Power Management Systems for Biomass-Based Energy Harvesting

Energy harvesting aims to convert ambient available energy from the surrounding environment into usable electrical energy. There have existed many energy sources can be found to harness environmental energy, but the focus of this thesis is to harvest energy from aquatic environment to power up underwater devices. Microbial fuel cells (MFCs) are important energyharvesting devices for underwater sensors and electronic devices. MFCs are a promising technology that converts bio-energy in the biomass substrate through electrochemical reactions into electricity. Due to the low voltage and power at MFC outputs, a power management system (e.g., power converter) is needed to boost the low voltage to a usable level by these devices. This thesis thus, presents power management circuits for biomass energy harvesting sources. New architectures and design techniques are discussed to achieve high system efficiency and effective design for MFCs. The first part of this thesis focuses on the development of the maximum power extraction from energy sources by deploying an inductorless power converter (i.e. capacitive power converter). The maximum power extraction is not targeted for a specific energy sources, but rather is designed for both low-power energy source and high-power energy source without increasing complexity of system and the need of power hungry peripheral circuits. Proposed power converter is divided into two stages; a number of first-stage in parallel and shared-stage. The first-stage maximizes power extraction from the energy source while the shared-stage operates as a conventional charge pump. The peak end-to-end efficiency is enhanced by 98% as compared to the conventional converter. The proposed inductorles power converter has been implemented on a 0.13μm CMOS process. The second part of the thesis discusses energy combiner architecture for multiple microbial energy harvesting sources. Combining four identical MFCs (i.e. the same material, size and structure) through their power converter is achieved by deploying digital circuit to allow them to connect in-order to either a load or a battery. Proposed design let’s all sources contribute to the output and minimize the overall efficiency. The proposed efficient energy combiner architecture is implemented on a 0.13μm CMOS process. The remainder of the thesis deals with power management circuits that have ability to recover bioturbation issue in MFCs. A unique issue in marine sediment MFCs is related to underwater bio-stress, referred to as bioturbation is discussed. Solution to bioturbation issue brings new requirements on the design of power management systems (PMSs). The third part of the thesis presents an off-the-shelf power management system for multi anode MFCs. The PMS has been tested through a prototype BFMC. Experimental results demonstrate the effectiveness of this design for multi anode MFCs. The last part of the thesis discusses an integrated circuit for multi anode MFC to detect automatically impaired anodes. The evaluation is made in using a 90nm CMOS technology. The proposed design provides 42% more efficiency than conventional design under the worst-case scenario.