Research On Design Theory And Control Method Of Free-piston Linear Generation System

Free-Piston Linear Generator,FPLG,is a novel energy converter,which has attractive application prospects specially on the hybrid electric vehicles(HEVs)as a range-extender because of its promising features such as high efficiency,high power density,low emissions,multi-fuel flexibility and compact etc.However,so far,long-term stable operation is still a common and international challenge that is remained to be resolved urgently.Aiming at this problem,this thesis proposes some innovative ideas specifically for the system design theory and control method.A series of theoretical research and experimental works are carried out as follows:(1)Decoupling design of the free-piston linear generation system.The theory and method of a new decoupling matching design approach based on the energy conversion and efficiency distribution of the coupling system are proposed especially for designing a two-stroke gas-spring rebounded FPLG.The theoretical guidance and determination principles of the structural and operational parameters of the internal combustion engine(ICE),linear electric machine(LEM)and gas spring(GS)are derived respectively.The feasibility and versatility of the decoupling design approach are verified preliminary through Matlab/Simulink simulation.Besides,the structural and electromagnetic design scheme of the LEM is determined.And its performances are analyzed and optimized with the ANSOFT finite element analysis(FEA).Based on the modular design idea,a 15 k W LEM power module that has 94% generating efficiency at least is designed.An unique structure integration scheme is proposed.Particularly,the performances of the LEM especially under various load or various reciprocating frequency are analyzed with the FEA simulation.(2)Thermodynamics modeling and simulation of the hybrid system.The model of the ICE,LEM and GS are derived mathematically.A simulation model of the hybrid system is established with Matlab/Simulink.The thermodynamic characteristics such as the free piston motion,forces profiles and in-cylinder pressure distribution features are analyzed.Also,the output characteristics of the voltage,current and electric power are evaluated.The effects of the coupled parameters such as the system equivalent stiffness,cyclic fuel injection,ignition position,initial pressure of the GS,the load and the moving mass etc.on the output electric power and system efficiency are analyzed comprehensively,which provides a good theoretical basis for the performances optimization and stable operation control.(3)Full cycle operation processes and basic control strategy analysis of the system.A full cycle operation control strategy is proposed for the startup,stable operation,fault recovering and stopping processes.The operations sequences of the ICE including the injection,ignition,intake and exhaust based on the piston motion states are determined.In order to verify the feasibility of the strategy,the piston motion states under various operating conditions are simulated with Matlab/Simulink.(4)Study of the nonlinear control method of the free-piston motion.A nonlinear trajectory tracking control method for free-piston motion based on the virtual crankshaft and dissipative Hamilton energy shaping theory is proposed.The relationship between the crankshaft radius,equivalent virtual crankshaft speed and the piston trajectory,the effective electric power and system overall efficiency are derived.The effects of the parameters of the virtual crankshaft on the piston trajectory and system output performances are thereby analyzed.A piston trajectory optimization model with the optimal system efficiency is established.And the feasibility of the optimization model is verified through simulation.The dissipative Hamilton model of the FPLG is derived.The nonlinear feed-back control laws based on the energy shaping are designed.Ultimately,the feasibility and effectiveness of the proposed nonlinear control method is verified through Matlab/Simulink simulation.(5)Functions test of the ICE operations and LEM performances validate.In order to test the functions of the ICE operations such as the fuel injection,ignition,intake and exhaust,a testing platform is established.And the validity and reliability of the ICE operations are validated.A 15 k W LEM prototype is developed.A performances test platform specifically for the LEM which is suitable for long stroke,high power and high thrust conditions.A data acquisition system based on Labview is developed.The performances of the LEM are tested and the rationality of the FEA design scheme of the LEM is thereby validated by experiment,which provides good experimental conditions for the follow-up system integration and performances optimization.Above mentioned works cover the theoretical approach for both the system design and control issues.The author is trying to plan a complete and clear research route,which is of significance for avoiding unstable operation risks from each link from the original system matching design,the system integration,and prototyping testing.The research works has both theoretical and method innovations,which provides an essential basis for the follow-up study.