Internal Model Control: Robust Digital Controller Synthesis for Multivariable Open-Loop Stable or Unstable Systems.

The two-step Internal Model Control procedure is used for the synthesis of multivariable discrete controllers for open-loop stable or unstable plants. The plant models used in the proposed method are transfer function matrices. In the first step the controller is designed so that the L{SUB 2^-}error (sum of squared errors) is minimized for every setpoint or disturbance vector in a set and their linear combinations. A modification is then introduced to avoid the potential problem of intersample rippling. In the second step a low-pass filter is designed so that stability and good performance characteristics are maintained in the presence of model-plant mismatch. The continuous plant output is considered in order to avoid bad intersample behavior. The filter parameters are obtained as the result of a minimization of a non-conservative robustness measure, the Structured Singular Value. Special filter structures have to be used for open-loop unstable or ill-conditioned plants