Q-parameterisation/µ robust control of a CSI-fed induction motor drive system

Abstract

The current source inverter (CSI)–fed induction motor (IM) drive system is an open loop stable system, however, due to model uncertainties and operation at different operating points, the system exhibits poor performance and may loose stability. This paper utilises the Q–parameterisation with µ–analysis to design a controller for a CSI–fed induction motor drive system in order to achieve robust stability and robust performance. The set of all stabilising controllers is characterised by a free parameter Q. This parameter is chosen through optimisation to achieve robust stability and robust performance. First, the nonlinear dynamic equations of the CSI–fed IM are described in state space form, then these equations are linearised around an operating point. Second, the Q–parameterisation with µ–analysis is explained. Third, the control problem is formulated as an optimisation problem in Q with robust stability and nominal performance as constraints and the robust performance is assessed with µ. Finally, the proposed controller is applied to a CSI–fed example system. A sixth order controller which achieves both robust stability and robust performance is obtained. The simulation results showed that robust stability and robust performance are achieved.