Adaptive Fractional Order Sliding Mode Control for PMSG with Disturbance Observer

In this paper, a new adaptive fractional-order sliding mode controller is designed for a Permanent Magnet Synchronous Generator (PMSG) to track the maximum power point. The controller objective is to track the desired generator speed to extract the maximum power from the wind turbine system in the presence of parametric uncertainty and external disturbances. First, a new fractional order sliding surface is defined. To ensure the stability of the closed-loop system in the sliding model controller it is required to know the upper bounds of uncertainties and disturbances, where it is difficult to calculate these bounds for practical applications such as wind turbines. Therefore, the control signal parameters are estimated online by the proposed adaptive laws, in order to increase the convergence rate of the state variables to the reference value and reduce the chatting phenomenon, also to increase the system robustness against external disturbances and parametric uncertanity. On the other hand, due to the unknown disturbance dynamics, a disturbance observer is designed to estimate external disturbances and parametric uncertainty. Then, the stability of the general closed-loop system together with the disturbance observer is performed using Lyapunov's theory. Finally, the simulation results considering two different scenarios; first for step wind changes with external disturbance, second for changes in sine wind speed with parametric uncertainty. The results are compared with conventional sliding mode controller and results show the effective performance of the proposed controller in tracking the reference value, increasing its robustness against uncertainty and disturbance and reducing the chatting phenomenon.