Study On Control Strategy And Parameter Optimization Of Power-Split Dual-Mode Hybrid Electric Bus

As a major part of the mass transit,the energy saving and environmental protection of city bus have become the focus of new energy vehicle technology research and development.Power-split hybrid electric system which has a huge potential for energy saving and emission reduction is the most meaningful way to solve the problems.According to the different power flow types,power-split system can be divided into input-split,output-split and compound-split three different modes.And generally,systems with only one power-split mode are called single-mode systems,such as Toyota's THS(Toyota Hybrid System)configuration.Similarly,systems with two power-split modes are called dual-mode systems which are usually made of input-split mode and compound-split mode.Compared with single-mode system,dual-mode system has better fuel economy and power performace.Therefore,power-split dual-mode system is suitable for city bus which has high-power demand and environmental requirement.The current dissertation aims to explore a power-split dual-mode system applied in city bus.The parametric design method,parametric optimization and energy saving potential of the hybrid city bus are researched.First,dynamic relationships and efficiency characteristic of the dual-mode system are studied and analyzed.Then energy management strategy,the transmission efficiency,mode switching condition and power requirements are all taken into consideration to complete the parameter design of the dual-mode hybrid system.In order to verify the rationality of design parameters,the co-simulation of Matlab/Simulink and Cruise is performed.Third,due to the close relationship between the characteristic parameters of planetary systems and the power performance and fuel economy of the vehicle,these parameters are optimized in order to improve fuel economy under the premise of ensuring the power.Based on the i SIGHT software,the vehicle model built by Cruise and the control stategy model built by Matlab/Simulink are integrated into i SIGHT operation environment.The Multi-Island GA algorithm provided by i SIGHT software is used to optimize parameters,with the balance of electricity as the constraint condition and the minimum equivalent fuel consumption as the optimization target.The results show that parameters optimization improves the fuel economy of the vehicle.The last but not least,in order to further study the energy-saving potential of dual-mode system,the dynamic programming algorithm(DP)is applied.Then,taking the typical city driving cycle in China as the target cycle condition,the DP algorithm is used to find the optimal solution.According to the optimization results,the control rules of the engine in the power-split mode are extracted and applied in the control stategy of vehicle.The presented control rules are validated through the co-simulation of Matlab/Simulink and Cruise software.Simulation results show that the optimization of control strategy base on DP futher improves the fuel-saving rate.In conclusion,the presented parametric design method,parametric optimization method and control strategy optimization based on DP would contribute to the design theory and optimization method for the application of the power-split dual-mode system in the field of city bus.