| As the most basic component of the Internet of Things(Io T),Wireless Sensor Networks(WSNs)nodes have been widely used in the areas of sharing economy,smart home,and forest protection monitoring.For the rapidly developing WSNs,the nodes are mainly powered by conventional chemical batteries.Due to limited battery storage,batteries need to be replaced periodically.In order to achieve self-powering of WSN nodes,researchers have proposed to power the nodes by harvesting environmental energy around the WSN nodes.Vibration energy and thermal energy are two kinds of energy sources widely existed in the environment.The piezoelectric energy and the thermoelectric transducer can respectively convert these two energy sources into electric energy,but the output electric signal of the transducer cannot directly supply power to the electronic device,so an interface circuit with rectification,voltage regulation,and even maximum power tracking is required between the transducer and the load.In this thesis,the materials,device structure,equivalent circuit model and typical interface circuit of piezoelectric and thermoelectric transducers are introduced in detail.Then,according to their voltage output characteristics,four self-powered energy harvesting interface circuits are studied and designed.The main research contents of this thesis are as follows:1.An efficient self-powered series synchronized switch harvesting on inductor circuit is designed.The circuit detects the positive and negative peaks of the open circuit voltage of the piezoelectric element by a simplified passive positive/negative peak detector.Not only reduces the energy consumption of the circuit.Moreover,the phase difference between the voltage peak and the switching action moment is reduced,and the efficiency of energy extraction is improved.Simulation and experiment show that the maximum output power can be increased to 4.5 times that of the standard energy harvesting circuit.2.A self-powered serial and parallel alternating synchronized switch harvesting on inductor(SPASSHI)circuit for piezoelectric energy harvesting is presented.The proposed circuit works in two different modes: at the positive peak of the open circuit voltage of the piezoelectric transducer(PZT),it turns on the switch in series with the load,and operates in the SSSHI mode;at the negative peak of the open circuit voltage of the PZT,it turns on the switch in parallel with the load and operates in the P-SSHI mode.The SPA-SSHI circuit does not need a rectifier bridge,reduces the power loss of the circuit,and hence improves the piezoelectric energy harvesting efficiency of the circuit.Theoretical analysis,simulation and experiment verify the effectiveness of the SPA-SSHI circuit.The experimental results show that the maximum output power of the circuit can reach 5.96 times that of the ideal standard energy harvesting(SEH)circuit.3.A piezoelectric energy and thermoelectric energy synergistic harvesting circuit is designed.The circuit structure uses an active peak detector to control the switch of the synchronous electronic charge extraction circuit,and supplies the peak detector by harvesting the thermoelectric energy.The harvesting efficiency of piezoelectric energy is improved.The simulation results show that the harvesting efficiency of the circuit is increased by 41.9% compared with the self-powered synchronous electronic charge extraction circuit.4.A hybrid self-powered synchronous electronic charge extraction circuit is designed.The circuit detects the peak value of the piezoelectric voltage,and simultaneously extracts the piezoelectric energy and the thermoelectric energy when the peak value is reached,thereby realizing the fusion acquisition of the two energies.Simulation and experimental tests show that the proposed circuit can effectively harvesting the thermoelectric energy and piezoelectric energy synchronously.Compared with existing circuits,it has obvious advantages in terms of capture efficiency,self-power and load correlation. |
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