Research On Variable-Load Control For Stable Operation Of Free-Piston Engine Generator

Free-Piston Engine Generator(FPEG)is a new type of power unit.It has the advantages of simple structure,variable compression ratio,high thermal efficiency and multi-fuel adaptation,which is one of the preferred solutions for hybrid electric vehicles and other mobile power plants.However,it is difficult to maintain the stable running of FPEG,and the problems caused by uncertain factors such as combustion fluctuation are the most prominent.Therefore,the stable running of FPEG is a challenging task.In this paper,the effects of Variable-Load Control(VLC)on stable running of FPEG were studied.Through previous studies,it can be seen that the electrical load had a significant effect on the running of FPEG.Based on this conclusion,the method of regulating the movement of the piston by adjusting the load is put forward to realize the stable running of FPEG.This method acted on the expansion stroke,which was the control operation for the current combustion state.By detecting the compression ratio of this combustion and the peak cylinder pressure,the variable load was adjusted by the deviation to balance the energy change due to the combustion fluctuation.The adjustment process was completed before the piston reaches the top dead center of the next compression stroke,which thereby greatly reduced the effect of this combustion state on the next compression stroke,and provided a stable operating condition for the next combustion.The use of VLC could isolate the interaction of two adjacent combustions,and created the basic conditions for the stable operation of FPEG.The IGBT was used to build the equivalent load to achieve the changes of load impedance.It can be confirmed by simulation that VLC could achieve the stable control of compression ratio and peak cylinder pressure of FPEG,and in the case of combustion fluctuation,VLC could maintain the stable running of FPEG and reduce the occurrence of misfire,thus the effectiveness of which for stable FPEG running could be proved.Based on this study,a Two-Parameter Control method of controlling compression ratio and cylinder pressure simultaneously was proposed.The method integrated the VLC and the oil supply control.Through the construction of the load closed loop control and the oil supply control closed loop,the compression control and the cylinder pressure control were simultaneously realized under the control of the corresponding algorithm.The effectiveness of the method was verified by Simulink simulation.In the study,a dedicated ECU was designed to control the running of FPEG.Aiming at the running characteristics of FPEG,a half cycle control strategy was designed so that the ECU can continue to control the piston after the combustion is completed,so as to realize the full stroke control of the piston with the VLC.In order to test the effectiveness of the VLC method,a miniature carbon dioxide prototype was designed.The prototype uses compressed carbon dioxide as driving force,together with the ECU to form the experimental bench.In the experiment,the continuous running of the prototype was realized,and the effective control of the piston movement was realized,and the stability control of the compression ratio was realized.At the same time,through the experimental results of the prototype,the validity of the VLC Simulation model was verified.