The importance of structure in PIP control design

The proportional-integral-plus (PIP) controller has great flexibility in design terms. For example, it can be applied to multivariable systems described by backward shift, continuous-time or delta operator models. The present paper has further emphasised the flexibility of the approach in the context of the control structure selected for implementation. It has been demonstrated that the choice of structure has important consequences for the robustness of the final design to parametric uncertainty and its disturbance rejection characteristics.