Robust self-tuning fractional order PID controller dedicated to non-linear dynamic system

A novel Non-Linear Fractional order PID controller (NLF-PID) is designed for control of coupled and non-linear 2-link rigid robot. The structure of proposed controller comprises of non-linear hyperbolic function of instantaneous error and current state cascaded with Fractional Order PID (FO-PID). Non-linear function provides adaptive control ability while incorporation of fractional operator enhances flexibility of designed controller. To examine the comparative merits of NLF-PID controller, Non-linear PID (NL-PID), FO-PID and traditional PID schemes are also implemented. Design variables of controllers are optimally tuned using multi objective Non-dominated Sorting Genetic Algorithm II (NSGA-II) for small variation in control and error signal. Results prove that NLF-PID provides robust and efficient control of robotic arm as compared to other designed controllers for reference tracking, model uncertainty, disturbance and noise due to inherent shortcoming of sensor.