Novel Two-Stage Piezoelectric-Based Electrical Energy Generators for Low and Variable Speed Rotary Machinery

A novel class of two-stage piezoelectric-based electrical energy generators is presented for rotary machinery in which the input speed is low and varies significantly, even reversing. Applications include wind mills, turbo-machinery for harvesting tidal flows, etc. Current technology using magnet-and-coil rotary generators require gearing or similar mechanisms to increase the input speed and make the generation cycle efficient. Variable speed-control mechanisms are also usually needed to achieve high mechanical to electrical energy conversion efficiency. Presented here are generators that do not require gearing or speed control mechanisms, significantly reducing complexity and cost, especially pertaining to maintenance and service. Additionally, these new generators can expand the application of energy harvesting to much slower input speeds than current technology allows. The primary novelty of this technology is the two-stage harvesting system. The harvesting environment (e. g. wind) provides input to the primary system, which is then used to successively excite a secondary system of vibratory elements into resonance - like strumming a guitar. The key advantage is that by having two decoupled systems, the low-and-varying-speed input can be converted into constant and much higher frequency vibrations. Energy is then harvested from the secondary system's vibrating elements with high efficiency using piezoelectric elements or magnet-and-coil generators. These new generators are uncomplicated, and can efficiently operate at widely varying and even reversing input speeds. Conceptual designs are presented for a number of generators and subsystems (e. g. for passing mechanical energy from the primary to the secondary system). Additionally, analysis of a complete two-stage energy harvesting system is discussed with predictions of performance and efficiency.