Disturbance observer design for nonlinear systems represented by input-output models

A new approach to the design of nonlinear disturbance observers for a class of nonlinear systems described by inputoutput differential equations is presented in this paper. In contrast with established forms of nonlinear disturbance observers, the most important feature of this new type of disturbance observer is that only measurement of the output variable is required, rather than the state variables. An inverse simulation model is first constructed based on knowledge of the structure and parameters of a conventional model of the system. The disturbance can then be estimated by comparing the output of the inverse model and the input of the original nonlinear system. Mathematical analysis demonstrates the convergence of this new form of nonlinear disturbance observer. The approach has been applied to disturbance estimation for a linear system and a new form of linear disturbance observer has been developed. The differences between the proposed linear disturbance observer and the conventional form of frequency-domain disturbance observer are discussed through a numerical example. Finally, the nonlinear disturbance observer design method is illustrated through an application involving a simulation of a jacketed continuous stirred tank reactor syste

Offset-free nonlinear MPC for mismatched disturbance attenuation with application to a static var compensator

A generalized nonlinear model predictive control augmented with a disturbance observer is proposed in this brief to solve the disturbance attenuation problem of nonlinear systems with arbitrary disturbance relative degree. It is shown that the disturbances can be removed from the output channels by the proposed method with appropriately designed disturbance compensation gain. The property of nominal performance recovery is retained with the proposed method. The effectiveness of the proposed method is validated by applying it to a static var compensator system