A Hybrid Indoor Ambient Light And Vibration Energy Harvesting Micro-power System

Wireless sensor network has a broad application prospect in environment, medical,military, civil and other fields. However, the wireless sensor nodes have thedisadvantages of a giant number, wide distribution, deployed in harsh environments orinternal structure where human beings cannot involve in. Traditional battery has limitedenergy and frequent battery maintenance has becoming a bottleneck problem for moredeep development for wireless sensor network, so a new self-powered energyharvesting technology to replace traditional battery becomes the main focus ofresearches. The surroundings are filled with rich light energy and vibration energy, butthe solar energy and vibration energy have the disadvantages of incontinuous, randomand low energy density. A single form of energy harvesting technology cannot supplypower for sensor nodes effectively under special circumstance, so this paper focuses onstudying micro-power system for hybrid indoor ambient light and vibration energyharvesting.Firstly, this paper establishes a new solar cell model solution suited in indoor weaklight by comparing model simulation results with the experiment results, and the newsolution could accurately simulate the output characteristics of solar cells underlow-light illumination condition. The prediction accuracy error of short-circuit current,open-circuit voltage and voltage at the maximum power point is respectively less than2.55%,1.8%,6.25%, which indicates the proposed modeling method could provide atheoretical basis for the input energy prediction to achieve energy acquisition and powermanagement circuit. Secondly, an indoor light energy harvesting power managementsystem with a new MPPT circuit is designed and the efficiency to charge super cap isenhanced by3times than applying the direct charging method. Through calculation, thecircuit efficiency is71.9%. An energy instantaneous releasing circuit and voltagestabilizing circuit is designed, which forces super capacitor’ voltage to release downfrom2V to1V for powering a wireless temperature and humidity sensor node workingat least15cycles. The operating voltage of sensor node is2.8V. Thirdly, the outputcharacteristics of micro piezoelectric vibration energy collector based on wind isanalysised. The paper establishes the equivalent circuit model and designs thecorresponding vibration energy harvesting power management system with simulateddata, achieves the optimum impedance matching which is measured30K through controlling DC-DC converter works at DCM mode, the experiment results show theefficiency is increased3.33times. At last, a micro-power circuit for hybrid indoorambient light and vibration energy harvesting is designed. The efficiency is91.2%byusing a simple serial interface circuit,1.44times than the parallel interface circuit. Anew energy releasing circuit is designed， forcing the super capacitor to release voltagefrom4.4V to3V, and the energy total released is51.8mJ. The circuit can drive thesensor node operating more than10cycles. Moreover the lithium battery backup powersupply circuit is designed, which is used to solve the problem of urgent energy needcaused by insufficient energy in super capacitor and slowly charging in harshenvironment. When the voltage between the super capacitor reaches5V, releasing from5V to4.4V to charge the lithium battery to work for long time without frequentreplacement, the total energy released is28.2mJ.This paper achieves the MPPT for indoor light energy and the optimum impedancematching for vibration energy, using a micro-power circuit for hybrid indoor ambientlight and vibration energy harvesting to successfully power a wireless temperature andhumidity sensor node.