Abstract: When the high-speed electric multiple units（EMUs）pass through the long downslope route，speed

limit is required to meet the safety of train operation，the regenerative braking energy generated in this process is

returned to the traction network and may threaten the safety of power supply. At present，there are few studies on

regenerative braking energy by accurate vehicle-grid integrated models. Therefore，taking CRH3-type EMUs as an

example，an detailed analysis method was proposed. Firstly，based on the detailed equivalent circuit of vehicle-grid system，a model was established，and through the speed limitation analysis and force analysis of EMUs，the

regenerative braking power of EMUs for passing long downslope routes was calculated. Then，by fitting the

function between braking power and rotor speed，the instruction parameters of the model were solved，the rectifier voltage and catenary voltage of EMUs under different line conditions were simulated to estimate the safety of power supply. By comparing the simulation results and the experimental testing results at Chinese Cheng-Yu railway line，the correctness of the modeling method was verified，and it is more practical than the existing research. This study can provide reference for the design of mountain railways.

      Key words: regeneration braking process；traction power supply system；high-speed railway；long downslope

route；vehicle-grid model simulation