A novel sliding mode observer applied to the three-phase voltage source inverter

This paper describes a new approach to control flexible AC transmission systems (FACTS) under current and voltage sensor failures. In this work we focus mainly on the reactive power compensator and the power active filter. For this, the theory of estimators and observers are developed in detail for the three-phase voltage source inverter, which is the central structure of the aforementioned FACTS elements under study. Due to the nonlinear nature of the problem, the observer theory is developed in a nonlinear framework. In this light, we propose two nonlinear observers based on the sliding mode theory for two particular cases. In the first case, the observer allows us to overcome failures in the DC-link voltage sensor if we are able to measure the currents of the main. In the second case, we show that it is possible to overcome failures in all the AC-mains sensors if we measure only the DC-link voltage. Finally, the performance of these soft sensors is investigated by simulations in a control-loop which is based on the popular dead-beat space vector modulation technique