Improved Fractional-order Sliding Mode Controller for Frequency Regulation of a Hybrid Power System with Nonlinear Disturbance Observer

Abstract

With extensive integration of renewable resources and ever-rising consumer demand, the existing power systems inevitably experience the somber frequency instability problem. This work attempts to design and apply a nonlinear disturbances observer (NDO)-aided improved resilient controller to minimize the frequency deviation of a hybrid power system (hy-PS) following unknown/uncertain system disturbances. The NDO is developed to estimate time-varying uncertain bounded plant disturbance, including parametric uncertainties, load fluctuation, unsteady wind velocity, and unmodelled system dynamics. Subsequently, an active disturbance rejection control is implemented using an improved fractional-order sliding mode controller (iFOSMC) having NDO integrated to cope with system disturbances and offer finite-time asymptotic state convergence to the equilibrium point with least oscillations in control effort. Finite-time convergence of estimation error and asymptotic stability of the developed closed-loop system is also provided by applying the Lyapunov argument to guarantee the reliability of the proposed control algorithm. Besides, the mastery of the proposed NDO-aided iFOSMC compared to other well-known controllers has been demonstrated through comparative study under different perturbed conditions. The obtained system outputs show the high-effective performance of the proposed NDO-aided iFOSMC in terms of faster disturbance compensation, least chattering in control effort, and improved system outputs. The efficacy of the proposed frequency controller has also been tested against false data injection (FDI) attacks in a cyber-physical environment.