A Human-Machine Co-Driven Creep Control for an Electric Bus

Creep control is used for the starting control of an electric vehicle. For an electric bus, the mass load varies widely, and the road friction information is hard to measure or estimate when the bus is static. In this study, a finite state machine is proposed to determine the control categories, normal mode, steep mode, transition mode, and stop mode. In the normal mode, a proportional based motor torque control and a brake torque control operated by the driver are combined as the total wheel torque, and a human-machine co-driven control is realized. An anti-slip control is added after the co-driven control. In steep mode, a slope sensor is used to measure the gradient to change the control parameters to achieve starting control on a steeper slope. The transition mode is set to take into account that the allowable time of motor maximum torque may be used up. By the proposed co-driven control, the vehicle can start on low friction roads and slopes without wheels slipping or vehicle moving back, and the driver can control the creep speed by the brake pedal only. Finally, some simulations and experiments are conducted to verify the effectiveness of the control strategy.