Performance improvement of PI controller with nonlinear error shaping function: IDA-PBC approach

The general dilemma faced in a conventional linear proportional-integral (PI) controller is to achieve the best transient performance (i.e. fast rise time and low overshoot level) at the same time. However, fast response is usually accompanied by high overshoot level. On the other hand, very stable control without overshoot is usually achieved at the expense of a more sluggish response to set point changes and load disturbances. Therefore, compromise between fast response and low overshoot level should be made. In this paper, to overcome these contradictions and limitations, nonlinear error shaping function (ESF) is introduced to amplify gain at low error level but reduce gain at high error level. Firstly, interconnection and damping structure for the closed-loop system composed of PI controller and first-order plant is revealed based on the port-controlled hamiltonian with dissipation (PCHD) formation. Secondly, passivity analysis is performed by the interconnection and damping assignment (IDA) passivity-based control (PBC) algorithm. In simulation studies, several nonlinear error shaping functions are examined and compared to verify performance improvements.