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UBC Theses and Dissertations

Energy harvesting from ship vibration Yao, Yao

Abstract

Advances in low power electronic devices design open up the possibility of self powering a small wireless device from harvested ambient power. In a ship environment, low level vibration is considered as an appropriate power source to extract energy. After a survey of three mechanisms to convert mechanical motion to electricity, electromagnetic conversion was chosen as a mechanism of energy harvesting in this thesis. One of the major drawbacks of today's energy harvesters is that they are designed to provide power of only a few milliwatts and no power conversion control is integrated. Since the power requirement in this thesis is 0.3W, maximum power conversion becomes a critical objective in the harvester design. To achieve this objective, at first, a mathematical model of the electromagnetic converter (linear generator) with a resistive load was developed and the relations of system parameters to power output were deduced. Based on these relations, the design principles of the harvested are summarized into two steps: i) tune the natural frequency of the linear generator to match the main frequency of the vibration spectrum, ii) tune some electrical parameters to maintain the induced voltage at a optimal value which makes the electrical damping factor close to the mechanical damping factor. A power management circuit was designed to condition the power flow to a supercapacitor. The relations deducted with a resistive load still holds in the capacitive load circuitry and thus spring constant and duty cycle of a DC-DC converter become two adjustable variables to control the power. An algorithm " MCCT " makes sure the energy harvester performs maximum power conversion under any conditions based on adjustment of the two variables. Finally, the performance of the energy harvester is assessed under various disturbance scenarios by simulation.

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