Design considerations of harvested-energy management

Abstract

Using energy harvesting for powering autonomous sensor systems can meet the goal of perpetual operation. However, the uncertainty in system supply coupled with the size
constraints presents challenges in design of such systems. To address these challenges,this thesis is concerned with effective management of harvested-energy for matching
supply and demand in order to operate perpetually with uniform performance. The thesis focuses on two fundamental design considerations in addressing these challenges:
(i) managing variability of the energy harvesting source, and (ii) matching the demand with energy supply under the influence of non-ideal characteristics of the harvesting
system. To address the problem of variability of energy source, the thesis focuses on effective prediction of harvested-energy. An effective approach for evaluating the accuracy of solar energy prediction algorithm is proposed and optimised values of prediction algorithm parameters are determined to minimise prediction error. The problem of achieving uniform performance under the supply variability is addressed by proposing a new prediction based energy management policy. The results of the proposed policy are compared with other recently reported policies and it is shown that the proposed policy achieves up to 41% lower variance in performance and 30% lower dead time of the system, which is important to achieve the goal of perpetual operation. To address the problem of effective matching of supply and demand, the thesis considers the design of photovoltaic energy harvesting supply and storage subsystem in terms of its component’s non-ideal characteristics. The influence of these characteristics on supply and demand is identified using modeling of losses and component interdependencies, and empirically validated using a reference system design. Using the proposed modeling, the performance of recently reported energy management policies is evaluated to show that these are ineffective in achieving the goal of perpetual operation, and optimisations are proposed to address this.

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