Design of Robust H∞ Technique Using Linear Matrix Inequalities for Load Frequency Control

Abstract

In an interconnected power system, variation in frequency and tie line power exchange occurs subjected to changes in the load demand taking place in different areas. The primary control through local governors, although adjust the governor outputs in order to compensate the changes occurring in the load demand and tie line power exchange, the primary controls are not able to provide a full compensation for the load power changes. Therefore, a supplementary control is necessary for the power system to keep the system frequency at inconsequential values. The additional control mechanism must act to bring back the system frequency to it nominal value by adjusting the speed reference set-point. In this work, the method for robust decentralised control is proposed for load frequency control (LFC). For this, initially a plant transfer model is developed for a two area interconnected system with non-reheat thermal units. For this system, H∞ control design based on linear matrix inequalities (LMI) technique is presented to achieve robustness against uncertainties. The H∞ technique achieve the tuning of the parameters of the proportional-integral (PI) controller under LMI constraints. The robust performance of the proposed technique is tested on an interconnected two-area power system with non-reheat thermal turbine units for different load disturbances in the form of step perturbations. The system is implemented under MATLAB/SIMULINK environment. The simulation results for the developed controller are compared with two area interconnected system with non- reheat thermal units having conventional PID controller as the control mechanism. The results obtained demonstrate that the dynamic response obtained on introduction of robust control in the interconnected system is far more satisfactory than from the conventional control method used.