ABSTRACT
This work presents design and theoretical analysis of an adaptive fractional-order sliding-mode disturbance observer (FO-SM-DOB)-aided fractional-order robust controller for frequency regulation of a hybrid wind-diesel based power system, considering endogenous/exogenous system disturbances. Adaptive FO-SM-DOB is designed to estimate unknown/uncertain lumped system disturbances, including parametric uncertainty and exogenous disturbances. Afterwards, an improved fractional-order sliding mode controller (FOSMC) augmented with the estimated output of FO-SM-DOB is designed and applied to accelerate system dynamics with minimum chattering in the control effort. The Mittag-Leffler stability theorem affirms the finite-time convergence of disturbance estimation error. Moreover, the closed-loop asymptotic stability of the overall control system has been guaranteed by applying Lyapunov argument. The effectiveness of the suggested resilient fractional-order nonlinear frequency controller is theoretically validated by performing an extensive comparative study with SMC, FOSMC (without DOB), state observer-based SMC (SOB-SMC), second-order SMC (without DOB), and conventional integer/fractional-order controllers. Simulation results establish the supremacy of the proposed resilient fractional-order nonlinear frequency controller over its other counterparts concerning fast disturbance rejection, weaker chattering, and a high degree of robustness against unknown lumped system disturbances. Further, to demonstrate the practicability and validate the effectiveness of the proposed control strategy, magnetic levitation system and IEEE 39-bus New England power system are considered and successfully tested on MATLAB platform.
ABSTRACT
The work described herein compares the performance of different optimized controllers, viz. proportional-integral, proportional-integral-derivative (PID) with filter, two-degree-of-freedom (2DOF)-PID, 3DOF-PID, fractional-order-PID, cascade PI-PID, tilt-integral-derivative (TID), and cascade-TID (CC-TID) controllers in frequency regulation of a hybrid energy distributed power system (HEDPS). The HEDPS is integrated with a multi-unit hydrothermal power plant for ensuring stable power supply. Crow search algorithm has been adopted with chaotic mapping (CCSA) for fine-tuning of the controller settings mentioned above. Extensive analysis has been presented to confirm the superiority of the CC-TID controller compared to other prevalent controllers of state-of-art in terms of different performance specifications. The tuning competence of the CCSA has been demonstrated over conventional CSA and other available optimization techniques. To enhance the mastery of the controller, disturbance-observer (Dob) is developed to estimate fast-changing disturbance profiles and subsequently refines the control law. The controller's robustness is affirmed under random perturbations, presence of nonlinearities, and variation of parameters. The effect of integration of a geothermal power plant on the system performance has also been outlined. The efficacy of Dob-aided CC-TID controller in frequency regulation is validated thereof.
