechanical characteristics and evaluated their subsequent performance for two types of seals which reinforced characteristics with lower friction and anti-wear functions among the foremost important features in the automotive engine seals; one with the addition of glass fiber to PTFE(Polytetrafluoro ethylene); the other with the addition of self-lubricant molybdenumin addition to the glass fiber. Based on the configuration design of seal installed to the front part in the automotive engine, this study carried out interpretations on the stress and reaction for those two types of oil seals to compare the maximum stress and contact load generated from the seal steel, rubber and PTFE lip. This study also verified the stress concentration and anti-wear performance through the coefficient of friction, torque and durability test by producing two types of PTFE seals actually.