Research On Optimal Design Of Rule-based Control Strategy For PHEV From Dynamic Programming

The engine's frequent start/stop of the Plug-in hybrid vehicle dropped the temperature of emission exhaust and Selective Catalyst Reduction(SCR)in urban driving cycle.As a result,the SCR's efficiency was lowered and the vehicle's emission performance was decreased.Therefore,the whole vehicle control strategy should not only complete the power flow distribution and coordinate the parts of the power system,but also ensure the optimal control of the engine working point under the condition of satisfying the expected power output.And the whole vehicle control strategy should speed up the ignition of SCR catalytic converters,and make the overall fuel consumption and emission performance of hybrid power system to reach the optimum.The paper took the Plug-in diesel hybrid electric vehicle as the object of study.And focuses on the key issue of “a rule-based control strategy that can improve the fuel economy and emission performance of the entire vehicle from the optimization results of the dynamic programming algorithm”.The main work can be organized as follows.(1)The dynamic model of the vehicle components had been built on the Matlab/simulink platform on the basis of the known experimental data.The dynamic model of the whole vehicle including engine model,post-processing system model and ISG motor model,battery pack model,transmission system model and driver model had been established by combining theoretical modeling with experimental modeling.(2)The fuel consumption and emission-weighted minimum in the specific cycle conditions as the optimal control objective of hybrid vehicle had been proposed by means of dynamic programming algorithm.The multi-objective global optimization problem of fuel consumption and post-processing emissions for plug-in hybrid vehicles had been established,and the optimal values of optimal control variables and multi-objective functions had been obtained.By adjusting the weight coefficient in the objective function,we could obtain the optimal trade-off relationship between vehicle fuel economy and emissions.(3)According to the results of optimization calculation of dynamic programming algorithm,the control law of mode switching and energy distribution of power assembly had been summarized by means of statistical analysis and linear fitting method,and an improved CD-CS strategy based on DP optimization results had been formulated.The simulation results show that the improved CD-CS rule control strategy is 4.95% lower than the traditional CD-CS strategy,8.62% lower than the traditional CD-CS strategy in NOx and 6.06% lower than the traditional CD-CS strategy in PM.This also verifies that the control rules extracted based on DP can be used to optimize the rule strategy based on logic threshold.(4)The automatic code generation of rule control strategy had been realized on MATLAB/Simulink platform with TargetLink tool,and the transformation from model to product level C code had been completed.In addition,the hardware in loop simulation had been carried out,and the code had been downloaded to the object controller to test the experiment.The experimental results show that the code generated automatically by TargetLink tool can ensure the accuracy and reliability of the target controller to the Plugin hybrid transmission system,and its code size and execution efficiency are within the acceptable range.