Energy Harvesting from Hydraulic and Vibration Sources

This doctoral thesis, is divided in two main parts. The former is about load optimisation for a hydraulic energy harvester while the latter focuses on the design and fabrication of piezoelectric energy harvesters for the single supply pre-biasing circuit. An abstract for each part is reported below: ˆ Part I: The hydraulic power available in water pipes is usually wasted while it could be harvested and used to supply low power systems. To address this shortcoming, this study presents how load matching allows to harvest the maximum hydraulic power available in the environment. The hydraulic energy harvester considered in this study is composed of a hydraulic turbine and a permanent magnet generator. To estimate the optimal external load that maximises the power transfer, first a mathematical model of the harvester is introduced and then validated with experimental test. The benefit of this study consists in harvesting the maximum hydraulic power available for any input flow rate without changing physical parameters of the hydraulic turbine and the permanent magnet generator. Experimental and Simulation results show that by using the optimal load, the power transferred is maximum and consequently maximized power on the external load is available. ˆ Part II: The design and test of a novel screen printed piezoelectric energy harvester for the single supply pre-biasing (SSPB) circuit is presented. It was demonstrated in previous research that by using the SSPB circuit, power delivered to the load was over three times greater than that in the case of using a bridge rectifier circuit. For maximum power extraction from energy harvesters using the SSPB circuit, the SSPB switches must be triggered when the piezoelectric beam reaches its maximum point of displacement. Therefore, an accurate peak detection sensor is required. A new piezoelectric energy harvester integrating a small piezoelectric area for peak detection with a larger piezoelectric area for energy harvesting was designed and fabricated. The difference in capacitance between the peak detection sensor and the piezoelectric energy harvesting component leads to a phase difference between the two outputs if the load impedance is low. This phase difference can cause the switches to be triggered at the wrong time and thus reduce the efficiency of the SSPB circuit. A mathematical model was developed to study the phase dffierence. It was found both in simulation and experiments that impedance matching can be performed in order to eliminate the phase difference.