Nonlinear unknown input observer design for diesel engines

In this paper, the problem of designing a nonlinear unknown input observer (NIUO) for a general class of nonlinear systems in the presence of disturbances is addressed. This approach combined two criteria : the modified H_∞ criterion and mean value theorem. The first criterion allows to solve the problem of unknown input observer design in the presence of disturbances. While the second is used to express the nonlinear error dynamics as a convex combination of known matrices with time varying coefficients. A sufficient conditions for the existence of the unknown input observer is derived. The observer gains are obtained by solving the linear matrix inequality (LMI). The advantage of the proposed method is that no a priori assumption on the unknown input is required and also can be employed with a wider class of nonlinear systems. Performances of the proposed approach are shown through the application to a diesel engine model.