Investigation of a Complex Conjugate Matching Circuit for a Piezoelectric Energy Harvester

UoM administered thesis: Phd

  • Authors:
  • Ku Nurul Edhura Ku Ahamad

Abstract

The work described in this thesis is aimed at developing a novel piezoelectric cantilever energy harvesting circuit, so that more energy can be obtained from a particular piezoelectric harvester than is possible using conventional circuits. The main focus of the work was to design, build and test a proof of principle system, and not a commercial version, so as to determine any limitations to the circuit. The circuit functions by cancelling the capacitive output reactance of the piezoelectric harvester with a simulated inductance, and is based on an idea proposed by Qi in 2011. Although Qi’s approach demonstrated that the circuit could function, the system proved too lossy, and so a less lossy version is attempted here. Experimental and software simulations are provided to verify the theoretical predictions. A prototype amplified inductor circuit was simulated and tested. From the simulation results, although harmonic current losses were found in the circuit, it was found that the circuit should produce an amplified effective inductance and a maximum output power of 165mW. The effective inductance is derived from the voltage across the 2H inductor, and this voltage is amplified and applied to the circuit via an inverter, to provide an extra simulated inductance, so that the overall inductance can be resonated with the piezoelectric harvester output capacitance. Hence the capacitive impedance of the harvester is nearly cancelled. The study and analysis of the amplified inductor circuit was carried out for a single cantilever harvester. Both open loop and closed loop testing of the system were carried out. The open loop test showed that the concept should function as predicted. The purpose of the closed loop test was to make the system automatically adjust for different resonance frequencies. The circuit was tested at 52Vpp inverter output voltage, and demonstrated a harvested power of 145.5mW. Experimental results show that the harvester output power is boosted from 8.8mW as per the manufacturer data sheet to 145.5mW (16.5 times). This is approximately double the power available using circuits described in the literature.

Details

Original languageEnglish
Awarding Institution
Supervisors/Advisors
Award date1 Aug 2018