Output tracking of a bioreactor with nonminimum phase characteristic

A framework for the output tracking of nonlinear nonminimum phase systems is presented. The control problem is solved by a two degree of freedom design. A feedforward part generates an explicit trajectory for the nominal input and states by an analytic inversion of the plant to let the plant output follow an externally given reference trajectory. A gain scheduling controller stabilises the plant around these trajectories, the parameters of which are scheduled in dependence on the current nominal control signal and the nominal state vector. The design of the controller is based on a linear parameter varying model, which results from the linearisation of the plant about the nominal trajectories. An overview of techniques for the stable inversion of nonminimum phase systems is given. The approach is demonstrated on a bioreactor which shows maximum phase behaviour