Study Of The Thermoelectric Conversion And Its Energy Storage System Based On The Stirling Cycle

General fossil fuels stored in nature,such as coal,petroleum,natural gas and so on,can be applied directly in people's daily life and industrial production in the process of combustion in the form of heat energy.However,a considerable part of the heat energy above mentioned is lost into the atmosphere uncontrollably,which not only causes a huge energy waste,but also makes the atmosphere heat pollution.Therefore,some countries have spent a lot of manpower and material resources to develop the research work for waste heat recovery and utilization,some of which were waste heat recycling directly,and others made the waste heat to be converted to mechanical energy or electrical energy before reuse.In this paper,one continuously thermal-mechanicalelectrical conversion system based on the Stirling cycle,as well as its corresponding electrical energy storage system armed at middle and low temperature resoures were established and studied.The whole thermoelectrical conversion system designed could realize energy conversion and storage for dispersed heat resource,and even low temperature heat energy resource effectively.The most important step forward provided with the designed system can be that it is a suit of conversion and storage system consisted of a free piston Stirling engine and a line power generator,through middle boost step,finally,realizing waste heat reuse.According to current developing status at home and abroad,as well as frontier science problem,thermo-mechanical conversion system,mechanicalelectrical conversion system and energy storage system were designed and studied in this thesis.Furthermore,simulation and experiment works were carried out in order to evaluate the performance of every model in the designed system.The results show that such system is competent to realize the energy conversion from low-power thermal to electrical energy and its storage for battery.The main study results are shown in the following:First,in the thermal-mechanical conversion model system,the geometry and dimensions of a single cylinder free-piston Stirling engine model were designed and calculated for dispersed low temperature according to the feature of the heat resource referring to automobile exhaust and solar energy collector,which laid a foundation for matching connection with the subsequent linear mechanical/electrical conversion model.Simultaneously,a magnetic spring resonant displacer piston sub-system is designed in order to ensure the start procedure and conversion efficiency of the low-power Stirling engine.The displacer piston can also provide both a required stiffness and actuation forces.What's more,the performance of the magnetic system can adjust the gas working medium pressure in the chamber during starting and running.In the model,the power piston is not connected with displacer piston directly,which is also designed to be a mass-spring resonant subsystem with gas working medium matching displacer piston and possesses a same resonant frequency for two pistons equaling to nominal frequency of the system.Following,the running performance of the designed Stirling model was analyzed based on the dynamic simulation with the isothermal analysis method,obtaining the related p-V diagram and its power and conversion efficiency.Otherwise,this low power Stirling engine model fabricated can provide a clear understanding of the Stirling cycle operation,which offers thinkings for higher power Stirling engine production.The analysis method used in this thesis which is verified by prototype testing also possesses reference value for Stirling engine design.Second,in mechanical-electrical conversion model system,for direct use of the linear reciprocating motion from the free piston Stirling engine output,a cylindrical permanent magnet linear generator model was designed based on the law of electromagnetic induction,which could achieve the conversion process from the mechanical energy into electrical energy.Through theoretical calculation and experimental verification,the mover array structure,its optimal size and the number of stator winding were ultimately determined,moreover,the relationship between mover and stator windings in number and size was also obtained.In the generator model,the mover structure of the linear power generator model had adopted the quasi-Halbach magnetization method.That is,the permanent magnets for the mover of the engine were connected in homopolar by a ferromagnetic ring,which not only significantly increased the magnetic field strength in the air gap,but also obtained the approximate sine waveform for the output voltage curve.In addition,the no-load magnetic field distribution and load voltage and current waveform characteristics were analyzed by Ansoft simulation about the energy conversion model.Through calculation of the load power and conversion efficiency of the power generator model,it indicated that the average power was 0.103 W,the average winding copper consumption was about 0.0465 W and the nominal efficiency could reach as high as 68.9% without calculating the other work loss.Finally,the natural frequency and the maximum no-load induction electromotive force were determined by experiment and simulation,the values of which were 11 Hz and 1.3V,respectively.The experimental results indicated that the induced voltage of the linear power model was significantly increased by this quasi-Halbach array design.Third,in micro energy storage system,in order to realize the micro energy storage referring to the conversion model in this thesis,a boost energy storage system was designed.The system mainly consisted of a starting circuit made of capacitor charge pump to enable the first boost,from 0.5V to 1V or more,which could start the DC-DC convertor,and the final output valtage was as high as 5V,which was enough to charge the accumulator.Based on this design,the functional properties of each energy storage system unit were verified by simulation results of the HSPICE software.Furthermore,a 0.0096 F capacitance was added into rectifier and voltage divider circuit to obtain the RLC series resonant with internal induced impedance in above-mentioned micro heat energy/electrical energy storage system,which maximized the sharing voltage amplitude on the external divider resistance.After voltage boosting circuit,the reliability of the energy storage system in running progress was further promoted,the stability and effectiveness of the system were also improved.Thus,the system was optimized from above aspects discussed.