Research On The Control Strategy Of Stable Operation Of Linear Range Extender Based On Backstepping Method

The linear range extender(LRE)has the advantages of high thermal efficiency,multi-fuel applicability and low friction loss due to the free motion characteristics of the piston and without the constraint of the crank connecting rod mechanism.It has an attractive prospect in the range extension applications of hybrid electric vehicles,unmanned aerial vehicles and robots.However,due to the lack of mechanical mechanism to limit the amplitude boundary of the piston,the piston is easily affected by the interference of combustion factor and load,and is easily separated from the stable motion boundary.Therefore,the precise control of the piston motion trajectory has become a key measure to solve the instability of LRE.In this thesis,for the purpose of long-term stable operation of LRE,the nonlinear vibration equation of piston under the coupling model of combustion gas force,electromagnetic force of linear motor,friction force and mechanical spring force is established by mechanical analysis of reciprocating vibration characteristics of piston.Meanwhile,based on the engine compression,expansion,exhaust,and scavenging processes,a full cycle periodic motion simulation model of LRE was constructed,and the accuracy of the simulation model was verified by experiments.Then,the instability process of LRE is deeply explored by replacing combustion variation with energy input fluctuation and combining with full cycle simulation model.Simultaneous,considering that the conventional PID control algorithm cannot meet the control problems of high-order nonlinearity and strong coupling characteristics of the system,a nonlinear controller based on backstepping method design is proposed to solve the cycle combustion fluctuation instability and direct misfire events of LRE.The specific research work and conclusions are as follows:1.The control strategy of instability recovery of cyclic combustion fluctuationAiming at the instability problem of LRE cycle combustion fluctuation,based on the principle of energy regulation,the piston instability state as a guide,and the goal of balancing combustion fluctuation,a continuous adjustment method of electromagnetic force is established by using the mapping relationship between load and electromagnetic force in this thesis.Then,based on the backstepping method design principle,the piston displacement and speed are used as feedback parameters,and the trajectory tracking adaptive control model is constructed by coupling the piston dynamic model.Meanwhile,the ideal working condition is given as the reference trajectory,and the effect of the controller under the interference of cyclic combustion fluctuation is further analyzed.The results show that the trajectory tracking adaptive controller can eliminate the cyclic combustion fluctuation in the current expansion stroke and keep the piston of LRE always tracking the movement under the expected target trajectory.Simultaneous,the controller can accurately and quickly estimated the slowly changing friction coefficient of the system,which shows good adaptive characteristics.2.The control strategy of misfire fault recovery with dynamic driving forceIn order to solve the direct misfire problem of LRE,the working mode of linear motor is switched and the input of external excitation source is adopted in this thesis.The piston displacement,speed and linear motor current are taken as feedback parameters,and the piston dynamic model is the hub.Based on the backstepping method design principle,the displacement-speed-current three closed-loop control model is established by coupling the linear motor model.The outer loop adopts displacement closed-loop control and the inner loop adopts speed-current closed-loop control.Meanwhile,taking the ideal working condition as the piston reference trajectory,the dynamic response of the piston,the response of the excitation force and the dissipation force are analyzed,and the effect of the controller is further revealed.The results show that using the dynamic driving force misfire fault recovery control strategy can quickly move the piston’s current expansion stroke to the calibrated bottom dead center position according to the normal combustion condition trajectory after the occurrence of a misfire event.The recovery time for misfire faults is fast,but the instantaneous current of the motor is high,and there are high performance requirements for linear motors.3.The control strategy of misfire fault recovery with constant driving forceIn order to solve the LRE misfire event,this thesis also proposes a constant driving force misfire fault recovery control strategy.Taking the piston amplitude limit under ideal working conditions as the motion reference boundary,a misfire solver was constructed based on the principle of energy conservation,and the theoretical misfire driving force was calculated.Meanwhile,based on the backstepping method design principle,a constant motor thrust control model is established.The simulation results show that compared with the dynamic driving force misfire control strategy,the constant driving force misfire recovery control strategy has longer recovery time and lower control accuracy,but it has lower performance requirements for linear motors and is easier to control.Simultaneous,the input electric energy is only less than half of the recovery control strategy of the dynamic motor driving force misfire fault in the control process.Besides,the motor constant thrust controller designed based on the backstepping method also achieves a constant motor thrust at a fixed value.