Week-6 Challenge: EV Drivetrain

1. Which types of power converter circuits are employed in electric and hybrid electric vehicle?

Power electronic converters:

In Electric and Hybrid vehicel,the power elctronics converters are considered as the key elemets that interface their power to the drive train of the EVs .It requires advanced DC-DC/DC-AC converters to adapt the output voltage and current levels with high power quality.

AC-DC Converter (On Board Chrager):-

AC to DC converters are mostly used in Plug in hybrid electric vehicles(PHEV) & Plug in electric vehicles(PEV).These vehicles get their propulsion power from an external electricity source (charging stations) which is alternating current .The battery needs to be changed using a direct current source .For this purpose ,AC to DC converter is employed in a PHEV & PEV.

DC-DC Converter:-

DC-DC Converter can be used to interface the elements in the electric power train ny boosting or chopping the voltage levels .By introducing DC/DC converters one can choose the voltage variation of the devices and the power of each device can be controlled .The power of the DC/DC converter depends on the characteristics of the vehicle such as top speed,acceleration time from 0 to 100Km/h,weight,maximum torque and power profile .

DC-AC Converter (Inverter)

The DC/AC converter is required to convert the dc power to suitable ac power for the electrical machine .The power output from battery pack (DC current) is converted using inverter to be used in electric motor.(AC Current).

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%?

Given:

Battery voltage= 72 V

Rated armature current= 400 A

Armature resistance Ra= 0.5Ω,

Motor constant KΦ= 0.7 Volt

Duty cycle=70%

Solution:

Vehicle output voltage(Vo) is given by

Vo=V*Dutycycle

Vo=72*0.70

Vo=50.4 V

Vehicle Voltage=50.4 V

Equation for vehicle torque is given by,

T=(Vo-KΦ).KΦ/Ra

where

T=Vehicle torque

Vo=Vehicle Voltage

ω=Speed of Vehicle

KΦ=Motor current

Ra=armature resistance

Substituting all these values in eqn,

T=(50.4-0.7ω).0.7/0.5

T=70.56-0.98ω

T=24.7+0.0051.ω^2

We get a quadratic eqn,

0.0051.ω^2+0.98.ω-46.94=0

Solving the eqn we get,

ω=38.85 rad/s and ω=-230.95 rad/s

Steady state speed of the vehicle=38.95 rad/s

3. Develop a mathematical model of a DC Motor for the below equation using Simulink.

ω= V/Kϕ -Ra/Kϕ^2 .T

Model:

Result:

4. Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

Explain in brief about author’s perspective.

The following points can be concluded from the above topic

• In the beginning author describes the dominance of ICE (Internal Combustion Engine) in the world of automobile industry and also discuss different types of engines .He explains that all engines were similar and it was upto the user to select according to the requirement.
• He aslo speaks about induction motor and brushless motor and presents his view that these two technologies will be widely used for the coming years.He also explains the working of both 3-phase induction motor and brushless Dc motor
• Now the author has done comparison between these two technologies and stated some advantages and disadvantages of each.
• Induction motor have some advantages like it has no magnets .The motor has the ability to start under load .Some disadvantages of induction of induction motors are they cannot opearte at DC .When used with utility power they are constant speed machines When operated from utility power,they have limited starting torque and somewhat limites running peak torque capabilities ,when compared to DC type machines .
• Brushless DC motor have some advantages lmuch less rotor heat is generated with the DC bRushless drive .The peak point energy efficiency for a DC brushless drive will typically be a few percentage points higher than for an induction drive .Some disadvantages of Brushless DC motor are as machine size grows ,the magnetic losses increase proportionality and part load efficiency drops.Permamnent magnet are expensive and difficult to handle due to very large forces ,whwen any ferrromagnetic gets close to them.
• Finally the author couldn't choose which drive is better than the other but makes it clear that 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