Research On Power Unit Control Strategy Of Electric Drive Vehicle

With the aggravation of global environmental pollution and energy crisis,the replacement of traditional vehicles by new energy vehicles has become an inevitable trend.Series hybrid electric vehicle has the advantages of simple system structure,high working efficiency and strong power expansion ability.It develops rapidly in recent years and has become a research hotspot in the automotive industry.Intelligent power unit is one of the core components of series hybrid electric vehicle.It provides enenrgy for the vehicle when the vehicle is running.In this paper,its control strategy and fuel economy will be deeply studied.Firstly,based on the power following energy management strategy of the whole vehicle,the power unit control scheme of engine speed control and generator torque control is determined,and the hierarchical speed control strategy and the hierarchical fault treatment strategy are formulated.Then,the woking characteristics of the engine,generator and its controller are analyzed,and their mathematicle models are established with the actual selected model parameters as input.Finally,the control strategy and mathematicle model are combined to build a aomplete control-oriented power unit system model.The simulation results show that the designed control strategy can make the power generation of the power unit follow the change of the target power well,and also verify the effectiveness of the established mathematical model.On the basis of the above work,the coupling parameters affecting the system efficiency were determined by analyzing the coupling relationship between the engine and generator efficiency,aiming to inprove the fuel economy and efficiency of the power unit.Combined with the universal characteristic curve of the engine and the efficiency curve of the generator,particle swarm optimization algorithm was used to optimize the parameters,and the optimal energy efficiency curve of the power unit system was obtained.Then,the fuzzy control algorithm is used to extend the curve into the interval,and a general method for designing the optimal enenrgy efficiency working interval of the power unit is formed.Finally,the simulation results show that the power unit has better fuel economy when working in the designed optimal energy efficiency range.When the power unit of the series hybrid vehicle is overloaded suddenly,the engine torque load rate would be too high,which would lead to abnormally operation.In order to solve this problem,the load compensation fuzzy controller is designed on the basis of the original control strategy.The input of the controller is the engine torque laod rate,the target and the actual torque of the torque difference.The output of the controller is the generator torque adjustment.By controlling the torque of generator,the engine torque load rate could be regulated,so that avoiding the engine working near the critical condition.The simulation results show that the strategy improves the working characteristics of the power unit effectively,improves the robustness of the power unit.Finally,the design method of the optimal energy efficiency interval and the laod compensation strategy were verified by building the power unit test bench and writing the control program.The experimental results show that the fuel economy of the power following strategy based on the optimal energy efficiency interval is better than that of the traditional power following strategy,The system with load compensation control strategy has better dynamic characteristics under sudden laoding than the system without this strategy,and the rotational speed torque an quickly and stably follow the power change.