• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.4
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• pp.748-757
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• 2007

This paper is intended to solve the technical problem that fails in large-capacity induction motor starting due to serious voltage drop during starting period. One induction motor that is established already can reach in steady-state using reactor starting method but the voltage magnitude of PCC (point of common coupling) has dropped down a little. When the same capacity induction motor is installed additionally in the PCC, where the existing induction motor is operating, voltage drop becomes more serious by starting of additional induction motor. As a result, the additional induction motor fails in starting. Therefore, voltage compensation method is proposed so that all of two induction motors can be started completely. First, modeling technique is described in order to implement starting characteristics of large induction motor. And then, this paper proposes strategic starting scheme by proper voltage compensation that use no-load transformer tap control (NLTC) and step voltage regulator (SVR) for starting of two large induction motors successfully and improving the feeding network voltage profile during the starting period. The induction motor discussed in this paper is the pumped induction motor of 2500kVA capacity that is operating by KOWACO (Korea Water Resources Corporation). Modeling and simulation is conducted using PSCAD/EMTDC software.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.215-216
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• 2014

This paper proposes a control algorithm for permanent magnet synchronous generator with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage offshore wind power system under unbalanced grid conditions. The proposed control algorithm particularly compensates for the unbalanced grid voltage at the point of common coupling in a collector bus of offshore wind power system. This control algorithm has been formulated based on the symmetrical components in positive and negative rotating synchronous reference frames under generalized unbalanced operating conditions. Instantaneous active and reactive power are described in terms of symmetrical components of measured grid input voltages and currents. Negative sequential component of ac input current is injected to the point of common coupling in the proposed control strategy. The amplitude of negative sequential component is calculated to minimize the negative sequential component of grid voltage under the limitation of current capability in a voltage source converter. The proposed control algorithm makes it possible to provide a balanced voltage at the point of common coupling resulting in the generated power of high quality from offshore wind power system under unbalanced network conditions.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.47-48
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• 2016

Parallel distributed generators (DGs) in the islanded micro-grid are normally controlled with the aid of the droop control scheme. However, the traditional droop control methods which use the P-${\omega}$ and Q-E curve to share power between DGs are still concerned to improve the accurate of reactive power sharing and variation of frequency and voltage at the point of common coupling (PCC). This paper proposes a control scheme to solve the limitation of microgrid in islanded operation such as reactive power sharing accuracy and PCC voltage and frequency restoring. In order to achieve the control objective, a secondary control is implemented with both central controller and local controller by using the low bandwidth communications. The effectiveness of the proposed control scheme is analyzed through the simulation.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.351-352
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• 2015

This paper proposed a new control strategy for voltage source inverter (VSI) of effective fifth and seventh harmonic reduction in the point of common coupling (PCC) in islanded microgrid under nonlinear load without any additional hardware devices. The non-linear load regularly causes such harmonic distortion, which harmfully affect the performance of other loads or other distributed generation (DG) sources connect to the PCC. In order to improve the quality of delivered output voltage, these harmonic must be rejected. The proposed control strategy is developed based on the current controller formed by resonant controller parallel with a proportional integral controller, which perform on the fundamental reference frame. The reference current is estimated based on the voltage harmonic and the injecting power. The simulation and experimental results are shown to verify the effectiveness of proposed control method.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1513-1522
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• 2018

This paper proposes a new islanding detection method for inverter-based distributed generators by continuously injecting a negligible amount of 2nd order harmonic current. The proposed method adopts a proportional resonant (PR) controller for the output current control of the inverter, and a PR filter to extract the 2nd order harmonic voltage at the point of common coupling (PCC). The islanding state can be detected by measuring the magnitude ratio of the 2nd order harmonic voltage to the fundamental voltage at the PCC by injecting a 2nd order harmonic current with a 0.8% magnitude. The proposed method provides accurate and fast detection under grid voltage unbalance and load unbalance. The operation of the proposed method has been verified through simulations and experiments with a 5kW hardware set-up, considering the islanding test circuit suggested in UL1741.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.205-207
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• 2005

In this paper, the Point of Common Coupling (PCC) is selected to analyze harmonic characteristic of distribution system by IEC 61000 - 3 - 6 in Electromagnetic Compatibility(EMC). Harmonic voltage and current were measured at the PCC of real distribution system. Harmonic distribution, nonlinear load component and Total Harmonic Distortion(THD) were verified by measurement. The effective and accurate modelling of real distribution system were proved through a analysis of harmonic impedance, voltage and current in steady-state. Harmonic transfer characteristic in distribution system were summarized and investigated through a analysis of harmonic voltage and harmonic current in harmonic current source.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.3124-3132
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• 2011

Scott transformers have widely used to convert three phases into two phases and compensate the unbalance. Theoretically, the loads of the two secondary phases are same, no unbalance appears in the PCC(point of common coupling). But Due to the uncertainty of traction load, the unbalance are generally presented at the PCC. In this paper The amount of the voltage unbalance is expressed in the ratio of the negative sequence voltages to the positive sequence voltage. We tried to compensate the unbalance using SVC(Static Var Compensator）in an unbalance traction loads state by modeling. The SVC are installed and controlled to provide different amounts of reactive power compensation.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.1
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• pp.1-10
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• 2015

This paper proposes a control algorithm for permanent magnet synchronous generators with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage off-shore wind power system under unbalanced grid conditions. Specifically, the proposed control algorithm compensates for unbalanced grid voltage at the PCC (Point of Common Coupling) in a collector bus of an off-shore wind power system. This control algorithm has been formulated based on symmetrical components in positive and negative synchronous rotating reference frames under generalized unbalanced operating conditions. Instantaneous active and reactive power is described in terms of symmetrical components of measured grid input voltages and currents. Negative sequential component of AC input current is injected into the PCC in the proposed control strategy. The amplitude of negative sequential component is calculated to minimize the negative sequential component of grid voltage under the limitation of current capability in a voltage source converter. The proposed control algorithm enables the provision of balanced voltage at the PCC resulting in the high quality generated power from off-shore wind power systems under unbalanced network conditions.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.197-198
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• 2011

A technique to manage harmonic pollution at the point of common coupling (PCC) has been presented using a control chart. The recursive least-squares technique has been used to estimate the parameters of the Thevenin equivalent load model. With the estimated data from the measured voltage and current waveform at the PCC during certain period violating upper control limit, the individual contributions to the distortion of voltage waveform at an interested harmonic frequency have been calculated and shown by simple graph.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.172-176
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• 2005

Phase Lacked Loop(PLL)은 분산전원을 계통연계시 동기설정을 위해 중요한 장비이다. 이러한 동기설정은 Point of Common Coupling(PCC)에서 계통 전압을 검출하여 크기와 위상을 동일하게 설정하여 전력변환장치에서 전력을 출력한다. 일반적으로 PCC에서 계통전압을 검출하였을 때 고조파, 상간불평형은 전력변환장치 출력 왜곡을 야기 시킨다. 본 논문에서는 이러한 출력왜곡을 감소시키기 위한 3상 PLL을 모델링하여, 그 제어 성능을 시뮬레이션을 통해 확인하였다.