A backstepping approach to multivariable robust constraint satisfaction with application to a VTOL helicopter

A recursive procedure is proposed to reduce a set of inequality constraints of high relative order to single constraints of relative order one for a class of uncertain, multi-input nonlinear systems. A modification of a nominal control signal on the newly constructed constraints guarantees robust constraint satisfaction. The resulting robust invariant controller is applied to the constrained flight and the obstacle avoidance problem of a VTOL helicopter.