Regenerative Braking

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Context (TH): Regenerative braking is an important mechanism in electric vehicles that increases their energy use efficiency.

What is Braking?

Braking is the mechanism by which an automotive vehicle in motion slows down.
A faster vehicle has more kinetic energy than a slower one, so braking primarily removes this kinetic energy from the vehicle.
The law of energy conservation means this removed energy must go somewhere.
For example,
- Disc brakes (a type of mechanical brake) press pads against a spinning disc and use the friction to convert kinetic energy into heat, which is dissipated through holes in the discs.
- Induction brakes use magnets to induce electric currents in a spinning metal wheel. These currents create opposing magnetic fields, slowing the wheel and dissipating energy as heat.

Regenerative braking is a type of dynamic braking that converts the wheels’ kinetic energy into a form that can be stored and reused.
In electric vehicles, a battery powers a traction motor that propels the vehicle by converting electrical to mechanical energy.
During regenerative braking, this motor acts as a generator. It converts mechanical energy back into electrical energy, stored separately in a battery or fed back into the traction motor.

Rheostatic braking is another type of dynamic braking.
It sends current to resistors that dissipate energy as heat.
A vehicle must often have both regenerative and rheostatic braking in case the recovered electrical energy can’t be stored or used immediately.

A motor has two essential parts: a rotating rotor and a stationary stator. In a rudimentary design, the stator with permanent magnets or electromagnets surrounds the rotor with current-carrying wire coils.
When a charged particle, such as an electron, moves in a magnetic field, it experiences a force known as the Lorentz force. The direction of this force depends on the direction of electric current in the wire.
This is when the coiling helps. The coiled wire in the motor has currents flowing in opposite directions at its ends, creating magnetic fields in the stator that push and pull the rotor.
These opposing forces act until the voltage stabilises, enabling the motor to convert electrical energy into rotary motion.
In a generator, mechanical energy from an external source can be fed to the rotor to induce a current in the stator.
Simply speaking, an electric (or hybrid) vehicle can implement regenerative braking by switching the traction motor between these two configurations.

Regenerative braking alone isn’t sufficient to stop an electric vehicle; it must be combined with a conventional system that dissipates kinetic energy as heat.
Regenerative braking systems alone often cannot prevent vehicles from rolling back downhill. Therefore, it must also have a conventional braking system.
Regenerative brakes recover less energy as the vehicle’s speed decreases.

Flywheels can be used to store energy by increasing their rotational speed.
Flywheels are efficient because they can quickly absorb and release energy.
Advanced carbon-composite flywheels can spin up to 50,000 rpm in a vacuum.
These flywheels can be connected to engines to manage power output, such as in Formula One racing, or to gyroscopes to help submarines and satellites navigate.