Regenerative Brakes: How Do They Work in EVs?

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As we have seen, electric vehicles and also hydrogen-based vehicles are now emerging in the global market and people are also concerning about the global warming and within that the demand of renewable energy is also flourishing accordingly. Now I am going to discuss regenerative braking which every EV owner or those who are planning to get a new EV should know about. The regenerative braking is a critical technology in electric vehicles (EVs) and hybrid vehicles using electric motors rather than a traditional friction braking system.

How Regenerative Braking works in EV?

As we know, energy cannot be destroyed nor created, in traditional hydraulic braking systems, when you press the brake pedal, the brake pads create friction with the rotors to slow down the vehicle. This friction converts the car’s kinetic energy (motion) into heat and due to it, there is a loss of energy.

While in the case of regenerative braking in EVs, it uses electric motor to stop the car. When you brake the car, the motor changes its role and instead of consuming energy, it generates electricity. This is achieved by using the vehicle’s motion to turn the motor, which then acts as a generator. This system captures kinetic energy that would otherwise be lost during braking and converts it into electrical energy, which is then stored in the vehicle’s battery. Here’s a detailed look at how regenerative braking works and its benefits.

How does Regenerative Braking charge the battery?

When the car is moving due to its speed and its other extra weight, kinetic energy is created and this kinetic energy is the main source of energy for regenerative braking. With the help of regenerative braking technology in electric vehicles (EVs) collects the movement of the vehicle and this movement or motion is converted back into electrical energy later stored in the battery. So, when the driver tries to stop the car or slow down the acceleration, the speed of the car decelerates.

In most of the EVs, the electric motor is taking an important step for moving the vehicle forward. When your vehicle is moving, the motor uses electrical energy from the battery to create mechanical energy that moves the wheels. However, when the driver pushes break in an EV, the regenerative braking starts. In this process, the motor works as a generator and it is converting the car’s motion or mechanical energy into electrical energy. This process helps to recover energy that would be lost in traditional cars and it is making the car more efficient.

The efficiency of regenerative breaking of an EV more specifically 60-70 percent energy efficiency relies on various factors, such as velocity of the vehicle, breaking frequency and health of the battery. Now a days there are more effective methods of regenerative breaking where user can adjust the level of breaking accordingly to the need of vehicle for maximum output.

Does EV regenerative Braking use Brake pads and why?

There are a few reasons why brake pads required in an EV:

1. Low-speed braking: Regenerative braking is most effective at high speeds where there is a requirement of more kinetic energy to convert into electrical energy. At low speeds, energy recovery is not possible, so friction brakes are needed to bring the vehicle to a complete stop. According to the report published by the MDPI Energies that the constraints and challenges of implementing regenerative braking have some limitations such as the battery state of charge (SOC) that finally results in reducing the effectiveness of the battery at slow speeds.

2. Emergency braking: In the emergency situations where the driver needs to stop his vehicle quickly, friction brakes provide the necessary stopping power. So, the regenerative braking alone may not be sufficient to stop the vehicle at that particular time.

3. Battery limitations: If the battery in your vehicle is already fully charged or if it is too cold due to the weather condition, it may not be able to accept the additional energy from regenerative braking. In these cases, the friction brakes are used as an alternative.

However, because regenerative braking handles a significant portion of the vehicle’s braking needs, the brake pads in an EV typically last much longer than those in a conventional vehicle.

What are the Disadvantages of regenerative braking?

Although regenerative braking offers many benefits, it does have some limitations and potential drawbacks:

1. Reduced effectiveness at low speeds: As mentioned earlier, regenerative braking is less effective at low speeds due to its less kinetic energy conversion. This means that drivers may need to rely more on friction brakes to stop-and-go traffic or when parking.

2. Inconsistent brake feel: Some drivers may find that the transition between regenerative braking and friction braking can feel inconsistent or unnatural. This may take some getting used to. However, there is a improvement in the new EV models.

3. Increased complexity: Regenerative braking systems are having different complexity and expensive to the vehicle’s powertrain as compared to the traditional braking systems, which could potentially lead to higher maintenance costs if components fail. The main components of this systems are electric motor, battery or capacitor.

4. Battery limitations: The effectiveness of regenerative braking can be limited by the state of charge and temperature of the battery. If the battery is full or too cold, it may not be able to accept the energy from regenerative braking.

Despite these limitations, the advantages of regenerative braking, such as improved energy efficiency and reduced brake wear, generally mitigate the disadvantages in EVs.

Which motor is used in regenerative braking?

There are different types of electric motor used in an EV plays a crucial role in regenerative braking. The most common types of motors used in EVs are:

1. AC Induction Motors: An AC induction motor is using alternative current (AC) to create a rotating magnetic field in the stator. The stator is winding by coils of wire so when alternating current (AC) flows through these windings, it creates a rotating magnetic field. This magnetic field of the stator and rotor interact with each other and creates torque which causes the rotor to spin and drives the vehicle’s wheels. In the case of regenerative braking, the inverter converts the AC generated by the motor into DC, which is then used to charge the battery.

2. Permanent Magnet Synchronous Motors (PMSM): PMSMs are more efficient than AC induction motors and offer better power density. It uses permanent magnets in the rotor, which create a constant magnetic field in the rotor. The stator is powered by a three-phase AC supply, which interacts with the rotor’s magnetic field to produce motion. During regenerative braking, the rotating magnet creates a current in the stator winding and it generates electricity to charge the battery.

Is regenerative braking AC or DC?

Regenerative braking consists of both AC and DC electrical systems. The motor that is used in an EV typically operates on AC power, while the battery stores the energy and it generates DC power.

During regenerative braking, the motor acts as a generator and it is producing AC power with necessary torque and provide speed control for driving the vehicle. This AC power must be converted to DC to charge the battery. The component that is required for this conversion is called an inverter.

The inverter is an electronic device that can convert DC to AC when the motor is rotating the vehicle and AC to DC during regenerative braking. It uses semiconductor switches, such as insulated-gate bipolar transistors (IGBTs) or metal-oxide-semiconductor field-effect transistors (MOSFETs). So, to perform this conversion, these switches help the inverter to efficiently manage the process.

In summary, regenerative braking involves the motor generating AC power, which is then converted to DC by the inverter to charge the battery.