Three-area Power System Research Articles

Robust LFC in a Deregulated Environment: Multi-objective Control Approach

This paper addresses a new decentralized robust load-frequency control (LFC) design in a multi-area power system under deregulation based on bilateral policy scheme. In each control area, the effect of bilateral contracts is taken into account as a set of new input signals to modify the traditional LFC structure. The LFC problem is considered as a multi-objective control problem and formulated via a mixed H2/H∞ control technique, then it is easily carried out to synthesis the desired low-order robust controllers by solving standard linear matrix inequalities (LMI). A three-area power system example with possible contract scenarios and a wide range of load changes is given to illustrate the developed approach. The results of the proposed multi-objective control strategy are compared with pure H∞ design. The resulting controllers are shown to maintain the robust performance and minimize the effect of disturbances and specified uncertainties.

Robust decentralised load-frequency control using an iterative linear matrix inequalities algorithm

The load-frequency control (LFC) problem has been one of the major subjects in electric power system design/operation and is becoming much more significant today in accordance with increasing size, changing structure and complexity of interconnected power systems. In practice LFC systems use simple proportional-integral (PI) controllers. However, since the PI controller parameters are usually tuned based on classical or trial-and-error approaches, they are incapable of obtaining good dynamical performance for a wide range of operating conditions and various load changes scenarios in a multi-area power system. For this problem, the decentralised LFC synthesis is formulated as an HN-control problem and is solved using an iterative linear matrix inequalities algorithm to design of robust PI controllers in the multi-area power systems. A three-area power system example with a wide range of load changes is given to illustrate the proposed approach. The resulting controllers are shown to minimise the effect of disturbances and maintain the robust performance. List of symbols Dfi frequency deviation DPgt governor valve position DPci governor load setpoint DPti turbine power DPtiei net tie-line power flow DPdi area load disturbance

Decentralized robust adaptive load frequency control using interactions estimation

In this paper, a new model reference decentralized adaptive output feedback controller is proposed for load-frequency control (LFC) of large-scale power systems with unknown parameters. The main problem with a decentralized robust LFC is that the interactions are treated as disturbances. This results in a conservative control action to maintain stability in the worst-case scenario. Furthermore, to improve the performance of the decentralized LFC, the proposed method estimates the interactions from other subsystems to modify the adaptive controller so that the interactions are effectively neutralized. The other important features of the proposed controller are: (1) no prior information about the system parameters is required, (2) random changes in the operating conditions are traced, (3) only the local input–output data are needed, (4) the robustness of the overall system against the system parameter uncertainties is guaranteed. To show the effectiveness of the proposed controller, a three-area power system is studied. The simulation results are promising and highlight the remarkable performance of the controller even in the presence of both plant parameter changes and high interactions.

Robust load frequency control using genetic algorithms and linear matrix inequalities

In this paper, two robust decentralized control design methodologies for load frequency control (LFC) are proposed. The first one is based on H/sub /spl infin// control design using linear matrix inequalities (LMI) technique in order to obtain robustness against uncertainties. The second controller has a simpler structure, which is more appealing from an implementation point of view, and it is tuned by a proposed novel robust control design algorithm to achieve the same robust performance as the first one. More specifically, genetic algorithms (GAs) optimization is used to tune the control parameters of the proportional-integral (PI) controller subject to the H/sub /spl infin// constraints in terms of LMI. Hence, the second control design is called GALMI. Both proposed controllers are tested on a three-area power system with three scenarios of load disturbances to demonstrate their robust performances.

Decentralized robust adaptive-output feedback controller for power system load frequency control

In this paper, a new model reference-decentralized robust adaptive-output feedback controller is proposed for the load frequency control (LFC) of large-scale power systems with unknown parameters. This control strategy requires only local input–output data and can follow random changes in the operating conditions. The controller is designed such that the trajectory errors and the control gains of each area remain uniformly bounded. In the proposed method, firstly an adaptive observer is designed to estimate the state variables and system parameters using local data only. Then a locally linear combination of the estimated states and the model reference states are used to design a robust adaptive-output feedback controller for each area. Simulation results for a three-area power system show that the proposed controller achieves good performance even in the presence of plant parameter changes and system non-linearities.

A new decentralized robust controller design for multi-area load–frequency control via incomplete state feedback

This paper deals with load-frequency control of multi-area power installation. The robust control theory is utilized to decouple the areas for a decentralized robust load-frequency controller. The proposed controller ensures that the overall multi-area power system is asymptotically stable. A new technique is included to exclude feedback from any immeasurable state. The product comprises a set of local load-frequency controllers, one for each area. The design and operation of each local controller requires solely the corresponding area's parameters and state measurements. Measurements of the immeasurable states are unnecessary. System parameter uncertainties and generation rate constraints are included in the simulation study of three-area power system. Good results are reported.

A new decentralized robust controller design for multi‐area load–frequency control via incomplete state feedback

This paper deals with load–frequency control of a multi-area power installation. The robust control theory is utilized to decouple the areas for a decentralized robust load–frequency controller. The proposed controller ensures that the overall multi-area power system is asymptotically stable. A new technique is included to exclude feedback from any immeasurable state. The product comprises a set of local load–frequency controllers, one for each area. The design and operation of each local controller requires solely the corresponding area's parameters and state measurements. Measurements of the immeasurable states are unnecessary. System parameter uncertainties and generation rate constraints are included in the simulation study of a three-area power system. Good results are reported. Copyright © 1998 John Wiley & Sons, Ltd.

Robust decentralised load–frequency control of multi-area power systems

A robust decentralised load-frequency controller, based on the Riccati-equation approach, is proposed for multi-area power systems with parametric uncertainties. It comprises N local robust load-frequency controllers for a N-area power system. N interlinked Riccati equations are produced initially which are separated via a decoupling technique. Bounds of system parametric uncertainties are included in these Riccati equations to improve the robustness of the intended controller. One local robust load-frequency relationship is obtained by solving the corresponding decoupled Riccati equation. It operates on its local measurements; feedback from other areas is not needed. The overall system is asymptotically stable, for all admissible system parametric uncertainties, when all the local load-frequency controllers are working together. Good performance is reported from the studied three-area power system even in the presence of the generation-rate constraint.

Transmission constrained maintenance scheduling of generating units: a stochastic programming approach

This paper presents a new methodology for maintenance scheduling that takes into account inter-area transfer limitations and stochastic reliability constraints. The optimization model is based on the Benders decomposition technique. The objective of this model is to determine a minimum cost maintenance schedule, subject to technological and system reliability constraints. The model may also be used to assess the adequacy of existing transmission limits under a given set of planned outages of generating units. Case studies with a realistic three-area power system are presented and discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Reliability evaluation of a three-area power system

Abstract This paper evaluates the reliability of a three-area power system. It considers a new algorithm to determine the amount of MW assistance available to a deficient area in a power pool. The algorithm considers the area of interest and its neighboring areas in terms of their two-area reliability and then extends the results to the multi-area system. The linear flow model is used to calculate the energy supply to the importing area in the power pool, where the tie lines may impose limits on import-export capabilities. This approach does not set any restrictions as to how the areas may be interconnected.

Effect of Coordinated Correction of Tie-Line Bias Control in Interconnected Power System Operation

Nathan Cohn's newly proposed technique of coordinated, system-wide correction of time error and inadvertent interchange is examined and validated by computer simulations. Area and system performances are investigated for a sudden change in load or generation in a three-area power system. The following effects are examined: changing the time of correction; simultaneous versus individual correction of time error and inadvertent interchange; the type of disturbance; the governor delay time; and the presence of sustained errors.