Feedback-Feedforward Position and Speed Control of DC Motors by Fractional-Order PI^{\nu} Controllers

Abstract

This paper proposes a double loop control scheme for position and speed control of a DC motor, which employs fractional-order PIn controllers. The design of the controllers requires the setting of six parameters, i.e. for each controller the proportional gain and the integral time constant, and the noninteger order of integration. To this aim, closed-form tuning formulas are derived to fulfil the required frequency domain specifications. The general formulation of the problem allows extending the tuning formulas explicitly to a wide class of systems. Then, it is shown how to introduce a feed-forward action to improve trajectory tracking performance. Finally, it is derived an equivalent fractional order controller, reducing the nested loops to a single control loop, and simplifying the control architecture. Simulation results show the effectiveness of the proposed approach, even in the presence of plant nonlinearities.