A New Filtered High Gain Observer Design for the Estimation of the Components Concentrations in a Photobioreactor in Microalgae Culture

Abstract

This paper deals with the estimation of the concentrations of the biomass microalgae and the dissolved carbon dioxide from the measurements of the average intensity irradiated over the reactor in a photobioreactor. To achieve the estimation objective, a Filtered High Gain Observer (FHGO) is designed for a class of non uniformly observable systems which includes the photobioreactor model. The main feature of the proposed FHGO lies in its filtering capabilities which allow to obtain relatively smooth estimates in the presence of noisy output measurements. Of fundamental interest, the FHGO design is first carried out by assuming that the output measurements are available in a continuous manner before being extended to the case of sampled outputs leading thereby to a continuous-discrete time FHGO which inherits the main properties of the original FHGO. For comparison purposes, a Standard High Gain Observer (SHGO) designed for non uniformly observable systems has also been used to estimate the components concentrations. Both estimates, issued from the FHGO and SHGO are compared and the obtained results clearly highlight the FHGO capabilities.