| Wireless Sensor Networks（Wireless Sensor Networks,WSNs）are combined by a large number of remotely distributed sensor nodes and is widely used in medical monitoring,industrial production,intelligent logistics,environmental monitoring and other fields;batteries are its dominant form of energy supply up to present.Although the technology of battery miniaturization is developing,the problems such as life span,limited capacity and frequent battery replacement still exsit,which restrict the development of the WSN.Since the environment is full of various forms of energy,such as solar energy,wind energy,vibration energy in industrial environments,thermal energy from temperature differences,electromagnetic energy radiated by communication equipment,and so on.Harvesting the environmental energy can provide energy supply for the WSN nodes,however,the intensity of the specified energy varies time to time and the output of the transducers is very weak in most of the time,harvesting a single energy may result in the instability of energy supply of the WSN nodes.In the actual environment,the same kind of environmental energy often shows different strengths and weaknesses in different spatial locations.Effectively harvesting homogeneous（same type）multi-source environmental energy can improve the coutput power.In the same application scenario,the environmental energy that can be harvested is diverse.To convert these（different types）heterogeneous multi-source environmental energy into electric energy can realize complementarity and improve the stability of node energy supply.It can effectively prolong the service life of the battery,and even realize the node self-powered supply without battery.Therefore,the research on efficient hybrid harvesting method of multi-source environmental energy has important significance and application value.This dissertation analyzes the characteristics of multi-source transducers and energy harvesting circuit,the mechanism of multi-source energy conversion,and the key factors of the harvesting efficiency.The methods to improve the harvestin efficiency and output power of multi-source energy are studied from the homogeneous（same type）multi-source energy harvesting,auxiliary heterogeneous（different types）multi-source energy harvesting,matrix multi-source energy harvesting,and so on,the theory and experimental verification are carried out.The main research works are summarized as follows:（1）The direction,frequency and amplitude of vibration in the environment are random.Therefore,multi-source piezoelectric transducers can be installed to harvest more vibration energy.In the process of vibration,the output of multi-source piezoelectric transducers may be synchronized,and the multi-source piezoelectric transducers will occupy the inductor at the same time,resulting in energy loss.Aiming at the problem that it is impossible to harvest energy from multiple piezoelectric transducers with arbitrary phase difference,a self-powered multi-source series synchronous switching inductor circuit is proposed.Passive peak detection and switching circuit is designed to make the direction of inductor current of the positive half cycle and the negative half cycle consistent,solve the problem of energy backflow and self consumption of multi-source piezoelectric energy harvesting circuit.The energy harvesting efficiency is improvd.The peak output power ratio（POPR）between the circuit and the standard circuit can reach 3.7,but the coefficient of BW0.9 is only 0.17,which means that the output power is greatly affected by the load.Therefore,a multi-source synchronous charge extraction and inversion circuit is proposed.The designed passive switching circuit replaces the traditional diode rectifier bridge to reduce the circuit loss and improve the conversion efficiency.At the peak voltage point,partial charge is extracted and the residual is inversed to improve the energy harvesting output power.The POPR of the circuit reaches 3.45 and shows a higher BW0.9（0.83）,which reflects higher output power and better load adaptability.（2）Environmental energy is time-varying.Sometimes some environmental energy is very weak while some environmental energy is strong.Hharvestinging weak environmental energy often"The loss outweighs the gain".Therefore,an auxiliary multi-source environmental energy harvesting method is proposed,which uses the thermoelectric transducer as the auxiliary energy,harvests the weak thermoelectric energy as the auxiliary energy,and assists the energy harvesting of the piezoelectric transducer.The passive energy auxiliary and energy harvesting circuit is designed.The energy auxiliary circuit loads the weak thermoelectric energy at both ends of the piezoelectric transducer.It not only harvests the thermoelectric energy and piezoelectric energy,but also improves the peak voltage of the piezoelectric transducer and increases the power and efficiency of piezoelectric energy harvesting.（3）The biggest problem of multi-source environmental energy harvesting circuit is the interaction between multi-source energy.How to effectively manage and harvest multi-source energy is the basis of efficient multi-source environmental energy harvesting.The existing methods either use diodes or time-sharing multiplexing for isolation,but diodes will cause energy loss,and the time-sharing multiplexing method requires additional detection and control circuits,which increases the circuit loss.Hence,a matrix multi-source energy acquisition circuit is proposed,and an isolated active rectifier（IAR）is designed.At the positive and negative extreme points,the piezoelectric and thermoelectric energy can be harvested together,and the extracted instantaneous inductor current and energy can reach the maximum,which improves the energy harvesting efficiency,IAR effectively isolates the multi-source piezoelectric and thermoelectric energy arranged in the matrix,prevents the internal consumption of multi-source energy and reduces the energy loss. |
