• Journal of Power Electronics
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• v.8 no.1
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• pp.10-22
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• 2008

The wind-driven doubly fed induction generator (DFIG) is currently under pressure to be more grid-compatible. The main concern is the fault ride-through (FRT) requirement to keep the generator connected to the grid during faults. In response to this, the paper introduces a novel model and new control scheme for the DFIG. The model provides a means of direct stator power control and considers the stator transients. On the basis of the derived model, a robust linear quadratic (LQ) controller is synthesized. The control law has proportional and integral actions and takes account of one sample delay in the input owing to the microprocessor's execution time. Further, the influence of the grid voltage imperfection is mitigated using frequency shaped cost functional method. Compensation of the rotor current pulsations is proposed to improve the FRT capability as well as the generator performance under grid voltage unbalance. As a consequence, the control system can achieve i) fast direct power control without instability risk, ii) alleviation of the problems associated with the DFIG operation under unbalanced grid voltage, and iii) high probability of successful grid FRT. The effectiveness of the proposed solution is confirmed through simulation studies on 2MW DFIG.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.107-109
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• 2006

The additional matters appear to be considered in several aspects for building up power-quality measuring system of transmission system(high voltage system) compared to distribution system(middle or low voltage system). Like in distribution system, input signals are also received from PT and CT source of voltage and current respectively in transmission system and applied in accordance with a certain rate. In this case, very big error rate can be occurred according to the specification of the measuring system as the applying rate is bigger than in distribution system beyond comparison. In addition, when the abnormal signal occurred such as sag/swell, interruption, transient etc., power quality of other sites linked to the system also should be checked to find the accurate cause of the abnormal power-quality signals from the corresponding site. Accordingly, the accurate diagnosis on the condition of Power quality for the system depends on the way how the synchronization system is brought along for each site. This paper will suggest the solution for the most effective system building focused on how to solve the problem of the error rate and synchronization described in the above when building up the measuring system of power quality for transmission system.

• Proceedings of the KIPE Conference
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• 2006.06a
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• pp.432-434
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• 2006

The additional matters appear to be considered in several aspects for building up power-quality measuring system of transmission system(high voltage system) compared to distribution system(middle or low voltage system). Like in distribution system, input signals are also received from PT and CT source of voltage and current respectively in transmission system and applied in accordance with a certain rate. In this case, very big error rate can be occurred according to the specification of the measuring system as the applying rate is bigger than in distribution system beyond comparison. In addition, when the abnormal signal occurred such as sag/swell, interruption, transient etc., power quality of other sires linked to the system also should be checked to find the accurate cause of the abnormal power-quality signals from the corresponding. site. Accordingly, the accurate diagnosis on the condition of power quality for the system depends on the way how the synchronization system is brought along for each site. This paper will suggest the solution for the most effective system building focused on how to solve the problem of the error rate and synchronization described in the above when building up the measuring system of power quality for transmission system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.7
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• pp.1436-1441
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• 2004

Abnormal current-voltage characteristics of an oxide semiconductor have been investigated and a novel method of detecting reducing gases utilizing self-heating mechanism of sensing layer without an additional heater has been developed. Planar-type sensors based on WO3-doped SnO2 were fabricated using a screen-printing technique. The applied voltage across the sensing layer caused heating of the sensing layer and the current abruptly varied upon exposure to a gas mostly as a result of surface reactions. A unique and fascinating aspect of the gas sensing scheme is that no additional heater is necessary for detection. The new sensing method has been applied to C2H5OH gas in this preliminary work.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.11
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• pp.107-113
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• 2016

All circuits in power input can only use the power provided by an external power supply. General electronic circuits use a secondary supply generated by a converter using a primary power in the power input. But protection and detection circuit for over-voltage circuit or under-voltage in power input have to use that input power because there is no other supply in power input. Therefore, previous electronics for satellite can protect only over-voltage using a zener diode, and can't detect over-voltage and under-voltage events, and provide a detection capability for over-voltage and under-voltage only for secondary supply. The proposed circuit can detect over-voltage and under-voltage using a single supply for the primary power input, +28V, with the threshold characteristics for MOS-FET, and the accuracy for a detection circuit is increased by 2.5%.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.12 no.4
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• pp.136-145
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• 1998

