Monitoring and control of the processes involved in the capture and filtering of biogas using FPGA embedded fuzzy logic

This article focuses on the development of an intelligent control platform capable of improving the capture and filtration of biogas with the aim of raising the calorific value of the fuel. The biogas was produced in an upflow anaerobic sludge blanket (UASB) reactor at the sewage treatment plant (STP) located near to the town of Los Angeles, Campo Grande, Mato Grosso do Sul, Brazil. For the purposes of system identification, the concentrations, flow rates and pressures of the gases were continuously monitored before and after the filtering processes. The fuzzy proportional derivative controller described herein was required to sustain maximum biogas flow whilst ensuring that the concentration of oxygen did not exceed a predetermined point (the SetPoint) regardless of the variation in load received by the digester. The controller input was oxygen concentration, and the processed output signal was sent to an inverter responsible for raising or lowering the speed of the compressor used in the capture of the biogas. The controller design was developed using MATLAB software and implemented in a field-programmable gate array (FPGA)-embedded Nios II processor. The embedded control algorithm was validated with the aid of ModelSim software. Electronic circuits were developed to allow the FPGA board and the sensors and actuators to communicate via protocols widely used in the industrial setting. This design factor, taken together with the incorporation of reconfigurable hardware and the facility of changing the rules of the fuzzy controller, afforded maximum flexibility of the control platform for use in other applications.