• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.1
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• pp.74-80
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• 2007

This paper proposes the novel open-fault detection/isolation scheme of inverter switch in two-phase excited VSI. This scheme identify open-fault using voltage sensor at lower switches of each phase according to the operating mode. It has benefit of simple implementation, fast detection and robustness in the load so that stab of the system is improved. Also, at faulty mode, it minimizes faulty effect and makes possible continuous operation through the reconfiguration procedure applying four-switch operation. The validity of proposed fault detection scheme is verified by experimental results.

• Journal of Power Electronics
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• v.17 no.3
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• pp.798-810
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• 2017

This paper presents a combined system of a small-capacity inverter and multigroup delta-connected thyristor switched capacitors (TSCs). The system is referred to as a hybrid static compensator (HSC) and has the functions of dynamic reactive power compensation and harmonic suppression. In the proposed topology, the load reactive power is mainly compensated by the TSCs. Meanwhile the inverter is meant to cooperate with TSCs to achieve continuous reactive power compensation, and to filter the harmonics generated by nonlinear loads and the TSCs. First, the structure and mathematical model of the HSC are discussed Then the control method of the HSC is presented. An improved reduced order generalized integrator (ROGI)-based selective current control method is adopted in the inverter to achieve high-performance reactive and harmonic current compensation. Meanwhile, a switch control strategy is proposed to implement precise and fast switching of the TSCs and to avoid changing the time delay needed by the conventional switch strategy. Experiments are implemented on a 20 KVA HSC prototype and the obtained results verify the validity of the proposed HSC system.

• Journal of Power Electronics
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• v.19 no.1
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• pp.11-23
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• 2019

In this study, a novel zero voltage zero current transition (ZVZCT) bidirectional DC-DC converter is proposed by employing coupled inductors. This converter can turn the main switch on at ZVZCT and it can turn it off with zero voltage switching (ZVS) for both the boost and buck modes. These characteristics are obtained by using a simple auxiliary sub-circuit regardless of the power flow direction. In the boost mode, the auxiliary switch achieves zero current switching (ZCS) turn-on and ZVS turn off. Due to the coupling inductors, this converter can make further efficiency improvements because the resonant energy in the capacitor or inductor can be transferred to the load. The main diode operates with ZVT turn-on and ZCS turn-off in the boost mode. For the buck mode, there is a releasing circuit to conduct the currents generated by the magnetic flux leakage to the output. The auxiliary switch turns on with ZCS and it turns off with ZVT. The main diode also turns on with ZVT and turns off with ZCS. The design method and operation principles of the converter are discussed. A 500 W experimental prototype has been built and verified by experimental results.

• Progress in Superconductivity and Cryogenics
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• v.9 no.1
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• pp.47-52
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• 2007

This paper presents characteristics analysis of persistent current switch(PCS) system on a small scale by using YBCO coated conductor(CC). A high temperature superconductor(HTS) PCS system mainly consists of a PCS, a HTS magnet load and a magnet power supply(MPS). To design the optimal heater triggering switch. the three-dimensional heat conduction model was analyzed by finite element method(FEM). The electrical equivalent model considering the n-value of CC was applied to analyze current decay during persistent current mode. In the experiment and simulation, the heater was applied with a current of 0.43A and the current was ramped up to 10A and 20A with 0.2A/s. Finally, experimental results of the HTS PCS system have been compared with the theoretical results. It has been concluded that flux creep can not influence the results because the operating current was 40% of critical current and optimal sequential operation of the PCS system is indispensable to enhance its performance.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.8
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• pp.1463-1471
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• 2009

In this paper, a new algorithm of Integrated Volt/Var Control (IVVC) is proposed using Volt/Var control for the Distribution Automation System (DAS) based on the modeling of the distributed load and the distributed current. In the proposed, the load flow based on the modeling of the distributed load and the distributed current are estimated from constants of four terminals using the measurement of the current and power factor from a Feeder Remote Terminal Unit (FRTU). For Integrated Volt/Var Control (IVVC), the gradient method is applied to find optimal solution for tap and capacity control of OLTC (On-Load Tap Changers), SVR (Step Voltage Regulator), and SC (Shunt Condenser). What is more Volt/Var control method is proposed using moving the tie switch as well as IVVC algorithm using power utility control. In the case studies, the estimation and simulation network have been testified in Matlab Simulink.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.1110-1113
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• 2002

A Single-Stage Single-Switch power-factor- correction(PFC) AC/DC Converter with universal input is presented in this paper. The PFC Converter can be achieved based upon the continuous current mode(CCM). The switch has less current and voltage stresses over a wide range of load variation so that a low voltage rating device can be used. The presented converter features high power factor high efficiency, and low cost. An 90W prototype was implemented to show that it has 70% efficiency with low voltage stress over universal line input.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.9
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• pp.1013-1020
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• 1992

The conductivity variation of a high resistivity bulk silicon semiconductor, whose electrodes were deposited with aluminum vapor, was studied experimentally by measuring the X-ray intensity and current flow, which was developed by X-ray radiation while applying a pulse voltage to the silicon, in a load resistor connected to the semiconductor. The current flow observed immediately as the X-ray radiated, and when the X-ray decreased. It was found from the observation of switching current for the X-ray intensity and the voltage applied in the semiconductor that the switching current of the semiconductor increased as the intensity of the X-ray and the applied voltage increased. In case of lower applied voltage, the switching current for higher applied voltage depended on the intensity of the X-ray radiated due to the saturation of electron and hole.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.1
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• pp.82-90
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• 1999

A pulse frequency control method for single-switch three-phase buck rectifiers is comprehensively studied in this paper. The proposed pulse frequency control method leads the three-phase buck rectifier to a high performance system that can draw the nearly sinusoidal input-line currents. The simulated and experimental results demonstrate that the system provides low total harmonic distortion of the input-line currents, high-power factor, and good output voltage regulation against load change.

• Proceedings of the KIEE Conference
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• 2003.04a
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• pp.341-348
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• 2003

Photovoltaic systems normally use a maximum power point tracking (MPPT) technique ta continuously deliver the highest possible power to the load when variations in the insolation and temperature occur. A simple method of tracking the maximum power points (MPPs) and forcing the boost converter system to operate close to these points is presented through deriving small-signal model and transfer function of boost converter. This paper aims at modeling boost converter including equivalent series resistance of input reservoir capacitor by state-space-averaging method and PWM switch model with properly designed controller for maximum photovoltaic power tracking control.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.71-73
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• 1995

This paper presents an optimization technique using genetic algorithms(GA) for loss minimization in the distribution network reconfiguration. Determining switch position to be opened for loss minimization in the radial distribution system is a discrete optimization problem. GA is appropriate to solve the multivariable optimization problem and it uses population, not a solution. For this reason, GA is attractive to solve this problem. In this paper, we aimed at finding appropriate open sectionalizing switch position using GA, which can lead to minimum transmission losses.