This paper describes the FFT and coefficient analysis of vibration signals for preventive diagnosis of a mold transformer at normal and abnormal state. Varying applied voltage, loading current and temperature as control variables for he experiment, measurement variables such as magnitude of vibration signals, frequency spectrum and time series coefficient were analyzed. The vibration signals by variation of control variables were measured by acceleration sensor adhered on the surface of winding and core, and measurement variables were calculated using dat acquisition system. After analyzing the normal state, the structural distortion was also simulated. The vibration signals at abnormal state were measured by the same control variables variation as the normal state. As a result, vibration signals between normal and abnormal state could be distinguished by comparison of the perpendicular and horizontal vibration signal.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.2
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• pp.93-101
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• 2023

In this study, a deep learning algorithm was used to diagnose electric potential signals obtained through CIPS and DCVG, used indirect inspection methods to confirm the soundness of buried pipes. The deep learning algorithm consisted of CNN(Convolutional Neural Network) model for diagnosing the electric potential signal and Grad CAM(Gradient-weighted Class Activation Mapping) for showing the flaw prediction point. The CNN model for diagnosing electric potential signals classifies input data as normal/abnormal according to the presence or absence of flaw in the buried pipe, and for abnormal data, Grad CAM generates a heat map that visualizes the flaw prediction part of the buried pipe. The CIPS/DCVG signal and piping layout obtained from the 3D finite element model were used as input data for learning the CNN. The trained CNN classified the normal/abnormal data with 93% accuracy, and the Grad-CAM predicted flaws point with an average error of 2m. As a result, it confirmed that the electric potential signal of buried pipe can be diagnosed using a CNN-based deep learning algorithm.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.36 no.6
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• pp.418-423
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• 1987

In the course of the investigation to the field dependent electrical conducation mechanism in polypropylene, an abnormal conduction phenomena such as voltage controlled negative resistance charateristics has been observed at the junction of two regions charateriged by schottky effect and space charge effect respectively. This abnormal characteristics was observed initially about 110MV / m of the field strength and at 25 , however, the field strength where it observed was decreased and the apparent feature of negative charateristics was less pronounced as increasing ambient temperature. Although the observations of analogous characteristics in other materials such as polyethylene, polymethylemethactylate, and polystyrene have already been reported together with plausible explanation by Toureille and others, however, it was found that the proposed concept by those authors was little use to the present observations for quantitative discussions. Accordingly we tried to adapt another conceptual discussion based on Gibbons's formulation pertaing to the saturatio trend of the field dependent drift velocity of carriers towards the thermal velocity corresponding to the ambient temperature so that the quantitative explanatio on the observed facts has been succeeded to some estent of reasonable acceptance.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.1342-1346
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• 2004

Recently, the load increasement and regenerative system of electrified railway system make a difficult to distinguish between the load current and fault current and it need a new intelligent protection system. The failure of traction system cause collapse of the other systems from high tension current. The over current from abnormal situation produces high tension current flow, high temperature are, voltage instability and current cutting, and break down railway systems. Protective system of traction system playa role of which detect and isolate failure points. In this paper, we proposed intelligent algorithm for discriminating normal and abnormal situation instead of the system being operated abnormally.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.34C no.8
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• pp.49-63
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• 1997

This paper presents a current sensor that detects defects in CMOS integrated circuits using the current testing technique. The current sensor is built in a CMOS integrated circuit to test an abnormal current. The proposed circuit has a very small impact on the performance of the circuit under test during the normal mode. In the testing mode, the proposed circuit detects the abnormal current caused by permanent manufacturing defects and determines whether the circuit under test is defect-free or not. The proposed current sensor is simple and requires no external voltage and current sources. Hence, the circuit has less area and performance degradation, and is more efficient than any previous works. The validity and effectiveness are verified through the HSPICE simulation on circuits with defects.