Week-6 Challenge: EV Drivetrain

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

In EV's and HEV's the power electronic converters are considered as the key elements and interface their power source to the drivetrain of EV's. In order to design highly efficient converters for EV power system,advanced AC/DC and DC/DC convertersare required to alter teh output voltage and current levels with high power quality.

AC_DC Converter(chopper):

It is the most commonly used in PHEV's and BEV's.The battery needs to charge with DC current so AC to DC converter is used.

DC-DC converter:

It can be used to interface the elements in the electric power train by boosting or chopping the voltage levels.The main dc-dc converter changes dc power from an on_board 200-800 high voltage battery into low dc voltages to power headlights,interior lights,wiper and window motors,fans,pumps and many other systems within electric vehicles.

DC-AC Converter(inverter):

The DC/AC Converter is required to convert the dc power to a suitable ac power for the electric machine. The power output from the battery pack is converted using inverter to be used in electric motor.

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%?

Solution:

Vehicle output voltage(V) is :

V=Rated voltage* Duty Cycle

V=72*0.070

vehicle voltage=50.4V

Equation of torque is T=(V-ω.K_ϕ).K_ϕ/R_a

T=(50.04-0.7.ω)*0.7/0.5

T=70.56-0.98ω

Vehicle torque speed characteristic is

comparing with eqn1

70.5-0.98ω=24.7+0.0051ω^2

we get quadratic equation is

0.0051ω ^2+0.98ω -46.94=0

so ω =38.85 and -230.95

take positive value so,ω=38.85 rad/s.

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

ω">ω= V/Kϕ">ϕ -Ra/Kϕ">ϕ^2*T

Solution:

consider V=220V

Kϕ=0.9

Ra=0.7

Simulink Model screenshoot:

scope result:

4. Induction Versus DC brushless motors by wally Rippel,Tesla.Explain in brief.

Wally Rippel is a long-time of electric vehicles. Prior to joining Tesla Motors, he was an engineer at AeroVironment, where he helped develop the EV1 for General Motors and was featured in the documentary movie,Who killed the electric car? Wally has also worked for the Jet propulsion Laboratory on electric vehicle battery research, among other projects. In 1968, as a Caltech undergraduate student, he built an electric car (a converted 1958 Volkswagen microbus) and won the Great Transcontinental Electric Car Race against MIT.

In the beginning author describes the dominance of IC engines in the world of automobiles industry and also discuss the types of engines.

Then he explains about the 3 phase induction motor and a brushless DC motor.

Induction motor have some advantages they are it has no no magnets.it has ability to start under load.some disadvatages they cannot operate from the DC;AC is a must.

When compared to DC type machine Brushless DC motor have some advantages like much less rotor heat is generated with the DC brushless drive.disadvantages is permanent magnet is expensive and difficult to handle due to large force that come into play when anything ferromagnetic gets close to them.

Finally the author couldn't choose which drive is better than others, the drives maintain dominance for the high performance pure electric vehicles.