Energy Management And Engine Torque Tracking Control For HEVs

With the continuous growth of the world's car ownership,energy shortages and environmental pollution have become urgent problems to be solved by all mankind.The development of new vehicles with low fuel consumption and low emissions has become the industry's top priority.As a result,hybrid vehicles,which have the advantages of both traditional cars and electric cars,have stepped onto the stage of history.Hybrid vehicles are equipped with two power sources,engine and motor,and their fuel-saving capacity depends largely on the energy management strategies of these two power sources.In order to improve fuel economy,this paper proposes an instantaneous fuel consumption minimum strategy based on mode separation to distribute the torque of the engine and the motor,and then obtain the desired torque of the engine and the motor.The tracking effect of the expected torque of the engine directly affects the dynamics and stability of the vehicle,so we designed a data-driven MPC torque tracking controller to track the engine torque,and obtained the desired bottom control amount by optimizing the solution: throttle opening,Air-fuel ratio and ignition advance angle.Since the air-fuel ratio system is relatively complex and cannot directly apply the control amount to the actuator,an air-fuel ratio model predictive controller is designed to track and control the desired air-fuel ratio.Firstly,we take the series-parallel hybrid electric vehicle as the research object,and match the parameters of each component of the power system.In order to obtain the required torque of the vehicle in real time,a longitudinal dynamic model of the vehicle was established based on the system parameters,and compared with the integrated model in GT-Power software to verify the accuracy of the dynamic model.Because this paper studies the energy management strategy based on the principle of minimum instantaneous fuel consumption,based on the collected engine effective fuel consumption data and motor efficiency data,the engine instantaneous fuel consumption rate model and the motor instantaneous fuel consumption rate model are established.Based on the above model,the minimum fuel consumption strategy based on mode separation is designed.In order to verify the improvement effect of the proposed energy management strategy on fuel economy,the proposed scheme is compared with the energy management strategy based on rules and dynamic programming respectively.The NEDC cycle conditions simulation is used to verify the proposed energy management strategy's Effectiveness.Second,the tracking accuracy of the engine's expected torque and exhaust emissions directly affect the overall performance of the hybrid vehicle.In order to accurately track the expected torque on the premise of meeting emissions,we design a torque tracking controller to track the expected torque.Since the engine is a complex,strongly coupled,non-linear system and cannot be modeled based on the mechanism,we select the appropriate throttle opening,air-fuel ratio,speed,and ignition advance angle excitation data to act on the engine system,and then collect and process the system I / O data,and use the data-driven method to establish a torque and emission prediction model,and the accuracy of the model is simulated and verified.Finally,taking throttle opening,air-fuel ratio and ignition advance angle as control variables,engine output torque,CO and NOx emissions as output variables,comprehensively considering the system constraints,a data-driven MPC torque tracking controller was designed and implemented in GT-The torque simulation accuracy and emission performance were verified in the POWER and Simulink joint simulation environment.Finally,considering that the desired air-fuel ratio optimized by the torque tracking controller cannot directly affect the system,we design a corresponding air-fuel ratio tracking controller.In order to improve the response speed of the controller,an air-fuel ratio feedforward controller is designed by the method of MAP table calibration.In addition,in order to reduce the effect of the inherent time lag of the air-fuel ratio system and improve the tracking accuracy,an air-fuel ratio system model with time lag was established,and an MPC air-fuel ratio feedback controller was designed based on this model,and verified by different simulation conditions the Rapidity and accuracy of the controller.After verifying the performance of the energy management strategy,torque tracking controller and air-fuel ratio tracking controller respectively,the above three-layer controllers are combined and optimized,and the performance of the three-layer cascade controller is verified by simulation.