Research On Energy Management For Hybrid Power System Of Lithium Battery And Ultra Capacitor

Electric vehicles have received great attention because of their advantages of energy saving and environmental protection.At present,lithium batteries are used in most electric vehicles as their main energy source.However,the use of lithium batteries alone may lead to overheating of the battery pack and shorten its life,an auxiliary energy is then equipped.With quick charge and discharge,high power density and long life,the ultra-capacitor can be combined with lithium batteries to form a hybrid system as a power source for an electric vehicle.In this paper,the following research is carried out on the energy management of hybrid systems:Firstly,this paper analyzes and summarizes the current development status and main research methods of energy management strategies at home and abroad.Focusing on the shortcomings in traditional energy management strategies,the main research contents of this paper are proposed.The research platform used in the experiment is introduced,the equivalent model of lithium battery and ultra-capacitor is established according to the working principle and characteristics of each energy storage unit,and the relationship between power and speed required for vehicle is derived.Secondly,in order to reduce the energy loss of the hybrid system,based on the rule-based energy management strategy,two energy management strategies are designed:composite energy management strategy based on rules and nonlinear predictive control,and composite energy management strategy based on rules and Q-learning reinforcement learning.In the two strategies,when the vehicle is in the driving state,the energy management of the hybrid power system is completed by the non-linear predictive control and Q-learning reinforcement learning respectively,while in other cases,the energy management of the hybrid power system is carried out according to the rules directly.Finally,ECE and UDDS driving cycles are selected for simulation and experiment on MATLAB simulation platform and electric vehicle experimental platform,respectively.Simulation and experimental results show that the proposed two strategies can achieve reasonable power distribution,reduce the energy loss of the system,reduce the use of lithium batteries,and extend the life of lithium batteries.At the same time,the composite energy management strategy based on rules and Q-learning reinforcement learning performs better in real-time energy management.