Energy Management Of Plug-in Hybrid Electric Vehicle Considering Optimization Of Equivalence Factor

In recent years,automobile as a resource consumption product has been paid much more attention due to natural resource consumption and people's increasing awareness of environment protection.In the automotive development process,energy-saving and emission reduction has always been one of the main themes throughout the development.It is still necessary to develop hybrid electric vehicles at current stage because of the limitations of technical bottlenecks.Optimization is an indispensable part of hybrid electric vehicles,which mainly includes topology optimization,component size optimization and energy management strategy optimization.The energy management generally consists of rule-based control strategy based on human experience and the control strategy based on optimal control theory.In this paper,energy management strategies are researched based on the topology of a parallel plug-in hybrid electric vehicle,the main contents are as follows:1.Optimal control and analysis of equivalent consumption minimization strategy.From optimal control aspect,performance index function,optimal control problem constraints and its solution theories are discussed.The performance index functions often used in vehicles are illustrated and the existence of optimal solutions is simply analyzed;Three kinds of solving theories of optimal control problem and their relations and drawbacks are summarized,the details and numerical methods in the practical solving process are also concluded.In terms of equivalent consumption minimization strategy,its theoretical foundation is expounded in the form of formula derivation from the two aspects of Pontryagin's minimum principle and the physical background of equivalent consumption minimization strategy;The research status of this strategy in recent years is summarized.2.Using dynamic programming to solve the equivalence factor.The mathematical models of engine,motor,battery,vehicle and other components are established;Under a given driving cycle,the equivalence factor and gear are taken as the control variables,the state of charge as state variable and the minimization of fuel consumption as the performance index function of the optimal control problem,and dynamic programing is used to solve this problem.In the solving process,the measures to reduce the computation efforts are expounded which include the array definition,the comparison of interpolation method and the circulation way of loop body;The boundaries of state variable are obtained to reduce the numerical error caused by dynamic programing;According to the results,the optimal control solutions are traversed under a given driving cycle when the different initial value of state variable is given,the initial MAP of equivalence factor concerning the battery state of charge and power demand is obtained under NEDC,UDDS,10-15 respectively,and the initial MAPs of the three driving cycles are fused to obtain the final one for the simulation analysis.3.Vehicle model establishment and simulation analyses.The model is established through AMESim and Matlab/Simulnk software and rule-based control strategy is formulated;The comparison between the rule-based control strategy and equivalent consumption minimization strategy based on dynamic programing is made,the results show that the fuel economy of the latter is better than the former although both of them are worse than the global optimal results,however,it is possible to apply the MAP of equivalence factor concerning the SOC and power demand in practice which overcomes the drawbacks of dynamic programming;The simulation analyses are also made under US06,HWFET,JC08 driving cycles and the results show that equivalent consumption minimization strategy based on dynamic programing is better than the rule-based control strategy.4.Summarize the full text and analyze the inadequacies of the proposed strategy.