Week-6 Challenge: EV Drivetrain

AIM:

1. To get to know the types of Converters used ih HEV and EV.
2. To find the speed using Torque-speed relation
3. to get to know about induction and DC brushless motor.

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

A Motor drive consist of a power converter and the controller. The power converter and the controller. The power electronic converter handlesthe flow of bluk power from the source to the motor input terminals. The controller process the command input and the feedback information to generate the switching signals for power converter semiconductor switches.

The power converter can be DC drive supplying a DC motor or an AC drive supplying AC motor.

A DC/DC converter in its basic form converts unregulated DC into a certain level of DC voltage as output.

These switching action is so fast so we use PWM (pulse width modulation.) to turn ON and OFF.

The power converter is made of high power fast acting semiconductor device such as bipolar junction transistor. There are some other transistors such as MOSFET, IGBT, SCR, GTO, MCT. These devices are used as on-off electronics switch to convert the fixed supply voltage into a variable voltage frequency supply.

'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 input is converted into a high voltage output it is a it is a step up converter Whereas when a high voltage input is converted into a low voltage output it is a step down converter.

Different types of converters:

2. An electric Vehicle's Powertrain with 72V battery pack in the shown in the diagram below. The duty ratio for acceleration operation is 'd1' and for the braking operation the duty cycle is 'd2'

The other parameters of the electric vehicle are given below.

Motor and Controler parameters:

Rated Armature voltage =72V

Rated Armature current =400A

Ra = 0.5 ohm

k phi = 0.7 volt second

Chopper Switching frequency=400Hz

The Vehicle Speed-Torque characteristics are given by the below

What is EV steady- state if the duty cycle is 70%

As the Torque formula is given, we need to find the speed in rad/sec. Use the other expression available which is given below:

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

T= Torque

V=Armature voltage

R=Resistance

w=Speed (Rad/sec)

Compare the two equations:

24.7+0.0051*w^2=((v*k)/R)-((k^2)*w/R)

24.7+0.0051*w^2=(72*0.7*0.7)/0.5-(0.7^2/0.5)*w

=24.7+0.0051*w^2

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

w^2+192.15*w=8992.15=0

In order to find the roots use following formula

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

As the speed value cannot be negative

Omega (w)= 38.9 rad/sec

3. Explain in brief about the author's perpspective

In the article of the Induction motor and DC brushless motor, the author has mentioned about the -ve side of both induction and DC motor. In the blog the basis construction of both the induction and DC motor is explained

In the case of DC brushless motor, permanent magnets are used which produces a rorating magnetic field. This magnetic field when a current curring conductor is placed in that field it experiences the force in the rotor side and tend to rotate the rotor.

Where as in care of induction motor the current is supplied to stator which results in the generation of EMF when this EMF comes in contact with the rotor which is generally a squirrel cage type, this results in current induced in the rotor. Unlike the DC motor the rotor consist ofbars around them in which get induced and the rotor starts rotating

One of the main differences is that much less rotor heat is generated with DC brushless drive. Rotor cooling is easier and peak efficiency is generally higher for this motor. It is mentioned that the DC brushless can drive at the unit power factor, where as the best power factor for the induction motor is about 85%

In the case of DC brushless motor the strength of the magnetic field is adjustable when at low speed the maximum torque is required therefore magnetic feild should be higher Where as there iss no adjustment in Induction motor.

The construction of DC brushless motor is Costly compared to induction motor due to the use of permanent magnets(PM).

However the speed of DC depends on voltage where as the induction motor speed depends on frequency which is difficult to control.

Learning outcomes:

Types of Convertes used in HEV and EV.

Found out the velocity using speed torque equation

Got to know the differences between the Induction motor and DC brushless motor.