Design Of Piecewise Linear Model Predictive Controller For Air Path System Of Diesel Engine

At present,in order to reduce emissions and energy consumption,the main technologies commonly used in diesel engines are exhaust gas recirculation(EGR)and variable geometry turbocharger(VGT).Among them,EGR can effectively reduce the emission of nitrogen oxides(NOx)by the way of exhaust gas backflow,and VGT can improve the engine power by changing the turbine speed,so as to improve the fuel economy.However,there is a strong coupling relationship between VGT and EGR because VGT affects the change of inlet pressure and the flow through EGR valve,and vice versa.However,it is very difficult to decouple the diesel engine air system with strong coupling and nonlinear characteristics.Therefore,in order to obtain the ideal control effect and avoid the more difficult decoupling process,this paper establishes an improved control oriented model of diesel engine air system,further designs a piecewise linear model predictive controller with integral function,and verifies the effectiveness of the controller through simulation.The specific research contents of this paper are as follows:Firstly,the control oriented air system model of diesel engine is established.The least square method is used to calibrate the parameters of steady-state sub models such as gas flow rate and charging efficiency under different working conditions.Then,the dynamic sub models of intake manifold pressure,exhaust manifold pressure and turbine speed are constructed by mechanism analysis.Finally,the overall model is built in Simulink and compared with the real test data of diesel engine to verify the accuracy of the model,which lays the foundation for the design of model predictive controller of diesel engine.Secondly,a piecewise linear model predictive control(MPC)optimal controller is designed.By designing a dynamic optimization problem to reduce NOx emission,the EGR rate and inlet pressure are selected as the optimization objectives,and the optimal steady-state operating point is taken as the dynamic tracking objective.In order to reduce the control error caused by model error,the integral of EGR rate is added to the objective function as a new state,so as to improve the dynamic performance of EGR rate and reduce the steady-state error of EGR rate.Finally,the piecewise linear MPC control experiment of diesel engine air system is carried out.Through the simulation test,the influence of MPC controller parameters such as prediction interval,control period and weight coefficient on the control effect is studied,and then the appropriate MPC control parameters are determined.Furthermore,the MPC controller for diesel engine air system is compared with the existing PID controller,and the control performance such as overshoot and steady-state error is analyzed,which proves the effectiveness of the proposed piecewise linear MPC controller.