| With the increasingly prominent issues of environmental protection and energy security,hybrid electric vehicles have received extensive attention from consumers and researchers due to their remarkable fuel economy without mileage anxiety.In the current research on energy-saving control technology for HEVs,most of them only focus on the energy management of multiple power sources,and the optimization of the driving speed is not considered sufficiently.This thesis takes the charge-sustaining series hybrid electric vehicle as the research object,focusing on the hilly driving scene,the two levels of energy-saving driving and energy management are studied in turn based on the idea of sequential optimization,and a hierarchical control framework with high computational efficiency for online control is designed by using the proposed global speed and SoC trajectory planning method.Firstly,deriving from the characteristics of the propulsion structure of the series powertrain,aiming at the minimum total energy consumption of the DC bus,the global speed optimization problem is first solved by off-line dynamic programming,and the basic energy-saving mechanism has been summarized.In order to achieve fast calculation,the solution of the original global optimization problem is decomposed into two layers.The inner layer derives the analytical solution of the speed and control law of the local road section,and the outer layer constructs a dynamic programming framework with the road section as the basic discrete stage where the analytical solution of the road segment in the inner layer is exploited to obtain approximate global optimization solution.On this basis,combined with the ordered sample clustering of road section information,a fast optimization method is proposed.The simulation results show that the total demand energy consumption obtained by the proposed method can be reduced by up to 4.3% compared with the cruise condition,and is only2.3% different from the offline optimal solution.Secondly,the characteristics of the globally optimal SoC trajectory and the fuelsaving principle of the series HEV are analyzed by using the numerical simulation results of the Pontryagin’s minimum principle.The results show that the optimal SoC trajectory when driving on hilly roads is closely related to the spatial distribution of the demand power,and exhibits approximately piecewise linear characteristics.Based on the analyzed features and combined with the power split analytical rules derived by the PMP,a global SoC trajectory planning method with low computational cost is designed.The simulation results show that in the test scenario with speed planning and accurate slope information,the proposed method can obtain the approximate global optimal SoC trajectory.Finally,based on the above-mentioned global speed and SoC planning methods,a hierarchical control framework for speed and energy management is proposed.The upper planning layer calculates the long-term state trajectory,and the lower layer is the SoC tracking layer,which performs instantaneous power split while tracking the SoC reference trajectory.The numerical simulation results show that the speed planning effectively reduces the energy consumption of the propulsion system,and the SoC planning also directly improves the overall operation efficiency of the auxiliary power unit.In addition,due to the reduced peak power demand by speed planning,the operating duration of the auxiliary power unit in the inefficiency zone during power split is further reduced.A Model-in-the-Loop test platform is built,and the forward simulation of the hierarchical control framework is implemented.The test results show that compared with the online energy management strategies without speed and SoC reference trajectory,the proposed hierarchical control framework achieves 1.8% to37.1% fuel saving benefits under 10 sets of actual terrain tests,which verifies the effectiveness of the control framework. |
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