Week-6 Challenge: EV Drivetrain

Week-6 Challenge: EV Drivetrain

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Challenge

EElango Ponnuswamy9 Oct 2022

Which types of power converter circuits are employed in electric and hybrid electric vehicle?
Ans
	We have 3 types of power converters using on electric and hybrid electric
	1	AC-DC on board chargers
	2	DC-DC convertors
	3	DC-AC convertors(Invertors)
1	AC-DC on board chargers
	This one we can using in charging station

	DC-AC convertors(Invertors)

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

This one used for using home charging

2,quest

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%?

Ans

Given values

Armature voltage= 72 V

Rated armature current= 400 A

Ra= 0.5Ω, KΦ= 0.7 Volt second

Chopper Switching frequency= 400 Hz

Vv = Battery Voltage (V) * Duty Cycle

Vv = 72 * 0.70

Vehicle voltage = 50.4V

Now, Equation for Vehicle torque is given by: -

`T_v= ((V_v- ω.K_∅ )*K_∅)/R_a`

Where;

`T_v`= Vehicle Torque (N-m)

`V_v` = Vehicle voltage (Volts)

`ω`= steady state speed of vehicle (rps)

`K_∅`= Motor constant

`R_a`= Armature Resistance

`T_v= ((50.04 - 0.7*ω)*0.7)/0.5`

`T_v=70.56-0.98*ω`

`T_v=24.7+0.0051*ω^2`

Solving these two equations,

`70.56-0.98*ω =24.7+0.0051*ω^2`

We get a quadratic equation:

`0.0051*ω^2+0.98*ω-46.94=0`

Since quadratic equation, we get two values of ;

`ω`= 38.85 rad/s and `ω` = -230.95 rad/s

We take the positive value;

Steady state speed of vehicle = = 38.85 rad/s

Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

Explain in brief about author’s perspective.

	My conclusion is that DC brushless drives will likely continue to dominate in the hybrid and coming plug-in hybrid markets

1	In the beginning, author describes the dominance of Internal Combustion Engines (ICE) in the world of automobile industry and also discuss different types of engines.
2	He explains that all engines were similar and it was up to the user to select according to their requirement.
3	He speaks about induction motor and brushless DC motors and presents his view that these two technologies will be widely used for the coming years.
4	Then he explains the working of both 3-phase induction motor and a brushless DC motor.
5	Now he has done comparison between these two technologies and stated some advantages and disadvantages of each.
6	Induction motor have some advantages like: it has no magnets. The motor has the ability to start under load.No inverter is needed
7	We have some disadvantages of Induction motors are: They cannot operate from DC; AC is a must. Shaft speed is proportionate to line frequency
8	Hence, when used with utility power, they are constant speed machines. When operated from utility power,
9	They have limited starting torque and somewhat limited running peak torque capabilities, when compared to DC type machines.
10	Brushless DC motor have some advantages like: much less rotor heat is generated with the DC brushless drive
11	The peak point energy efficiency for a DC brushless drive will typically be a few percentage points higher than for an induction drive
12	Some disadvantages of Brushless DC motor are: as machine size grows, the magnetic losses increase proportionately and part load efficiency drops
13	Permanent magnets are expensive and difficult to handle due to very large forces that come into play when anything ferromagnetic gets close to them
14	Finally the he couldn’t choose which drive is better than the other but makes it clear that DC brushless drives will likely continue to dominate in the hybrid and coming plug-in hybrid markets
15	Induction drives will likely maintain dominance for the high-performance pure electrics.

DC-DC convertors

DC-DC converters can be used to interface the elements in the electric power train by boosting or chopping the voltage levels.

By introducing DC/DC converters one can choose the voltage variation of the devices and the power of each device can be controlled.such as top speed, acceleration time from 0 to 100 Km/h, weight, maximum torque, and power profile (peak power, continuous power).

The power of the DC/DC converter depends on the characteristics of the vehicle