• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.9
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• pp.89-98
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• 2014

A diagnostic fluoroscopy X-ray system uses a 32kW or greater X-ray generator for obtaining real-time moving images and high-resolution images. Fluoroscopy X-ray systems have to use a high-capacity AC power source to perform long-time low-power fluoroscopy and short-time high-power spot exposure. In this paper, we propose a hybrid type X-ray generator for fluoroscopy X-ray system which can perform fluoroscopy and spot exposure with a low-capacity AC power source and an energy storage device. The characteristics of energy storage devices are compared and each energy storage device is modelled to equivalent circuit. And the characteristics of available energy are analyzed as a function of output voltage and power. A 32kW class hybrid X-ray generator with EDLC as an energy storage device for fluoroscopy X-ray system was constructed, and its validity was verified by means of simulations and experiments.

• Journal of Power Electronics
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• v.14 no.5
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• pp.834-841
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• 2014

This paper proposes new active switched-capacitor and switched-inductor Z-source inverter (ASC/SL-ZSI) topologies, which can provide a higher boost ability with a small shoot-through time. The proposed ASC/SL-ZSIs inherit all of the advantages of the classical ZSI, and have a stronger voltage boost inversion ability when compared with the classical ZSI. Thus, the output ac voltage quality is significantly improved. In addition, more cells can be cascaded in the impedance network in order to obtain a very high boost ability. The proposed topologies can be applied to photovoltaic or fuel-cell generation systems with low-voltage renewal sources due to their wide range of obtainable voltages. Both simulations and the experimental results are carried out in order to verify performance of the proposed topologies.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.2
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• pp.130-134
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• 2020

Metal oxide varistors (MOVs) protect circuits and devices from transient overvoltages in electric power systems. However, a MOV continuously deteriorates owing to manufacturing defects or repetitive protective operations from transient overvoltages. A deteriorated MOV may result in a short circuit or a line-ground accident. Previous studies focused on the analysis of deterioration mechanisms and condition diagnosis techniques for MOVs owing to their recent growth of use. An accelerated deterioration experiment under the same conditions in which a MOV operates is essential. In this study, we designed and fabricated a surge generator that can apply a surge current to a MOV connected to AC mains. The coupling network operates at a low impedance against the surge current from the surge generator and transfers the surge current to the MOV under test. It also acts as a high impedance against AC mains for the AC voltage not to be applied to the surge generator. The decoupling network operates at a high impedance against the surge current and blocks the surge current from AC mains. It also acts as a low impedance against AC mains for the AC voltage to be applied to the MOV under test. The prototype surge generator can apply the 8/20 us up to 15 kA on AC voltages in the approximate range of 110~450 V, and it fully operates on a LabVIEW-based program.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.11 no.4
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• pp.109-116
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• 1997

This paper describes the surge protective device combined with varistor and LC low pass filter on AC power circuits. Up to now varistors alone have been used as a surge protective device on AC power circuits, but it gives negative effects on the equipments to be protected due to the steep rise and high remnant voltage. Therefore in this work, for the purpose of improving the cutoff performance of surge protective device on AC power circuits, the hybrid-type surge protective device with varistor and LC filter was designed and prepared. And the experiments for operational characteristics and clamping performance of the surge protective device were carried out with an 1.2/50[$\mu$s] impulse generator. As a result, the proposed surge protective device with the combination of varistors and LC filter can limit the surge voltage to lower value and reduce the value of dV /dt to very small values. Also the attenuation of high-frequency voltages across the output port is effectively provided by LC filter. Therefore this result may be all the more helpful avoiding both damage and upset of electronic systems.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1833-1842
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• 2016

In grid-connected converter control, grid voltage feedforward is usually introduced to suppress the influence of grid voltage distortion on the converter's grid-side AC current. However, owing to the time-delay in control systems, the suppression effect of the grid voltage distortion is seriously affected. In this paper, the positive effects of the grid voltage feedforward control are analyzed in detail, and the time-delay caused by the low-pass filter (LPF) in the voltage filtering circuits and digital control are summarized. In order to reduce the time-delay effect on the performance of the feedforward control, a voltage feedforward control strategy with time-delay compensation is proposed, in which, a leading correction of the feedforward voltage is used. The optimal leading step used in this strategy is derived from analyzing the phase-frequency characteristics of a LPF and the implementation of digital control. By using the optimal leading step, the delay in the feedforward path can be further counteracted so that the performance of the feedforward control in terms of suppressing the influence of grid voltage distortion on the converter output current can be improved. The validity of the proposed method is verified through simulation and experiment results.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.5
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• pp.423-432
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• 1999

