• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1777-1788
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• 2017

This paper presents the design and dynamic analysis of a stand-alone microgrid with high penetration of renewable energy. The optimal sizing of various components in the microgrid is obtained considering two objectives: minimization of levelized cost of energy (LCOE) and maximization of renewable energy penetration. Integrating high renewable energy in stand-alone microgrid requires special considerations to assure stable dynamic performance, we therefore develop voltage and frequency control method by coordinating Battery Energy Storage System (BESS) and diesel generators. This approach was applied to the design and development of Gasa Island microgrid in South Korea. The microgrid consists of photovoltaic panels, wind turbines, lithium-ion batteries and diesel generators. The dynamic performance of the microgrid during different load and weather variations is verified by simulation studies. Results from the real microgrid were then presented and discussed. Our approach to the design and control of microgrid will offer some lessons in future microgrid design.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1357-1368
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• 2017

The lack of controllability over the wind causes fluctuations in the output power of the wind generators (WGs) located at the wind farms. Distribution Static Compensator (DSTATCOM) equipped with Battery Energy Storage System (BESS) can significantly smooth these fluctuations by injecting or absorbing appropriate amount of active power, thus, controlling the power flow of WGs. But because of the component aging and thermal drift, its harmonic filter parameters vary, resulting in performance degradation. In this paper, Quantitative Feedback Theory (QFT) is used as a robust control scheme in order to deactivate the effects of filter parameters variations on the wind power generation power smoothing performance. The proposed robust control strategy of the DSTATCOM is successfully applied to a microgrid, including WGs. The simulation results obviously show that the proposed control technique can effectively smooth the fluctuations in the wind turbines' (WT) output power caused by wind speed variations; taking into account the filter parameters variations (structural parameter uncertainties).

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.513-520
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• 2018

Since Paris Climate Change Conference in 2015, many policies to reduce the emission of greenhouse gas have been accelerating, which are mainly related to renewable energy resources and micro-grid. Presently, the technology development and demonstration projects are mostly focused on diversifying the power resources by adding wind turbine, photo-voltaic and battery storage system in the island-type small micro-grid. It is expected that the large-scaled micro-grid projects based on the regional district and town/complex city, e.g. the block type micro-grid project in Daegu national industrial complex will proceed in the near future. In this case, the economic cost or the carbon emission can be optimized by the efficient operation of energy mix and the appropriate construction of electric and heat supplying facilities such as cogeneration, renewable energy resources, BESS, thermal storage and the existing heat and electricity supplying networks. However, when planning a large residential town or city, the concrete plan of the energy infrastructure has not been established until the construction plan stage and provided by the individual energy suppliers of water, heat, electricity and gas. So, it is difficult to build the efficient energy portfolio considering the characteristics of town or city. This paper introduces an energy mix optimization(EMO) method to determine the optimal capacity of thermal and electric resources which can be applied in the design stage of the real large-scaled residential town or city, and examines the feasibility of the proposed method by applying the real heat and electricity demand data of large-scale residential towns with thousands of households and by comparing the result of HOMER simulation developed by National Renewable Energy Laboratory(NREL).

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.11
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• pp.1584-1589
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• 2012

The grid-interconnected microgrid can be able to operate with and without the utility microgrid to supply electricity. when the microgrid operates in grid-connected mode, the frequency of the microgrid synchronizes with the system frequency. In this case, the frequency of the microgrid has small variation which is able to change the output of distributed generation with a droop controller. Thus, the small variation of frequency can make the distributed generation generate unnecessary electricity consistently. In this paper, we propose a frequency droop control with a dead band so as to prevent the distributed generations from generating unnecessary output while in grid-interconnected mode. In addition, a distributed generation can have a restoration control to restore the frequency changed by a droop control as a rated frequency. Also, we state the problem of restoration control with a dead band, and propose its solution when the microgrid operates in stand alone mode. We simulate the proposed droop control using PSCAD/EMTDC to verify the validity of the control.