Wireless sensor networks and portable electronic devices, such as mobile phones, media players, digital cameras and iPods, require local electric power supplies. Although these devices are operational all the time, they consume just a few milli-or micro-watts. This means energy harvesting from the environment is an attractive option for powering these devices. Mechanical energy harvesters can use electromagnet, electrostatic or piezoelectric approaches. Of these, electrostatic devices are found to be the most suitable approach for harvesting mechanical energy since they are compact, sensitive to low level mechanical energy, easier to integrate in small scale systems, not requiring smart materials, simple to fabricate, inexpensive and simply structured using less circuitry. Most of electrostatic harvesters proposed in previous studies use mechanical vibration. However, only a few studies have investigated harvesting rotational mechanical energy. The objective of this thesis is to investigate the possibility of harvesting rotational mechanical energy from wind using the electrostatic approach. The proposal involves capturing wind energy using a micro wind turbine then converting it into usable electrical energy. This work first considers general design considerations and the design procedure that must be followed to construct a suitable electrostatic based wind energy harvester. Second, it describes the operating principles of various parts needed to design a novel efficient electrostatic harvesting system. The new harvester consists of a micro wind turbine, a gearbox, a multi-pole variable capacitor or capacitor array, an LC to LC energy transfer circuit, a capacitance sensing system and a microcontroller. The harvesting process has three main steps. First, wind energy is captured and converted into mechanical power using the micro wind turbine. Second, mechanical power is converted into electrical power using the variable capacitor in three phases: pre-charge, harvest and reset. Third, the electrical energy is processed and stored in a Lithium ion battery. The proposed harvester was simulated using Matlab/Simulink to study energy transfer throughout the three energy harvesting phases. Energy analysis was then carried out to study the effect of varying the structure of the multi-pole capacitor on the amount of harvested energy. Results from the simulation for capacitance variation from 2.5 nF to 0.6 nF indicated that an eight-pole variable capacitor can produce 29.43 μJ/sec at a wind speed of 10 m/sec, while a capacitor array of the same capacitance variation with 10 capacitors in the array can produce 295 μJ/sec at a wind speed of 10 m/sec. The results of experiments were carried out to test wind harvesting using a two-pole capacitor proved that the proposed harvester is capable of powering an RF transmitter to transmit wind speed information wirelessly.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:683895 |
| Date | January 2014 |
| Creators | Aljadiri, R. T. |
| Publisher | Coventry University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://curve.coventry.ac.uk/open/items/9ee6a6e1-bd1d-4717-b48d-ee48fefb4657/1 |
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