Optimal Control Of Dual Planetary Gear Hybrid Electric Vehicle Based On Optimal Transmission Efficiency

Hybrid electric vehicle(HEV)can improve vehicle fuel economy,and has the advantages of dynamic performance and driving range,which has been the research hotspot in the field of new energy vehicle.In particular,the hybrid electric vehicle with d ual planetary gear dynamic coupling mechanism not o nly can realize the complete decoupling of torque and speed between engine and wheels,but also has the better high-efficiency transmission range compared with the single planetary arrangement structure.However,dual-planetary hybrid electric vehicle may generate power circulation during operation and reduce the transmission efficiency of the system,which is not conducive to the performance of the fuel economy.For this problem,a dual planetary gear hybrid electric vehicle is introduced in this paper.By revealing the working characteristics of the d ual planetary dynamic coupling mechanism,an energy management strategy of dual-planetary gear hybrid electric vehicle based on optimal transmission efficiency is proposed.O n this basis,the optimization method of engine output torque is studied to optimize the operation point of the engine and improve the fuel economy of the vehicle.Firstly,the relationship between speed and torque of different power split type hybrid system is systematically established based on the lever theory,and the influence of the vehicle transmission ratio on the transmission efficiency of the hybrid system is revealed based on electric power balance theory.The power circulation mechanism of the dual planetary dynamic coupling mechanism is revealed through in-depth analysis of the relationship between the speed and torque of the engine and the two motors,which provides a theoretical basis for the optimization of the energy management strategy.Secondly,the energy management strate gy of the dual-planetary hybrid electric vehicle is studied,the mechanical point(MP)control strategy based on the optimal transmission efficiency of the hybrid system is proposed,and the optimal engine speed under the hybrid driving mode is determined.The whole vehicle model and the control strategy model are built based on AVL/Cruise and Matlab/Simulink platform,respectively.The results of the combined simulation show that the mechanical point strategy can avoid the power circulation effectively and reduce the power output of the motors,improve the system transmission efficiency and increase the equivalent fuel economy by 3.46% compared with the engine optimal operating line(OOL)control strategy.Then,to solve the problem that the distribution of engine working points is relatively dispersed and the part of points are distributed in the low efficiency range under the mechanical point control strategy,the engine torque optimization strategy is designed based on fuzzy control algorithm,the input and output variables are defined,and membership function,fuzzy domain and fuzzy rules are also designed in the paper.The simulation results show that the engine torque optimization strategy based on fuzzy algorithm can reduce the fuel consumption by 6.92% compared to the previous optimization.Finally,the power consumption of the motor is equivalent to the fuel consumption,and the goal is to minimize the equivalent fuel consumption of the whole vehicle.The fuzzy membership function and fuzzy rules are optimized by particle swarm optimization(PSO)to reduce the influence of expert experience and knowledge on energy optimal distribution of dual planetary gear hybrid electric vehicle.The simulation results show that the energy management strategy optimized by particle swarm optimization algorithm can optimize the working points of engine and two motors,the final value of the battery SOC is kept within a reasonable interval,and the equivalent fuel consumption of t he whole vehicle is reduced by 3.59% compared compared with that without PSO algorithm.