Turkish Journal of Electrical Engineering and Computer Sciences




This study examines the gain and phase margins (GPMs) based robust stability margins in the parameter space of fractional order proportional-integral (FOPI) controller for a micro-grid (MG) system with communication time delays. Fluctuations in renewable energy sources (RESs), uncertainties in parameters of system components and communication delays could adversely affect the dynamical analysis and frequency stability of the MG system. Such a MG system has an interval characteristic due to the parametric variations and the interval transfer functions defined by Kharitonov's theorem, which presents a solution for checking of robust stability. Therefore, this study addresses the robust stability regions containing a set of robust FOPI controller gains for all possible transfer functions of the MG system by a simple graphical method working in controller parameter space. In this way, the impact of fractional order degree of integral controller on the robust stability regions is exhaustively examined by the graphical method. Additionally, robust performance of the interval MG system in terms of design specifications including GPMs is analyzed, and the effect of GPMs on the robust regions is investigated by the graphical method. Results indicate that GPM parameters provide the desirable performances for the MG and fractional order of integral controller considerably increases the robustness of the stability margin of the MG when compared with the integer order PI controller.


Micro-grids, gain and phase margins, robust stability region, fractional-order controller

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