Application of a nonlinear observer for estimation of variables in a PEM fuel cell system

Abstract

This work details the implementation of a nonlinear observer in a proton exchange membrane fuel cell system (PEMFC). This observer estimates the hydrogen pressure at the anode channel outlet, the mass flow, and the operational cell voltage. The knowledge of these variables is very important to ensure reliable operation of the fuel cell power system. The observer is based on a cell model based on mass balance, the Nernst equation, and voltage drops. To model the operational voltage of the cell, voltage drops due to activation, ohmic drops, voltage drops due to concentration, voltage drops due to fuel crossover, and internal currents were considered. An equation that describes the behavior of the mass flow at the anode channel outlet was proposed to complement the model to avoid more instruments in cell system, using such equation is possible to estimate others variables of the fuel cell. A nonlinear observer based on model was implemented; however, it was necessary to find a suitable gain to ensure the convergence of this one. The functionality of the observer was evaluated by comparing the estimated values to those calculated by the model. The error was evaluated in steady state, subjecting the observer and the model of the fuel cell system under different electric current demands. The observer showed sensitivity to the changes in current demand; on the other hand, the error percentages were approximately of zero on steady state.