Research On The Velocity Trajectory Planning Of The Autonomous-rail Rapid Tram

With the rapid development of the urban public transportation system,traffic system intelligentization is gradually coming into the limelight.The Autonomous-Rail Rapid Tram(ART)innovatively integrates the advantages of rail transit and buses,which provides the possibility of constructing a diversified,three-dimensional and modernized urban public transportation systems.The research on the velocity trajectory planning of the ART in the urban open road environment can alleviate traffic congestion,reduce energy consumption and further meet people’s demand for efficient,comfortable and environmentally friendly operation,which is one of the important research directions of the ART’s intelligent driving technology.The ART’s velocity trajectory planning is studied based on dynamic planning and pseudospectral method,and the relevant simulations are designed to verify the feasibility and effectiveness.The main contents and contributions of this paper are as follows.Firstly,the longitudinal multi-particle dynamics model of the ART is developed by analyzing the longitudinal force of each carriage during operation and considering the gradient resistance,the rolling resistance and other factors.Besides,the efficiency MAP of the motor and the ART’s energy consumption in driving are formulated.Based on the performance indexes of ART’s driving safety,punctuality and economy,the multi-objective optimal control problem is constructed considering terrain and traffic lights.And the optimal velocity trajectory planning strategy based on dynamic programming algorithm is proposed to guarantee the punctuality of operation and minimize energy consumption.In addition,the influence of the weight coefficient in the objective function of the optimal control problem on the driving energy consumption and time is discussed and analyzed.In order to solve the velocity trajectory replanning problem under emergency situations such as sudden obstacles and signal indicator changes during the ART’s operation,the real-time velocity trajectory planning strategy based on pseudospectral method is studied.The multi-interval nonlinear optimal control problem is transformed into a nonlinear planning problem by considering the operation constraints of punctual operation,road conditions and dynamics model.Moreover,the optimal number of Legendre-Gauss-Lobatto(LGL)points is given by discussing the mechanism of the points number on the accuracy and time of the pseudospectral method.The simulation comparison verifies that the pseudospectral method has certain energy-saving effect while ensuring the on-time arrival of the ART,and the high real-time performance can be used for real-time online planning.Finally,a joint Truck Sim/Pre Scan/Simulink simulation platform is built to experimentally verify the feasibility and effectiveness of the proposed velocity trajectory planning method.The simulation results show that the strategy based on dynamic programming can obtain the global optimal velocity trajectory under the condition of meeting the punctuality,which has the best energy-saving effect.When an unexpected obstacle occurs during operation,continuing to track the velocity trajectory solved by dynamic programming cannot guarantee that the ART arrives at the station on time,while the strategy based on pseudospectral method can complete the velocity trajectory planning for the remaining section in a relatively short time,which not only ensures the punctuality of the ART’s operation but also offers better economy.