• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.4
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• pp.322-332
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• 2013

Conventional single-phase series quasi Z-source voltage compensator can not compensate for voltage sag less than 50% that frequently occurs in the industrial field. In this study, single-phase series quasi Z-source voltage sag-swell compensator which can compensate the voltage variation of entire range is proposed. The proposed system is composed of two quasi Z-source AC-AC converters connected in series with output terminal stage. Voltage sag less than 50% could be compensated by the intersection switching control of the upper converter duty ratio and of the upper converter duty ratio. Also the compensation voltage and its flowchart for each compensation mode are presented for entire sag-swell region. To confirm the validity of the proposed system, a DSP(DSP28335) controlled experimental system was manufactured. As a result, the proposed system could compensate for the voltage sag/swell of 20% and 60%. Finally, voltage compensation factor and THD(Total Harmonic Distortion) according to voltage variation and load change were measured, and voltage quality shows a good results.

• Journal of the Korea Convergence Society
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• v.4 no.1
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• pp.33-41
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• 2013

This paper presents an adaptive recursive least squares algorithm (ARLS) for detecting voltage sag and voltage swell events in power systems. Different methods have been developed to detect voltage sag and voltage swell. Some of them use window techniques, which are too slow when voltage sag or swell mitigation is required. Others depend on the extraction of a single non-stationary sinusoidal signal out of a given multi-components input signal, and therefore they don't consider the harmonic components in calculating the voltage root mean square value (rms). The method, proposed in this paper, is capable of estimating the voltage rms taking into account all harmonic components. The method is tested by applying it to different, simulated signals using ATP program, and compared with voltage sag detection algorithms.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.25-27
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• 2002

This paper describes a new economical voltage sag and swell generator suitable to the evaluations of high power custom power devices such as DVR (Dynamic Voltage Restorer) and DSTATCOM (Distribution Static Compensator). This system was designed to generate the several power quality disturbances in MVA power ratings - voltage sag and swell, under voltage, over voltage and harmonic distortions. The basic idea for voltage sag and swell is to use the voltage drop across a reactor, while the voltage swell is to use the step-up transformer and the TCR(Thyristor Controlled Reactor). In this paper, two identical 3 phase TCRs and a step-up transformer with tap changer are used. Additional harmonic filters are added to reduce the voltage distortion when TCRs are operated. Simulation results are given for several cases of voltage sag and swell generations.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.1
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• pp.102-107
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• 2005

This paper describes a new voltage sag-swell generator for the test of custom power devices such as UPS, DVR, DSTATCOM, SSTS, etc. Voltage sag, swell, outage, and unbalance generation mechanism and the operating principle are described for the proposed scheme. The usefulness of the scheme is proved through simulations and experiments. The proposed scheme has good features of simple structure, high reliability, wide range of sag and swell variation, and easy control. Especially, the scheme can provide a cost-effective implementation of a power quality disturbance generator. Therefore, it is expected that the scheme will contribute to the self implementation of the system with low cost in laboratory.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.9
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• pp.36-43
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• 2010

This paper proposes a new type of voltage sag-swell compensator based on a Z-source AC-AC converter. The proposed topology employs a pulse width modulation (PWM) Z-source AC-AC converter along with a injection transformer. A safe commutation strategy is used to eliminate voltage spikes on switches without snubber circuit. During a voltage sag or swell, the proposed system controls the adding or missing voltage and maintains the rated voltage of sinusoidal waveform at the terminals of the critical loads. The proposed system is able to compensate 20[%] voltage swell and is also able to compensate 60[%] voltage sag. In order to control and detect the voltage sag and swell, the peak voltage detection method is applied. Also, the operating principles of the proposed system are described, and a circuit analysis is provided. Finally, PSIM simulation and experimental results are presented to verify the proposed concept and theoretical analysis.

• Journal of the Korean Society for Railway
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• v.16 no.4
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• pp.272-277
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• 2013

Power quality is a term that is now extensively used in power systems applications, and in this context the voltage, current, and phase angle are discussed widely. In particular, different algorithms that are capable of detecting the voltage sag and swell information in a real time environment have been proposed and developed. Voltage sag and swell play an important role in determining the stability, quality, and operation of a power system. This paper presents ANFIS (Adaptive Network based Fuzzy Inference System) models with different membership functions to build the voltage shape with the knowledge of known system parameters, and detect voltage sag and swell accurately. The performance of each method has been compared with each other/other methods to determine the effectiveness of the different models, and the results are presented.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.6
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• pp.626-633
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• 2005

This paper proposes a new 2MVA SSFG(Sag Swell Flicker Generator) injecting voltage by using series inverter. The proposed SSFG composes series inverter, DC capacitor as energy storage, rectifier and voltage clamp circuit. This SSFG is designed to generate typical power disturbances, such as voltage sag/swell, over/under voltage and voltage flicker. Also it is designed to generate unexpected voltage phase jumping waveform by controlling the series inverter. In this paper, three kinds of control methods for the proposed 2MVA SSFG we investigated by PSIM simulation. Also typical voltage sag, swell, flicker waveforms are implemented by adopting effective control method.

• Proceedings of the KIPE Conference
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• 2013.11a
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• pp.258-259
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• 2013

Load connection or disconnection makes instantaneous sag & swell in 3-phase grid. When unbalance state occurs, between sensed phase voltage and actual phase voltage may have discrepancy. It makes difficult to detect accurate sag & swell, so it is hard to satisfy the standard for switching ESS system to UPS mode. In this paper, we analyzed unbalanced 3-phase voltage, and compensated the actual sag & swell magnitude.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.4
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• pp.327-334
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• 2010

This paper deals with a single-phase dynamic voltage restorer(DVR) with a quasi Z-source topology. The proposed system based on a single-phase quasi Z-source PWM ac-ac converter which have features such as the input voltage and output voltage are sharing ground, and input current operates in continuous current mode(CCM). For the detection of voltage sag-swell, peak voltage detection method is applied. Also, the circuit principles of the proposed system are described. During the 60% severe voltage sag and 30% voltage swell, the proposed system controls the adding or missing voltage and maintains the rated voltage of sinusoidal waveform at the terminals of the critical loads. Finally, PSIM simulation and experimental results are presented to verify the proposed concept and theoretical analysis.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1314-1321
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• 2014

A new simplified topology for a dynamic voltage restorer (DVR) based on direct converter with a reduced number of switches is presented. The direct converter is fabricated using only three bi-directional controlled switches. The direct converter is connected between the grid and center-tapped series transformer. The center-tapped series transformer is used to inject the compensating voltage synthesized by the direct converter. The DVR can properly compensate for long-duration, balanced, and unbalanced voltage sag and swell by taking power from the grid. The switches are driven by ordinary pulse width modulation signals. Simulation and hardware results validate the idea that the proposed topology can mitigate sag of 50% and swell of unlimited quantity.