Antiwindup for modelreference adaptive control schemes with ratelimits Abstract   This paper proposes an antiwindup like scheme for an LTI plant with ratelimits. The plant is controlled using a modelreference adaptive controller, making the antiwindup design problem highly nonlinear. It is assumed that the ratelimit is modelled as a first order feedback loop for which the state is unavailable, but that the bandwidth of this loop is known. The antiwindup scheme uses a xe2x80x9chedgingxe2x80x9d term and a xe2x80x9cpositive    xcexbc   xe2x80x9d term. The structure of the problem makes the ratelimit case considerably more difficult than the magnitude limit case. Nevertheless it is proved that convergence of the system state to the ideal model can be accomplished under conditions similar to those found in antiwindup compensation for purely linear systems.

On the need for switchedgain observers for nonmonotonic nonlinear systems Abstract   This paper focuses on the challenges in observer design for nonlinear systems which are nonmonotonic. A class of nonlinear systems is considered in which the process dynamics and output equations are both composed of nonlinear vector functions of scalar combinations of the states. The nonlinear functions are assumed to be differentiable with bounded derivatives. An observer design algorithm that requires solving just a single linear matrix inequality for exponentially convergent state estimation is developed. The developed algorithm works effectively when the involved nonlinear functions are monotonic. However, it fails when all or even some of the system functions are nonmonotonic. Both numerical computation and analytical results show that the observer design LMI has no feasible solutions when either all output functions or all process dynamics functions are nonmonotonic. Further, other constant gain LMIbased observer design methods from literature also fail when the involved nonlinear functions are all nonmonotonic, no matter how small the Lipschitz constant or the Jacobian bounds of the nonlinearities. This limitation has not previously been recognized in observer design literature. To overcome this limitation, a hybrid observer that switches between multiple constant observer gains is developed that can provide global asymptotic stability for systems with nonmonotonic nonlinear functions. Hybrid observers with switched gains enable existing observer design methods to be utilized for nonmonotonic nonlinear functions with finite local extrema. The application of the developed hybrid observer to two motion estimation applications, one a vehicle position tracking problem on roads and another a piston position estimation problem for an industrial actuator, are demonstrated.