Design Of Regenerative Braking Control System For Distributed Drive Electric Bus

In the face of today’s increasingly serious energy problems,the development of electric vehicles has become a new trend in countries all over the world.Electric vehicles running on clean energy driven by motors can also be used for energy recovery,which is an outstanding advantage in terms of energy saving.Among the electric vehicles,distributed-drive in-wheel motor electric vehicles are gradually accepted by manufacturers because of their rapid response,precise control and efficient transmission,and distributed-drive electric buses driven by in-wheel motors are beginning to appear on the market.In this paper,a braking energy recovery strategy that takes account of yaw stability and roll stability is designed using a tandem braking approach with a four-wheel independent drive in-wheel motor electric vehicle as the research object.The front and rear axle braking torque is distributed according to the I-curve during braking,which ensures stability under linear braking.In the tandem braking mode,the use of motor braking as much as possible under the premise of safety can improve the braking energy recovery efficiency.In this paper,the allowable output torque of the motor is obtained by taking the battery SOC value,motor external characteristic curve,battery power,vehicle speed and braking intensity as conditions,and comparing it with the distributed front and rear axle torque to obtain the motor braking torque and hydraulic braking torque,while an electro-hydraulic switching smoothing strategy is designed to ensure the comfort of braking.Based on the linear two-degree-of-freedom model and the linear quadratic programming(LQR)algorithm,the vehicle yaw stability controller is designed with the error between the reference and actual values of the yaw rate and the side slip angle as the input and the additional yaw moment as the output,which is distributed equally to the four wheels to achieve yaw stability control.The vehicle roll stability controller is designed based on a linear three-degree-of-freedom model and the Model Predictive Control(MPC)algorithm.The input is the roll angle and the roll rate,and the additional yaw moment determined is applied to the vehicle by means of an external front wheel brake.The vehicle vertical load is estimated and the conventional LTR roll judgement is improved.The estimated vertical load is used for calculating the LTRs,and the LTRs are used as a condition for switching the yaw stability and roll stability,and a coordinated control strategy for the yaw and roll stability is designed.The whole control strategy is implemented in MATLAB/Simulink.The control strategy is verified by a joint simulation platform established by MATLAB/Simulink and Trucksim.Six operating conditions are designed to verify the distribution of electro-hydraulic braking torque,the braking torque smoothing strategy,the yaw stability control strategy,the roll stability control strategy,the coordination control strategy and the energy recovery effect in the braking strategy.The simulation results show that the distribution of electro-hydraulic braking torque at low,medium and high braking intensities is in accordance with the control strategy,the torque smoothing strategy can greatly reduce the torque fluctuation during electro-hydraulic braking force switching,and the yaw stability control strategy can ensure that the yaw rate follows the target value well and the side slip angle is stable within a certain range.The roll stability control strategy and the coordinated control strategy can help prevent the vehicle from rolling over to a certain extent.The energy recovery effect is obvious under NEDC operating conditions.Based on the simulation tests,a hardware-in-the-loop simulation platform was built using the NI real-time cabinet,the CAN communication board and the real vehicle controller,the control strategy was burned into the vehicle controller,the Trucksim vehicle model,the driver model and the battery model were downloaded into the real time cabinet,data transfer was carried out through CAN communication,and the control strategy was tested for HIL.The differences between the HIL test verification results and the simulation results are within acceptable limits and have good consistency.