Sliding mode observers: a survey

Abstract

Sliding mode observers have unique properties, in that the ability to generate a sliding motion on the error between the measured plant output and the output of the observer ensures that a sliding mode observer produces a set of state estimates that are precisely commensurate with the actual output of the plant. It is also the case that analysis of the average value of the applied observer injection signal, the so-called equivalent injection signal, contains useful information about the mismatch between the model used to define the observer and the actual plant. These unique properties, coupled with the fact that the discontinuous injection signals which were perceived as problematic for many control applications have no disadvantages for software-based observer frameworks, have generated a ground swell of interest in sliding mode observer methods in recent years. This article presents an overview of both linear and non-linear sliding mode observer paradigms. The use of the equivalent injection signal in problems relating to fault detection and condition monitoring is demonstrated. A number of application specific results are also described. The literature in the area is presented and qualified in the context of continuing developments in the broad areas of the theory and application of sliding mode observers.

Keywords:

• sliding mode
• observers
• equivalent injection
• fault detection
• condition monitoring

Acknowledgements

The work and support of the ‘Pump Team’ within the Centre for Condition Monitoring, Diagnostics and Reconfigurable Control in the Department of Engineering at the University of Leicester, which is reported in outline in the sub-section on Fault detection via parameter monitoring, is gratefully acknowledged. Many conversations over the years with Dr Chris Edwards of the University of Leicester and Dr Thierry Floquet of the Ecole Centrale de Lille which have shaped the discussion of sliding mode observers as presented in this survey article are also gratefully acknowledged. The time spent proof reading an early draft of the manuscript by Dr Alexandre Seuret of the University of Leicester is gratefully acknowledged.