• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.580-590
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• 2018

Active distribution system (ADS) considering distributed generation (DG) and electric vehicle (EV) is an effective way to cut carbon emission and improve system benefits. ADS is an evolving, complex and uncertain system, thus comprehensive model and effective optimization algorithms are needed. Battery swapping station (BSS) for EV service is an essential type of flexible load (FL). This paper establishes ADS planning model considering BSS firstly for the minimization of total cost including feeder investment, operation and maintenance, net loss and carbon tax. Meanwhile, immune binary firefly algorithm (IBFA) is proposed to optimize ADS planning. Firefly algorithm (FA) is a novel intelligent algorithm with simple structure and good convergence. By involving biological immune system into FA, IBFA adjusts antibody population scale to increase diversity and global search capability. To validate proposed algorithm, IBFA is compared with particle swarm optimization (PSO) algorithm on IEEE 39-bus system. The results prove that IBFA performs better than PSO in global search and convergence in ADS planning.

• 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 the Korean Vacuum Society
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• v.16 no.6
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• pp.483-488
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• 2007

Current feeder system (CFS) for Korea superconducting tokamak advanced research(KSTAR) project plays a role to interconnect magnet power supply (MPS) and superconducting (SC) magnets through the normal bus-bar at the room temperature(300 K) environment and the SC bus-line at the low temperature (4.5 K) environment. It is divided by two systems, i.e., toroidal field system which operates at 35 kA DC currents and poloidal field system wherein 20$\sim$26 kA pulsed currents are applied during 350 s transient time. Aside from the vacuum system of main cryostat, an independent vacuum system was constructed for the CFS in which a roughing system is consisted by a rotary and a mechanical booster pump and a high vacuum system is developed by four cryo-pumps with one dry pump as a backing pump. A self interlock and its control system, and a supervisory interlock and its control system are also established for the operational reliability as well. The entire CFS was completely tested including the reliability of local/supervisory control/interlock, helium gas leakage, vacuum pressure, and so on.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.17 no.1
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• pp.17-30
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• 2018

Currently, the global climate change response paradigm has been changed to a universal response system in which all nations, not the developed countries, participate. Korea has also set a target of 25.9 million tons of transportation greenhouse gas reduction targets by 2030. Korean society is expected to enter the super aging society in 2026. In this study, to reduce the greenhouse gas emissions in public transport and to improve the convenience of transportation vulnerable, we estimate the willingness to pay(WTP) and social benefits assuming that the existing feeder buses are replaced with medium-sized low floor electric buses. To this end, survey was conducted on bus users in the metropolitan area and WTP was estimated by using contingent valuation method(CVM), which is one of the non-market value evaluation methods. As a result of estimation of WTP, the average WTP is 51.4 (won / time person), estimated the economic benefits were 50 million won on weekdays and 40 million won on weekends in Gyeonggi Province in 2014.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.7
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• pp.809-815
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• 2018

Distributed generations (DGs) using renewable energy resources in power systems have been widely integrated, and many of these DGs have intermittency. DGs can significantly affect the overall voltage profile of the system through the reactive power control for a voltage support. Therefore, in the planning stage of the optimal operation and dispatch of voltage regulation devices, DGs' hosting capacity with the reactive power control scheme should be considered. In this paper, we model the IEEE 34-bus test feeder, including all essential equipment. An optimization method is utilized to determine the optimal siting and operation of the voltage regulation devices in the presence of DGs with reactive power control scheme. Finally, we compare the optimal results of the each case to analyze the relationship among the hosting capacity of the DGs and voltage regulation devices operation.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.5
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• pp.162-168
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• 2004

Service restoration is an emergency control in distribution control centers to restore out-of-service area as soon as possible when a fault occurs in distribution networks. Therefore, it requires fast computation time and high quality solutions for load balancing. In this paper, a load balance index and heuristic guided best-first search are proposed for these problem. The proposed algorithm consists of two parts. One is to set up a decision tree to represent the various switching operations available. Another is to identify the most effective the set of switches using proposed search technique and a feeder load balance index. Test results on the KEPCO's 108 bus distribution system show that the performance is efficient and robust.