• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2003년도 하계학술대회
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• pp.286-288
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• 2003

In this paper, in order to obtain a large differential phase shift with a little change in applied voltage, a ferroelectric reflective load circuit has been designed on top of barium strontium titanate $(Ba,Sr)TiO_3$ [BST] thin film. The design of the ferroelectric reflection-type phase shifter is based on a reflection theory of terminating circuit, which has a reflection-type analogue phase shifter with two ports terminated in symmetric phase-controllable reflective networks. To achieve large amounts of phase shift in low bias-voltage range, the effects of change of capacitance and transmission line connected with two coupled ports of a 3-dB $90^{\circ}$ branch-line hybrid coupler have been investigated. A large phase shift with a small capacitance change in the parallel terminating circuit has been demonstrated in the paper.

• 전기학회논문지
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• 제64권1호
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• pp.1-7
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• 2015

This paper proposes probabilistic reliability evaluation model of power system considering Wind Turbine Generator(WTG) integrated with Energy Storage System(ESS). Monte carlo sample state duration simulation method is used for the evaluation. Because the power output from WTG units usually fluctuates randomly, the power cannot be counted on to continuously satisfy the system load. Although the power output at any time is not controllable, the power output can be utilized by ESS. The ESS may make to smooth the fluctuation of the WTG power output. The detail process of power system reliability evaluation considering ESS cooperated WTG is presented using case study of Jeju island power system in the paper.

• 수산해양기술연구
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• 제22권1호
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• pp.29-33
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• 1986

This paper aims at finding out the optimum operating condition to reduce fuel consumption for the training ship Pusan 402 with controllable pitch propeller. For this purpose, this paper examints the variation of ship speed and fuel consumption in accordance with the change of engine revolution and propeller pitch. The results obtained are as follows: 1. When engine revolution is constant, the ship speed sluggishly increases according to the increase of propeller pitch but fuel consumption extremely increases. The higher revolution the engine is, the more remarkable this tendency is. 2. As the engine revolution becomes lower, the fuel consumption per mile decreases. Howt.er = the fuel consumption under the same engine revolution differs according to the propeller pitch. 3. Specific fuel consumption is uniformed about 180g/ps.h at any case of load. 4. Among the various operating conditions which yield the same ship speed, fuel consumption lowers in the case of lower engine revolution and larger propeller pitch.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.1304-1310
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• 2015

In remote islands, due to expense of existing generation systems, installation of photovoltaic cells (PVs) and wind turbines has a chance of reducing generation costs. However, in island power systems, even short-term power fluctuations change the frequency of grids because of their small inertia constant. In order to compensate power fluctuations, the authors proposed the power consumption control of pumps which send water to tanks. The power control doesn’t affect water users’ convenience as long as tanks hold water. Based on experimental characteristics of a pump system, this paper shows methods to determine reference power consumption of the system with compensation for short-term PV fluctuations while satisfying water demand. One method uses a PI controller and the other method calculates reference power consumption from water flow reference. Simulations with a PV and a pump system are carried out to find optimum parameters and to compare the methods. Results show that both PI control method and water flow calculation method are useful for satisfying the water demand constraint. The water demand constraint has a little impact to suppression of the short-term power fluctuation in this condition.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.473-474
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• 2015

This paper proposes probabilistic reliability evaluation model of power system considering Wind Turbine Generator(WTG) integrated with Energy Storage System(ESS). Monte carlo sample state duration simulation method is used for the evaluation. The power output from WTG units usually fluctuates randomly. Therefore, the power cannot be counted on to continuously satisfy the system load. Although the power output at any time is not controllable, the power output can be utilized when needed if ESS is available. The ESS may make to smooth the fluctuation of the WTG power output. The detail process of power system reliability evaluation considering Multi-ESS cooperated WTG is presented using case study of Jeju island power system in the paper.

