Research On Nonlinear Dynamics And Energy Mangement Strategy Of The Power-Split Hybrid System

Plug-in Hybrid Electric Vehicles(PHEV)take advantages of both traditional vehicles and Battery Electric Vehicles(BEV);nevertheless,to achieve the efficiency superiority,the coupling and transmission process of powers and the Energy Management Strategy(EMS)must be of high efficacy.Selectable One Way Clutches(SOWC)can be used to simplify transmission system and increase transmission efficiency;however,they also form complex coupled dynamic relationships with the gears,which show high influences on the transmission qualities.Besides,traditional EMS cannot fully develop the efficiency advantages of PHEV because of lacking global information.This paper takes power-split PHEV as the research object,and aims to increase its comprehensive energy conversion efficiency.Based on the researches on nonlinear dynamic characteristics of the coupled system of SOWC and power-split Planetary Gear Train(PGT),and parameter design influences of SOWC,an EMS involving traffic information and probabilities is proposed,considering the development trend of intelligence and network.The researches have important theoretical and practical meanings for guiding the applications of SOWC,improving transmission efficiency,EMS and the comprehensive energy conversion efficiency of PHEV.Different from most researches that have one element of the single stage PGT fixed with the rack to form a single degree of freedom(DOF)system,the power-split PGT in hybrid electric vehicles is a single stage PGT with two DOFs that the sun gear,the carrier and the ring gear of the PGT are all float.To study the nonlinear dynamic characteristics of the coupled system with inputs of SOWC,the nonlinear model of the power-split PGT is derived considering clearance,time-varying mesh stiffness and synthetic transmission error of the PGT.The coupled model of SOWC and PGT is established and the dimensionless model is also constructed thereafter to increase solving precision and make the system comparable.The researches lay the foundation of latter researches.To study the nonlinear dynamic characteristics of the coupled system,bifurcation structures and the roads to chaos such as period-doubling bifurcations,quasi-periodic bifurcations,paroxysmal bifurcations et al are studied,with bifurcation diagrams,phase trajectory,Poincaré map,and vibration characteristics,considering the working model of both fixed-axle transmission and power-split transmission.The nonlinear dynamic influences of inertia moment of the carrier,quantity of the small planetary gear and working modes of SOWCs are investigated.The researches find that if input stimulations are ignored,a floating carrier or a carrier with less inertia moment renders a wider stable solution region.Besides,properly configured SOWC contribute to decrease jump and bifurcation,and make the solution stable under low excitation frequency before the chaos range.To improve the iterative applications of SOWC and guide the optimal parameter configuration of each of the three SOWC,further studies of nonlinear dynamics on parameters' changing trends of SOWC are proposed.The researches find that unstable solution occurred to the coupled system on lower frequency range,if the equivalent radius and stiffness of the SOWC are increased.The increase of damping ratio of the SOWC renders higher maximum dynamic loads of the SOWC;however,increasing the damping ratio of the SOWC connected to the sun gear can greatly decrease vibrations and maximum dynamic loads of the PGT on the entire working range.Considering the studies of nonlinear characteristics of the coupled system and the development trend of intelligence and network,a pure strategy model with uncertainty of traffic situations based on Dynamic Programming(DP)algorithm is proposed.By combing with best response in game theory and taking multiple future traffic situations and accordingly possibilities into account,the strategy contributes to better distributions of the electric energy.To improve classical DP algorithm,a modified DP algorithm that dynamically construct solution region and replace finding procedure with solving procedure is proposed.By establishing mapping relationship with State Of Charge(SOC)and the index of SOC,the modified DP algorithm improves state transfer algorithm and storage structure,and realizes more than 75% improvement of computational efficiency.