Disturbance Observer Based Controller Under Noisy Measurement for Tracking of nDOF Uncertain Mismatched Nonlinear Interconnected Systems

This article analyzes a recent result on tracking control of nonlinear, mismatched interconnected systems and points out its drawback with regard to noise amplification that originates from numerical differentiation of tracking error. One of the objectives of the article is to propose two remedial measures and show their improvements by analysis for performance and stability. In the first remedy, the derivative of the tracking error is obtained without recourse to numerical differentiation while the second remedy offers a solution that does not need the derivative of the tracking error. Another objective of the article is to propose an extension to decentralized sliding mode control of interconnected systems. Unlike other published results, the extension can assure local sliding in each subsystem. The proposed remedies are validated by numerical simulation, and experimentation on a laboratory coupled tank system. A discussion with a generalized extended state observer based method and comparative simulations with other well-known methods are carried out.