Week-6 Challenge: EV Drivetrain
1. Which types of power converter circuits are employed in electric and hybrid electric vehicle?
2. An Electric Vehicle's Drivetrain with 72V battery pack in shown in the diagram below. The duty ratio for acceleration operation is 'd1' and for the braking operation the duty ratio is2'. The other parameters of the electric vehicle is given below,
Motor and Controller Parameters:
Rated Armature voltage= 72 V
Rated armature current= 400 A
Ra= 0.5Ω, KΦ= 0.7 V-s
Chopper Switching frequency= 400 Hz
The vehicle characteristics are given by the equation
TTR=24.7+0.0051w2
What is EV steady state speed if duty cycle is 70%?
3. Refer to the blog on below topic:
Induction Versus DC brushless motors by Wally Rippel, Tesla
Explain in brief about author’s perspective.
.....................................................................................................................................................
Q1. Which types of power converter circuits are employed in electric and hybrid electric vehicle?
ANS- AC TO DC... RECTIFIER
DC TO AC .. INVERTER
DC TO DC to step up and step down voltage
some times there are An Integrated Multifunctional Bidirectional AC/DC and DC/DC Converter for Electric Vehicles Applications
ac to dc--- from this we can charge car battery as home supply ac and battery dc input
dc to ac -- from dc battery of car given to ac input of moter.
dc to dc ---electric load in car ...In electric engineering, a DC to DC converter is a category of power converters and it is an electric circuit which converts a source of direct current (DC) from one voltage level to another,DC/DC converters can be designed to transfer power in only one direction, from the input to the output. However, almost all DC/DC converter topologies can be made bi-directional.
https://www.intechopen.com/books/electric-vehicles-modelling-and-simulations/dc-dc-converters-for-electric-vehicles for for info .
we see one eg of car model on broad and off board
to study this conversion we can visit this site https://www.mdpi.com/1996-1073/9/7/493/htm
as per the car company and the model design is different .
Q2)
2. An Electric Vehicle's Drivetrain with 72V battery pack in shown in the diagram below. The duty ratio for acceleration operation is 'd1' and for the braking operation the duty ratio is 2'. The other parameters of the electric vehicle is given below,
Motor and Controller Parameters:
Rated Armature voltage= 72 V
Rated armature current= 400 A
Ra= 0.5Ω, KΦ= 0.7 V-s
Chopper Switching frequency= 400 Hz
The vehicle characteristics are given by the equation
TTR=24.7+0.0051w2
What is EV steady state speed if duty cycle is 70%?
ANS-
FORMULA USED:
----The Rolling Resistance Force
Frr = μrr . m . g
----Drag Force
Fad = 0.5.Cd.p.A.v^2
The Total Tractive Force
Fte = Frr + Fad
Speed-Torque Equation for DC Motor
w = (V/kϕ)-(T.R/(k(ϕ)^2)
SOLUTION:
We find the Rolling Resistance Force
Frr = μrr . m. g ................Frr = 0.009*1000*9.81.............Frr = 88.29 N
Then we find the Drag Force
Fad = 0.5.Cd.p.A.v^2....Fad = 0.5*0.2*1.1614*2*v^2....Fad = 0.232*v^2....
velocity can be written as a product of angular speed and radius. V=r.ω
Fad = 0.232*(0.28)^2*ω^2
Fad = 0.01821*ω^2
The Total Tractive Force
Fte = Frr + Fad
Fte = 88.29+(0.01821*ω^2)................(Equation-1)
We know that
Fte =G.T/r Substituting in (1)
(1 *T)/0.28 = 88.29+(0.01821*w"2)
TTR = 24.72+0.0051*ω^2.............(Equation-2) The vehicle characteristics are given by the equation(2) and it's derived
TTR=24.7+0.0051ω2
Which is given in the question
We know that
Speed-Torque Equation for DC Motor
ω= (V/kϕ)-(T.R/(k(ϕ)^2)
By rearranging it in form torque equation
T = ((V.kϕp)/ R)-(w.(kϕp)^2/ R)
Before that,
In the question, it given that the duty cycle is 70%
Therefore we need the find out the voltage at 70% duty cycle
V = 72*0.7 = 50.4V
T = ((50.4*0.7)/0.5)-((ω.(0.7)"2)/0.5)
T_m = 70.56-(ω*0.98)............Equation (3)
At the steady state condition of EV
T_TR = Tm
Now substituting the values of T_TR and Tm i.e equation (2) and (3)
24.72+0.0051*ω^2 = 70.56-(ω*0.98)
(0.0051*ω^2) + (0.98*ω)-45.84 = 0 by solving quadratic qquation we get http://www.math.com/students/calculators/source/quadratic.htm
Omega value will be in positive
ω= 38.90 rad/sec
RESULT: 38.90 rad/s = 371.467637 RPM
EV steady state speed if duty cycle is 70% is, ω = 38.90 rad/sec
Q) Induction Versus DC brushless motors by Wally Rippel, Tesla
ans -- in starting author says technology is evolving first there were lead acid battery and dc brush moter and now li-ion battry and brushless dc moter....and alo moters are are looking is that we will
see both induction and brushless machines “duke it out” for many years to come. Each will have its loyal proponents and religious detractors now we will se both working and its conctruction difference limitations
DC brushless drives,---
the rotor includes two or more permanent
magnets that generate a DC magnetic field .