• KIEAE Journal
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• 제17권3호
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• pp.99-106
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• 2017

Purpose: Most modern office buildings adopt the curtain wall system in order to provide occupants with the sense of openness and high-technology, which requires large window area. As a result, the amount of solar radiation increases, negatively affecting cooling load during the summer and increasing energy costs. However, the performance of window itself is not sufficiently controllable parameter to control thermal comfort and solar radiation. Therefore, a shading device such as venetian blind is required to control them and thus a variety of studies have been performed thus far. So, the purpose of this study is to improve the performance of blind through the development of blind control algorithm. Method: Among various input variables for the control of venetian blinds, the vertical solar radiation has been selected in this study as the primary input variable and the optimal control algorithm for venetian blinds were developed for each window orientation. Result: The developed optimal control algorithm has a positive effect on building energy savings.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권11호
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• pp.5271-5289
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• 2016

On large-scale data analysis platforms deployed on cloud infrastructures over the Internet, the instability of the data transfer time and the dynamics of the processing rate require a more sophisticated data distribution scheme which maximizes parallel efficiency by achieving the balanced load among participated computing elements and by eliminating the idle time of each computing element. In particular, under the constraints that have the real-time and limited data buffer (in-memory storage) are given, it needs more controllable mechanism to prevent both the overflow and the underflow of the finite buffer. In this paper, we propose an auto regulated data provisioning model based on receiver-driven data pull model. On this model, we provide a synchronized data replenishment mechanism that implicitly avoids the data buffer overflow as well as explicitly regulates the data buffer underflow by adequately adjusting the buffer resilience. To estimate the optimal size of buffer resilience, we exploits an adaptive buffer resilience control scheme that minimizes both data buffer space and idle time of the processing elements based on directly measured sample path analysis. The simulation results show that the proposed scheme provides allowable approximation compared to the numerical results. Also, it is suitably efficient to apply for such a dynamic environment that cannot postulate the stochastic characteristic for the data transfer time, the data processing rate, or even an environment where the fluctuation of the both is presented.

• 전기학회논문지
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• 제61권8호
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• pp.1099-1106
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• 2012

Microgrid is a new electrical energy system that composed of various generators, renewable energy, batteries and loads located near the electrical customers. When Microgrid is interconnected with large power system, Microgrid don't need to control the frequency. But in case of the outage or faults of power system, Microgrid should control the frequency to prevent the shutdown of Microgrid. This paper presents the frequency control methods using the droop function, being used by synchronous generators and EMS(Energy Management System). Using droop function, two battery systems could share the load based on locally measured signals without any communications between batteries. Also, we suggest that EMS should control the controllable distributed generators as P/Q control modes except batteries to overcome the weakness of droop function. Finally we suggest the two batteries systems to prolong the battery's life time considering the economical view. The validation of proposed methods is tested using PSCAD/EMTDC simulations and field test sites at the same time.

• 조명전기설비학회논문지
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• 제30권3호
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• pp.79-85
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• 2016

This paper analyzed the influence of wind power fluctuations in grid frequency of a stand-alone microgrid that is hybrid generation system with diesel generator, wind turbine, and Battery Energy Storage System (BESS). The existing island area power system consists of only diesel generators. So the grid frequency can be controllable from load change. But hybrid generation system with Renewable Energy Sources (RES) such as wind energy that has the intermittent output can bring power quality problems. BESS is one of the ways to improve the intermittent output of the RES. In this paper, we analyzed the role of BESS in a stand-alone microgrid. We designed a modelling of wind power system with squirrel-cage induction generator, diesel power system with synchronous generator, and BESS using transient analysis program PSCAD/EMTDC. And we analyzed the variation of the grid frequency according to the output of BESS.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제51권9호
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• pp.515-521
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• 2002

This paper presents the scheme that improves control responsibility and stability of the controlled-PM electromagnet levitation system with zero Power controller. A magnetically levitation system is used widely because friction can almost be disappeared. But it is difficult to control due to restraint of controllable area and nonlinear characteristics of electromagnetic force, which is proportioned to a square of the magnetic flux density and is in inverse proportion to a square of the air-gap. So, the application of observer theory in which the levitation system is considered to be a linear dynamic model has resulted in omitting the time dependence on mover's speed. Consequently, the performance of the observer is quite poor during transients. Therefore, this paper proposed the controlled-PM electro-magnetic levitation control method in which the variable load is estimated by using the reduced order extended luenverger observer and its system is controlled at a new zero power equilibrium air-gap position. It is also verified that the proposed control method improve the control performance through simulation and experiment.