Research On Internal Combustion Free Piston Linear Power Generation Control System

Since the 21st century,energy problems and environmental pollution problems have become increasingly serious.The research and development of electric vehicles can not only improve energy utilization,but also protect the environment.Limited by the development of battery technology,the range of pure electric vehicles is shorter,and hybrid electric vehicles are more feasible and practical.The engines of hybrid electric vehicles are mainly divided into traditional engines and free piston engines.Compared with the traditional engine,the free piston engine eliminates the crank connecting rod mechanism.The efficiency of the engine is greatly improved and the volume and weight are greatly reduced.Firstly,this paper has modeled and simulated the start-up process and steadystate process of the internal combustion free piston linear power generation system.Aiming at the starting process of the system,dynamic analysis and modeling simulation are carried out.Aiming at the steady state power generation process of the system,a thermodynamic model and a dynamic model are established and the electromagnetic force of the motor is proportional to the speed according to the circuit model of the linear motor.At the same time,the influence of the change of the moving part mass and the load on the system work was studied.The results show that when the moving part mass increases,the piston speed decreases and the stroke increases;when the load decreases,the piston speed increases and the stroke also increases.Then,aiming at the problem of d-q axis coupling caused by coordinate transformation and the change of q-axis current caused by linear reciprocating motion of the motor,a complex vector model of linear motor is established and a feedback decoupling PI current regulator and complex Vector PI current regulator are designed.Based on the d-q axis voltage equation of the motor,a predictive control current regulator is designed.The results show that the regulation performance of the three current regulators is almost the same in the electric state;the speed following error of the complex vector PI current regulator is the smallest in the power generation state,and the d-q axis current fluctuations of the three regulators are basically the same.In terms of the following speed of the q-axis current,the predictive control current regulator is the fastest,followed by the complex vector PI current regulator,which has greatly improved from the traditional feedback decoupling PI current regulator.Next,based on the linear relationship between the electromagnetic thrust of the linear motor and the speed,the PI speed regulator is designed.Since the speed curve is similar to a sinusoidal curve,this article designs a quasi-proportional resonant controller based on the internal model principle.The results show that the quasiproportional resonance speed regulator can greatly reduce the following error compared to the PI speed regulator,and the fluctuation of the d-axis current of the motor is also reduced.At the same time,the resonant controller is used to compensate the speed loop.The results show that,since the error when using the quasiproportional resonance controller is already very small,the speed following error is almost unchanged after the harmonic compensation is used,but the d-axis current fluctuation is smaller and the q-axis current value is also smaller.The controlling effect of the complex vector PI current regulator is the best.Finally,the battery charge and discharge control system based on two-phase interleaved cascade bidirectional DC-DC converter was investigatived.The working principle of two-phase interleaved cascade bidirectional DC-DC converter is analyzed and the converter filter is designed The converter is modeled with small signals and the corresponding transfer function is derived.In Buck mode,a multisection constant current and constant voltage charging algorithm is used.In Boost mode,voltage and current double closed-loop control is used.The results show that during charging,during multi-stage constant current switching and constant current to constant voltage switching,the response speed is faster and the current does not appear to be overcharged;during discharge,the motor bus voltage fluctuations are small.