Robust sliding-mode observer for unbounded state nonlinear systems

Abstract

Designing a full-state observer for nonlinear systems has always been accompanied by challenges and restrictive constraints. Mainly, applying a state observer in nonlinear systems with non-minimum phase characteristics is more challenging when the limiting constraints are not satisfied due to diverging internal dynamics. In this paper, a robust sliding-mode observer approach has been successfully employed to estimate the states of nonlinear systems with unbounded and diverging dynamics. The design principles of this observer are based on applying a classifying algorithm in single-input single-output and multiple-input multiple-output nonlinear systems. It is noteworthy that this observer is highly robust against disturbance, uncertainty and measurement noise, and its conditions are less conservative compared to previous nonlinear sliding-mode observers. One novel feature of the proposed observer is that while the system's state gets unbounded and diverged in fault-occurring scenarios or critical circumstances, this observer retains accuracy. The efficiency of the proposed observer is verified in the simulation results for two nonlinear industrial systems, including a hydro-turbine power generation plant and a continuous stirred tank reactor.

Keywords:

• Full state observer
• sliding-mode observer
• internal instability
• unbounded state
• non-minimum phase system
• nonlinear system

Acknowledgments

The authors would like to thank the anonymous reviewers for their constructive and valuable comments. This study's simulation and calculation files are available from the corresponding author or on reasonable request.

Disclosure statement

No potential conflict of interest was reported by the author(s).