NONLINEAR TRACKING AND INPUT DISTURBANCE REJECTION WITH APPLICATION TO PH CONTROL

This paper presents a nonlinear observer-based controller configuratio n for a class of nonlinear single-input single-output systems with cer tain observability and stability properties. Particular attention is p aid to the effect of input disturbances typically present in chemical processes. It is pointed out that conventional feedback linearizing in ternal model controllers reject output disturbances linearly, but that they can experience significant performance degradation in the presen ce of input disturbances. This problem is shown to originate in the la ck of the linear superposition property. It is proven that the propose d control architecture rejects constant input disturbances from the co ntrol signal and then recovers linear reference tracking. The convenie nt tuning and improved performance are illustrated for pH neutralizati on.