• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.1
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• pp.100-105
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• 2010

This paper describes a capacity of distributed generation which will be interconnected at low voltage distribution systems. In order to set the capacity of distributed generation, a voltage variation of distribution system is considered. Besides, the capacity of distributed generation is classified according to a capacity of pole transformer and loads. The system constructions in this paper are analyzed by using PSCAD/EMTDC. In the immediate future, it is expected to increase the installation of New and renewable energy systems which are generally interconnected to distribution power systems in the form of distributed generations like photovoltaic system, wind power and fuel cell. So the study of this kind would be needed to limit the capacity of distributed generation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.2
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• pp.232-239
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• 2007

There is an increasing concern to interconnect DG(Distributed Generation) units into a distribution system and operate and maintain the system power quality within a proper level to distribution companies, regional electricity utilities and industrial customers. Recently, this situation makes many experts estimate a next generation of distribution system which is composed of some micro-grids. But the proposed micro-grid is only mentioned as a small grid with some DG units, some power quality compensators, communication and control equipments. In this paper, a topology and an operation/control algorithm of the micro-grid which is able to supply the electricity with high reliability and quality, are proposed.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.450_451
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• 2009

최근 부하증가에 대한 안정적 전력공급과 환경문제 해결은 전 세계적 이슈로 등장되고 있으며, 그 해결책으로써 분산형전원(Distributed generation, DG)에 대한 관심이 높아지고 있다. DG는 경제적 효율적 이유로 기존 전력계통과 연계해 운전되는데, 태양광이나 풍력과 같은 재생에너지를 이용한 DG의 불확실하며 빈번한 출력변동은 배전계통의 전압조정을 어렵게 만든다. 배전계통의 전압조정을 위해 배전용변전소의 부하시 탭 변환기(Under Load Tap Changer, ULTC)가 이용되고 있다. ULTC는 부하변동에 따른 배전선로상 전압강하를 보상하는 선로 전압강하보상법(Line Drop Compensation, LDC)에 의해 조정된다. LDC 전압조정법에서, 측정된 뱅크전류와 미리 설정된 LDC 정정치(LDC parameters, 부하중심점 전압과 등가 임피던스)를 이용해 ULTC의 송출전압을 결정한다. LDC 정정치 설계시, 기존에는 ULTC 탭 동작횟수를 줄이는 것이 주요 목표였고, 이 목표는 DG 도입을 제한하는 큰 원인이 되고 있다. 그러므로 본 논문에서는 DG 도입을 증가시키는 새로운 ULTC 전압조정법을 제시하고 모델 배전계통 시뮬레이션을 통해 그 유효성을 확인한다.

• Journal of Power Electronics
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• v.16 no.1
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• pp.329-339
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• 2016

Owing to mismatched feeder impedances in an islanded microgrid, the conventional droop control method typically results in errors in reactive power sharing among distributed generation (DG) units. In this study, an improved droop control strategy based on secondary voltage control is proposed to enhance the reactive power sharing accuracy in an islanded microgrid. In a DG local controller, an integral term is introduced into the voltage droop function, in which the voltage compensation signal from the secondary voltage control is utilized as the common reactive power reference for each DG unit. Therefore, accurate reactive power sharing can be realized without any power information exchange among DG units or between DG units and the central controller. Meanwhile, the voltage deviation in the microgrid common bus is removed. Communication in the proposed strategy is simple to implement because the information of the voltage compensation signal is broadcasted from the central controller to each DG unit. The reactive power sharing accuracy is also not sensitive to time-delay mismatch in the communication channels. Simulation and experimental results are provided to validate the effectiveness of the proposed method.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1590-1599
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• 2016

The installation of distributed generation (DG) in the electrical networks has numerous advantages. However, connecting and disconnecting of DGs (CADD) leads to some problems in coordination of protection devices due to the changes in the short circuit levels in the different points of network. In this paper, an adaptive method is proposed based on available setting groups (SG) of relays. Since the number of available SG is less than possible CADD states, a classifying index (CI) is defined to categorize the several states in restricted setting groups. Genetic algorithm (GA) with a suitable objective function (OF) is used as an optimization method for the classification. After grouping, a modified coordination method is applied to achieve optimal coordination for each group. The efficiency of the proposed technique is demonstrated by simulation results.

