Transient Modeling And Start-stop Control Of Engine In An HEV

There are two driving source of the hybrid vehicle, in the process of vehicle driving,there is frequent switching between the two driving sources, so there is frequent start-stop in engine. Frequent start-stop of engine will lead to the fuel consumption and lower down rode comfortableness, therefore it is necessary for us to achieve a good engine start-stop control.First, this thesis expounds the proposed hybrid engine start-stop problem, introducing different types of hybrid control strategies, comparing the advantages and disadvantages of the current start-stop technology. Then put forward the control demand of this topic, namely by controlling the output torque of the starting motor to make the engine speed tracking with reference, thus start-stop control problem can be described as speed tracking problem. Hybrid vehicle system is a rapid system, so we need to establish a transient model which reflects the speed fluctuation. According to its working principle the corresponding mathematical model is derived. Using the platform of AMESim to establish a transient model, and the simulation model is testified by dynamic analysis of model.Then, a model of the control system of engine and motor connection is deduced, the model can be simplification in derivation, reciprocating inertia moment in the experimental measurements relative to the engine indicated torque is small, so the engine can be reciprocating inertia moment ignored, a belt drive is an ideal transmission process, so the motor and the engine speed difference is small, which can be ignored. On this basis,using differential flat feed-forward plus feedback LQR(linear quadratic regulator,LQR)in engine start-stop control, using the theory of differential flatness start-stop system feedforward controller is designed, the feed-forward control points work as balance point then the model is linearized, and the LQR controller is designed for feedback control, feedforward and feedback control structure can make the motor output meet fast-response and follow up on the expected engine speed. LQR controller based on differential flatness could not solve the fluctuation of speed, so adopted the "Triple-step" control method of nonlinear system, and the start-stop system controller is deduced in detail. The controller design has three parts: homeostatic control, feed-forward control and error control, the controller gain is dependent on the system state, and has adaptability with changes in working condition. On this basis, considering the interference of the system, the uncertainty of model simplified and parameter, assumes that the start-stop system bounded disturbances, under the framework of ISS(Input to State Stability,ISS) theory the robustness of the closed-loop system is analyzed and theoretically proved that the system has anti-jamming performance.Finally, using simulation software AMESim and MATLAB/Simulink to conduct joint simulation experiments, through comparison and analysis of the experimental results the feasibility and effectiveness of the control system is verified.In this thesis, the engine start-stop control scheme is proposed and the corresponding experiments are conducted, and the controllers are discussed in detail the derivation,provided some ideas in design of the control system of engine start-stop. In the actual engine start-stop control system the following problems remain to be done, the motor is not ideal motor, thus in the practical application is still need to consider the motor control problems. In addition, in this thesis the hybrid control system of automobile engine startstop validation is conducted under the condition of offline, work needs to be done in the real engine start-stop system on the bench test to verify its real-time and effectiveness.