Analysis and Optimization of Asynchronously Controlled Electrostatic Energy Harvesters

Abstract

Mechanical to electrical energy conversion employing variable capacitors is assisted by electronic circuits that can have synchronous or asynchronous architectures. The later does not require synchronization of electrical events with mechanical motion, which eliminates difficulties in gate clocking and the power consumption associated with intelligent control circuitry. However, implementation of asynchronous energy harvesting circuits with the mechanical-to-electrical converter can be detrimental to the performance of the converter when done without concurrent optimization of the mechanical device and the circuit, an aspect mainly overlooked in the literature. This paper carries out system level analysis of electrostatic micro-generators with asynchronous control and charge fly-back mechanism to optimize the useful energy generated by the harvester. Our theoretical and experimental investigations show that there is an optimum value for either the storage capacitor or cycle number for maximum scavenging of ambient energy via asynchronous electrostatic transduction. The analysis also indicates that the maximum power is extracted from the system when approaching synchronization of mechanical and electrical events. However, there is a region of interest where the storage capacitor can be optimized to produce almost 70% of the ideal power, taken as the power harvested with synchronous converters when neglecting the power consumption associated with synchronizing control circuitry. Theoretical predictions are confirmed by measurements on an asynchronous energy harvesting circuit implemented with a macro-scale electrostatic converter prototype.Index Terms-Ambient vibrations, asynchronous switched mode operation, electrostatic energy conversion, energy harvesting circuits, modeling and optimization.

Electrostatic Energy Harvesting Systems: A Better Understanding of Their SustainabilityElectrostatic Energy Harvesting Systems: A Better Understanding of Their Sustainability

“…Kempitiya et al [34] presented an electrostatic generator with asynchronous control and charge flyback mechanism to optimise the useful energy generated by the harvester. The authors' theoretical and experimental investigations showed that there is an optimum value for the storage capacitor and the cycle number for maximum scavenging of ambient energy.…”

Silicon-integrated electrostatic energy harvesters

“…In either case, the robustness of the completed device is compromised due to high strain on the suspension system and should be compensated for by adding in-plane and out-of-plane stoppers to the device and package design. For in-plane devices, having a thick device layer has been shown to be optimal in terms of energy gain per harvesting cycle [12][13]. The tradeoff is that thick device layers limit the width of capacitive gaps created by DRIE due to aspect ratio limitations.…”

“…System modeling also shows that the maximum power is extracted when the system approaches synchronous operation. However, there is a region of interest where the storage capacitor can be optimized to produce almost 70% of the ideal power taken as the power harvested with synchronous converters when neglecting the power consumption associated with synchronizing control circuitry [13].…”

Model and prototype of a green electrostatic harvester of vibration energy

“…In the second phase, the charges at higher potential are transferred to a load. Finally, the distance of the plates decreases and the capacitance returns to its initial value, ready for a new cycle [3], [6].…”