• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1225-1227
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• 2005

A Bi-2223 tape has beer developed for power applications such as a fault current limiter, a power cable and a superconducting magnetic energy storage system. In such applications, the Bi-2223 tape carries time varying transport current and in addition experiences time varying external magnetic field. It is well known that the external magnetic field not only causes magnetization loss in the Bi-2223 tape, but also drastically increases transport loss due to a so-called "dynamic resistance". We developed an evaluation setup, which can measure transport loss in external at magnetic fields. Using this equipment, we measured the dynamic resistances for various amplitudes and frequencies of an external ac magnetic field perpendicular to the face in the tape. Simultaneously we investigated the effect of an external ac field on transport loss with different experimental conditions. This paper describes test results and discussions on correlation between the dynamic resistance and the transport loss for the Bi-2223 tape.

• Progress in Superconductivity and Cryogenics
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• v.8 no.3
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• pp.59-62
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• 2006

For electric power applications of Bi-2223/Ag superconducting tapes, a transport characteristic is important issue. A transport characteristic is strongly depends on the magnitude and direction of external time-varying magnetic field. To verify a effect of external magnetic field, we manufactured a prototype magnet and obtained transport characteristics with respect to the magnitude, the direction and the frequency of external magnetic field. The data acquired in this paper will be used as a source for the study of HTS electric power applications which is supposed to carry on.

• Journal of Positioning, Navigation, and Timing
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• v.13 no.2
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• pp.179-187
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• 2024

The performance of a Strapdown Inertial Navigation System (SDINS) relies heavily on the accuracy of sensor error calibration. Systematic calibration is usually employed when only a 2-axis turntable is available. For systematic calibration, the body frame is commonly defined with respect to sensor axes for ease of computation. The drawback of this approach is that sensor axes may undergo time-varying deflection under temperature change, causing pseudo gyro bias. The effect of pseudo gyro bias on navigation performance is negligible for low grade navigation systems. However, for higher grade systems undergoing rapid temperature change, the error is no longer negligible. This paper describes in detail conditions leading to the presence of pseudo gyro bias, and proposes two techniques for mitigating the error. Experimental results show that applying these techniques improves navigation performance for precision SDINS, especially under rapid temperature change.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.8
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• pp.25-32
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• 2012

In this paper, we propose a method for improving the performance of low complexity LS channel estimation for OFDM in fast time varying channels. The CE-BEM channel model used for the low complexity LS channel estimation has a problem on its own and deteriorates channel estimation performance. In this paper, we first use time domain windowing in order to remove the effect of ICI caused by data symbols. Then samples are taken from the results of the LS channel estimation and the effects of the windowing are removed from them. For resolving the defect of CE-BEM, the channel responses are recovered by interpolating the resultant samples with DPSS employed as basis functions the characteristics of which is well matched to the time variation of the channel. Computer simulations show that the proposed channel estimation method gives rise to performance improvement over conventional methods especially when channel variation is very fast and confirm that not only which type of functions is selected for the basis but how many functions are used for the basis is another key factor to performance improvement.

• Computational Structural Engineering
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• v.1 no.2
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• pp.101-109
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• 1988

The evaluation of the system reliability is generally quite difficult and costly as the structure becomes large and complex, especially when it is subjected to multiple time varying loads, and for redundant structures which have many possible modes of failur, e.g., system collapse through the formation of plastic hinge mechanisms. In reality most loadings acting on the structures are random in intensity as well as in occurrence time and duration. To include the load variability in time, the loads are described in terms of stochastic processes. Based on a tri-modal upper bound, a point estimate for the system reliability has been developed for more accuracy without extensive computational effort. This tri-modal point estimate also ensures the continuity of the system reliability function, which is a necessary condition in many nonlinear programming techniques. In addition, the Load Coincidence method, by which the combined effect of time varying loads are taken into account, has been modified to suitable for cases with an always-on load.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.5
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• pp.473-477
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• 2005

A Bi-2223 tape has been developed for power applications such as a fault current limiter, a power cable and a superconducting magnetic energy storage system. In such applications, the Bi-2223 tape carries time varying transport current and in addition experiences time varying external magnetic field. It is well known that the external magnetic field not only causes magnetization loss in the Bi-2223 tape, but also drastically increases transport loss due to a so-called 'dynamic resistance' We developed an evaluation setup, which can measure transport loss in external at magnetic fields. Using this equipment, we measured the dynamic resistances for various amplitudes and frequencies of an external at magnetic field perpendicular to the face in the tape. Simultaneously we investigated the effect of an external ac field on transport loss with different experimental conditions. This paper describes test results ana discussions on correlation between the dynamic resistance and the transport loss for the Bi-2223 tape.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10b
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• pp.852-857
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• 1990

The purpose of this paper is to design a robust controller for a class of time-varying systems with bounded disturbance described by the differential equation. The robust desiging method proposed in this paper, called "incentive design method" is different from developed designing methods in the past, and has following properties. The robust control law designed by this method can guarantee a certain value of the cost functional no matter how the disturbance vary within the given bounds. Here, the certain value of the cost functional may not be a saddle-point value, but is the value selected by a system designer. Therefore, the bounded disturbance has at least no bad effect on the value of the cost functional during finite interval of time. The method is based on the theory of incentive differential games. In addition, the form of control law is constructed by the system designer ahead of time. A numerical illustrative example is given in this paper. It is shown from this derivation and this numerical example that the approach developed in this paper is effective and feasible for some practical control problem.l problem.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.518-521
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• 1999

This paper describes high speed squirrel cage induction motor drives without speed sensors using neural network based on Kalman filter Learning. High speed motors are receiving inverasing attentions in various applications, because of advantages of high speed, small size and light weight with same power level. Larning rate by Kalman filtering is time varying, convergence time fast, effect of initial weight between neurons is small.

• Investigative Magnetic Resonance Imaging
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• v.24 no.2
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• pp.67-75
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• 2020

When a patient takes an MRI scan, the patient has a risk of unexpected injuries due to the intensive electromagnetic (EM) field. Among the injuries, the tissue heating by the time-varying EM field is one of the main issues. Since an implanted artificial structure with a conductive material aggravates the heating effect, lots of studies have been conducted to investigate the effect around the implants. In this review article, a mechanism of RF heating around the implants and related studies are comprehensively investigated.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.161-163
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• 1998

The interruption performance of EHV class gas circuit breakers critically depends on the flow conditions inside interrupter and the external circuit conditions. In case of puffer type gas circuit breakers the flow conditons are significantly influenced by arcing time. In this paper the calculated results of RRRV and pressure rise at current zero with varying arcing time are presented and the effect of arcing time on the thermal interruption performance of EHV class gas circuit breakers is analyzed.