• Journal of Biomedical Engineering Research
• /
• v.25 no.6
• /
• pp.465-469
• /
• 2004

We propose a new training system for the improvement of equilibrium sense using unstable platform. This system consists of unstable platform, computer interface and various softwares. The unstable platform was a simple structure of elliptical-type which included tilt sensor and wireless RF module. To evaluate the effort of balance training, we measured the parameters such as the moving time to the target and duration to maintain cursor in the target of screen. Balance training was carried out for two weeks and we classified the subjects into two groups by the training program. As a result, the moving time was reduced and duration time was lengthened through the repeating training of equilibrium sense using training program of sine curve trace(SCT) and Block game. Especially, there was remarkable improvement at direction which was too difficult for the subjects to balance their body. It was showed that this system had an effort on improving equilibrium sense and might be applied to clinical use as an effective balance training system.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.18 no.12
• /
• pp.1855-1869
• /
• 1993

For the traditional ALOHA system without capture, the Markov chain obtained using the number of backlogged users at each slot if shown to be non-ergodic. So the infinite population ALOHA with fixed retransmission probabilities is unstable for any choice of the arrival rates and retransmission probabilities. The capture ALOHA system of also shown to be unstable for any arrival rate unless it has perfect. In this paper, we study a stabilization policy for capture ALOHA system that controls the retransmission probabilities and prove the stability of its multidimensional Markovian model by empolying a continuous Lyapunov function, and thus identify the stability region. We also study a delay performance through computer simulation th show the stability for any input rate below the maximum achievable channel throughput.

• Proceedings of the KIEE Conference
• /
• 2006.07a
• /
• pp.16-17
• /
• 2006

In this paper, RCF analysis method which is very powerful to analyze non-continuous systems with switching elements is applied to small signal stability problems. As an effect of switching operations, the eigenvalues of system can be changed and newly unstable oscillation modes may be occurred. Also, changing firing angles of switching equipments may make the system stable or unstable. As an illustrating example, the oscillation modes of the system with different firing angles are computed by the RCF analysis method.

• Journal of Institute of Control, Robotics and Systems
• /
• v.15 no.8
• /
• pp.804-811
• /
• 2009

This paper deals with the relationship between zeros and step response of the second and third order LTI(Linear Time Invariant) SISO(Single-Input and Single-Output) systems. As well known, if a system has a single unstable zero, it shows the step response with undershoot and, on the other hand, a stable zero slower than the dominant pole causes the system to have the step response with overshoot. Generally, in the case of a system with two unstable real zeros, it is known to have B type undershoot[7]. But there are many complex cases of the step response extrema corresponding to zeros location in third order systems. This paper investigates the whole cases depending on DC gains of the additive equivalence systems and they are to be classified by the region of zeros which are related to the shape of the step response. Moreover, monotone nondecreasing conditions are proposed in the case of complex conjugate zeros as well as the case of two stable zeros.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.55 no.1
• /
• pp.13-17
• /
• 2006

In this paper, the RCF(Resistive Companion Form) analysis method which is used to analyze small signal stability problems of non-continuous systems including switching devices. The RCF analysis method is mathematically rigorous and computes eigenvalue of the system periodic transition matrix based on discrete system analysis method. As an effect of switching operations, the eigenvalues of the systems are changed and newly unstable oscillation modes may be occurred. As an illustrating example, the oscillation modes of the system with different switching time intervals are computed exactly by the RCF analysis method and the results show that ON/OFF time intervals of switching equipments are important factors to make the system stable or unstable. This result shows that the RCF analysis method is very powerful to analyze small signal stability problems of power systems including switching devices such as FACTS equipments.

• Solar Energy
• /
• v.19 no.4
• /
• pp.63-69
• /
• 1999

The conventional grid connected PV(Photovoltaic) system has a unstable output pattern due to its dependence on the weather condition, although solar-cell array averagely has a regular output characteristics to have a peak output nearly at noon. Therefore assuming the high density grid connection in the future, this unstable output pattern can be one of the main reasons to generate power disturbance such as voltage variation, frequency variation and harmonic voltage generation in low voltage distribution line. However general grid connected solar-cell system do not have functions to cope with these disturbances. Therefore this study proposed a advanced type grid connected PV system with functions to suppress output power fluctuation due to solar-cell array output variation and showed the levelling effect of fluctuation due to instantaneous array output variation.

• Proceedings of the KIEE Conference
• /
• 1993.07a
• /
• pp.76-78
• /
• 1993

This paper describes an efficient method of computing any desired number of the most unstable eigenvalues and eigenvectors of a large scale multi-machine power system. Approximate eigenvalues obtained by Hessenberg process are refined using Rayleigh quotient iteration with cubic convergence property. If further eigenvalues and eigenvectors are needed, the procedure described above are repeated with deflation. The proposed algorithm can cover all the model types of synchronous machines, exciters, speed governing system and PSS defined in AESOPS. The proposed algorithm applied to New England test system with 10 machines and 39 buses produced the results same with AESOPS in faster computation time. Also eigenvectors computed in Rayleigh quotient iteration makes it possible to make eigen-analysis for improving unstable modes.

• Journal of Drive and Control
• /
• v.16 no.2
• /
• pp.36-42
• /
• 2019

The ESP (Electronic Stability Program) is an active control system that controls the posture of the vehicle by sensing the unstable state of the vehicle during braking, driving, or turning. The system works if the vehicle becomes unstable and it is very dangerous to develop it in the actual vehicle. For this reason, many studies have been carried out on the method of developing with simulation such as SIL / EIL. Some advanced companies have already applied it to the product development process. In this study, ESP hydraulic system and braking device model were constructed using SimulationX to build ESP SIL / EIL model. The hydraulic system model was constructed using the actual design parameters and the performance of the hydraulic model was verified by comparing with the actual vehicle test.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2006.10a
• /
• pp.441-442
• /
• 2006

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.41 no.7
• /
• pp.694-700
• /
• 1992

The digital computer control systems which are used in time sharing control or remote control may experience intermittent interruptions. Further it can be made unstable by the intermittent interruptions of a control computer. This paper presents a mathematical model with intermittent computer interruptions and an unstable output response through simulation. Also it presents to improve the control quality using extrapolation method in interrupt synchronizing feedback path.