Abstract
The paper aims to solve the problem of liquid level and leakage flow rate estimations for a state coupled four-tank process, that is why an UIO is developed to simultaneously estimate the unmeasured state variables and the perturbations considered as unknown inputs. We have proposed a state repartition that allows putting the model of the quadruple tank system to the canonical form for which the design of the observer is more easier. The observation scheme that uses a combination of high-gain observers and sliding mode observers allows improving robustness in the state estimation quality and a perfect reconstruction of the disturbance waveforms.
Highlights
The unknown inputs (UI) estimation issue and its mathematical formulation have received considerable interest over the last two decades in several domains
Sliding mode observers- (SMO-) based UI estimation is investigated in several works [9, 10]
The high-gain observer- (HGO-) based approaches have been successfully used in the conjoint estimation of state variables and UI or faults
Summary
The unknown inputs (UI) estimation issue and its mathematical formulation have received considerable interest over the last two decades in several domains (secure communication [1], civil engineering [2], biomedical domain [3], chemistry [4], etc.). The framework given in [7] discusses the UI estimation subject in different conditions Such assumption is recently released in [8], where the authors propose a systematic design methodology for state observers for a large class of nonlinear systems with bounded exogenous inputs. In [12], under some global Lipschitz assumptions, a cascade HGO for a large class of nonlinear MIMO systems is designed in such a way that each subobserver provides an estimation of one component of the UI vector except the last one which achieves a reconstruction of the whole state variables. An extension of the HGO by a sliding mode term that follows the disturbance vector for affine input nonlinear MIMO class is investigated in [21].
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