This paper proposes a 12­pulse diode rectifier system with low kVA components suitable for powering switch mode power supplies or ac/dc converter applications. The proposed 12-pulse system employs a polyphase transformer, a zero sequence blocking transformer (ZSBT) in the dc link, and an interphase transformer. Results produce near equal leakage inductance in series with each diode rectifier bridge ensuring equal current sharing and performance improvements, The utility input currents and the voltage across the ZSBT are analyzed the kVA rating of each component in the proposed system is computed. The 5th , 7th , 17th and 19th harmonics are eliminated in the input line currents resulting in clean input power. The dc link voltage magnitude generated by the proposed rectifier system is nearly identical to a conventional to a conventional 6-pulse system. The proposed system is suitable to retrofit applications as well as in new PWM drive systems. Simulation and experimental results from a 208V , 10kVA system are shown.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.5
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• pp.95-103
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• 2013

Protection of the electrical and electronic equipment against surges in low voltage AC power distribution systems is based on wide applications of surge protective devices(SPDs). Cascade application of SPDs located at the service entrance of a building and near sensitive equipment is intended to ensure the optimal voltage protection level and energy sharing among cascade SPDs. In this paper, when surges impinge at the service entrance of the building of interest, the protection characteristics of two-stage cascade SPD systems were investigated. The influence of the distance between the upstream and downstream SPDs on the voltage protection level and energy sharing of the two-stage cascade SPD systems were analyzed experimentally. It was found that the energy sharing of two-stage cascade SPD systems strongly depends on the distance between the two SPDs and the component of SPD. As the distance between the two SPDs increases, the energy absorbed by the upstream SPD increases while the energy absorbed by the downstream SPD decreases. Consequently, it is desirable to select the upstream and downstream SPDs having the proper energy capability with due consideration of the distance between the two SPDs.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.12
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• pp.1647-1656
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• 2013

Although the demand for electricity has been increasing these days, it becomes more difficult to find new sites for large-scale power generation plants near urban areas due to environmental and economic issues. Therefore, new power plants are forced off to rural or desolate coastal areas. As a result, there is significant regional imbalance in power generation and consumption between urban and rural areas in South Korea. This paper investigates the feasibility of high-voltage DC (HVDC) system as a candidate for electric power transmission system from east-coastal sites to metropolitan area. To this end, this paper analyzes transient stability and dynamic impact of a HVDC transmission system and compares the results to conventional high-voltage AC (HVAC) transmission systems via PSS/E simulation. This paper also examines the effect of HVDC system to voltage variation and low-frequency resonance in the neighboring buses in the grid using ESCR(Effective Short Circuit Ratio)과 UIF(Unit Interaction Factor) indices.

• Journal of Power Electronics
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• v.11 no.5
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• pp.734-742
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• 2011

In this paper a robust method is presented for the combined design of STATCOM and Power System Stabilizer (PSS) controllers in order to enhance the damping of the low frequency oscillations in power systems. The combined design problems among PSS and STATCOM internal ac and dc voltage controllers has been taken into consideration. The equations that describe the proposed system have been linearized and a Fuzzy Logic Controller (FLC) has been designed for the PSS. Then, the Particle Swarm Optimization technique (PSO) which has a strong ability to find the most optimistic results is employed to search for the optimal STATCOM controller parameters. The proposed controllers are evaluated on a single machine infinite bus power system with the STATCOM installed in the midpoint of the transmission line. The results analysis reveals that the combined design has an excellent capability in damping a power system's low frequency oscillations, and that it greatly enhances the dynamic stability of power systems. Moreover, a system performance analysis under different operating conditions and some performance indices studies show the effectiveness of the combined design.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1715-1717
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• 1997

This paper deals with the dead operation characteristics of the earth leakage circuit breaker(ELB) caused by impulse voltages. The surge protective devices for electronic circuit and AC power lines are becoming more widely used. It is possible to give rise to the malfunction of ELB due to the operation of surge protective devices, and the interruption of AC power lines brings about several disadvantages such as low reliability of electronic and informational systems, economical loss, and etc. The dead operation characteristics of the ELB from impulse voltages were measured under the conditions of KS C 4613 and the test circuit with a varistor. As a result, the peak current value of the zero-phase sequence circuit of the ELB is increased as the surge voltage and stray capacitance increase. All of the ELBs used in this work were satisfied with the lightning impulse dead operation test condition defined in KS C 4613. However one specimen only did not cause dead operation in the condition of the test circuit with a varistor. There is high possibility that a large portion of the ELBs connected with the AC power lines having the surge protective devices bring about the dead operation.