Regenerative Braking

Regenerative braking is a process of charging battery when brakes are applied on electric vehicle or hybrid electric vehicle by converting kinetic energy into electrical energy.


In moving conditions a vehicle has kinetic energy, kinetic energy increases with increase in speed of vehicle. When conventional brake is applied, the kinetic energy changed into heat energy while vehicle slows down or stops. In electric vehicles our target is to optimize the energy uses as much as possible while keeping its performance at best. We know the charge in battery is directly proportional with the range of EV. By converting kinetic energy into electrical energy instead of wasting it as heat, we can increase the efficiency of the vehicle.


The efficiency of regenerative brake is about 70%, which means about 70% of the kinetic energy is converted in power to charge the battery.


Working:


As we know to start movement a vehicle we need higher torque initially and with increase in speed torque decreases.

The wheel of electric vehicle is connected with motor with a gear arrangement, the motor is connected with control which is further connected with battery



Fig. 1: Regenerative Cycle



The two basic parts of motor are stator and rotor, at running conditions the speed of rotor's magnetic field is greater than that of stator's.

When brakes are applied the speed of rotor's magnetic field decreases below stator's magnetic field, at this point the poles in stator changes and it starts regeneration and supplying power to the source.

One more thing to keep in mind is for regeneration we need to stop the supply of power as soon as brakes are are applied and this is done with the help of controller, as soon as it recognizes that accelerator pedal is released it cuts off the supply from battery to motor.

Now how the brake works? Due to this process back EMF is produced in motor which causes resistance and resistance results in braking.

The regenerative braking is not effective when we need sudden brake action that is why we use friction brakes as backup.


The benefits of regenerative braking is we use the recovered energy or we can say we recover the energy which gets wasted.

Also it reduces brake shoe wears.


Some advantages and disadvantages of regenerative braking are-


The advantages are as follows-


+It increases the range of vehicle,

+It conserves the energy, that is avoid loss of energy.

+In HEVs it increases fuel economy.


The disadvantages are

-Extra apparatus is required, makes system complicated

-High maintenance cost

-Friction brake is needed as backup


We can say regenerative braking is one of the greatest innovation which help us to convert the kinetic energy into heat energy instead of heat which is complete waste.

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