DESIGN OF DECENTRALIZED ROBUST LFC IN A COMPETITIVE ELECTRICITY ENVIRONMENT

Hossein Shayeghi - Heidar Ali Shayanfar

   A new decentralized robust controller for Load Frequency Control (LFC) in a deregulated electricity environment is presented in this paper. It is shown that subject to a condition based on the H_∞ norm and structured singular values (μ), each local area controller can be designed independently such that stability of the overall closed loop system is guaranteed. A generalized model for LFC scheme is developed based on the possible contracted scenarios. To achieve decentralization, the interfaces between control areas and the effects of load following contracts are treated as a set of new input disturbance signals in the control area dynamical model. In order to minimize the effects of the load disturbances under contract variations with large demand changes and to achieve desired level of robust performance in the presence of modeling uncertainties and practical constraints on control action the idea of mixed H₂/H_∞ control technique is used for solution of the LFC problem. This newly developed design strategy combines the advantage of the H₂ and H_∞ control synthesizes and gives a powerful multi-objectives design addressed by the Linear Matrix Inequality (LMI) techniques. The effectiveness of the proposed method is demonstrated on a three- area power system with possible contracted scenarios under large load demands. The results of the proposed controller are compared with the conventional PI controller and are shown to maintain robust performance in the presence of specified uncertainties and system nonlinearities.

Keywords: LFC, decentralized control, deregulated power system, mixed H₂/H_∞ control, robust control, LMI, large scale system

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