An optimized self-powered switching circuit for non-linear energy harvesting with low voltage output

Harvesting energy from environmental sources has been of particular interest these last few years. Microgenerators that can power electronic systems are a solution for the conception of autonomous, wireless devices. They allow the removal of bulky and costly wiring, as well as complex maintenance and environmental issues for battery-powered systems. In particular, using piezoelectric generators for converting vibrational energy to electrical energy is an intensively investigated field. In this domain, it has been shown that the harvested energy can be greatly improved by the use of an original non-linear treatment of the piezoelectric voltage called SSHI (Synchronized Switch Harvesting on Inductor), which consists in intermittently switching the piezoelectric element on a resonant electrical network for a very short time. However, the integration of miniaturized microgenerators with low voltage output (e.g. MEMS microgenerators) has not been widely studied. In the case of low voltage output, the losses introduced by voltage gaps of discrete components such as diodes or transistors can no longer be neglected. Therefore the purpose of this paper is to propose a model that takes into account such losses as well as a new architecture for the SSHI energy harvesting circuit that limits such losses in the harvesting process. While most of the study uses an externally powered microcontroller for the non-linear treatment, this circuit is fully self-powered, thus providing an enhanced autonomous microgenerator. In particular this circuit aims at limiting the effect of non-linear components with a voltage gap such as diodes. It is shown both theoretically and experimentally that the harvested power can be significantly increased using such a circuit. In particular, experimental measurements performed on a cantilever beam show that the circuit allows a 160% increase of the harvested power compared to a standard energy harvesting circuit, while the classical implementation of the SSHI shows an increase of only 100% of the output power in the classical case.