• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.137-139
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• 1988

A reactive power compensator whitch employs a three phase voltage source PWM converter is presented and analysed in this study. In this study, instantaneous reactive power compensator by the theory of instantaneous real and imaginary power are theoretically studied how to compensate reactive power occured by fundamental and harmonic reactive current. And we showed the compensation characteristics by comparing the experimental results with those of computer simulation.

• Journal of Electrical Engineering and Technology
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• v.8 no.3
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• pp.507-515
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• 2013

This paper proposes a compensation method for the $2^{nd}$-order harmonic of single-phase grid-connected wind power generation systems. Theoretically, a single-phase grid-connected inverter system has no choice but to cause the $2^{nd}$-order harmonic to DC-link voltage. The reference active current is affected by the DC-link voltage. The output current from the reference active current is distorted by the $1^{st}$ and $3^{rd}$-order harmonic. The proposed method can compensate, conveniently, the reference active current with the $2^{nd}$-order harmonic. To reduce the $2^{nd}$-order ripple in the reference active current, proposed method takes a PR controller as a feed-forward compensator. PR controllers can implement selective harmonic compensation without excessive computational requirements; the use of these controllers simplifies the method. Both the simulation and experimental results agree well with the theoretical analysis.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.3
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• pp.101-108
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• 2004

AC electric railroad system receives its power from 3-phase transmission system, Since, trainloads are changing continuously, the voltages for the single-phase load fluctuate in the train garage, and moreover, the fluctuating voltages generate high-order harmonics. This means that there is the difficulty in maintaining power quality in the power system. Therefore, a Static Var Compensator(SVC), which in general compensates the reactive power, is used in order to balance the trainload. In this paper, PSCAD/EMTDC is used for the analysis of harmonic generation in the train garage using SVC. The Total Harmonic Distortion(THD) of voltages is calculated using PSCAD/EMTDC dynamic simulation. As a result, the train garage using SVC improves power quality.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.4
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• pp.368-376
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• 1999

This paper studies the operational characteristics of thyristor controlled shunt compensator in a simple power t transmission system. With Fourier series representation of the thyristor switching action and the system parameters, t the thyristor current equations are derived, which transmit the required real power of the simple power transmission s system. Bisection algorithm is used to solve the thyristor current equations, which informs the thyristor firing an밍e, t the thyristor conduction an밍e, the power flows and the harmonic characteristics. The stability analysis is performed w with the theory of Poincare mapping for the nonlinear discrete periodic dynamic system. EMTP simulations at the v various operating points show the transient characteristics of the thyristor controlled shunt compensator and C correspond to the results calculated with Fourier series representation and the stability analysis.

• Proceedings of the KIPE Conference
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• 2018.11a
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• pp.95-97
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• 2018

The power quality of Single Phase Grid-Connected Inverters (GCIs) has received much attention with the increasing number of Distributed Generation (DG) systems. However, the performance of single phase GCIs get degraded due to several factors such as the grid voltage harmonics, the dead time effect, and the turn ON/OFF of the switches, which causes the harmonics at the output of GCIs. Therefore, it is not easy to satisfy the harmonic standards such as IEEE 519 and P1547 without the help of harmonic compensator. To meet the harmonic standards a certain kind of harmonic controller needs to be added to the current control loop to effectively mitigate the low order harmonics. In this paper, the harmonic compensation is performed using a novel robust harmonic compensation method based on Digital Lock-in Amplifier (DLA). In the proposed technique, DLAs are used to extract the amplitude and phase information of the harmonics from the output current and compensate it by using a simple PI controller in the feedforward manner. In order to show the superior performance of the proposed harmonic compensation technique, it is compared with those of conventional harmonic compensation methods in terms of the effectiveness of harmonic elimination, complexity, and implementation. The validity of the proposed harmonic compensation techniques for the single phase GCIs is verified through the experimental results with a 5kW single phase GCI. Index Terms -Single Phase Grid Connected Inverter (SPGCI), Harmonic Compensation Method, Total Harmonic Distortion (THD) and Harmonic Standard.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.5
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• pp.409-415
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• 2012

This paper presents a new software-based on-line dead-time compensation technique for a single-phase grid-connected photovoltaic (PV) inverter system. To prevent a short circuit in the inverter arms, a switching delay time must be inserted in the pulse width modulation (PWM) signals. This causes the dead-time effect, which degrades the system performance around zero-crossing point of the output current. To reduce the dead-time effect around the zero-crossing point of grid current, a harmonic mitigation of grid current is used as an additional part of the synchronous frame current control scheme. This additional task mitigates the harmonic components caused by the dead-time from the grid current. Simulation and experimental results are shown to verify the effectiveness of the proposed dead-time compensation method in the single-phase grid-connected inverter system.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1672-1682
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• 2017

For grid-connected LCL-filtered inverters, the inverter-side current can be used as the control object with one current sensor for both LCL resonance damping and over-current protection, while the grid-voltage feedforward or harmonic resonant compensator is used for suppressing low-order grid current harmonics. However, it was found that the grid current harmonics were high and often beyond the standard limitations with this control. The limitations of the inverter-side current control in suppressing low-order grid current harmonics are analyzed through inverter output impedance modeling. No matter which compensator is used, the maximum magnitudes of the inverter output impedance at lower frequencies are closely related to the LCL parameters and are decreased by increasing the control delay. Then, to improve the grid current quality without complicating the control or design, this study proposes designing the filter capacitance considering the current harmonic constraint and using a PWM mode with a short control delay. Test results have confirmed the limitation and verified the performance of the improved approaches.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.1988-1994
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• 2014

In a single-phase grid-connected power system consisting of a DC/DC converter and a DC/AC converter, the current drawn from renewable energy sources has a tendency to be pulsated and contains second-order frequency ripple components, which results in several drawback such as a power harvesting loss and a shortening of the energy source's life. This paper presents a new second-order harmonic current reduction scheme with a fast dc-link voltage loop for two-stage dc-dc-ac grid connected systems. In the frequency domain, an adequate control design is performed based on the small signal transfer function of a two-stage dc-dc-ac converter. To verify the effectiveness of proposed control algorithm, a 1 kW hardware prototype has been built and experimental results are presented.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.379-384
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• 2000

The reactive and harmonic current components of dc loads can be compensated by the three-phase hybrid power filter (HPF) system. After compensation, the resulting current has sinusoidal and in-phase components with the source voltage. The HPF system is constructed by an active filter and passive filters. The passive filter reduce the 5th and 7th harmonic of the load current. The active filter compensates the remainder of the load current. Using the HPF system, a low cost harmonic compensator can be made. Performance of the HPF system is verified through simulation,

• 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.