Byoung-Kon Choi

Improvement of system damping by using the differential feedback in the load frequency control

The power system stability mostly depends on the surplus kinetic energy which is stored in the generator during the fault period. The steam valve control is the most direct method to control the surplus kinetic energy. This paper proposes a new LFC scheme with a modified PID controller which improves the system damping. The proposed frequency controller is designed to guarantee the stability of frequency control for any change in the feedback gain of frequency deviation. The proposed LFC scheme adopts the nonwindup cutoff model for the steam valve position. It has been shown that the steam valve control is the most direct method to control the surplus kinetic energy stored in the generator during the fault period and control performance significantly depends on steam valve modeling. The proposed LFC scheme has been applied for two sample systems, 4-machine 10-bus and New England 39-bus systems.

Modified PID load-frequency control with the consideration of valve position limits

This paper proposes a new load frequency control (LFC) scheme with a modified PID controller which guarantees the stability of the LFC loop for the wide control ranges of PID feedback gains. By observing the fact that the ratios between PID gains have more information than the individual gains, we proposed a modified PID controller by implementing feedback circuits by differentiating and integrating the output of the flyball speed governor. The proposed control scheme guarantees wide-range stability boundary of the PID gain controls, which can be easily checked by observing the root locus diagram. This paper shows that the valve position limits can be modeled in several ways, and that the control performance significantly depends on steam valve modeling in the case of large disturbances. The proposed LFC scheme has been tested for a sample 4-machine 10-bus system.

The development of equivalent system technique for deriving an energy function reflecting transfer conductances

This paper shows that a well-defined energy function can be developed to reflect the transfer conductances for multi-machine power systems under an assumption that all transmission lines have uniform R/X ratios. The energy function is derived by introducing a pure reactive equivalent system for the given system. In this study, a static energy function reflecting transfer conductances is also derived as well as the transient energy function. The proposed static energy function is applied to voltage stability analysis and tested for various sample systems. The test results show that the accuracy of voltage stability analysis can be considerably improved by reflecting transfer conductances into the energy function.

Slack-bus independent penalty factor for spot pricing under deregulation

Recently, deregulation has been a hot issue in electric power industries with the introduction of the bidding system to electric power markets. One of the main topics associated with the deregulation is spot pricing, where the exact analysis of transmission loss and the method of calculating reliable penalty factor play an important role. Penalty factors calculated with conventional methods is highly dependent on the location of the slack bus, which brings about unfair competition to IPPs (independent power producers). This paper presents a new method of calculating the exact and reliable penalty factor independent of the change of the slack bus. The proposed method is tested on IEEE 14 bus system, New England 39 bus system and OH-145 bus system. The test results show that the proposed method can give more reliable information of the penalty factors to the spot pricing system.

Brief Estimating the domain of attraction for power systems via a group of damping-reflected energy functions

The well-known Lyapunov direct method provides precise and rigorous theoretical backgrounds for stability analysis of nonlinear systems. However, incorporating damping effects into accurate estimates of the domain of attraction has proved difficult, which is pointed as a minor but crucial drawback. This paper presents a new method to derive a group of Lyapunov functions to reflect the damping effects by considering the first integral of motion obtained from the system governing equations when transfer conductances are neglected. A systematical approach of converting some part of damping loss into some appropriate system energy terms is developed. Examples show that the proposed method remarkably improves the estimation of the region of attraction compared with the conventional approach.

Fast and reliable distribution system load flow algorithm based on the Y/sub BUS/ formulation

This paper presents a new and efficient method for solving the load flow problem in distribution systems. A simple algebraic matrix equation to solve the load flow problem is derived by using the complex power balance equations. By adopting the rectangular coordinate, which requires the neglect of only second order terms in the linearization procedure, the proposed method gives better convergence characteristics than the conventional Newton Raphson (NR) or the fast decoupled load flow (FDLF) methods. Only diagonal elements of the Jacobian matrix are subjected to be updated while other elements remain constant. This enhances the proposed algorithm considerably in computation speed. The proposed method can be applied to both radial and meshed networks. The proposed algorithm is tested with 33, 302, 700, and 1004-bus sample systems. The test results show that the proposed method can be well applied to the distribution system with wide ranged R/X values. The computation speed is remarkably improved compared with the conventional NR and FDLF methods.

Slack-bus independent penalty factor for regional spot pricing under deregulation

Abstract Recently, the deregulation has been a hot issue in electric power industries with the introduction of the bidding system to electric power markets. One of the main topics associated with the deregulation is spot pricing where the exact analysis of transmission loss and the method of calculating reliable penalty factor play an important role. Penalty factors calculated with conventional methods are highly dependent on the location of the slack bus, which brings about unfair competition to Independent Power Producers (IPPs). This paper presents a new method of calculating the exact and reliable penalty factor independent of the change of the slack bus. The proposed method is tested on IEEE 14 bus system, New England 39 bus system and OH-145 bus system. The test results show that the proposed method can give more reliable information of the penalty factors for the regional spot pricing.

Estimation of maximum loadability in power systems by using elliptic properties of P-e curve

This paper presents an efficient algorithm to estimate the maximum load level for heavily loaded power systems with the load-generation variation vector obtained by ELD (economic load dispatch) and/or short term load forecasting while utilizing the elliptic pattern of the P-e curve. It is well known the power flow equation in the rectangular coordinate is fully quadratic. However, the coupling between e and f makes it difficult to take advantage of this quadratic characteristic. In this paper, the elliptic characteristics of P-e curve are illustrated and a simple technique is proposed to reflect the e-f coupling effects on the estimation of maximum loadability with theoretical analysis. An efficient estimation algorithm has been developed by utilizing the elliptic properties of the P-e curve. The proposed algorithm is tested on IEEE 14 bus system, New England 39 bus system and IEEE 118 bus system, which shows that the maximum load level can be efficiently estimated with remarkable improvement in accuracy.

Improved method of maximum loadability estimation in power systems by transforming the distorted P-e curve

This paper presents an improved method to estimate the maximum load level for heavily loaded power systems with the load-generation variation vector obtained by ELD (economic load dispatch) and/or short term load forecasting by using the elliptic pattern of the P-e curve. The previous study suggested a simple technique of removing e-f coupling, where only high voltage load flow solutions to calculate transforming angle of system reference is needed. The proposed algorithm is improved to require only one load flow solution at a specific load level in addition to the operating point at the beginning stage, which reduces the computation time and the iteration number of estimation. The proposed method can be efficiently applied to heavily loaded systems with the combination of CPFlow when the reactive power limit and ULTC (under load tap changer) are considered. In this paper, the effect of ULTC on the estimation of maximum loadability index is also investigated. The proposed algorithm is tested on IEEE 14 bus system, New England 39 bus system and IEEE 118 bus system.

Analysis of polarized linear electric network with two-reactance components

This paper introduces the concept of polarized linear electric network and proposes a new approach to analyze it. It is well-known that the internal impedance of salient-pole generator has two reactance X/sub d/, X/sub q/ corresponding to the direct and quadratic current components. Two different reactance possessed by one circuit element provide the polarization characteristics in the current transfer. This study proposes a new analysis method which shows that the linearity of the polarized linear network makes it possible to calculate generator currents in one step for the given internal voltages and rotor angles of the generators. Tests have been performed for the sample systems, which shows remarkable improvement in computation time.