Jong-Gi Lee

Extended integral control for load frequency control with the consideration of generation-rate constraints

This paper presents an extended integral control to load frequency control (LFC) scheme with the presence of generation rate constraints (GRC) in order to get rid of overshoot of the conventional proportional-integral (PI) control. The conventional LFC scheme does not yield adequate control performance with the consideration of the singularities of speed-governor such as rate limits on valve position and GRC. In order to overcome this drawback, an extended integral control is developed for the PI control of the speed governor in the presence of GRC. The key idea of the extended integral control is using a decaying factor to reduce the effects of the error in the past. The decaying factor greatly affects the control performance, and should be carefully selected. This study determines the decaying factor in proportion to the degree of deviation in several levels. The computer simulation has been conducted for the single machine system with various load changes. The simulation results show that the proposed controller based on extended integral control yields much improved control performance, compared to the conventional PI controller.

Power system load frequency control using noise-tolerable PID feedback

This paper presents a new PID (proportional, integral and differential) control scheme based on the feedback of averaged derivatives to realize a noise-tolerable differential control with its application to the load frequency control in the power system. It is well known that the LFC (load frequency control) is exposed to the quite noisy environment. The noisy environment has made it difficult to adopt the differential feedback loop since the derivatives of the signals deteriorated by high frequency noise causes the system instability. This paper proposed a new PID control scheme adopting averaged derivative of the signal as the differential feedback signal in order to remove the effects of high frequency noise. This study deals with an application of the average differential feedback to the LFC problem in the power systems. The proposed control scheme has been tested for the load frequency control of power systems.

Uniqueness of static voltage stability analysis in power systems

Diverse theories have been established in voltage stability analysis since various aspects have been observed during voltage collapse phenomena. Through rigorous mathematical investigation, this paper shows that all the major methods used in static voltage stability analysis, i.e. Jacobian method, voltage sensitivity method, real and reactive power loss sensitivity method and energy function method-provide an identical result to show the uniqueness of static voltage stability analysis in theory. The tests for sample systems have shown that an identical result can be obtained from the various analysis methods.

Extended integral based governor control for power system stabilization

This paper presents an extended integral control to the speed-governor system for damping power system oscillations. The power system oscillations mostly stem from the surplus kinetic energy which is stored in the generator during the fault period. The effective control of the surplus energy can be the most direct method to achieve the system stabilization. The LFC (load frequency control) loop can be utilized as a direct method to control the surplus energy. The proposed controller based on the extended integral control is applied to speed-governor to damp out the local and interarea mode oscillations. The proposed controller also provide good performance under presence of the singularities of speed-governor such as limits on valve position and GRC (generation rate constraints). The computer simulation has been conducted for the two-area multimachine system with various load changes. The simulation results show that the proposed controller yields much improved control performance, compared to the conventional PI controller.

Allocation of Transmission Loss for Determination of Locational Spot pricing

The deregulation problem has recently attracted attentions in a competitive electric power market, where the cost must be earmarked fairly and precisely for the customers and the Independent Power Producers (IPPs) as well. Transmission loss is an one of several important factors that determines power transmission cost. Because the cost caused by transmission losses is about 3-5%, it is important to allocate transmission losses into each bus in a power system. This paper presents the new algorithm to allocate transmission losses based on an integration method using the loss sensitivity. It provides the buswise incremental transmission losses through the calculation of load ratios considering the transaction strategy of an overall system. The performance of the proposed algorithm is evaluated by the case studies carried out on the WSCC 9-bus and IEEE 14-bus systems.

Equivalent mechanical model of power systems for energy-based system analysis

This paper presents a new mechanical analogy of power systems for energy-based system analysis based on an equivalent mechanical model (EMM). The EMM is developed on the basis of mechanical analogy of power system by using spring connected rod-inertia system. The proposed EMM introduces an imaginary spring for the analogical correspondence to the transfer conductance of a transmission line with discussion of its energy storage properties. The imaginary spring produces its forces acting on the both ends perpendicular to its displacement vector. The rod-inertia system is completely analyzed in order to show that it has just the same dynamic equations as the power system. The proposed EMM provides theoretical background for energy-based analysis of power systems, which enables us to utilize well-known theories such as Lagranges equation.

ECONOMIC DISPATCH ALGORITHM BY λ-P TABLES REFLECTING ACTUAL FUEL COST CURVES

Abstract This paper presents a new approach to economic dispatch (ED) problems with actual fuel cost curves using a λ-P table method. Conventional ED algorithms are developed on the basis of approximated fuel cost function, which cannot be adapted to actual fuel cost curves properly. In this paper, a λ-P table method is proposed to improve accuracy of ED solution. It is noted that the proposed algorithm is very simple and has some advantages in considering the must-run condition and modifying the ED solution associated with generator addition/elimination. Numerical results of the proposed algorithm are compared with those of the conventional algorithms.

Energy-based approach to power transfer system analysis

This paper presents a new theoretical approach to energy-based power system analysis for multibus power transmission systems. On the basis of mechanical analogy, an exact energy integral expression is derived for lossy multibus systems through rigorous energy analysis. A simple rigid rod model of mechanical power transfer system is introduced to address the physical meanings of potential energy terms associated with transfer conductances as well as transfer susceptances. Finally, energy-based analysis has been proposed to show that the energy function has all information of the power system characteristics.

Double Circuit Simultaneous Contingency Analysis

Abstract This paper proposes a new approach to simultaneous contingency analysis with Double Circuit Simultaneous Faults. To improve the accuracy and the computation speed of the contingency analysis, the Peterson method has been adopted with the ShennanMorrison formula and a matrix decomposition method. The triangular factor table technique is also adopted, to compute the inverse matrix in the loadflow calculation. Based on these methods, simulation considering several cases show that double circuit simultaneous faults analysis suggested in this paper offer fast loadflow computation in short time by calculating relative accurate phase angle variation

Energy-Based Power System Analysis with the Equivalent Mechanical Model

Abstract This paper presents a new theoretical approach to energy-based power system analysis using the equivalent mechanical model for multibus power transmission systems. On the basis of mechanical analogy, an exact energy integral expression is derived for lossy multi-bus systems through rigorous energy analysis. A simple rigid rod model of mechanical power transfer system is introduced to address the physical meanings of potential energy terms associated with transfer conductances as well as transfer susceptances. Finally, energy-based analysis has been proposed with the Lagranges Equations and Hamiltonian Equations, which shows that the energy function has all information of the power system characteristics.