• Journal of Institute of Control, Robotics and Systems
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• v.9 no.8
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• pp.610-615
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• 2003

This paper proposes a nonlinear virtual coupling fur haptic interface, which offers better performance while maintaining stability of the system. The nonlinear virtual coupling is designed based on a human response model. This human response model exploits delay between the human Intention and the actual change of arm impedance. The proposed approach provides with less conservative constraints for the design of stable haptic interface, compared with the traditional passivity condition. This allows increased performance that is verified through experiments.

• Journal of Institute of Control, Robotics and Systems
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• v.9 no.8
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• pp.585-591
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• 2003

A virtual force is generated and fed back to the operator to make the teleoperation more reliable, which reflects the relationship between a slave robot and an uncertain remote environment as a form of an impedance. In general, for the teleoperation, the teleoperated mobile robot takes pictures of the remote environment and sends the visual information back to the operator over the Internet. Because of the limitations of communication bandwidth and narrow view-angles of camera, it is not possible to watch certain regions, for examples, the shadow and curved areas. To overcome this problem, a virtual force is generated according to both the distance between the obstacle and the robot and the approaching velocity of the obstacle w.r.t the collision vector based on the ultrasonic sensor data. This virtual force is transferred back to the master (two degrees of freedom joystick) over the Internet to enable a human operator to estimate the position of obstacle at the remote site. By holding this master, in spite of limited visual information, the operator can feel the spatial sense against the remote environment. It is demonstrated by experiments that this collision vector based haptic reflection improves the performance of teleoperated mobile robot significantly.

• 제어로봇시스템학회:학술대회논문집
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• 1995.10a
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• pp.191-194
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• 1995

This paper evaluates the influences of sex on the human emotions while coexisting with robots. When we consider human vision, robot's motion is the most important parameter which influences human emotions and must be well controlled for males and females emotions. On the other hand, when we consider human touch of sense, which is effective for cooperation transmitting mutual forces, the softness of robot is an important parameter for human emotions and must be also well controlled for males and females emotions. From these points of view, at first, we evaluate robot's motion under four different shapes of velocity pattern while handing over a cup to humans. Second, we evaluate robot's softness realized by impedance control. From the first experiment, we concluded that the conditions of choosing an adequate maximum velocity value and locating the velocity peak at the center or the first half of the duration are necessary for male's emotions. In addition, the smooth velocity decrease in the last part of the velocity pattern's duration is desired for female's emotions. From the second experiment, we concluded that females prefer lighter values of virtual impedance characteristics than males and any small increase on the heaviness of virtual impedance values is followed by the negative exponential change on human emotions.

• Proceedings of the Korea Multimedia Society Conference
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• 2001.11a
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• pp.260-264
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• 2001

This paper presents virtual reality using 6-DOF Haptic interface. It is proposed reappearance of force using 6-DOF Haptic device that was designed by previous studies and 3D image considered time delay. The performance of conventional control is excellent in the case of the exactly known dynamic model of the robot, but degrades seriously as the uncertainty of the model increases. The virtual reality using 6-DOF Haptic interface is presented here to overcome such that, and verified through the experiment.

• Proceedings of the KIEE Conference
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• 2004.07d
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• pp.2693-2695
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• 2004

Recently A virtual environment provides patient with stimuli which arouses phobia, and exposing to that environment makes him having ability to over come the fear. ECG and HRV are used in most virtual reality system. GSR is electrical impedance of biological tissues and the changes in impedance accompanying physiological activity. GSR is better than ECG or HRV for explaining mental states in other study. In this study, we will analysis GSR signal when a acrophobia patient and a normal is on high floor.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1467-1476
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• 2019

Grid unbalanced faults can cause core saturation of power transformer and produce lower-order harmonics. These issues increase the electrical stress of power electronic devices and can cause a tripping of an entire HVDC system. In this paper, based on the positive-sequence and negative-sequence impedance model of a VSC-HVDC system as seen from the point of common connection (PCC), the resonance problem is analyzed and the factors determining the resonant frequency are obtained. Furthermore, to suppress over-voltage and over-current during resonance, a novel method using a virtual harmonic resistor is proposed. The virtual harmonic resistor emulates the role of a resistor connected in series with the commutating inductor without influencing the active and reactive power control. Simulation results in PSCAD/EMTDC show that the proposed control strategy can suppress resonant over-voltage and over-current. In addition, it can be seen that the proposed strategy improves the safety of the VSC-HVDC system under unbalanced faults.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.5
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• pp.499-508
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• 2002

In this paper, a novel wireless parallel operation algorithm of N+l redundant UPS system with no control interconnections for load-sharing is presented. The proposed control system eliminates the sensing noise and interconnections interference of conventional parallel operation system. To reduce a reactive power deviation in wireless control method, this technique automatically compensates for inverter parameter variation and line impedance imbalances with wireless auto-tuning method. In addition, to increase reliability on transient characteristics of parallel operation, a virtual injected impedance is adopted to eliminate a circulation current among inverter modules. Simulation results are provided in this paper to prove the proposed novel wireless algorithm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.7
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• pp.1139-1146
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• 2001

A tapered impedance-matching line is designed by an inverse scattering method for the one-dimensional medium. The phase compensation factor(PCF) is introduced in order to reduce the error in the inverse scattering process to reconstruct the permittivity profile. By estimating the permittivity profile of the virtual one-dimensional dielectric medium whose reflection characteristic is the same as that of the specified matching line, the matching line is synthesized. The method can be used to design impedance-matching lines with arbitrary passband characteristics without any equivalent circuit analysis. The inevitable errors in the method using the time-domain reflection coefficient can be avoided by using the frequency-domain reflection coefficient.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.342-343
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• 2019

This paper explores the power distribution problem of parallel-connected inverter system which supplies auxiliary power for railway facilities. We propose a droop control method which facilities power distribution and restrain of voltage drop by tracking the average power control command by adjusting the virtual impedance. The performance of proposed droop method is verified by the PSIM simulation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.714-725
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• 2003

The theory of the current-type electromagnetic flowmeter for a high temporal resolution was developed for two-phase flow measurements. To predict the output of the current-type flowmeter, the three-dimensional virtual potential distribution C and the newly introduced flow pattern coefficient f were derived and computed. The output of flowmeter depends on the liquid conductivity (sensitive to temperature) and flow configurations of the two-phase flow with the sinusoidal excitation over 100 Hz. The flow pattern coefficient was specially devised to separate the dependency on the flow configuration of the two-phase flow from that on the liquid conductivity which can be expressed with the calibration of single-phase flow. Using the finite difference method, the three-dimensional virtual potential distributions were computed for the electrode of finite size. By taking derivative of the virtual potential, the weight functions were evaluated and compared with existing analytic series solution for the point-electrode. There was a reasonable correspondence between the present and existing results. In addition, the flow pattern coefficients were evaluated for annular flows with various film thicknesses, and compared with the experimental results by the impedance spectroscopy. The numerical results agreed well with the experimental data.