Predictive Control Of Power-Split Hybrid System In The Transient Process

With the rapid development of the national economy,the problems of energy consumption and pollution emissions have become increasingly prominent.To cope with its challenges,five ministries including the Ministry of Industry and Information Technology jointly released the “Parallel Management Measures for the Average Fuel Consumption of Passenger Vehicle Enterprises and Credits for New Energy Vehicles”(referred to as the “dual credit policy”).Under its guidance,hybrid technology as one of the most effective energy saving and emission reduction technologies is in a booming period.After years of development,in the domestic market of hybrid vehicles,China’s OEMs have been able to compete with foreign OEMs.However,through careful analysis,it can be found that most of China’s OEMs prefer series hybrid,parallel hybrid and series-parallel hybrid,but few OEMs are interested in power-split hybrid.The power-split hybrid system can decouple the engine and the wheel through the planetary gears.Part of the engine power is used to drive the vehicle and the rest is used to charge the battery.The speed of the engine can be adjusted continuously,which is the most unique advantage of the power-split hybrid system compared with other hybrid systems.Because of this,the power-split hybrid system has better energy saving potential under urban conditions.In the past,the academic research focused on the input power-split hybrid system represented by Toyota THS system,but the research on the compond power-split hybrid system is still lacking.Compared with the input power-split hybrid system,compond power-split hybrid system has its unique dynamic characteristics.All the actuators in the system have electronic continuously variable ratios.This dissertation takes the compond power-split hybrid system as the research object.Aiming at the transient process of the system in different modes,the strategy and algorithm of multi-objective tracking control are studied in depth.By optimizing the torque of the engine,two motors and the wet clutch,the goal of improving driving comfortable and economy is realized.This dissertation carries out research work from three aspects:(1)For the hybrid system with separated clutch,the engine is started by the slipping of the separated clutch.The synchronization of the engine is controlled by the clutch torque,and the engine torque can be regarded as measurable torque disturbance.In the dynamic start-up process of the engine,both of the engine feedback torque and clutch torque have deviations,and the clutch torque has time delay.For the dynamic engine-start mode,the engine target torque is large,which increases the difficulty of the synchronization process.In this paper,the Smith predictor and linear active disturbance rejection controller are combined to solve this problem.The linear extended observer is used to estimate the torque disturbance including engine torque and clutch torque control deviation,and the torque disturbance converges to the real value within 100 ms.The Smith predictor is used to compensate for the influence of clutch torque delay.The clutch target torque calculated by the linear active disturbance rejection controller improves the closed-loop control of engine speed in the synchronization stage,avoids the continuous oscillation of torsional damper after rapid engine synchronization,and meets the requirements of driving comfort.(2)The electronic continuously variable gear in pure electric mode is the basis of compound power-split hybrid gear and also a multi-input multi-output system.In this paper,the dynamic equations of the whole powertrain in this gear are established,and the strong coupling characteristics between input and output are analyzed.Based on this equations,a multivariable Kalman observer is designed to realize the observation of the planetary carrier speed and the transmission output torque.An optimization control method based on MIMO control structure is proposed and a multivariable model predictive controller is designed to optimize the multi-objective tracking control of planetary carrier speed and transmission output torque in the transient process.Model predictive control can better cope with the time delay due to the signal transmission and the response characteristics of the actuators.The root mean square error of carrier speed control can be reduced by 70%.(3)For the electronic continuously variable gear in pure electric mode,another control method combining dynamic decoupling and predictive function control is also proposed in this paper.For the decoupled control of the planet carrier speed and transmission output torque,the predictive function controller is designed respectively.The dynamic compensation between the control loops is improved by predicting the output variables in the future time domain.Compared with the control method based on MIMO control structure and multivariable model predictive controller,this method can also improve the multi-objective tracking control under transient conditions and deal with the system input and output delay effectively.(4)Compond power-split hybrid gear is an over-actuated strong coupling system with multiple inputs and multiple outputs,and engine torque can be regarded as measurable disturbance.The torque response characteristics of the engine and the motor are quite different.In order to give full play to the advantages of the power-split system,it is necessary to continuously adjust the torque and speed of the engine under complex working conditions.The change of the engine torque also affects the control of the engine speed.In this paper,the dynamic equations of the whole powertrain are derived,and the MIMO control method is proposed.A model predictive controller based on Laguerre function is designed,which can optimize the multi-objective tracking control of engine speed and transmission output torque.The root mean square error of engine speed control can be reduced by 61%.