A modified sliding mode control of a nonlinear methane fermentation process

Plamena Zlateva

doi:10.1051/e3sconf/202016705007

Abstract

A continuous methane fermentation process for biogas production is considered. This biogas production process is described by a system of two nonlinear differential equations and one nonlinear algebraic equation. The paper purpose is to propose an approach for designing a modified sliding mode control (so-called binary control) of a nonlinear methane fermentation process. The control design is carried out with direct use of nonlinear model and on-line measurement for two variables only (the concentration of the organic pollutants and biogas production rate). The model of the sliding mode control is developed with respect to an auxiliary input variable in order to obtain the smooth signal of the dilution rate, which is need in the fermentation processes. The state variables, external disturbance, process output and control input are varied in the known intervals. The asymptotic output stabilization problem is solved. The good system robustness with the designed modified sliding mode control (the binary control) about various disturbances is proved through simulation investigations inMATLABusingSimulink.

Highlights

Nowadays, a very useful source of green energy is biogas [1, 2]
The control design is carried out with direct use of nonlinear model. The model of this sliding mode control is developed with respect to an auxiliary variable in order to obtain the smooth signal of the dilution rate
It is well known that the control input signal, dilution rate D(t), in fermentation processes has to be smooth

Summary

Introduction

A very useful source of green energy is biogas [1, 2]. Worldwide, there is increasing interest in its wider use as an environmental fuel [3,4,5,6]. The biogas production is done by anaerobic digestion (oxygen-free environment) of various organic material with the help of the methanogenic bacteria [4,5,6,7] This methane fermentation process generally carried out in continuously stirred tank bioreactors [8]. The methane fermentation process is usually described by a system from ordinary differential equations with uncertain parameters For these reason it is needed the developing of sophisticated control algorithms based on nonlinear models [9,10,11]. The control design is carried out with direct use of nonlinear model The model of this sliding mode control is developed with respect to an auxiliary variable in order to obtain the smooth signal of the dilution rate

A mathematical model of the methane fermentation process

Problem statement for control design

Transformation of the nonlinear model

Model of the modified sliding mode control

Simulation investigations

Conclusions