Frequency-Domain Tuning of a Robust Optimal 2-DOF Fractional Order PID Controller for a Maglev System

Two-degree-of-freedom (2-dof) proportional-integral-derivative (PID) controllers are better than the 1-dof counterpart in the sense that the former can predominantly reduce large overshoot and settling time without affecting the steady-state performance provided that a suitable tradeoff is chosen between reference tracking and rejection of the disturbance signal. Again, fractional order (FO) calculus is suitable to realize the dynamics of a controlled system and smoothen control action. This article amalgamates both of these control actions and develops a novel 2-dof FOPID controller for stabilization and precise position control of an unstable and nonlinear magnetic levitation system. A set of frequency-domain parameters are optimized to evaluate controller's orders and gains by adopting equilibrium optimizer, a new and efficient technique in the field of modern metaheuristics algorithms. It has been observed that the proposed 2-dof control architecture outperforms the 1-dof control counterpart in terms of time- and frequency-domain indices, reference tracking, robust stability analysis, and cancellation of disturbance signal. The efficacy of the proposed controller has been verified by comparing performance characteristics with existing controllers both in simulation and experimentation.