Study On Nonlinear Optimal Control Method Of Electrically Assisted Turbocharged Diesel Air-path System

Electrically assisted turbocharger(EAT)technology is designed to improve the poor transient response performance caused by turbo lag,and insufficient output torque at low-speed,and insufficient utilization of exhaust gas energy by adding an assisted motor to the supercharger of a traditional turbocharged diesel engine.However,the introduction of assisted motors not only increases the degree of freedom of control system of the diesel engine air path system,but also makes the system a "mechanicalelectrical" highly coupled complex system,which brings challenges to the design of reliable and efficient air path control systems.The coordinated control of multiple actuators will affect the performance of the diesel engine system in terms of power,fuel economy and emissions.So,this paper conducts research on the multi-objective optimization control of the electrically assisted turbocharged diesel engine air path system,and proposes a air path optimization control scheme based on a layered structure to achieve energy consumption optimization and multi-state goals of the air path system rapid tracking control,which improves the performance of the engine.The specific work revolves around the following aspects:First,based on the idea of mean value modeling,combined with the mechanism model and polynomial fitting,a control-oriented electrically assisted turbocharged air path system model was established.Expanded on the high-precision traditional turbocharged diesel engine model,the construction of EAT diesel air system simulation model was completed to realize the function of EAT,and the reasonable verification of function of EAT air system simulation model was carried out through the dynamic analysis.The accuracy of the control-oriented EAT air system model is verified by comparing the output of simulation experiment with simulation model.Secondly,the intake manifold pressure,exhaust manifold pressure,and Exhaust Gas Recirculation(EGR)flow of the air system are selected as the controlled variables by analyzing the effects of multiple actuators on the state of the air path.Based on the premise of satisfying the driver's torque demand,the sensitivity analysis of the diesel engine energy consumption affected by the working point of multiple sets of actuators is carried out.In order to meet the control needs of multi-objective optimization of EAT diesel engine air path system,a layered EAT air path optimization control scheme combining upper-layer exhaust manifold pressure trajectory optimization and lowerlayer multi-object trajectory tracking is proposed.Then,aiming at the characteristics of multi-optimal targets,constraints and coupled nonlinearity in the EAT lower layer air path tracking control system,a multiobject tracking controller for air path system based on nonlinear model predictive control is proposed.The controller realizes the rapid tracking control of the intake manifold pressure,exhaust manifold pressure and EGR flow by adjusting the turbine variable nozzle,assisted motor and EGR valve,and ensure that the engine runs within the safety constraints.The simulation based on the high-precision model is compared with the traditional control method to verify the effectiveness the proposed control method.Finally,towards the requirements of reference trajectory optimization in the lowerlevel controller,considering the characteristics of the coupling EAT air path "mechanical-electrical",and aiming at the optimization of engine energy efficiency,optimization method of exhaust manifold pressure reference trajectory based on an equivalent fuel consumption minimum strategy(ECMS)was proposed.This method uses the desired exhaust manifold pressure feasible area table and real-time battery SOC feedback obtained by steady-state calibration to convert the battery's energy consumption into fuel consumption.Taking the equivalent total fuel consumption of the system as the goal,the reference trajectory of the expected exhaust manifold pressure can be solved online by looking up the table dynamically.In addition,the reference trajectory of the desired intake manifold pressure and EGR flow was obtained by looking up the table.Through the joint simulation of the upper-lower control system,the effectiveness of the layered control strategy is verified.