Energy Management Strategy And Component Sizing Of Vehicle HESS Base On Pseudospectral Method

As an effective way to alleviate environmental pollution and energy security,automotive electrification is gradually being promoted globally.As the core part of electric vehicles,the characteristics of energy storage systems will affect the power and economy of the vehicle.The increment of electric vehicles with lithium-ion batteries has reduced the environmental pollution to a certain extent.However,the current cruising range of electric vehicles and the durability of batteries have yet to be improved,and the the replacement cost of battery is also very high.Therefore,how to solve the problem of the life and cost of electric vehicle energy storage system has become a research hotspot in the academia and industry.Ultracapacitor have the advantages of high power density,long service life,and large charge and discharge currents,which can make up for the shortage of lithium batteries.Combining ultracapacitor with battery to form a hybrid energy storage system(HESS)is a good solution to the above problems of electric vehicles.The research is conducted on a passenger car.The battery life,system energy consumption and component cost are selected as the goal.The researches on the topology of HESS,characteristics and models of the components,energy management strategy and component sizing optimization of HESS have been conducted.On the basis of the characteristic analysis of different HESS configurations,the appropriate topology is selected considering the characteristics of the objective vehicle.And the characteristics of key components are analyzed.The capacity,internal resistance and polarization characteristics of the lithium-ion battery are tested and analyzed.The relationship between open circuit voltage(OCV)and battery state of charge(BSOC)is measured.The capacity,internal resistance and charge-discharge characteristics of the ultracapacitor are analyzed.Finally,the efficiency characteristics of the bidirectional DC/DC converter are analyzed.Based on the vehicle parameters and motor parameters,the normalized motor efficiency model is established.The battery equivalent Thevenin model with charge and discharge internal resistance characteristics,the ultracapacitor RC model,and the system power balance model are established.The above establishment of models and the preliminary component sizing laid the foundation for the energy management strategy and component sizing optimization.An energy management strategy optimization method based on Radau pseudospectral method is proposed.The battery life model with penalty factor as the objective function.The battery life in the HESS electric vehicle is compared with the single battery energy source under the NEDC cycle condition.The feasibility of the Radau pseudospectral method for solving the single-object energy management strategy of HESS is verified.Considering that the battery life and system energy consumption in the HESS often conflict with each other,the energy management strategy optimization has been transformed into a multi-objective optimization problem.Objective function including battery life and system energy consumption are constructed,and the Radau pseudospectral method is used to solve the problem.In the Pareto solution set,base on the respective battery life and system energy,the solutions of the longest battery life,the lowest system energy consumption and the balance optimal solution between them are analyzed and discussed.By comparing the balance optimal solution and the calculation result of single battery energy source,the conclusions can be drawn that the energy management strategy of the HESS optimized by Radau pseudospectral method extend the service life of the battery while reducing the system energ y consumption.The energy management strategy and component sizing optimization for HESS has a high coupling relation.Thus,on the basis of the aforementioned multi-objective energy management strategy optimization method,a component sizing optimization method is provided.The parallel numbers of battery and ultracapacitor are selected as the optimization variables,and the system energy consumption,battery life and component cost are selected as objective functions.Moreover,the influence of mass change of battery and ultracapacitor is also taken into account.The conclusions can be drawn in the multi-objective optimization results that with the increment of component cost,the battery life and system energy consumption also increase.Also,the designer according to different emphasis of the objective functions,the optimal total cost can be obtained under corresponding weight coefficients.