Week-6 Challenge: EV Drivetrain

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

Types of power converter which are employed in electric and hybrid electric vehicles are:

1. AC to DC(Rectifier)
2. DC to DC(Chopper)
3. DC to AC (Invertor)
4. AC to AC (Cycloconverters)


- AC to DC(Rectifier):

A rectifier is an electrical device that converts the alternating current to direct current, which flows in only one direction. In Electric vehicle, the converter is built inside the car which is known as the onboard charger, that is nothing but a Rectifier. It converts power from AC to DC and then feeds it into the car battery. this is the most
common charging method for electric vehicles today.

- DC to DC(Chopper):

A DC-to-DC converter is an electronical circuit that converts a source of direct current from one voltage level to another. Power levels range from very low (small batteries) to very high (high-voltage power transmission).Thr chopper circuit is connected between DC input source and DC load. The Chopper consist of power electronic switching device such as thyristors which is used to produce the required voltage supply. DC charger has a converter inside the charger itself, so it can feed power directly to the car battery and does not need the onboard charger to convert it

DC chopper is mainly used is DC drives, that is Electric vehicles and hybrid vehicles.

- DC to AC (Invertor):

A power inverter is an electronic device that changes direct current to alternating current. The voltage, frequency and overall power handling depend on the design of the specific device. The inverter does not produce any power, the power is provided by the DC source.

- AC to AC Converter(Cycloconverters):

AC to AC converter is used for converting the AC waveforms with one particular frequency and
magnitude to the waveform with another frequency at another magnitude. This conversion is
mainly required in case of speed controlling of a machine, for low frequency and variable
voltage magnitude application.

Q2. An Electric Vehicle's Drivetrain 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 is2'. 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 V-s

Chopper Switching frequency= 400 Hz

The vehicle characteristics are given by the equation

TTR=24.7+0.0051w2

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

The given Motor and Controller Parameters:
Rated Armature voltage= 72 V
Rated armature current= 400 A
Ra= 0.5Ω,
KΦ= 0.7 V-s
Chopper Switching frequency= 400 Hz
The vehicle characteristics are given by the equation
TTR=24.7+0.0051w2


DC machine Torque speed relation:

`T=(V.Km(phi))/(Ra)-(Km(phi)^2)/(Ra).omega`

Where,
T- Motor Torque
V- voltage supply
Ra- Armature Resistance
Km(`phi`)- Motor constant
`omega`- Angular speed of the motor

Solution:
Voltage(motor)= voltage of armature*dutycycle
Voltage =72*0.7=50.4volts
`T=(V.Km(phi))/(Ra)-(Km(phi)^2)/(Ra).omega`
Motor_T= (50.4*(0.7))/0.5-((0.7)^2/(0.5))*w ------- (Eq 1)
Given,TTR=24.7+0.0051w2 ---------(Eq 2)
(50.4*(0.7))/0.5-((0.7)^2/(0.5))*w=24.7+0.0051w2
We solve the equation to get `omega` by using the quadratic formula;

Where,
a=0.0051
b= 0.98
c= -45.89
The 2 solution are:

`omega`= -230.06 rad/sec and 38.95rad/sec

The vehicle is moving in forward direction, so we take the positive value as 38.95rad/sec

Q3. Refer to the blog on the below topic:
Induction Versus DC brushless motors by Wally Rippel, Tesla
Explain in brief about the author’s perspective.

Brief explanation of the blog :

He says that the future of the EV technology cannnot be predicted and it purely depends on the requirement. He then throws his views on induction and brushless motor on their technolog, similaritites and disimalarities.

He finds that the induction motor have great utility, it haasa the ability to go directly compatible with conventional system. While brushless mototr requires an inverter system. He further lets us know about the limatations of the induction motor that it requires AC power source, that would eventually require an inverter and feedback signal.

His conclusion is 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 pure electrics.

So, he clearly means that there is no clear winner in the future of EV and HEV and there could be a new technology.