EnTON – Energy Transfer Optimizing Circuits for Energy Harvesting Applications

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Energy Harvesting enables the conversion of ambient energy into electrical energy in order to provide power to devices that otherwise would be battery or cable driven. Considering applications like Industry 4.0 or the Internet of Things, numerous sensors must be mounted in decentralized locations to perform condition monitoring, for example. Powering these devices by cables or batteries is both maintenance and cost intensive which is why energy harvesting is a key technology for such applications.Motivated by its mathematically proven efficiency of 100%, the objective of this research project is to evaluate for the first time a fully-integrated implementation of the energy harvesting approach Constant Load Emulation. This research will focus on a matched load resistance with the emphasis on a function based on both the input and the output voltage. Although usually neglected, only two cases can tolerate this simplification: the boost buck converter in discontinuous conduction mode and the boost converter in boundary mode. For a general applicability, the input as well as the output dependence must be considered to avoid a reduction in efficiency.To meet this objective, innovative circuit design techniques will be explored and evaluated in order to reduce the power consumption compared with the state of the art for both the maximum power point tracking (MPPT) and the switch-mode converter. Considering the two MPPT-approaches, Arithmetic Load Matching and Hill Climbing, calculation methods will be derived using ultra-low-power analog circuits based on the voltage-to-current characteristic of the MOS transistor. An ultra-low-power calculation technique for an input and output voltage-dependent duty cycle is required for the Arithmetic Load Matching. For the Hill Climbing approach, an ultra-low-power analog circuit is envisioned for calculating the converted energy. Furthermore, innovative circuit design techniques will be developed to reduce both the switching delay and the power consumption of the zero-current detector resulting in a high performance switching converter. Overall, the implementation of compact and energy-efficient harvesting systems using off-the-shelf inductances of a few hundred micro-henry will thus become feasible.After a theoretical evaluation, all approaches will be implemented and their performance verified by means of an application-specific CMOS integrated circuit.