Modelling and Design of Electrostatic Based Wind Energy Harvester

摘要

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 areoperational all the time, they consume just a few milli-or micro-watts. This means energyharvesting from the environment is an attractive option for powering these devices. Mechanicalenergy harvesters can use electromagnet, electrostatic or piezoelectric approaches. Of these,electrostatic devices are found to be the most suitable approach for harvesting mechanical energysince they are compact, sensitive to low level mechanical energy, easier to integrate in smallscale systems, not requiring smart materials, simple to fabricate, inexpensive and simplystructured using less circuitry. Most of electrostatic harvesters proposed in previous studies usemechanical vibration. However, only a few studies have investigated harvesting rotationalmechanical energy. The objective of this thesis is to investigate the possibility of harvestingrotational mechanical energy from wind using the electrostatic approach. The proposal involvescapturing wind energy using a micro wind turbine then converting it into usable electricalenergy. This work first considers general design considerations and the design procedure thatmust be followed to construct a suitable electrostatic based wind energy harvester. Second, itdescribes the operating principles of various parts needed to design a novel efficient electrostaticharvesting system. The new harvester consists of a micro wind turbine, a gearbox, a multi-polevariable capacitor or capacitor array, an LC to LC energy transfer circuit, a capacitance sensingsystem and a microcontroller. The harvesting process has three main steps. First, wind energy iscaptured and converted into mechanical power using the micro wind turbine. Second, mechanicalpower 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 transferthroughout the three energy harvesting phases. Energy analysis was then carried out to study theeffect 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 aneight-pole variable capacitor can produce 29.43 μJ/sec at a wind speed of 10 m/sec, while acapacitor array of the same capacitance variation with 10 capacitors in the array can produce 295μJ/sec at a wind speed of 10 m/sec. The results of experiments were carried out to test windharvesting using a two-pole capacitor proved that the proposed harvester is capable of poweringan RF transmitter to transmit wind speed information wirelessly.