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General Studies 3 >> Science & Technology

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1. Context
The impulse to be sustainable — driven by the incessant pressure to lower our emissions — often manifests as lowering consumption and increasing reuse alongside reforms like tweaking consumer behavior. Electric vehicles are the site of many of these changes, aided by state-led incentives and subsidies. Regenerative braking is an important mechanism in these vehicles that increases their energy use efficiency.
2. What is an Electric Vehicle?
Electric vehicles (EVs) are automobiles powered by electricity stored in rechargeable batteries, rather than traditional internal combustion engines. Here's a brief overview:
  • Zero direct emissions
  • Rechargeable via charging stations or home chargers
  • Lower operating costs compared to gasoline vehicles
  • Increasing range capabilities
  • Growing market share globally
Types of Electric Vehicles
  • Battery Electric Vehicles (BEVs)
  • Plug-in Hybrid Electric Vehicles (PHEVs)
  • Hybrid Electric Vehicles (HEVs)
3. What is Braking?
  • Braking is the process that slows down a moving vehicle. A faster vehicle has more kinetic energy than a slower one, so braking primarily involves the reduction of this kinetic energy. According to the law of energy conservation, the energy removed during braking must be transferred elsewhere.
  • One example is the disc brake, a type of mechanical brake. It operates by pressing brake pads against a disc attached to the rotating wheels, using friction to convert some of the wheels' kinetic energy into heat. This is why disc brakes have holes in the discs—to improve heat dissipation.
  • Another example is the induction brake, commonly used in trains. It uses a magnet to create circular electric currents in a spinning wheel made of a conductive material like metal.
  • These currents generate their own magnetic field, which opposes the external magnet's field, creating a drag on the wheel and slowing it down. In energy terms, the metal resists the flow of the circular currents and dissipates the energy as heat
4. What is regenerative braking?
  • Regenerative braking is a system designed to convert the kinetic energy of a vehicle's wheels into a form that can be stored and reused. This process allows the vehicle to recover some of the energy that would otherwise be wasted when the vehicle slows down or stops.
  • Regenerative braking is a type of dynamic braking. In electric vehicles, which are becoming more common on Indian roads, a battery onboard the vehicle stores electric power drawn from the grid.
  • When the vehicle moves, the battery powers an electric motor, known as the traction motor, which converts electrical energy into mechanical energy to propel the vehicle.
  • During regenerative braking, the traction motor operates as a generator, converting mechanical energy back into electrical energy. This electric current is then stored in the vehicle's battery.
  • In some cases, such as with trains, the current is fed back into the traction motor. Another type of dynamic braking is rheostatic braking, where the current is directed to resistors that dissipate the energy as heat.
  • Vehicles often use both regenerative and rheostatic braking to ensure that excess electrical energy can be managed if it can't be stored or used immediately
5.Motor to Generator
  • A motor consists of two fundamental parts: a rotor, which rotates, and a stator, which remains stationary. In a basic design, the stator is made up of permanent magnets or electromagnets, while the rotor is composed of current-carrying wires arranged in coils. The stator surrounds the rotor.
  • When a charged particle, such as an electron, moves within a magnetic field, the field exerts a force on the particle called the Lorentz force.
  • The direction of this force, which can either push or pull the wire containing the electron, depends on the direction of the electric current.
  • The coiling of the wires is crucial. The current flows in opposite directions at the two ends of the coil, so the magnetic fields generated by the stator will push one end of the coil and pull the other.
  • These opposing forces act on the two sides of the rotor until the voltage across the wire stabilizes, thus converting electrical energy into rotary motion.
  • In a generator, mechanical energy from an external source is applied to the rotor to generate a current in the stator. By switching the traction motor between motor and generator configurations, an electric or hybrid vehicle can implement regenerative braking
6. Challenges of regenerative breaking
  • Although regenerative braking is a straightforward energy recovery mechanism, it has some limitations. For instance, it often cannot bring an electric vehicle to a complete stop on its own.
  • It must be used in conjunction with a conventional braking system that dissipates some of the kinetic energy as heat.
  • Additionally, a conventional braking system is needed to prevent vehicles from rolling backward on a slope, which many regenerative brakes cannot prevent.
  • Another limitation is that the amount of energy recovered by regenerative brakes decreases as the vehicle's speed decreases. Despite these drawbacks, regenerative braking can significantly enhance an electric vehicle's energy efficiency in stop-and-go traffic
7.More ways to recover energy
  • The design of a regenerative brake depends on the form of energy to which the mechanical energy from the wheels is converted. In an electric vehicle, this energy is directed into a generator to produce a current, which is then stored in a battery or a supercapacitor.
  • Similarly, the mechanical energy can be used to increase the angular momentum of a rotating flywheel. Flywheels are particularly advantageous because they can absorb energy much faster than other systems.
  • With each unit increase in speed, flywheels store exponentially more energy. Engineers have developed flywheels made of carbon composites that can spin up to 50,000 rpm in a vacuum.
  • These flywheels can be connected to a reciprocating engine to regulate or boost its output, as seen in Formula One racing, or linked to a gyroscope to aid in the navigation of submarines and satellites.
  • Additionally, the recovered kinetic energy can be used to power a pump that compresses air, which can be useful for starting internal combustion engines
For Prelims: Regenerative braking,  Electric vehicles, advantages of using flywheels
For Mains: GS III- Science & Technology
Source: The Hindu

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