• Journal of Electrical Engineering and Technology
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• v.8 no.6
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• pp.1261-1268
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• 2013

This study proposes a voltage and reactive coordinative control strategy with distributed generator (DG) in a distribution power system. The aim is to determine the optimum dispatch schedules for an on-load tap changer (OLTC), distributed generator settings and all shunt capacitor switching on the load and DG generation profile in a day. The proposed method minimizes the real power losses and improves the voltage profile using squared deviations of bus voltages. The results indicate that the proposed method reduces the real losses and voltage fluctuations and improve receiving power factor. This paper proposes coordinated voltage and reactive power control methods that adjust optimal control values of capacitor banks, OLTC, and the AVR of DGs by using a voltage sensitivity factor (VSF) and dynamic programming (DP) with branch-and-bound (B&B) method. To avoid the computational burden, we try to limit the possible states to 24 stages by using a flexible searching space at each stage. Finally, we will show the effectiveness of the proposed method by using operational cost of real power losses and voltage deviation factor as evaluation index for a whole day in a power system with distributed generators.

• Journal of Power Electronics
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• v.19 no.1
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• pp.234-243
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• 2019

Studying the control strategy of a microgrid under the load unbalanced state helps to improve the stability of the system. The magnitude of the power fluctuation, which occurs between the power supply and the load, is generated in a microgrid under the load unbalanced state is called negative sequence reactive power $Q^-$. Traditional power distribution methods such as P-f, Q-E droop control can only distribute power with positive sequence current information. However, they have no effect on $Q^-$ with negative sequence current information. In this paper, a stationary-frame control method for power sharing and voltage unbalance compensation in islanded microgrids is proposed. This method is based on the proper output impedance control of distributed generation unit (DG unit) interface converters. The control system of a DG unit mainly consists of an active-power-frequency and reactive-power-voltage droop controller, an output impedance controller, and voltage and current controllers. The proposed method allows for the sharing of imbalance current among the DG unit and it can compensate voltage unbalance at the same time. The design approach of the control system is discussed in detail. Simulation and experimental results are presented. These results demonstrate that the proposed method is effective in the compensation of voltage unbalance and the power distribution.

• Proceedings of the KIPE Conference
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• 2004.07a
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• pp.141-143
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• 2004

Distributed generation(DG) using microturbine will be adopted widely because of its various usages and merits such as high heat efficiency, environmental-friendliness. Commercialized DG using microtubine that rotates up to $60,000\~100,000[rpm]$ converters mechanical power to electricity by permanent magnet synchronous machine. This paper presents comparative test and simulation results of PMSM as generator. Test was done by diode rectifier and inverter. Parameters used in the simulation are driven from FEM analysis. Under various speed and load conditions, V-I characteristics matches well and it suggests the possibility of high speed PMSM as generator. DG operating at stand alone and grid connection mode will be developed.

• Proceedings of the KIEE Conference
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• 2001.07a
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• pp.16-18
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• 2001

Recently, a study on operation in parallel between Distributed Generation(DG) unit and power distribution system has been growing interest in power distribution system. But, introducing the DG unit causes the problem due to rising the voltage variation on power distribution system. So, This paper presents the effect of introducing DG unit on distribution system. For this simulation, KEPCO distribution system is used.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.6
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• pp.465-472
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• 2016

A nonlinear load causes harmonic distortion and hampers the performance of other loads or distributed generation (DG) sources connected to the point of common coupling (PCC). This study proposes a new control strategy to reduce harmonic components, such as fifth and seventh harmonics, at the PCC under nonlinear loads in islanded microgrids, which comprise more than two DG sources. The proposed control scheme enables the DG source to share the power commanded by the control center as well as to compensate for the voltage harmonics at the PCC. The reference current is estimated from the voltage harmonics and injecting power; thus, the control scheme is implemented without any additional hardware devices. The simulation and experimental results are presented to verify the effectiveness of the proposed control method.