Coordinated control strategy for a rotating flywheel pendulum

The rotating flywheel inverted pendulum (RFP) is an underactuated mechanical system requiring a nonlinear model to represent its full state behavior. To drive the pendulum from any initial condition to the unstable upper position, two controllers are usually required. Due to energy limitation, a nonlinear swing-up control is needed to bring the pendulum to the vicinity of the desired final position where a linear controller keeps the pendulum around the upper unstable equilibrium point. In a recent paper, a simple linear controller was proposed by the authors to stabilize the RFP assuring internal stability, for initial conditions near the unstable equilibrium point, using a linearized model for parameter design. In this paper, the full state space is considered for the initial conditions. A nonlinear model of a lab RFP is derived and, based on this model, a nonlinear energy based swing-up controller is combined with a local linear stabilizing controller allowing for transferring the pendulum from its stable rest position to the upward unstable angular position, stabilizing it and compensating a wide range of disturbances. A new lab prototype is described, developed to compare simulation with experimental results, validating the performance of the proposed coordinated control scheme.