• Journal of Power Electronics
• /
• 제10권3호
• /
• pp.270-276
• /
• 2010

In this paper, a capacitance estimation scheme for DC-link capacitors for single-phase AC/DC PWM converters is proposed. Under the no-load condition, a controlled AC current (30[Hz]) is injected into the input side, which then causes AC voltage ripples at the DC output side. Or, a controlled AC voltage can be directly injected into the DC output side. By extracting the AC voltage/current and power components on the DC output side using digital filters, the capacitance value can be calculated, where the recursive least squares (RLS) algorithm is used. The proposed methods can be simply implemented with software only and additional hardware is not required. From the experiment results, a high accuracy estimation of capacitances less than 0.85% has been obtained.

• 전기학회논문지
• /
• 제58권8호
• /
• pp.1544-1550
• /
• 2009

In this paper, a new single phase voltage sag/swell compensator using direct power conversion is proposed. A new compensator consists of input/output filter, series transformer and direct ac-ac converter, which is a single-phase back-to-back PWM converter without dc-link capacitors. Advantages of the proposed compensator include: simple power circuit by eliminating dc link electrolytic capacitors and thereby, improved reliability and increased life time of the entire compensator; simple PWM strategy or compensating voltage sag/swell at the same time and reduced switching losses in the ac-ac converter. Further, the proposed scheme is able to adopt simple switch commutation method without requiring complex four-step commutation method that is commonly employed in the direct power conversion. Simulation and experimental results are shown to demonstrate the advantages of the new compensator and PWM strategy. A 220V, 3kVA single-phase compensator based on the digital signal processor controller is built and tested.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
• /
• 제52권4호
• /
• pp.177-182
• /
• 2003

We have proposed the dimming controller using the AC chopper technique. The AC chopper changes the amplitude of the input source voltage with the same frequency. The conventional dimming controller is operated by controlling voltage phase with the triac. It has bad characteristics of the input current THD and the input power factor But the dimming controller using the ac chopper technique has a low current THD and a good power factor. The developed dimming controller is consist of the IGBT and the low pass filter. The system is operated by the variation circuit of the input source voltage and the microprocessor.

• 대한전기학회논문지:전력기술부문A
• /
• 제52권4호
• /
• pp.177-177
• /
• 2003

We have proposed the dimming controller using the AC chopper technique. The AC chopper changes the amplitude of the input source voltage with the same frequency. The conventional dimming controller is operated by controlling voltage phase with the triac. It has bad characteristics of the input current THD and the input power factor But the dimming controller using the ac chopper technique has a low current THD and a good power factor. The developed dimming controller is consist of the IGBT and the low pass filter. The system is operated by the variation circuit of the input source voltage and the microprocessor.

• 한국전기전자재료학회논문지
• /
• 제23권10호
• /
• pp.804-808
• /
• 2010

In this paper, we studied the dielectric breakdown voltage characteristics by the AC withstand voltage test on using green insulation dry air instead of $SF_6$ insulation gas used in the GIB (gas insulated bus) of 362 kV GIS (gas insulated switchgear). The AC withstand voltage test applied to the standard KEPCO's 362 kV GIB with dry air insulation, and the equivalence of dielectric breakdown voltage for dry air and $SF_6$ gas were examined, and the empirical formulas of dielectric breakdown voltage for dry air were calculated, and the criterion of AC withstand voltage test for dry air insulation was derived. Using the criterion, dry air can be used instead of $SF_6$ gas for 362 kV GIB in the factory acceptance test was confirmed.

• Journal of Power Electronics
• /
• 제13권5호
• /
• pp.829-840
• /
• 2013

The modified sinusoidal pulse-width modulation (SPWM) is one of the PWM techniques used in three-phase AC-DC buck converters. The modified SPWM works without the current sensor (the converter is current sensorless), improves production of sinusoidal AC current, enables obtainment of near-unity power factor, and controls output voltage through modulation gain (ranging from 0 to 1). The main problem of the modified SPWM is the huge starting current and voltage (during transient) that results from a large step change from the reference voltage. When the load changes, the output voltage significantly drops (through switching losses and non-ideal converter elements). The single-input single-output (SISO) approach with minor-loop voltage feedback controller presented here overcomes this problem. This approach is created on a theoretical linear model and verified by discrete-model simulation on MATLAB/Simulink. The capability and effectiveness of the SISO approach in compensating start-up current/voltage and in achieving zero steady-state error were tested for transient cases with step-changed load and step-changed reference voltage for linear and non-linear loads. Tests were done to analyze the transient performance against various controller gains. An experiment prototype was also developed for verification.

• 전기학회논문지
• /
• 제63권11호
• /
• pp.1588-1593
• /
• 2014

The scott transformer changes three-phase power to two single-phase power. However, this method causes unbalance and fluctuation of voltage by the change of electric railload. Recently, the AC railway system based on $3{\Phi}/1{\Phi}$ back-to-back (BTB) voltage source converter (VSC) has been proposed to solve these problems. Meanwhile, battery energy storage system (BESS) is used to compensate voltage instantaneously in power system. In this paper, BESS application to the AC railway system based on $3{\Phi}/1{\Phi}$ BTB VSC is suggested to compensate voltage instantaneously. The application effect is shown through simulation using MATLAB/SIMULINK.

• Journal of Power Electronics
• /
• 제15권1호
• /
• pp.10-17
• /
• 2015

A quasi-constant on-time controlled buck front end in combined discontinuous conduction mode and boundary conduction mode is proposed to improve power factor (PF).When instantaneous AC input voltage is lower than the output bus voltage per period, the buck converter turns into buck-boost converter with the addition of a level comparator to compare input voltage and output voltage. The gate drive voltage is provided by an additional oscillator during distortion time to eliminate the cross-over distortion of the input current. This high PF comes from the avoidance of the input current distortion, thereby enabling energy to be delivered constantly. This paper presents a series analysis of controlling techniques and efficiency, PF, and total harmonic distortion. A comparison in terms of efficiency and PF between the proposed converter and a previous work is performed. The specifications of the converter include the following: input AC voltage is from 90V to 264V, output DC voltage is 80V, and output power is 94W.This converter can achieve PF of 98.74% and efficiency of 97.21% in 220V AC input voltage process.

• Journal of Power Electronics
• /
• 제14권4호
• /
• pp.695-703
• /
• 2014

In this paper, a fault detection scheme for DC-link voltage sensor and its fault tolerant control strategy for three-phase AC/DC/AC PWM converters are proposed, where the Luenberger observer is applied to estimate the DC-link voltage. The Luenberger observer is based on a converter model, which is derived from the voltage equations of a grid-side converter and the power balance on a DC link. A fault of the voltage sensor is detected by comparing the measured value of the DC-link voltage with the estimated one. When a sensor fault is detected, a fault tolerant control strategy is performed, where the estimated DC-link voltage is used for the feedback control. The estimation error from the observer is about 1.5 V, which is sufficiently accurate for feedback control. In addition, it is shown that the observer performance is robust to parameter variations of the converter. The validity of the proposed method has been verified by simulation and experimental results.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제49권10호
• /
• pp.577-582
• /
• 2000

This paper analyze the interference problems, especially Ac corrosion when the gas pipeline is buried with power cable in the same submarine tunnel. This paper present the results of the study about interference mechanism(inductive coupling, conductive coupling, resistive coupling), AC corrosion, limitation of safety voltage, modeling of power cables, gas pipeline and grounding systems, analysis of induction voltage and optimal arrangement of power cables.