In turn, this magnetic field enters the stator core (a
core made up of thin, stacked laminations) and interacts with currents
flowing within the windings to produce a torque interaction between the
rotor and stator. As the rotor rotates, it is necessary that the magnitude
and polarity of the stator currents be continuously varied — and in just
the right way - such that the torque remains constant and the conversion
of electrical to mechanical energy is optimally efficient. The device that
provides this current control is called an inverter. Without it, brushless
motors are useless motors.
a brushless DC motor produces no starting torque when directly connected to fixed frequency utility power.
They really need the aid of an inverter whose “phase” is maintained in step with the angular position of the rotor.
One of the main differences is that much less rotor heat is generated with the DC brushless drive.
Rotor cooling is easier and peak point efficiency is generally higher for this drive.
The DC brushless drive can also operate at unity power factor, whereas the best power factor for
the induction drive is about 85 percent.
efficiency for a DC brushless drive will typically be a few percentage points higher than for an induction drive.
limitations
With DC brushless, as machine size grows, the magnetic losses increase proportionately and part load efficiency drops
Permanent magnets are expensive
Permanent magnet (PM) rotors are also difficult to handle due to very large forces that come into play when anything ferromagnetic gets close to them.This means that induction motors will likely retain a cost
advantage over PM machines
induction motor drives--
induction motor was invented by Nikola Tesla sometime before 1889.
Curiously, the stators for the 3-phase induction motor and the DC
brushless motor are virtually identical. Both have three sets of
“distributed windings” that are inserted within the stator core. The
essential difference between the two machines is with the rotor.A forerunner of the 3-phase
induction motor was invented by Nikola Tesla sometime before 1889.
Curiously, the stators for the 3-phase induction motor and the DC
brushless motor are virtually identical. Both have three sets of
“distributed windings” that are inserted within the stator core. The
essential difference between the two machines is with the rotor.
When a 3-phase induction motor is connected type 3-phase power, torque is produced the motor has the ability to start under load. No inverter is needed.
induction motors are directly compatible with conventional utility power is the main reason for their success.
Shaft speed is proportionate to line frequency.when used with utility power, they are constant speed machines
by inverter we can power IM variable speed also becomes possible simply by adjusting the inverter frequency. Still, torque performance is low compared with DC
machines.
Add some feedback loops such that the inverter produces the exact frequency that the motor “desires,” and the induction motor is now capable of competing with DC and DC brushless for vehicle applications.
induction machines have no magnets and B fields are
“adjustable,” since B is proportionate to V/f (voltage to frequency). This
means that at light loads the inverter can reduce voltage such that
magnetic losses are reduced and efficiency is maximized. Thus, the
induction machine when operated with a smart inverter has an
advantage over a DC brushless machine, there is no easy way of changing B
with permanent magnets.dc moter
which one is better
Both DC brushless and induction drives use motors having similar stators. Both drives use 3-phase modulating inverters. The only differences are the rotors and the inverter controls.
And with digital controllers, the only control differences are with control code. (DC
brushless drives require an absolute position sensor, while induction
drives require only a speed sensor; these differences are relatively
small.)
limitations.-
They cannot operate from DC
when operated from utility power, they have limited starting torque and somewhat limited
running peak torque capabilities
With induction, asmachine size grows, losses do not necessarily grow. Thus, induction
drives may be the favored approach where high-performance is
desired; peak efficiency will be a little less than with DC brushless, but
average efficiency may actually be better.
Induction machines are more difficult to control. The
control laws are more complex and difficult to understand. Achieving
stability over the entire torque-speed range and over temperature is
more difficult with induction than with DC brushless. This means added
development costs, but likely little or no recurring costs
conclusion-
DC brushless drives will likely continue to dominate in the hybrid and coming plug-in hybrid markets, and that induction drives will likely maintain dominance for the high-performance pure electrics.
so much of the hardware is common for both drives could mean that we will see induction and DC brushless live and work side by side during the coming golden era of hybrid and electric vehicles.