Design of Robust Controller for LFC of Interconnected Power System Considering Communication Delays

The usage of open communication infrastructure for transmitting the control signals in the Load Frequency Control (LFC) scheme of power system introduces time delays. These time delays may degrade the dynamic performance of the power system. This paper proposes a robust method to design a controller for multi-area LFC schemes considering communication delays. In existing literature, the controller values of LFC are designed using time domain approach which is less accurate than the proposed method. In proposed method, the controller values are determined by moving the rightmosteigenvalues of the system to the left half plane in a quasi-continuous way for a preset upper bound of time delay. Then the robustness of the proposed controller is assessed by estimating the maximumtolerable value of time delay for maintaining system stability. Simulation studies are carried out for multi-area LFC scheme equipped with the proposed controller using Matlab/simulink. From the results, it has been concluded that the proposed controller guarantees the tolerance for all time delays smaller than the preset upper bound and provides a bigger delay margin than the existing controllers.

Influence factors on natural frequencies of composite materials

Compared with traditional materials, composite materials have lower specific gravity, larger specific strength, larger specific modulus, and better designability structure and structural performance. However, the variability of structural properties hinders the control and prediction of the performance of composite materials. In this work, the Rayleigh–Ritz and orthogonal polynomial methods were used to derive the dynamic equations of composite materials and obtain the natural frequency expressions on the basis of the constitutive model of laminated composite materials. The correctness of the analytical model was verified by modal hammering and frequency sweep tests. On the basis of the established theoretical model, the influencing factors, including layers, thickness, and fiber angles, on the natural frequencies of laminated composites were analyzed. Furthermore, the coupling effects of layers, fiber angle, and lay-up sequence on the natural frequencies of composites were studied. Research results indicated that the proposed method could accurately and effectively analyze the influence of single and multiple factors on the natural frequencies of composite materials. Hence, this work provides a theoretical basis for preparing composite materials with different natural frequencies and meeting the requirements of different working conditions.