Week-6 Challenge: EV Drivetrain

ypes of power converter circuits are employed in electric and hybrid electric vehicle are

AC-DC Converter

DC-AC Converter

DC-DC Converter or Chopper circuit

AC-DC Converter:

This AC-DC converter circuit used as a charger in EV and HEV to charge the battery by getting supply from Electrical network or Grid which is AC in nature so we need to convert into AC-DC for this we need AC-DC converter.

DC-AC Converter:

This DC-AC converter circuit is also called as Rectifier circuit used in EV and HEV to give supply for induction motor by converting into DC power from battery module to AC power. This used in motor drive.

DC-DC Converter or Chopper circuit:

This DC-DC converter circuit is also called as Chopper circuit used in EV and HEV for increase or decrease the DC voltage level for the requirements.

This will be used for give supply for car infotainment systems like Auxillary accessoris, sound systems and dashboard.

This DC-DC Converter or Chopper circuit are catagorised into two types they are:

Step-down Chopper circuit: This circuit is used for decrease the DC voltage from high to required level say for eg. 100V DC to 10V DC. So, this circuit is called Step-down chopper circuit.

Step-up Chopper circuit: This circuit is used for increase the DC voltage from low to required level say for eg. 10V DC to 100V DC. So, this circuit is called Step-up chopper circuit.

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

Tv=25.7 - 0.0051ω^2

What is EV steady state speed if duty cycle is 70%?

Given Data:

Vbat= 72 Volts

d1=d2= 70%

Ia=400 Amps

Ra=0.5Ω

KΦ= 0.7 Volt second

f=400 Hz

Solution:

W.K.T The acual output of power converter Vo= Vbat*duty ratio

Vo= 72*70%

Vo= 50.4 V

We already know that DC motor speed torque charactristic equation.

T= (KΦ*V)/Ra - (KΦ^2*ω)/Ra

T= 50.4*0.7/0.5 - [(0.7^2)/0.5]ω

T=70.56 - 0.98ω------------ (1)

We already know that the vehicle speed-torque charactristissc equation is.

Tv=25.7 - 0.0051ω^2------------ (2)

Compare eqn. 1 and 2

70.56 - 0.98ω=25.7 - 0.0051ω^2

0.0051ω^2+0.98ω-45.86=0------------ (3)

Now divid the equation 3 by 0.0051 on both side.

ω^2+192.15ω-8992.15=0------------ (4)

The above equation 4 is in quadratic form

so w.k.t. ω =[−b±√b^2−4ac]/2a or ω =[−b±sqrt(b^2−4ac)]/2a

ω =[-192.15±sqrt(192.15^2−4(1*-8992.15)]/2(1)

ω =[-192.15±sqrt(36921.62+35968.6)]/2

ω =[-192.15±269.98]/2

ω =[-192.15+269.98]/2 & ω =[-192.15-269.98]/2

ω = 38.91 & ω =-231.065

Therefore the steady state speed of EV at 70% duty cycle ratio is 38.91 rad/sec.

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

ω= V/Kϕ -Ra/Kϕ^2 .T

For develop a mathematical model of a DC motor for a given equation. Here i have assume the values for all the constants.

V= 72 V

Ra=0.5Ω

KΦ= 0.7 Volt second

T=50Nm

To implement the Mathematical model in simulink here i have using some simulink blocks.

• Constant - Constant block gives constant array of value or signal. Here i am using this for voltage, resistance and motor torque.
• Sum- Sum Block is use to sum given inputs.
• Product- Product block is use to multiply the given inputs with a specified gain.
• Display- Display bock is use to see the final output speed of the DC motor.

Here Below i have shown the mathematical model of a DC motor for a given equation.

The display block shows DC motor speed as 51.84 rad/sec for the values I have assumed.

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 this blog the author Wally Rippel discussed about what are the diffrences and challenges are facing while using DC Brushless motor and Older one Nicola Tesla invented 3 phase induction motor elobratedly.

Initially the author comparing this drives with engine by giving one example choosing one best engine type for all the needs is too difficult. Why becuase there is no one best engine type it depends upon the personal requirements,price and performance needed.

This is also true for a electric drives. From this the author conclude one drive and one engine is not fit for all.

And then author compared the Induction motor and Brushless DC motor.

S.No	Induction motor	DC brushless motor
1	Induction motor consists of a rotor and the stator. Stator is a three coil winding passing through the slots of the stator which is made up of thin high permeable steel lamination inside a steel or cast iron frame.	The rotor inclues two or more permanent magnets and the stator comprises through the coils get energised and becomes an electromagnet and it is based on the operation between the interaction of permanent magnet and electromagnet.
2	IM has no permanent magnets	BLDC has two or more permanent magnets
3	Rotor cooling is easier and peak point efficiency.	Less rotor heat is generated
4	The power factor for IM is about 85%	BLDC operates at unity power factor.
5	As the IM size grows, magnetic losses does not necessarily increase which makes it more suitable where high performance is desired.	In BLDC motor as the machine size grows there is an increase in magnetic losses that causes the load efficiency to drop, which makes it not suitable high performance needed.
6	Cost is less compared to BLDC	Cost is high because of the use of permanent magnets
7	IM is mostly used in High- performance pure electric vehicle.	BLDC motor will used in hybrid and pulg-in hybrid vehicles.
8	Induction machines are more difficult to control. The control laws are more complex and difficult to understand.	Compared to IM BLDC motor are easy to control
9	No need for inverter the motor has the ability to start under load	Inverter is mandatory without inverter BLDC motors are useless.