Research On Single-pisotn Free Piston Linear Generator System

Free piston linear generator(FPLG)is a promising energy convertor with advantages as very simple structure and quite high power density,and it may be a good choice of range extender for electric cars.However,without the limitation of crank-link mechanism,the TDC and BDC of FPLG is changeable which causes problems as misfire and crash.FPLG have mainly three kinds of structures: single-piston,dual-piston and opposed-piston.Opposed-piston structure is complex,and has low power density;Dualpiston has the highest power density,but very difficult to control;Singlepiston has the simplest structure and easiest to control.Based on the original prototype,a single-piston FPLG principle prototype based on air spring is designed,the measurement and control system and control strategy are built.The starting,ignition and state switches of the prototype are successfully realized.A simulation model for the principle prototype is set up in Simulink.In order to guarantee the accuracy of model,the friction test and compression calibration test are conducted.According to the test results,the friction model is established.Parameters as compression polytropic index of cylinder and correction coefficients as air leakage rate coefficient and equivalent exhaust valve open position are calibrated.The correctness of the motor control program is verified by the startup process experiment,and the start-up parameters of the prototype are determined.The experimental results under natural inspiration show that with the increase of the equivalent ratio,the cylinder pressure and frequency increase,and the ignited percentage increases first and then decreases.With the delay of ignition position,the cylinder pressure decreases,the piston stroke increases,and crashes of safety limiter occur.Obvious cyclic misfire was found in the test of operation of the principle prototype under natural inspiration.The analysis of the test data shows that the misfire is caused by poor air exchange of the cylinder.It is verified that the reason of cyclic misfire is poor air exchange by experiments of FPLG under scavenging of combustion cylinder.It is found that the FPLG prototype can operate without misfire when the ignition position is 27mm~29mm,and the frequency fluctuation is reduced to 0.8%.Through the test,the control parameters of FPLG to achieve continuous and stable operation were determined,and the stable operation over 1000 cycles with frequency of 43.2Hz is achieved.Through the research of this paper,the stable operation of FPLG principle prototype is realized and the optimal control parameters are determined,which provides a reference for the subsequent research and prototype design.