Frequency Tracking of Vibrational Energy Harvester using Phase-Locked Loop (PLL)

In this paper, we report on an automatic frequency tracking of an electret-type vibrational energy harvester using a modified phase locked loop (PLL) controller. When the input vibration frequency changes, this system detects the phase difference between the input vibration and the harvester's oscillation and alters the resonant behavior of the harvester using the effective load resistance as a control parameter so that the harvester’s resonance is always matched with the incoming frequency. When driven by a 0.03 G sinusoidal waves at frequencies between 100.7 Hz and 102.0Hz, the controller maintains the harvester’s output to be at least 10 µW, while the output from a system without the controller rolls down to a few µW.