Research On Speed Control Of Lean Burn Natural Gas Engine In A Range Extender

The range-extended electric vehicle(REEV)can solve the problems of short range and long charging time of pure electric vehicles,and has the advantages of low cost and high vehicle efficiency.It is currently a hotspot in the new energy vehicle industry.The research on the engine speed system for range extender is helpful to promote the development of range-extended electric vehicles,and then promote the development of the whole new energy vehicle industry.In this thesis,the speed control strategy of lean burn natural gas engine for range extender is studied in order to improve the responsiveness and antidisturbance of engine speed system,and then to improve the responsiveness and stability of power output of the range extender system.The main research results are as follows:Aiming at the natural gas engine system model,the influence of gas fuel on the air flow into the cylinder is analyzed,and a scheme using air-fuel ratio to modify the air mass flow rate in the gas fuel engine is put forward.The air intake system model of the natural gas engine is established and engine torque model considering the influence of air-fuel ratio according to the air intake model is derived.In addition,aiming at the problem that the parameters in the engine torque model are difficult to calibrate,an improved torque model is designed.Then it is easier to calibrate the parameters and design the corresponding controller.Finally,the engine mathematical model is verified by co-simulations on the platform of Matlab/Simulink and GT-POWER.In order to improve the response speed and anti-interference performance of natural gas engine speed system in a range extender,a double closed-loop speed control scheme considering the dynamics of the throttle was proposed.The inner loop control scheme considering the dynamics of the throttle can improve the response speed of the intake pressure and reduce the interaction between the inner and outer loop systems;Aiming at the problem of calibration error and unknown torque disturbance in the outer loop speed loop,an adaptive control strategy with PI + feedforward compensation + load compensation +switch term is designed.The influence of tracking error of the inner loop system on the speed system is analyzed,and the stability and convergence of the outer system are explained.Co-simulations on the platform of GT-POWER and MATLAB/Simulink are designed to illustrate the effectiveness of the proposed strategy.In order to further improve the responsiveness and anti-interference of the speed system of the lean burn natural gas engine under medium and high load conditions,based on the double closed-loop control structure,the air-fuel ratio(AFR)additional torque is introduced as another input of the system besides the throttle valve,where the AFR additional torque is produced by setting AFR deviation from the nominal value and a multiinput model predictive control is proposed to handle the multiple inputs and constraints,guaranteeing that the AFR returns to the nominal value for efficiency and emissions.Cosimulations on the platform of GT-POWER and MATLAB/Simulink designed to verify the effectiveness of the algorithm.The turbocharger can effectively compensate for the decrease in engine output torque caused by the lean burn mode,but increase the engine torque delay time.To solve this problem,a new speed control scheme of the range extender is proposed,in which,the speed control strategy is implemented in the range extender control unit(RECU).In this way,the original control strategy of the engine ECU can be retained,and the ECU on the traditional vehicle can be directly used in the range extender,which reduces the development cost and increases the applicability of the RECU.In addition,the generator torque is introduced as an auxiliary input of the system besides the engine torque,and the anti-disturbance performance is improved by reconfiguring the undesired pole of the system.The effectiveness and practicability of the control scheme are verified by the co-simulations.In order to further verify the effectiveness and practicability of the algorithm proposed in this thesis,a range extender bench system was established.The bench experimental scheme is designed for each control strategy,and the experimental results and comparative analysis are given to show the effectiveness and practicability of the proposed strategy.