Research On Energy Management Strategy Of A Novel Hybrid Electric Powertrain Based On Flywheel Energy Storage

Energy conservation and carbon dioxide emissions reduction in transportation industry get more and more attention from many countries.As a transitional product for the complete electrification of vehicles,hybrid electric vehicle(HEV)combines the advantages of advanced internal combustion engine(ICE)and electric drive technology,and can effectively reduce energy consumption and emissions.However,most HEVs at present use battery as energy storage unit,which limits the performance of high power output and energy recovery,and frequent energy conversion also leads to a decrease in system efficiency.The energy storage flywheel has the advantages of high power density and high efficiency.Performance improvement can be achieved when the energy storage flywheel is applied in vehicles.However,there are still many deficiencies in the existing flywheel hybrid powertrain in terms of operating condition adjustment,system response,and energy efficiency.Therefore,in this paper,an electric flywheel energy storage system is combined with an ICE to form a novel hybrid electric powertrain based on flywheel energy storage,and the parameters matching,modeling and corresponding energy management strategy design are carried out around the powertrain,so as to achieve the goal of load leveling,power surge and efficient regenerative braking.The main research contents are as follows:(1)A novel hybrid electric powertrain based on flywheel energy storage is proposed.The dynamic characteristics of the powertrain are obtained by using the lever analogy method,and the output characteristics of operating modes are analyzed through the energy flow.The powertrain matching is completed according to the basic parameters of a commercial vehicle and the design index.Based on the working curves of the ICE,the division of vehicle operating modes are discussed,including electric driving mode,ICE-powered driving mode,hybrid driving mode and charging during driving mode.(2)According to the theoretical analysis results,a simulation model of the flywheel hybrid electric vehicle(FHEV)is built based on the AMESim.In order to improve the operating conditions of the ICE and adjust energy storage and release of the flywheel,a logic threshold control strategy is designed based on the Matlab/Simulink.A co-simulation model is established to compare the performance of FHEV and the prototype vehicle.The results show that the dynamic performance of FHEV is greatly improved.The operating points of the ICE are optimized,and the average thermal efficiency under CLTC-C condition is increased by 11.24%.The vehicle fuel economy is significantly improved,and the average fuel consumption in urban condition is reduced from 10.16 L/100 km to 6.07 L/100 km.The total braking energy recovery rate exceeds 54.88%,achieving the goal of efficient regenerative braking using the energy storage flywheel.(3)Fuzzy logic control is introduced to further optimize the system energy management strategy.A fuzzy controller that takes the ratio of vehicle torque demand to the maximum torque of ICE,battery state of charge and flywheel state of energy as inputs is designed,and the corresponding fuzzy rules are made to optimize the system torque distribution of the driving modes that the ICE participates in.The performance of fuzzy control and logic threshold control is simulated and compared.The results show that when the fuzzy control is adopted,the average efficiency of ICE and the average speed of energy storage flywheel are increased,and the electricity consumption is reduced.The equivalent fuel consumption of FHEV under CLTC-C and urban condition is reduced by 7.16% and 9.23% respectively on the basis of the logic threshold control.While the fuel economy is improved,the vehicle dynamic performance is not seriously affected,indicating that the fuzzy energy management strategy designed is effective and more applicable.