Development of LFT-based models for robust stability analysis of a generic electrical power system over all operating conditions

This paper develops a method to analyse robust stability of a generic electrical power system for safe-critical applications over all operating conditions. Standard methods can guaranty stability under nominal conditions but do not take into account any uncertainties of the model. In this work, stability is assessed by using a Structural Singular Value concept that can provide a measure of stability robustness of a Linear Fractional Transformation (LFT)-based linear system with structured parametric uncertainties. In line with this, the first step was to develop a parameter-dependent linear time-invariant state-space model of the system that is valid for all operating conditions. The model was obtained by symbolic linearisation of the system non-linear model and was further extended to include structured parametric uncertainties of the system. The developed approach was successfully applied to determine the critical destabilising torque of a 4 kW permanent magnet motor drive over the defined range of operating conditions. Matlab robust stability toolbox was used for this analysis. The results were validated against simulation and experimental data.