Metal Hydride Storage Tank State of Charge Estimation: A Switched Observer Approach

The state of charge (SOC) is an important indicator for metal hydride (MH) storage tanks monitoring and operation. This indicator cannot be directly measured, which motivates the design of real-time estimators. Nonetheless, the development of model-based estimators is a nontrivial task for this system, since the MH storage tank model is nonlinear and hybrid. To overcome these difficulties, this work proposes a novel nonlinear switched observer for an MH storage tank system. Based on differential detectability and recent results on contraction theory for switched systems, we present sufficient conditions for the convergence of the observer under the assumption that the observer and the plant have synchronized switching. Additionally, to guarantee this synchronization, we propose an estimator to determine the current system mode. The algorithm is then validated in a set of numerical simulations and in an experimental prototype.