• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전력기술부문
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• pp.141-144
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• 2002

This paper describes the correction of the protective relay equipped in the dedicated line used for connecting distributed generators (DG) to power grid. The fault current measured in a relaying point might be changed according to the fault conditions. Generally, the fault current of the line to line fault or the line to ground fault at the dedicated line is much higher than the protective set value due to the large fault level. However. when the high impedance fault is occurred in the dedicated line, we may not detect it because its fault level can be lower than the generating capacity of DG. And, the protective relay with conventional set value may generate a trip signal for insertion of DG due to the large transient characteristics of generators. Through the various simulations such as the fault in the dedicated line and the insertion of DG, we show that it would be necessary to modify the protective relay set value for detecting the high impedance fault occurred in the dedicated line and for preventing the mis-operation of protective relay caused by the insertion of DG.

• Journal of Electrical Engineering and Technology
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• 제8권4호
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• pp.737-743
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• 2013

The small-scaled onsite generators such as photovoltaic power, wind power, biomass and fuel cell belong to decarbonization techniques. In general, these generators tend to be connected to utility systems, and they are called distributed generations (DGs) compared with conventional centralized power plants. However, DGs may impact on stabilization of utility systems, which gets utility into trouble. In order to reduce utility's burdens (e.g., investment for facilities reinforcement) and accelerate DG introduction, the advanced operation algorithms under the existing utility systems are urgently needed. This paper presents the advanced voltage regulation method in power systems since the sending voltage of voltage regulators has been played a decisive role restricting maximum installable DG capacity (MaxC_DG). For the proposed voltage regulation method, the difference from existing voltage regulation method is explained and the detailed concept is introduced in this paper. MaxC_DG estimation through case studies based on Korean model network verifies the superiority of the proposed method.

• Journal of Electrical Engineering and Technology
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• 제2권2호
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• pp.165-171
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• 2007

This paper proposes a new islanding detection method for inverter-interfaced distributed generators (DG). To detect islanding conditions, this paper calculates the phase angle variation of the system voltage by using the phase-locked loop (PLL) in the inverter controllers. Because almost all inverter systems are equipped with the PLL, the implementation of this method is fairly simple and economical for inverter-interfaced DGs. The detection time can also be shortened by reducing communication delay between the relays and the DGs. The proposed method is based on the fact that islanding conditions result in the frequency and voltage variation of the islanded area. The variation depends on the amount of power mismatch. To improve the accuracy of the detection algorithm, this paper injects small low-frequency reactive power mismatch to the output power of DG.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전력기술부문
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• pp.65-68
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• 2002

Distributed Generators (DG) are rapidly increasing and most of them are interconnected with distribution network to supply power into the network. Therefore, DG may make significant impacts on distribution system operation. protection, and control with respect to the voltage regulation, voltage flicker, harmonics, fault current levels, the losses of the network, etc. These impacts would be demerits for both of DG and distribution networks. And the operation of DG may be influenced by the abnormal grid condition such as disturbances occurred in the neighboring distribution feeders as well as the feeder directly connected with DG. This paper describes the influence of fault occurred in the interconnected power network on the DG operation and the impact of DG on the network load during the interruptions of utility power.

• 전기학회논문지
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• 제58권8호
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• pp.1504-1511
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• 2009

By development of renewable energies and high-efficient facilities and deregulated electricity market, the operation cost of distributed generation(DG) becomes more competitive. The amount of distributed resource is considerably increasing in the distribution network consequently. Also, international environmental regulations of the leaking carbon become effective to keep pace with the global efforts for low-carbon paradigm. It contributes to spread out the business of DG. Therefore, the operator of DG is able to supply electric power to customers who are connected directly to DG as well as loads that are connected to entire network. In this situation, community energy system(CES) having DGs is recently a new participant in the energy market. DG's purchase price from the market is different from the DG's sales price to the market due to the transmission service charges and etc. Therefore, CES who owns DGs has to control the produced electric power per hourly period in order to maximize the profit. If there is no regulation for carbon emission(CE), the generators which get higher production than generation cost will hold a prominent position in a competitive price. However, considering the international environment regulation, CE newly will be an important element to decide the marginal cost of generators as well as the classified fuel unit cost and unit's efficiency. This paper will introduce the optimal operation of CES's DG connected to the distribution network considering CE. The purpose of optimization is to maximize the profit of CES and Particle Swarm Optimization (PSO) will be used to solve this problem. The optimal operation of DG represented in this paper is to be resource to CES and system operator for determining the decision making criteria.

• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1582-1589
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• 2016

In this paper the integration of Distributed Generation (DG) in radial distribution system is investigated by computing the optimal site and size of DG to be placed. An analytical expression based on equivalent current injection has been derived by utilizing topological structure of radial distribution system to find optimal size of DG to minimize losses. In the presented formulation, the optimal DG placement is obtained without repeatedly computing the load flow. The proposed formulation can be used to find the optimal size of all types of DGs namely Type-I, Type-II, Type-III and Type-IV DGs. The investigations are carried out on IEEE 33-bus and 69-bus radial distribution systems. The optimal DG placement results into reduction in active and reactive power losses and improvement in voltage profile of the buses.

• Advances in Energy Research
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• 제4권2호
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• pp.163-176
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• 2016

Rapid depletion of fossil based oil, coal and gas reserves and its greater demand day by day necessitates the search for other alternatives. Severe environmental impacts caused by the fossil fire based power plants and the escalating fuel costs are the major challenges faced by the electricity supply industry. Integration of Distributed Generators (DG) especially, wind and solar systems to the grid has been steadily increasing due to the concern of clean environment. This paper focuses on a new simple and fast load flow algorithm named Backward Forward Sweep Algorithm (BFSA) for finding the voltage profile and power losses with the integration of various sizes of DG at different locations. Genetic Algorithm (GA) based BFSA is adopted in finding the optimal location and sizing of DG to attain an improved voltage profile and considerable reduced power loss. Simulation results show that the proposed algorithm is more efficient in finding the optimal location and sizing of DG in 15-bus radial distribution system (RDS).The authenticity of the placement of optimized DG is assured with other DG placement techniques.

• 전기학회논문지
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• 제57권4호
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• pp.582-588
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• 2008

Microgrids are new distribution level power networks that consist of various electronically-interlaced generators and sensitive loads. The important control object of Microgrids is to supply reliable and high-quality power even during the faults or loss of mains(islanding) cases. This paper presents power control methods to coordinate multiple distributed generators(DGs) against abnormal cases such as islanding and load power variations. Using speed-droop and voltage-droop characteristics, multiple distributed generators can share the load power based on locally measured signals without any communications between them. This paper adopts the droop controllers for multiple DG control and improved them by considering the generation speed of distribution level generators. Dynamic response of the proposed control scheme has been investigated under severe operation cases such as islanding and abrupt load changes through PSCAD/EMTDC simulations.

• Journal of Power Electronics
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• 제14권2호
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• pp.324-340
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• 2014

Recent developments in power electronics technology have spurred interest in the use of renewable energy sources as distributed generation (DG) generators. The key component in DG generators is a grid-connected inverter that serves as an effective interface between the renewable energy source and the utility grid. The multifunctional inverter (MFI) is special type of grid-connected inverter that has elicited much attention in recent years. MFIs not only generate power for DGs but also provide increased functionality through improved power quality and voltage and reactive power support; thus, the capability of the auxiliary service for the utility grid is improved. This paper presents a comprehensive review of the various MFI system configurations for single-phase (two-wire) and three-phase (three- or four-wire) systems and control strategies for the compensation of different power quality problems. The advances in practical applications and recent research on MFIs are presented through a review of nearly 200 papers.

• 조명전기설비학회논문지
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• 제27권11호
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• pp.69-75
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• 2013

This paper proposes a new algorithm for the optimal placement of a step voltage regulator(SVR) in distribution system with Distributed Generators(DG) using a Particle Swarm Optimization(PSO). The objective function of this algorithm is to find optimal placement for minimum loss while maintaining each node voltage fluctuations within upper and lower limits. In the objective function of proposed algorithm, the deviations to reference voltage and the distribution loss are considered. To verify effectiveness of the proposed method, simulation is implemented using MATLAB.