Regenerative Braking
Imagine a time where electric cars do not need to be charged at stations but instead charge themselves while running; regenerative braking is a glimpse of this exact situation. An extremely simple logic that has an extremely large impact. It uses nothing but the basic contact force of friction to improve the flow of energy through the car.
Principle of the system
There are mainly three types: electric, hydraulic and the majorly used mechanical. Also called mechanical recuperation, its majority usage comes from its system based on a flywheel and a clutch. The flywheel stores the momentum of a slowing down car just like the rubber band stores elastic energy when stretched. During acceleration this very momentum is given back to the car first after which energy from the battery is used. The basic energy change from battery to car is electrical to kinetic after which it gets wasted as heat,friction or sound , however with the regenerative systems most of the wasted energy is converted back to chemical energy that gets stored in the battery as the axles switch their rotation. This is theoretically and practically possible due to the law of conservation of energy which states ‘Energy can neither be created or destroyed it can only be converted from one form to another” which proves that these conversions are possible as no energy can be removed in a closed system, it can only change form.
In the figure above, part a) shows the acceleration process where the battery supplies the energy, however part b) shows the braking process where the motor switches into the generator stage and takes back the energy from friction. The energy needed to be divided between brakes and regenerative braking. This usually favours regenerative braking, however due to the system being mechanical the recuperation might have energy losses through parts such as transformation losses through the inverter and ICE losses due to drag. This does not affect the stability of the vehicle and its ability to stop as each car is tuned to optimum energy requirements for friction braking.
The two categories of regenerative braking are similar to circuits, one is parallel and the other is series. Both use similar logic but there is a difference in the way energy is passed through the system.
The first diagram is parallel braking where it is noticeable that both thee systems friction and regen braking are activated simultaneously while in the rightmost diagram the friction braking system is activated after the regen system. The use of each strategy is dependent on the manufacturer of the vehicle.
Usage of system
The system has several benefits with regards to range and energy saving. Most effective when going downhill the system recharges the battery continuously compared to braking where it can recharge the battery sparsely. It can approximately increase the range of the vehicles by 10% allowing further travel on a smaller charge. For hybrid vehicles the number increases significantly due to them having a specified mode for regen braking using the IC engine. It can increase the range by almost 30% depending on factors like terrain, temperature and most significantly the type of vehicle. The efficiency of the same system can have varied effects of different vehicle types.
Conclusion
Due to this system being an addition to the friction braking system it cannot be used in a full fledged fashion that’s why it cannot be used at its full potential converting less kinetic energy back to electrical energy. Though the technology has these drawbacks the advantages are significant: it helps in the extension of the vehicle's range of motion, the reduction of the intensity of wear of the brake friction pairs, and therefore, the reduction of particle emissions that occur during braking, and additional assistance when slowing down or stopping the vehicle.
Reference:
https://iopscience.iop.org/article/10.1088/1757-899X/1271/1/012025/pdf