Research On Energy Management Strategy And Mode Transition Control For A Series-parallel Hybrid Electric Bus

Energy management strategy and coordinated control during drive mode transition fora series-parallel hybrid electric bus are key technologies to improve energy conversionefficiency and drivability of the hybrid bus. Therefore, research on energy distributionbetween multiple power sources and efficiency optimization under a given drive cycle, aswell as coordinated control of the hybrid powertrain during the dynamic process of modetransition for the series-parallel hybrid electric bus are of important significance inachieving efficient and smooth operation of the hybrid bus.For the series-parallel hybrid electric bus with predetermined powertrainconfiguration and components, research including vehicle dynamic modeling, drivabilityanalysis during the transition from pure electric mode to parallel mode, vehicle controlsystem design, hardware-in-the-loop (HIL) simulation experiment, and road test in thefield of energy management strategy and coordinated control for powertrain areaccomplished in this dissertation, for the purpose of improving the fuel economy anddrivability for the hybrid bus.Considering the requirements on the validation of the effectiveness for the proposedcontrol strategy and the analysis of drivability during mode transition, a dynamic model ofthe hybrid bus is built in Matlab/Simulink based on the powertrain configuration andenergy flow direction of the hybrid bus. The vehicle dynamic model is built usingtheoretical modeling approach combined with empirical modeling approach, and canadequately reflect the dynamic performance of the diesel engine and the electronicallycontrolled clutch. Thus, the dynamic response characteristics of the hybrid powertrain forthe set-points by the hybrid control unit (HCU) can be accurately described.For the energy distribution between multiple power sources and efficiencyoptimization of the hybrid bus, a real-time suboptimal energy management strategy isdeveloped based on iterative dynamic programming (IDP) approach and Elman neuralnetwork (NN). Public transportation systems always follow fixed and well-known routes,thus the drive conditions of the hybrid bus can be assumed to be known a prior. In the energy management strategy, the optimal control law is obtained via the IDP approach bydefining a cost function over a given drive cycle to minimize fuel consumption. Then, theoptimal control law by the IDP approach is converted from a time-varying sequence to astate-varying sequence by constructing an Elman NN. Thus, the optimal control law by theIDP approach can be used for real-time control of the hybrid bus. Finally, a HIL simulationtest bench for the HCU of the hybrid bus is constructed based on ETAS PT-LABCAR, andthe proposed real-time suboptimal energy management strategy is investigated using theHIL simulation test bench. The HIL simulation results validate the implementation of thereal-time control and demonstrate significant improvements in fuel economy with theproposed energy management strategy for the hybrid bus. The proposed control algorithmcan not only improve calculation efficiency for energy management strategy optimization,but also offer a new method to optimize energy management strategy.For the coordinated control of the hybrid powertrain during the dynamic process ofmode transition for the hybrid bus, the coordinated control algorithm using adaptive fuzzysliding mode approach is proposed, and a coordinated control strategy for the transitionfrom pure electric mode to parallel mode is developed with the aim of reducing the torquefluctuations in the powertrain and the longitudinal jerks of the vehicle, while satisfying thedriver’s torque request during the mode transition. First, the drivability of the hybrid busduring the transition from pure electric mode to parallel mode is analyzed. On this basis,the coordinated control principle and coordinated control system for the mode transition ofthe hybrid bus are proposed. Then, the coordinated control strategy is developed usingadaptive fuzzy sliding mode approach according to the operating status of the clutch, andthe engine throttle is restricted during the transition process. In the control strategy, theLyapunov’s direct method is utilized to obtain the adaptive law and to prove the stability ofthe designed control system. For the proposed coordinated control algorithm, theuncertainties by varying parameters and the deviation between the actual and target enginetorques are included in a unified interference item, thus the proposed coordinated controlsystem can avoid system parameter onboard identification while ensuring control accuracy.Furthermore, the interference is estimated by the adaptive fuzzy system to regulate thecontrol variables of the fixed-boundary-layer sliding mode controller, thus the proposedcoordinated control system can reduce tracking error while eliminating chatting effect.Simulation results show that the proposed coordinated control strategy for the hybrid buscan achieve a smooth transition from pure electric mode to parallel mode, and the operating conditions of the clutch can also be significantly improved.For the road test of the hybrid bus, a CAN bus-based onboard test system is developed.Pure electric mode to parallel mode transition experiment of the hybrid bus under a givendrive cycle is implemented by road test to validate the effectiveness of the proposedcoordinated control strategy. The results show that the torque fluctuations in the powertrainand the longitudinal jerks of the vehicle during the mode transition can be significantlyreduced, and a smooth transition can be achieved. Thus, the drivability of the hybrid buscan be improved.