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

This paper proposes a double loop control scheme for position and speed control of a DC motor, which employs fractional-order PI nu 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 non-integer 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.