Study On Energy Management Strategy For Power-split Constrained Piston Hybrid Power System

Under the current huge challenge of increasing global energy demand and environmental degradation,the development of new energy vehicles has reached a broad consensus in the international and domestic automotive industries.In recent years,as the core component of new energy vehicles,hybrid power system has been actively developed and researched by major vehicle enterprises and universities.The energy conversion process of the existing power-split hybrid system in the engine driven generator mode is complex,and the system efficiency needs to be further improved.Therefore,a power-split constrained piston hybrid power system is designed and studied in this paper,and three aspects of research work are carried out around the system,including system configuration analysis and vehicle modeling,design and optimization of energy management strategy,comparison of simulation results of different strategies and system energy utilization efficiency analysis under cycle conditions.The research work is as follows:Firstly,through the dynamic analysis of planetary gear mechanism,the working principle of power-split is explored.The structure connection scheme of the constrained piston hybrid system is analyzed and selected,and the parameters of each component are matched.On this basis,the forward modeling theory is used to build the vehicle simulation model,including driver model,constrained piston engine system model,motor model,battery model,transmission component model(including coupling mechanism model,main reducer model and wheel model)and vehicle dynamics model..Secondly,the control principle of the rule-based energy management strategy is briefly described,and the rule-based logic threshold energy management strategy is designed.The main steps are as follows: based on the leverage method,the working mode of the system is analyzed in detail,and the energy flow mode of each mode is analyzed in depth;the logic threshold parameters are selected and determined,the working mode switching rules and power distribution strategy are formulated;and the engine start-up and stop and working point control and motor braking energy recovery control mode are analyzed.After simulation analysis,the accuracy of the designed vehicle simulation model and the effectiveness of the designed rule-based energy management strategy are verified.Then,with the goal of reducing vehicle fuel consumption,an optimized energy management strategy based on equivalent fuel consumption minimization strategy(ECMS)is designed.Based on the basic principle of ECMS,the objective function of ECMS is established,and the range of equivalent factor and penalty function are analyzed and determined.Through the comprehensive analysis of the influence and characteristics of each key parameter on ECMS,the multi-objective optimization is carried out based on mode FRONTIER software,and the optimal parameters of ECMS under different cycle conditions are obtained.In order to improve the adaptive ability of ECMS under different conditions,an adaptive equivalent fuel consumption minimization strategy(A-ECMS)based on fuzzy PI control is established.The simulation results show that the A-ECMS based on fuzzy PI control can adjust the equivalent factor in real time,and has better adaptability to working conditions and better fuel consumption performance than ECMS.Finally,under different cycle conditions,the simulation results of different energy management strategies designed in this paper are compared and the system energy utilization rate is analyzed.The results show that the average fuel economy of A-ECMS strategy based on Fuzzy PI control under various working conditions is 7.70% higher than the average fuel economy of rule-based energy management strategy,3.90% higher than that of ECMS strategy fuel economy.The working point of the engine works near the high efficiency area as much as possible,and the working point of the motor moves to the high efficiency area,which achieves the goal of pre design and optimization.Through the comparative analysis of the calculation results of the energy utilization efficiency of the hybrid system,the results show that under the same conditions and the same SOC initial value conditions,the system energy utilization rate of A-ECMS strategy based on Fuzzy PI control is higher than that of rule-based and ECMS energy management strategy,and the maximum increase proportion reaches 5.43%.