• The Transactions of the Korean Institute of Electrical Engineers A
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• v.49 no.8
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• pp.374-379
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• 2000

The nodal marginal cost and the congestion charge are used as the econimic signals for the electricity price and new invetments in deregulated power systems. In this paper, the nodal marginal cost and the congestion charge are calculated by using the shadow prices resulted from the calculation of Optimal Power Flow(OPF). Linearization of inequality constraints and piecewise linear cost functions make an OPF problem LP-based forms. In order to use the shadow price, the Interior Point(IP) algorithm is applied as a solution technique to the formulation. This paper proposes an algorithm to determine efficients initial points which are guaranteed to be interior points.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.218-220
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• 1997

In power system, economic dispatch problem is to minimize fuel cost with inequality constraints of generator output. To solve this problem it is very important to express power loss equation that have Quadratic function of generator power included B-coefficient. This paper presents a method in determining B-coefficient by use A-matrix that is calculated by power flow considering voltage dependent static load model. The proposed algorithm is tested with IEEE 6 bus sample system, which shows the result in each cases by the change of load component factor.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.50 no.9
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• pp.406-410
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• 2001

This paper develops an efficient evolutionary programming based algorithm for solving the environmentally constrained economic dispatch problem in thermal power system. The proposed algorithm can deal with the power balance constraints and the emission constraints which are equality and inequality constraints, respectively. Numerical results show that the proposed algorithm can provide superior solutions within reasonable time through its application to a test system.

• Korean Journal of Veterinary Research
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• v.48 no.3
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• pp.357-361
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• 2008

Although power analysis is of important tool of research, investigators in veterinary medicine are unaware of the concepts of the statistical power. Two types of error occur in classical hypothesis testing and, those errors should be avoided, if possible. Since power is highly dependent on the sample size, whenever declaring non-statistically significant result they should consider the potential for committing a Type II error in their studies, which refers to the probability of falsely stating that two treatments are equivalent despite true difference between them. Also, sample size determination is one of the most important tasks facing the researcher when planning a diagnostic study, and provides valuable information on the characteristics of a test performance. This type of analysis forms the basis for proper interpretation of test results. The aim of this article was to re-evaluate some selected studies on diagnostic test reported in the domestic veterinary publications to determine the power and necessary sample size for inequality testing to ensure the desired power. Power calculations were illustrated using real-life examples of comparison of a new test and a reference test for detecting antibodies of various animal diseases. Factors affecting to the power were also discussed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.1
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• pp.8-13
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• 2007

During the last years, there has been an increased interest in the new energy such as photovoltaic(PV) system from the viewpoint of environmental pollution. In this regard, this paper estimates the power quality of grid-connected PV system. As the maximum power operating point(MPOP) of photovoltaic(PV) power systems alters with changing atmospheric conditions, the efficiency of maximum power point tracking(MPPT) is important in PV power systems. Moreover, grid-connected PV system occurs some problems such as voltage inequality and harmonics. Therefore, this paper presents the results of a grid-connected PV system modeling that contains incremental conductance MPPT controller by PSCAD/EMTDC simulator and investigates the influence that can occur in the grid-connected PV system from aspect of power quality, i.e. voltage drop, total harmonic distortion(TDD) and total demand distortion(TDD). For the case study, the measured data of the PV way in Cheongwadae, Seoul, Korea is used.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.36 no.9
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• pp.609-615
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• 1987

The optimal operation of power system is developed by alternately using real power dispatch and reactive power dispatch problem. The real power system scheduling process is formulated as an optimization problem with linear inequality constraints. A.C. loadflow method is used for the problem solution and line losses are considered. The constraints under consideration are generator power limits, load scehdling limits and line capacity limits. In solving the objective function the Dual Relaxation method is adopted. Tests indicate that the method is practical for real time application. The reactive power control problem uses the Dual Simplex Relaxation method as in the real scheduling case. Insted of minimizing the cost of power system, the objective is selected as to determine the highest possible voltage schedule. The constraints under consideration are the voltage limits at each node and the possibilities of supply or absobtion of reactive energy by generator units and the compensation facilities. Tests indicate that the method is practical for real time applications. The overall optimization methods developed in this paper proved to obtained fine results in minimizing object function compared with the method without using voltage control. And the overall voltage profiles were also improved.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.50 no.9
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• pp.424-430
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• 2001

A multi-level optimal power flow(OPF) algorithm has been evolved from a simple two stage optimal Power flow algorithm for constrained power economic dispatch control. In the proposed algorithm, we consider various constraints such as ower balance, generation capacity, transmission line capacity, transmission losses, security equality, and security inequality constraints. The proposed algorithm consists of four stages. At the first stage, we solve the aggregated problem that is the crude classical economic dispatch problem without considering transmission losses. An initial solution is obtained by the aggregation concept in which the solution satisfies the power balance equations and generation capacity constraints. Then, after load flow analysis, the transmission losses of an initial generation setting are matched by the slack bus generator that produces power with the cheapest cost. At the second stage we consider transmission losses. Formulation of the second stage becomes classical economic dispatch problem involving the transmission losses, which are distributed to all generators. Once a feasible solution is obtained from the second stage, transmission capacity and other violations are checked and corrected locally and quickly at the third stage. The fourth stage fine tunes the solution of the third stage to reach a real minimum. The proposed approach speeds up the two stage optimization method to an average gain of 2.99 for IEEE 30, 57, and 118 bus systems and EPRI Scenario systems A through D testings.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2002.05a
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• pp.203-206
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• 2002

This paper describes fuzzy control methodologies of the steam generator which have nonlinear characteristics in the nuclear power plant. Actually, the steam generator part of the power generator has a problem to control water level because it has complex components and nonlinear characteristics. In order to control nonlinear terms of the model, Takagj-Sugeno (75) fuzzy system is used to design a controller. In designing procedure, intelligent digital redesign method is used to control the nonlinear system. This digital controller keeps the performance of the analog controller. Simulation examples are included for ensuring the proposed control method.

• ETRI Journal
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• v.29 no.4
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• pp.445-451
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• 2007

An adaptive modulation scheme is presented for multiuser orthogonal frequency-division multiplexing systems. The aim of the scheme is to minimize the total transmit power with a constraint on the transmission rate for users, assuming knowledge of the instantaneous channel gains for all users using a combined bit-loading and subcarrier allocation algorithm. The subcarrier allocation algorithm identifies the appropriate assignment of subcarriers to the users, while the bit-loading algorithm determines the number of bits given to each subcarrier. The proposed bit-loading algorithm is derived from the geometric progression of the additional transmission power required by the subcarriers and the arithmetic-geometric means inequality. This algorithm has a simple procedure and low computational complexity. A heuristic approach is also used for the subcarrier allocation algorithm, providing a trade-off between complexity and performance. Numerical results demonstrate that the proposed algorithms provide comparable performance with existing algorithms with low computational cost.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.37 no.9
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• pp.591-599
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• 1988

After the short-term dynamics due to the major disturbance are over, the power system may lead to viability crisis state wherein there is possibility of cascading damage. This paper presents an emergency control algorithm to alleviate the obstacles of system frequency or bus voltage during the viability crisis state. The algorithm considers the effects of controlling reactive power sources for load shedding and generation reallocation in order to alleviate the obstacles. The problem is decomposed into a subproblem I and a subproblem II. The former minimizes system frequency deviation from nominal value and the latter voltage violation of load buses. The optimization problem is solved by a reduced gradient technique which can handle a great number of inequality constraints more easily. It has been verified that the use of the proposed algorithm for IEEE 14 bus system alleviates the obstacles efficiently during the viability crisis.