Research On Energy Management Strategy Based On Oil-Electric-Hydraulic Hybrid Power System

In order to solve the two major world problems of energy crisis and environmental pollution,major automotive countries have promulgated new emission standards,which seriously restricts the further development of the automotive industry.In terms of energy saving and emission reduction,hybrid electric vehicles(HEVs),as the only way for the development of traditional fuel vehicles to pure electric vehicles,have attracted wide attention at home and abroad.At the same time,various scientific research institutions and automobile manufacturers have begun research work on HEVs.This paper is based on the project of National Natural Science Foundation of China "Research on Coupling Characteristic and Control of Electro-hydraulic Hybrid Braking for CVT Heavy Hybrid Electric Vehicle Based on Safety,Efficiency and Smoothness"(Project Approval No.51575063).Taking a new type of hybrid power system as the research object,on the basis of matching the parameters of the power transmission system,the energy management strategy of its driving and braking modes has been done,and the specific work is as follows:(1)Based on the analysis of the structure scheme of the new hybrid power system,the parameters of key components such as engine,motor,battery,hydraulic pump/motor,and accumulator are designed by using the comprehensive analysis method of theoretical calculation and cycle conditions.By combining theoretical modeling with experimental modeling,not only the numerical model of the above key components is established,but also Driver model and vehicle dynamics model are established.(2)The working mode of hybrid electric vehicle is analyzed,and the selection strategy of driving mode based on hydraulic energy and electric energy is proposed.At the same time,the logic threshold energy management strategy based on the optimal working curve is proposed.In order to obtain lower manufacturing cost of the whole vehicle power system and energy consumption,the energy management strategy parameters and power system components parameters are optimized jointly.In this paper,the linear weight method is used to transform the multi-objective function into the single-objective function,and the genetic algorithm is used to optimize it.The dynamic simulation results show that the parameters of the power system can meet the requirements of the vehicle dynamic performance.(3)For driving conditions,a real-time energy management strategy based on the lowest instantaneous energy consumption cost is proposed.The strategy takes the instantaneous energy consumption cost of single power source driving mode or hybrid power driving mode as the objective function,takes vehicle demand torque,vehicle speed and the working range of related power components as constraints,and uses the Mesh traversal method to obtain the optimal results under different power requirements.Based on the analysis of braking force distribution strategy of traditional four-wheel drive vehicle,a braking force distribution strategy based on maximum energy recovery is proposed,and the working point of motor participating in braking is optimized.The simulation results show that the proposed energy management strategy can achieve the desired control objectives.(4)The global optimal energy management strategy based on dynamic programming is studied.Firstly,the optimization problem of energy management strategy is transformed into a multi-stage decision-making problem based on dynamic programming.Secondly,the variables,including battery state of charge,hydraulic accumulator state of charge,front axle torque distribution coefficient,speed ratio of continuously variable transmission and engine torque are discretized to shorten the optimization time.Then,the state transition equation for battery and hydraulic accumulator is established respectively.Finally,dynamic programming algorithm is compiled for reverse optimization,and control sequence is obtained by forward search.The simulation results show that the global optimal energy management strategy based on dynamic programming can make rational use of electricity and serve as an evaluation criterion for other strategies.(5)Under NEDC condition,the real-time energy management strategy based on the lowest instantaneous energy consumption cost is compared with the global optimal energy management strategy.The results show that the energy-saving effect of the proposed energy management strategy is similar to that of the global optimal energy management strategy.