Week-6 Challenge: EV Drivetrain
Question 1] Which types of power converter circuits are employed in electric and hybrid electric vehicle?
Answer:-
1] AC to DC Converter (Rectifier) :-
The prime source of electrical power coming from the grid is single/three-phase alternating current. While AC current is efficient for transmission purposes, many devices, drives, and electronic equipment require DC power supply that is fulfilled using rectifiers. A rectifier takes ac and converts it to DC. The rectifier is the most popular type of power electronics converter.
2] DC to AC Converter (Inverter) :-
An inverter or dc to ac converter takes dc power supply from the battery and converts it to ac. The process of inversion (dc to ac conversion) is particularly employed with battery banks in uninterruptible power supply systems and in solar power systems.
3] AC Voltage Regulator:-
An AC voltage regulator is an AC to AC converter that takes AC voltage at one level and provides AC voltage at other amplitude. Such converters are comprised of triac, thyristors, or SCR, GTO’s, IGBT’s or MOS controlled thyristors.
4] DC to DC Converter:-
A DC to DC converter (also known as chopper) is used for matching source voltage level with the component voltage level. They are further classified into three classes.
Buck converter: A converter which provides output voltage less than the input.
Boost converter: A converter whose output is higher than the input.
Buck-Boost converter: A converter whose output can either be higher or lower than the input.
5] AC/DC Converter:-
An AC/DC Converter can convert AC to DC and DC to AC. Such converters have the capability to operate as an inverter as well as a rectifier.
Question 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'.
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 Volt second
Chopper Switching frequency= 400 Hz
The vehicle speed-torque characteristics are given by the below equation
What is EV steady state speed if duty cycle is 70%?
Answer:-
Duty Cycle = 70% = 0.7
Voltage (V) = Rated Armature Voltage * Duty cycle
Voltage (V) = 50.4 Volt
As we know Torque_Speed Characteristics of DC motor is
`Tm = (frac{V*Kphi}{Ra})-(frac{omega*Kphi^2}{Ra})`
`Tm = (frac{50.4*0.7}{0.5})-(frac{omega*0.7^2}{0.5})`
Tm = 70.56-0.98*W.......eqn (1)
Given that
Tv = 24.7+(0.0051)*W^2.........eqn (2)
Comparing both equation
Tm = Tv
70.56-0.98*W = 24.7+(0.0051)*W^2
0.0051W^2 = 0.98W-70.56-24.7
0.0051W^2 = 0.98W-45.86 = 0 ........eqn (3) Its quadratic equation
formula for quadratic equation = `omega = frac{-b pm sqrt b^2-4ac}{2a}`
then we get, W = 38.9150 and W = -231.071
so steady state speed of EV is 38.9150 rad/sec
Question 3] Develop a mathematical model of a DC Motor for the below equation using Simulink.
ω= V/Kϕ -Ra/Kϕ^2 .T
Answer:-
Given =
Voltage (V) = 50.4 volt
Motor Constant (K_phi) = 0.7 volt-sec
Resistance of armature (Ra) = 0.5 ohms
Torque (T) = 33
Angular speed (W) = 38.33 rad/sec....
Question 4]
Refer to the blog on below topic:
Induction Versus DC brushless motors by Wally Rippel, Tesla
Explain in brief about author’s perspective.
Answer:-
Whally Rippel says that the he is seen lot of changes in the electric vehicle industries right from when he was young and when they used to use lead acid batteries and dc motor to now where most vehicles use lithium polymer cells and brushless dc motor or induction motor. He states that the two most commonly used motors are three phase induction motor and a brushless dc motor also called BLDC motor.
He also states that just like different typed of engine are suited to different appln then simillarly the motor in an electric vehicle are also of different type. The choice between an induction and BLDC motor depends purely on the applicaton and cost. For instance he describes how both motor works and by far the induction motor is more complex to design and understand as it has more components such an inverters that need feedback loops. But the induction motor if ideally designed can produced a large amount of torque for the provide load al,ost right from the start.
healso states about the construction of the motors where both have the same stator but they differ in the construction of the rotor. He talks about how hybrid electric vehicles adopts these motor based on their requirements and states that it BLDC motor is commonly used where as only pure electric like tesla roadster make the use of induction motor. In the end he claims its not possible to conclude which of two is best.
Thank you
Dharmesh Bonde...