Research On Hybrid Electric Vehicle Energy Management Based On Multi-Objective Optimization

Hybrid vehicles,as the best alternative to pure fuel vehicles at present,take into account the advantages of pure electric vehicles in terms of emission and pure fuel vehicles in terms of driving mileage.Since hybrid vehicles are equipped with two power sources,an engine and an electric motor,it is necessary to consider the reasonable distribution of energy when formulating vehicle control strategies for engineers.As an energy management strategy of hybrid vehicles with real-time optimization capability,the equivalent fuel consumption minimum strategy can effectively improve the shortcomings of frequent engine start-stops in hybrid system under the control of rule-based energy management strategy,and reduce the overall fuel consumption of hybrid system.Meanwhile,the use of multi-objective optimization algorithms to optimize the energy management strategy can further optimize the control effect.Furthermore,the combination of engine’s clean combustion technology and hybrid power system is also an effective means of energy saving and emission reduction.This paper provides a comparative analysis of hybrid energy management strategies to demonstrate the advantages of the equivalent fuel consumption minimum strategy over the regular power following control strategy from the perspective of fuel consumption and emissions,and optimize it.Furthermore,the engine hydrogen blending technology is combined with the hybrid power system,and the effect of using hydrogen energy on the energy saving and emission reduction of the hybrid power system is explored.The main work content and conclusions are as follows:(1)Model the hybrid vehicle,including the controlled vehicle model and the control strategy model.On the basis of this model,Simulink and AMESim co-simulation are employed to compare the equivalent fuel consumption minimum strategy and the power following control strategy.Results show that the minimum equivalent fuel consumption strategy under the WLTC and NEDC test cycles can reduce fuel consumption and HC emissions compared to the power follow control strategy;however,CO and NOx emissions increase.The cumulative length of acceleration and deceleration conditions is an important factor that affects the fuel economy and emissions of the hybrid power system.The engine response delay under transient conditions is not conducive to the improvement of performance by optimizing control strategies.Under WLTC cycle conditions,this phenomenon is particularly obvious.(2)Multi-objective optimization of the equivalent fuel consumption minimum strategy,comprehensively considering fuel consumption and CO,HC and NOx emissions.By adopting the NSGA-II multi-objective optimization algorithm,the calculation method of the equivalent factor of the original strategy is improved to make the energy distribution more reasonable.Under the WLTC cycle,the multi-objective optimized control strategy can reduce the fuel consumption of the hybrid power system and the emissions of three kinds of gaseous pollutants.The effect of multi-objective optimization depends on the choices of design variables,and conflicts between design variables may even cause the optimization algorithm to produce negative optimization effects.(3)Optimization in strategy makes the engine’s operating points gradually concentrate in the high-efficiency area,which results in the engine’s frequent medium-to-high load working state.Under this circumstance,the engine has low HC emissions,high CO and NOx emissions,and better fuel economy.Engine’s centralized working points resulted from multi-objective optimization algorithm enhance the auxiliary function of the motor and increase the running time and the discharge depth of the power battery.(4)The hybrid power system model is improved,and the pure fuel engine model is changed to a hydrogen-mixed engine model to explore the application potential of hydrogen energy in the hybrid power system.Results of bench experiments show that hydrogen improves the combustion efficiency of the engine,and choosing a proper hydrogen mixing ratio can improve fuel economy and reduce emissions.The simulation results in the improved hybrid power system show that the modified hybrid power system can reduce fuel consumption,HC emissions and CO emissions,however hydrogen-blended combustion increases the temperature of the mixture in the cylinder and also NOx emissions.