An electrostatic-electromagnetic hybrid generator with largely enhanced energy conversion efficiency

Abstract

For efficiently harvesting the widely distributed mechanical energy in the environment, we propose an electrostatic-electromagnetic hybrid generator with largely enhanced energy conversion efficiency. The hybrid generator includes an electromagnetic generator (EMG) and a two-phase freestanding-electret generator (FEG) with a volume of only 2% of EMG. One phase of FEG is used for control and the other phase for energy harvesting. Thanks to the fact that FEG’s output voltage is independent of frequency, a synchronously controlled voltage multiplier (SCVM) is designed, which is controlled by the output of FEG’s control phase, to efficiently store the energy from EMG. The conversion efficiency of SCVM is 64.1% at 400–600 rpm and maintains 22.8% at an ultra-low rotation speed of 50 rpm, which is 8.8 times that of the traditional voltage multiplier. At 50 rpm, the maximum output power of EMG and FEG at their matched resistance is 40.0 μW (2.5 W/m3) and 30.7 μW (107.8 W/m3), respectively. In addition, a micro hybrid generator fabricated from a commercial micro-EMG can drive one thermo-hygrometer and two timers working at the same time for 20 s with one blow, indicating its great potential for harvesting wind energy to power IoT nodes and wearable devices. This hybrid generator not only superimposes the output powers, but also greatly improves the energy conversion efficiency of EMG especially at low rotation speed, which expands the practical applications of electrostatic generators.