Week-6 Challenge: EV Drivetrain

AIM(1):-Which types of power converter circuits are employed in electric and hybrid electric vehicle?

• A motor drive consists of power converter and the controller.The power electronic converter handles the flow of power from source to the motor input terminal.
• The controller process the command input and the feedback information to generate the switching signals for power converter semiconductor switches.
• The power converters can be a DC drive supplying a DC motor or AC drive supplying an AC motor.
• A DC/DC converter used to converts unregulated DC input voltage at certain level to regulated DC output voltage at different level with very high frequency.The switches are turned on and off by pulse width modulation(PWM).
• The power converter is made of high power fast-acting semiconductors devices,such as a bipolar junction transistor.
• There are some other transistors such MOSFET,IGBT,SCR,GTO,MCT.These devices are used as on-off electronics switch to convert the fixed supply voltage to variable voltage and variable frequency.
• All these devices have a control input gate or base through which the devices are turned on and off as per the command generated by the controller.
• There are two types of step converters.when a low voltage input is converted into high voltage output it is a step-up converter.whereas when a high voltage input is converted into a low voltage output it is step down converter.

AIM(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%?

• As we know the torque equation,

`T=(V*K)/R - (w*K^2)/R`

Here,

T= torque

V= Avg voltage = armature rated voltage * duty cycle = 72*0.7 = 50.4

R= Armature resistance = 0.5 ohm

w= Speed in rad/sec

• By comparing two equation we get,

`24.7 + 0.0051*w^2 = (V*K)/R - (w*K^2)/R`

`24.7 + 0.0051*w^2 = (50.4*0.7)/0.5 - (0.7^2*w)/0.5`

`24.7 + 0.0051*w^2 = 70.56 - 0.98*w`

`0.0051*w^2 = 45.86 - 0.98*w`

`w^2 = 8992.16 - 192.166*w`

`w^2 + 192.16*w - 8992.16 = 0` .............1

• For quadratic equation of the form `ax^2+bx+c=0` the solutions are

`x_(1,2)=(-bpmsqrt(b^2-4ac))/(2a)`

• As we solve the equation 1 we get two solution x1=38.91,x2=(-231.07).But speed value can not be negative.
• So,

`w=38.91 (rad)/sec`

AIM(3):-Develop a mathematical model of a DC Motor for the below equation using Simulink.

ω">ωω= V/Kϕ">ϕϕ -Ra/Kϕ">ϕϕ^2 .T

AIM(4):-

Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

Explain in brief about author’s perspective.

• In the blog of induction and DC brushless motor,the author has mentioned about positives and negative side of both the induction and DC brushless motor is explained.
• In case of DC brushless motor,permanent magnets are used which produces a rotating magnetic field.This magnetic field when induces a current in the conductor.This current results in force generation in the rotor and this results in rotation of rotor.
• Whereas in case of induction motor, the current is supplied to the stator which results in the generation of emf, when this emf comes in contact with rotor which is generally a squirrel cage type,This results in current induced in the rotor.
• The rotor consists of conductor plates and placed in a cage like structure.This also consists of bars around them in which current get induced and rotor starts rotating.
• 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. It is mentioned that the DC brushless can drive at unit power factor, whereas the best power factor for the induction drive is about 85%.
• In case of DC brushless motor, the strength of the magnetic field is adjustable. When at low speed the maximum torque is required magnetic field should be maximum, i.e. inverter and motor current maintained at their lowest optimize efficiency.
• whereas there is no such adjustment in case of induction motor. As machine size grows, magnetic losses increases proportionally and part load efficiency drops. In case of induction motor, as machine size grows, losses do not necessary grow.
• The construction of DC brushless motor is costly compared with an induction motor, due to the use of permanent magnets.
• However thought the speed variation of induction motor depends upon the frequency input, it is difficult to control.

• Learning outcome:

• Types of converters used in HEV and EV vehicles.
• To find the angular velocity using the torque-speed expression.
• To know about the induction and DC motor and try to find the best options available for EV application.