Electric Vehicle University - 205a REGENERATIVE BRAKING
•Descargar como PPTX, PDF•
1 recomendación•1,842 vistas
THE CENTRAL QUESTION ... How does the electric motor serve to brake my EV and what are the underlying principles that enable braking to happen? COURSE ABSTRACT The use of regenerative braking as a mechanism for capturing and reusing a vehicle’s kinetic energy is presented. Basic kinetic energy concepts are discussed, the characteristics of an electric motor that allows it to become a generator are explored, the system diagram for a regenerative braking system is considered, and driving with regen is examined. To obtain a copy of the EVU study guide for this and other available EVU courses, please complete the form on this page. Course level: Intermediate
Recomendados
Recomendados
Más contenido relacionado
La actualidad más candente
La actualidad más candente (20)
Destacado
Destacado (10)
Similar a Electric Vehicle University - 205a REGENERATIVE BRAKING
Similar a Electric Vehicle University - 205a REGENERATIVE BRAKING (20)
Más de EVANNEX Aftermarket Tesla Accessories
Más de EVANNEX Aftermarket Tesla Accessories (20)
Último
Último (20)
Electric Vehicle University - 205a REGENERATIVE BRAKING
- 1. 1
- 2. 2 Regenerative Braking, part 1 EV-205a This course is presented as part of Evannex University—a free, open learning environment that presents concise, video-based mini-courses for those who have interest in electric vehicles (EVs) …
- 3. Kinetic energy - 1 From Wikipedia: “the energy it possesses due to its motion” “work required to accelerate an object” “the body maintains it KE unless its speed changes” “”the same amount of work is done …” 3
- 4. Kinetic energy - 2 Kinetic energy—equation KE = (Mass x velocity squared)/2 Physics — energy cannot be destroyed So, when speed (v) changes KE must be transformed into something else
- 5. Kinetic energy of a car A moving car: has a very large mass has a velocity KE is large at high speed How do we stop a conventional car? stop providing energy to the motor depress the brake pedal Energy is dissipated as heat
- 6. For ICE vehicles … As braking occurs, a significant amount of heat is created There is no easy way to recover this heat energy, and it is lost For an ICE vehicle 80 percent of the energy input to propel the car forward is lost to heat and other affects as the car is brought back to zero velocity
- 7. For EVs Braking can recapture as much as 40 to 50% of the vehicle’s kinetic energy, but NOT if you use the conventional braking paradigm Instead, control electronics recognizes that: power to the electric motor has been discontinued regenerative braking is then initiated
- 8. The Electric Motor The stator The rotor Current creates a magnetic field AC causes field to vary between N and S The rotor “chases” the magnetic field and rotates 8 Source: Tesla Motors
- 9. Motor to generator when an electric motor receives electric energy as input, it converts the energy derived from an electromagnetic field into mechanical energy transmitted by the motor’s rotor if input to the motor is electrical energy, output will be mechanical rotation but if the electric input stops and the mechanical rotation derived for the KE is used as ‘input’ the motor becomes a generator and produces electrical energy as output
- 10. 10 … a free study guide for all EVU mini-courses is available for download from our website … For a complete list of mini- courses and the study guide, visit: www.evannex.com
Notas del editor
- Any discussion of regenerative braking should begin with a brief explanation of kinetic energy. >>This, from Wikipedia: “In physics, the kinetic energy of an object >> is the energy that it possesses due to its motion. It is defined as the >> work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, >> the body maintains this kinetic energy unless its speed changes. >> The same amount of work is done by the body in decelerating from its current speed to a state of rest.”
- >> Represented as a mathematic equation: >> KE = (1/2 mass x velocity squared, measured in Joules From your high school physics class, you may recall that: >>energy cannot be destroyed >> So, what happens when the speed of an object of a given mass changes? >> the object’s KE must be transformed into something else and it’s this last observation that lies at the core of regenerative braking. But enough abstractions … lets talk about a moving car.
- >> A moving car is a large object traveling at a given speed: >> it has a very large mass >> and can have significant velocity >> so … it’s KE is impressive. Any unfortunate sole who has backed into his roadside mailbox understands this from personal experience >> How do we stop a conventional car? As I mentioned, as a car slows, it’s kinetic energy must be transformed into something else — another form of energy. >> First, you stop providing energy to the motor, thereby allowing air friction (drag) to slow the car >> Next, you depress the brake pedal Calipers press on disks and create friction that slows the rotation of the wheels Energy is dissipated as heat
- >> As braking occurs, a significant amount of heat is created >> There is no easy way to recover this heat energy, and it is lost >> For an ICE vehicle >> 80 percent of the energy input to propel the car forward is lost to heat and other affects as the car is brought back to zero velocity As an aside, some ICE vehicle manufacturers are also using regenerative braking systems to replace the alternator, which can sap as much as 10 percent of the energy output of a ICE. They store the electricity generated in a super capacitor, rather than a battery. That a good thing to do, but the EV approach is considerably more interesting.
- For electric vehicles, >> Braking can recapture as much as 40 to 50% of the vehicle’s kinetic energy, but not if your disc brakes are used as the sole mechanism for slowing the car >>Instead, control electronics recognizes that: >>power to the electric motor has been discontinued >>it then initiates regenerative braking
- To understand how regenerative braking happens, we have to look at the electric motor. As we discussed in an earlier EVU mini-course, >> Coils of copper wire run through a stack of thin steel plates and form a “stator.” >> The rotor is a steel shaft with copper bars running through it. It rotates, and ultimately, turns the wheels of the EV. But what makes the rotor rotate? >> The flow of alternating current into the copper windings of the stator creates a magnetic field. >> Alternating current causes the field to vary between N and S, appearing to move in a circular path >> The rotor “chases” the magnetic field and rotates as a consequence. One more important point—an electric motor exhibits an interesting “duality.” It can be a motor or it can be a generator. Let’s take a look at that.
- >> When an electric motor receives electrical energy as input, it converts the energy derived from an electromagnetic field into mechanical energy transmitted by the rotor. This provides torque — that is rotational energy — that causes the drive wheels of a vehicle to rotate. >> stated more succinctly, if input to the motor is electrical energy, output will be mechanical rotation or torque >> but if the electric input stops, and the mechanical rotation derived from the KE is used as ‘input’ >> the motor becomes a generator and produces electrical energy as output In the second part of the EVU mini-course, we’ll examine how these characteristics can be used to implement a regenerative braking system. We’ll also look at some of the driving characteristics of a regen system.