Time Delay Observer: A robust observer for nonlinear plants

Motivated by the idea of the time delay estimation used in the Time Delay Control, Time Delay Observer (TDO) has been constructed. Owing to this idea, TDO does not require a model, and hence is easy to design for nonlinear systems in the phase variable form, even when the plant dynamics is not well known. Not including a model, TDO turned out to be robust to parameter variations and computationally efficient; yet achieved better accuracy. For this observer the convergence property and the sensitivity to sensor noise have been analyzed. Then, in a simulation with a nonlinear plant, and in an experiment with a robot, TDO achieved an accuracy level similar to sliding observer and better than a Kalman filter. In an experiment on a pneumatic cylinder control, TDO reconstructed states much better than a numerical differentiator with low-pass filtering.