A power management system for isolated operation of microbial fuel cells with voltage protection

Abstract

Renewable energy sources are growing rapidly in the world. In 2020, they made up 29% of all the electric power generated. Microbial fuel cell (MFC) is a high-potential energy source in this category. It helps remove environmental contaminants such those in wastewater, decrease carbon dioxide in the atmosphere, and convert organic substrates to electricity through a bioelectrochemical reaction. However, due to its low power density, a single MFC cannot power most of common electronic applications. One solution to increase the power is to use multiple MFCs and connect them in parallel or series. However, these types of circuit configurations can result in overall lower power efficiency due to the unpredictable and unstable nature of MFCs. This study aims to design a power management system (PMS) for harvesting the maximum energy from the MFCs in the stack. The PMS controls the connection and disconnection of the MFCs such that each MFC operates independently. Consequently, should there be an MFC failure leading to unwanted MFC disconnection, the energy harvesting process from the other MFC(s) continues without interruption. The PMS is developed to consider the biochemical limitation of microorganism in order to expand their lifetime. This was accomplished by employing an MFC health protection algorithm. This algorithm prevents the weak MFC to participate in the energy harvesting process. Control techniques such as hysteresis control and the maximum power point tracking (MPPT) are executed to achieve these contributions. A high-efficiency DC-DC converter is selected as the back-end upconverter to boost the output voltage to a desirable level. The sliding mode controller (SMC), which is a voltage regulation (VReg) technique, is applied to the control of converter switching. The proposed controller maintains the output voltage of the converter within acceptable limits, regardless of the input voltage volatilities caused by the system nonlinearity. A two-level voltage reference was applied to the VReg technic to obtain higher levels of voltage and power at the load. A testing procedure was constructed to evaluate the PMS performance based on the real-world MFCs characteristics. To make this happen, numerous lab experiments on four real MFCs were conducted and the extracted data was classified into three benchmarks. Each benchmark replicates the electrical characteristics of model-based MFCs according to their wide range of ambient and operational conditions. These benchmarks were applied to a comparable approach from a previous study and its pros and cons were compared to the proposed PMS. The average load power (Ploadave) of 5.16 mW was obtained using the two-level VReg, which is 3.44 times more than utilizing the single-level VReg (1.5 mW). According to the PMS’s comparison results, the proposed PMS could successfully power the resistive load without interruption while multiple load power disruptions were observed in the previous study. Hence, the proposed PMS was reported to have a 41% higher Ploadave in this comparison in the case of multiple MFC failure Further improvement upon this study can be including a start-up circuit to the converter for autonomous operation of the system, a necessary feature for using MFCs in remote areas.

Date	16 Dec 2022
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Ghyslain Gagnon (Supervisor) & Lyne Woodward (Co-supervisor)