A ROBUST DECENTRALIZED POWER SYSTEM LOAD FREQUENCY CONTROL

This paper presents a new robust decentralized controller based on mixed H2/H1 control technique for the solution of Load Frequency Control (LFC) in a deregulated electricity environment. To achieve decentralization in each control area, the connections between this area and the rest of the system and the effects of possible contracts are treated as a set of new disturbance signals. It is shown that, subject to a condition based on the structured singular value (µ), each local area load frequency controller can be designed independently so that stability of the overall closed loop system is guaranteed. In order to minimize effects of load disturbances 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/H1 control technique is being used for the solution of LFC problem. This newly developed design strategy combines advantage of H2 and H1 control syntheses and gives a powerful multi- objectives design addressed by the Linear Matrix Inequalities (LMI) technique. To demonstrate the effectiveness of the proposed method a two-area restructured power system is considered as a test system under different operating conditions. The results of the proposed decentralized controller are compared with the conventional PI and pure H1 controllers and are shown to minimize the effects of load disturbance and maintain robust performance in the presence of specified uncertainties and system nonlinearities. K e y w o r d s: LFC, decentralized control, restructured power system, mixed H2/H1 control, robust control, LMI Global analysis of the power system markets shows that the frequency control is one of the most profitable ancillary services at these systems. This service is related to the short-term balance of energy and frequency of the power systems. The most common methods used to accomplish frequency control are generator governor response (primary frequency regulation) and Load Frequency Control (LFC). The goal of LFC is to reestablish primary frequency regulation capacity, return the frequency to its nominal value and minimize unscheduled tie-line power flows between neighboring control areas. From the mechanisms used to manage the provision this service in ancillary markets, the bilateral contracts or competitive offers stand out [1]. In the dynamical operation of power systems, it is usually important to aim for decentralization of control action to individual areas. This aim should coincide with the requirements for stability and load frequency scheduling within the overall system. In a completely decentralized control scheme, the feedback controls in each area are computed on the basis of measurements taken in that area only. This implies that no interchange of information among areas is necessary for the purpose of load frequency control. The advantages of this operating philosophy are apparent in providing cost savings in data communications and in reducing the scope of the monitoring network.