The Research Of Hybrid Energy Harvesting And Energy Management For Vibrations And Temperature Differences

Harvesting environmental energy and converting it into electrical energy are very significant to make low power consumption wireless sensor nodes(WSNs)be self-powered.However,a single energy source often has some shortcomings,such as non-persistent existence,low electrical power,and so on.Thus it is much necessary to study hybrid energy harvesting technologies.Vibrations and temperature differences are two common kinds of environmental energies,but they have different energy conversion characteristics.Therefore,how to simultaneously achieve the maximum conversion efficiency is a key problem.In this thesis,it is much valuable to study highly efficient hybrid energy harvesting and storage of vibrations and temperature differences.Due to different energy conversion characteristics,it is an effective way for hybrid energy harvesting of vibrations and temperature differences by using their own energy conversion circuit.And the key problem is how to improve their own conversion efficiency and efficiently manage two converted energies.In order to solve this problem,the mechanical structure of thermoelectric energy harvesting and the energy conversion circuit of vibration energy harvesting are optimally designed.Based on them,then an energy management circuit is proposed for hybrid vibration and temperature difference energy harvesting.The main contents and conclusions are as follows:1.In order to increase the temperature difference of thermoelectric generator(TEG),an optimal structure of thermoelectric energy harvesting is designed by utilizing the mechanism of heat isolator.At the same time,a temperature difference energy conversion circuit is optimally designed,where a power management chip is used for impedance matching.By this way,the energy conversion efficiency is improved effectively.2.Switching delay of self-powered parallel synchronized switch harvesting on inductor(P-SSHI)circuit is modeled theoretically.Then simulations are done to analyze influencing factors of the switching delay and their effects on the harvested power.The results demonstrate that switching delay will reduce the harvested power and the time constant of the envelope detector is a key factor.3.In order to reduce the switching delay for achieving higher harvested power,an improved self-powered P-SSHI(IP-SSHI)circuit is proposed and its switching delay is also modeled theoretically.Then,simulations are done and the results demonstrate that the self-powered IP-SSHI circuit has a lower switching delay and higher harvested power than self-powered P-SSHI circuit under the same vibration excitation.4.By combining a supercapacitor and a Li-polymer battery,a hybrid energy harvesting and management circuit is proposed for highly efficient harvesting and storing vibration and temperature difference energies.Then circuit simulations are conducted.The results show that: hybrid electrical energies from vibrations and temperature differences can be efficiently stored in a supercapacitor.If the harvested power is greater than power consumption of the load,the redundant power will recharge the battery.Once the harvested power is not enough,the battery will discharge to power the load.By this way,the load can work for a long time.5.An experimental system for hybrid vibration and temperature difference energy harvesting is designed.Then energy conversion circuits for vibrations and temperature differences,hybrid energy harvesting and management circuit and a self-powered WSN are tested,respectively.The results demonstrate that the performance of the proposed circuit agrees with theoretical values and the WSN can be self-powered by hybrid energy harvesting of vibrations and temperature differences.