• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.1
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• pp.22-27
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• 2012

Correct and fast detection of a micro-grid (MG) islanding is essential to the MG since operation, control and protection of the MG depend on an operating mode i.e., an interconnected mode or an islanding mode. When islanding occurs, the frequency of the point of common coupling (PCC) is not the nominal frequency during the transient state owing to the frequency rise or drop of generators in the MG. Thus, the active and reactive power calculated by the frequency domain based method such as Fourier Transform might contain some errors. This paper proposes an islanding detection algorithm for the MG based on the instantaneous active and reactive powers delivered to the dedicated line in the time domain. During the islanding mode, the instantaneous active and reactive powers delivered to the dedicated line are constants, which depend on the voltage of the PCC and the impedance of the dedicated line. In this paper, the instantaneous active and reactive powers are calculated in the time domain and used to detect islanding. The performance of the proposed algorithm is verified under various scenarios including islanding conditions, fault conditions and load variation using the PSCAD/EMTDC simulator. The results indicate that the algorithm successfully detects islanding for the MG.

• Journal of Power Electronics
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• v.17 no.4
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• pp.1088-1096
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• 2017

Load variations on a distribution line result in voltage fluctuations at the point of common coupling (PCC). In order to keep the magnitude of the PCC voltage constant at its rated value and obtain zero voltage regulation (ZVR), a D-STATCOM is installed for voltage correction. Moreover, the ZVR mode of a D-STATCOM can also be used to balance the source current during unbalanced loading. For medium voltage and high power applications, a D-STATCOM is realized by the cascaded H-bridge topology. In the ZVR mode, the D-STATCOM may draw unbalanced current and in this process is required to handle different phase powers leading to deviations in the cluster voltages. Zero sequence voltage needs to be injected for ZVR mode, which creates circulating power among the phases of the D-STATCOM. The computed zero sequence voltage and the individual DC capacitor balancing controller help the DC cluster voltage follow the reference voltage. The effectiveness of the control scheme is verified by modeling the system in MATLAB/SIMULINK. The obtained simulations are further validated by the experimental results using a dSPACE DS1106 and five-level D-STATCOM experimental set up.

• Journal of Power Electronics
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• v.13 no.3
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• pp.409-418
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• 2013

This paper presents an enhanced control strategy which consists of a proportional-integral controller and a repetitive controller (RC) for improving the voltage performance of distributed generation (DG) under nonlinear load conditions. The proposed voltage controller is able to maintain a sinusoidal voltage at the point of common coupling (PCC) of the DG regardless of the harmonic voltage drop in the system impedance due to nonlinear load currents. In addition, by employing the delay time of the RC at one-sixth of the fundamental period, the proposed RC can overcome the slow response drawback of the traditional PI-RC. The proposed control strategy is analyzed and the design of the RC is presented in detail. The feasibility of the proposed control strategy is verified through simulation and experimental results.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.256-257
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• 2012

This paper presents a new control strategy to improve voltage performance of distributed generation (DG) under nonlinear loads. The proposed voltage controller consists of a proportional-integral and a repetitive controller where the repetitive controller behaves as a bank of resonant controllers to compensate harmonic voltage drop on system impedance due to nonlinear load current. As a result, the voltage at the point of common coupling (PCC) of the DG is regulated to be sinusoidal waveform regardless of the presence of nonlinear loads. In order to validate the effectiveness of the proposed voltage controller, simulations are carried out using PSIM software and results are compared with those with the conventional PI controller.

• Journal of Power Electronics
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• v.7 no.3
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• pp.191-202
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• 2007

This paper deals with pulse multiplication in zigzag connected autotransformer based 12-pulse AC-DC converters feeding vector controlled induction motor drives (VCIMD) for improving the power quality at the point of common coupling (PCC) without using a Zero-Sequence-Blocking-Transformer (ZSBT). The proposed 24-pulse AC-DC converter is based on the principle of DC ripple re-injection technique for pulse multiplication and harmonic mitigation. The design of the autotransformer is carried out for the proposed AC-DC converter and the effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed AC-DC converter. Test results from a laboratory developed prototype, along with simulated results, are presented to validate the design and model of the proposed 24-pulse AC-DC converter.

• Journal of Power Electronics
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• v.7 no.1
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• pp.72-80
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• 2007

Voltage sags are one of the most frequently occurring power quality problems challenging power systems today. The Unified Power Quality Conditioner (UPQC) is one of the major custom power solutions that are capable of mitigating the effect of supply voltage sags at the load or Point of Common Coupling (PCC). A UPQC-Q employs a control method in which the series compensator injects a voltage that leads the supply current by $90^{\circ}C$ so that the series compensator at steady state consumes no active power. However, the UPQC-Q has the disadvantage that its series compensator needs to be overrated. Thus it cannot offer effective compensation. This paper proposes a new control scheme for the UPQC-Q that offers minimum power injection. The proposed minimum power injection method takes into consideration the limits on the rated voltage capacity of the series compensator and its control scheme. The validity of the proposed control scheme is investigated through simulation and experimental results.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.327-330
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• 2003

This paper proposes an estimation algorithm for the generating power of distributed generations(DG) interconnected with distribution networks. These days, DG are rapidly increasing and most of them are interconnected with distribution networks. The DG can supply power into the distribution network, which may make significant impact on fault current and the protection scheme of the interconnected distribution networks. Generally these influences of DG is proportioned as the distributed generator's power. Therefore, it is important to forecast the output power of distributed generator in PCC(point of common coupling). This paper presents the prediction method of DG's power by monitoring the current and phase difference.

• Journal of Electrical Engineering and Technology
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• v.11 no.1
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• pp.257-264
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• 2016

In this paper, new electric railway feeding system which has active transformer is modeled for evaluating the steady state analysis using PSCAD/EMTDC. Equivalent models including power supply, feeder, train and transformers are proposed for simplifying the model of the feeding system in high speed electric railway. In case study, simulation results applied to proposed model are compared with the conventional and new systems through the catenary voltage, three-phase voltage of PCC (Point of Common Coupling) and the efficiency of regenerative braking energy.

• Journal of Power Electronics
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• v.9 no.3
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• pp.386-395
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• 2009

In this paper, a new control algorithm for the dynamic voltage restorer (DVR) is proposed to regulate the load terminal voltage during various power quality problems that include sag, swell, harmonics and unbalance in the voltage at the point of common coupling (PCC). The proposed control strategy is an Adaline (Adaptive linear element) Artificial Neural Network (ANN) and is used to control a capacitor supported DVR for power quality improvement. A capacitor supported DVR does not need any active power during steady state because the voltage injected is in quadrature with the feeder current. The control of the DVR is implemented through derived reference load terminal voltages. The proposed control strategy is validated through extensive simulation studies using the MATLAB software with its Simulink and SimPower System (SPS) toolboxes. The DVR is found suitable to support its dc bus voltage through the control under various disturbances.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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• pp.1-7
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• 2011

Active power control scheme for distributed generation in microgrid consists of feeder flow control and unit power control. Feeder flow control is more useful than the unit power control for demand-side management, because microgrid can be treated as a dispatchable load at the point of common coupling(PCC). This paper presents detailed descriptions of the feeder flow control scheme for the hybrid system in microgrid. It is divided into three parts, namely, the setting of feeder flow reference range for stable hybrid system operation, feeder flow control algorithm depending on load change in microgrid and hysteresis control. Simulation results using the PSCAD/EMTDC are presented to validate the inverter control method for a feeder flow control mode. As a result, the feeder flow control algorithm for the hybrid system in microgrid is efficient for supplying continuously active power to customers without interruption.