New Concepts for Drag Torque Control in the Power Electronic Control Unit 2014-01-1910
The domains of powertrain and brake systems are continuously merging due to the integration of electric drives and their ability to generate high acceleration and recuperative torque. However, high recuperative torque might lead to a locking motor and consequently cause a stability issue in electric and hybrid vehicles. This paper focuses on the special case of recuperation by coasting; i.e., the torque request is set after releasing the accelerator pedal. In this case the mechanical brake is not used. For off-highway vehicles this new feature in the inverter will suppress the slipping and locking up of the tires, without the need of additional external sensors.
Slipping of the tires, e.g. when the tires lose grip, can occur due to excessive torque from the motor. In this case the motor torque exceeds the minimum feasible deceleration torque, given by road friction. We have developed a new non-linear control approach, which limits the requested torque directly inside the inverter (power electronic control unit). The control unit will monitor the torque and speed of the motor and validate their plausibility. When detecting an invalid decrease of the speed, the recuperation torque is reduced in order to control slipping. By this, the torque will stay as close as possible to the slip limit and recuperation performance is maximized.
In this paper the authors cover and show that it is feasible to control slipping of tires in hybrid passenger cars and off-highway vehicles only by taking into account detailed physical models of the electric motor, the vehicle and the road contact with-out any means of additional external sensors.