Week-6 Challenge: EV Drivetrain
1. Which types of power converter circuits are employed in electric and hybrid electric vehicle?
Three types of power converters are used in electric and hybrid electric vehicle they are
- AC-DC converters(recterfier)
- DC-AC inverters
- DC-DC converter
AC-DC CONVERTERS :
It is used to charge the battery in vehicle.A rectifier is an electrical device that converta alternating current (AC), which periodically reverses direction, t0 direct current (DC), which flows in only one direction. The reverse operation is performed by the inverter .The process is known as rectification
rectifier divided into three categories they are
- half wave rectifier
- full wave rectifier
- bridge rectifier
half wave rectifier :
half wave rectifier is singla phase supply,either the positive or negative half of the ac wave passed otherwise another half is blacked. half wave neeed a single diode in a single phase supply and three diode in three phase supply.
full wave rectifier :
A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Mathematically Full-wave rectification converts both polarities of the input waveform to pulsating DC (direct current), and yields a higher average output voltage. Two diodes and a center tapped transformer, or four diodes in a bridge configuration and any AC source (including a transformer without center tap), are needed.
DC-AC INVERTERS :
It is know as power inverters DC-AC inverters are used to change the direct current into alternating current. DC is relatively stable and positive voltage source.AC is usually sinusoidal or aquare fashion.
the most common use for inverter technologies is to change the battery source voltage in to ac signal. which can be used for most of electric and hybrid electric vehicle .A standard transformer is connected to the input DC signal via a switch, which quickly oscillates back and forth according the frequency requirements of the output. Because of the bi-directional current flow in the transformer’s primary coil, an AC signal is output through the secondary coils.
DC-DC CONVERTERS :
It is know as switching regulator. uses of dc-dc converter is reduce the voltage level.example the input of dc voltage is 24v it is convert into 5v or requring output to the circuit box.
2. An Electric Vehicle's powertrain 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 'd2'.
Motor and Controller Parameters:
Rated Armature voltage= 72 V
Rated armature current= 400 A
Ra= 0.5Ω, KΦ= 0.7 Volt second
Chopper Switching frequency= 400 Hz
The vehicle speed-torque characteristics are given by the below equation
equation of speed charteristics is
Wm=v/KΦ-Ra/(KΦ)2.T
we find torque charateristics there fore
Tm=v/(Ra).k-k^2w/Ra ------------------1
vehicle voltage=battery pack voltage *duty cycle
=72*70%
=50.4v
substuting all values in equation 1
Tm=(50.4/0.5)*0.7-(w/0.5)*(0.7)^2
Tm=70.56-0.98w
finally findout two torque -speed equation
Tv=24.7+(0.0051)W^2
Tm=70.56-0.98w
compare the two equations
24.7+(0.0051)W2=70.56-0.98W
we get
w=38.92rad/sec & w=-231.07 rad/sec
there fore
STEADY STATE SPEED IS 38.92RAD/SEC
3 . Develop a mathematical model of a DC Motor for the below equation using Simulink.
ω">ω= V/Kϕ">ϕ-Ra/Kϕ">ϕ^2 .T
workspace values:
4 . Refer to the blog on below topic:
Induction Versus DC brushless motors by Wally Rippel, Tesla
Explain in brief about author’s perspective.
dc brusless motor:
With brushless machines, the rotor includes two or more permanent magnets that generate a DC magnetic field (as seen from the vantage point of the rotor). 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.
induction motor:
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.
nlike the DC brushless rotor, the induction rotor has no magnets – just stacked steel laminations with buried peripheral conductors that form a “shorted structure.
While 3-phase induction motors have great utility, they also have some severe limitations. They cannot operate from DC; AC is a must. Shaft speed is proportionate to line frequency. Hence, when used with utility power, they are constant speed machines.
difference in two motors:
The essential difference between the two machines is with the rotor.
when operated from utility power, they have limited starting torque and somewhat limited running peak torque capabilities, when compared to DC type machines.
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.)
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. This means that the peak point energy efficiency for a DC brushless drive will typically be a few percentage points higher than for an induction drive.