Week-11 Challenge: Braking

EV 17TH LIVE BATCH

2.Que:

Regenerative braking allows electric vehicles to use the motor as a generator when the brake are applied, to pump vehicle energy from the brakes into an energy storage device. Regenerative braking is an effective approach to extend the driving range of an ev.

• The regenerative braking torque cannot be made large enough to provide all the braking torque of the vehicle as it might lead to deterioration in stability of vehicle. also as compared to torque value of acceleration torque of motor is much higher than decceleration torque.
• At high speed, the motor might be in its constant power region which cause less value of torque produced and this limits the amount of braking torque that is used for regeneration. Hence the peak value of acceleration torque and braking torque are not equal.

Electric and mechanical brakes co-ordination:

• The regenerative braking system may not be used under many conditions, such as with a high state of charge or a high temperature of the battery. In these cases, the mechanical braking system works to cover the required total braking torque.
• Thus,cooperation between the mechanical braking system and regenerative braking system is a main part of design of ev braking control strategy and is known as torque blending.

There are 2 different control strategies for braking combinations:

1.series control strategy

2.parallel control strategy

series control strategy:

• a combination of friction-based mechanical braking system with a regenerative braking system that transfer energy to battery with an integrated control, which distributes the required braking force between regenerative and mechanical braking system.
• series strategy could give an increase 15-30% in fuel efficiency and has more consistent braking due to good torque blending capability.

Parallel control strategy:

• combination of mechanical and regenerative braking system,operated simultaneously without an integrated control.
• The regenerative braking force is added to mechanical braking force which cannot be controlled.
• The regenerative torque is determined by considering the motor capacity,battery SOC, and vehicle velocity. The regenerative braking force is calculated from the brake control unit by comparing the demanded brake torque and motor torque available.

Application of Braking combination: EDIB(Electric Driven Intelligent Brake) in NISSAN LEAF

• EDIB allows and control optimization of regenerative brake and regular friction brake (hydraulic brake).
• The system produces an adequate braking force keeping energy regenration increased as much as possible.
• At higher speeds, a combination of regeneartive and friction braking is applied.
• At lower speeds,regerative braking is given a higher proprtion for maximised energy conversion.