Week-6 Challenge: EV Drivetrain

ARUNKUMAR P - Student of EV live batch16

Question.no:1.Which types of power converter circuits are employed in electric and hybrid electric vehicle?

Power Electronic Converters: -
In Electric and Hybrid Electric Vehicles (EV/HEV), the power electronic converters are considered as the key elements that interface
their power sources to the drivetrain of the EVs. In order to design highly efficient converters for the EV’s power system, advanced
DC/DC and DC/AC converters are required to adapt the output voltage and current levels with high power quality.
The 3 types of converters which are widely used in an Electric Vehicle are:

AC – DC Converter (On Board Charger): -
AC to DC converters are most commonly used in Plug-in Hybrid Electric Vehicles (PHEV) & Plug-in Electric Vehicles (PEV). These
vehicles get their propulsion power from an external electricity source (charging stations) which is alternating current. The battery
needs to be charged using a direct current source. For this purpose, AC to DC converter is employed in a PHEV & PEV.

DC – DC Converter: -
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.
The power of the DC/DC converter depends on the characteristics of the vehicle such as top speed, acceleration time from 0 to 100
Km/h, weight, maximum torque, and power profile (peak power, continuous power).

DC – AC Converter (Inverter): -

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

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Question.no: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%?

Given parameters:

The following input parameters are given: -
Battery pack voltage (V) = 72V
Rated armature current = 400 A
Armature Resistance (R ) = 0.5Ω
Motor constant (K ) = 0.7
Chopper Switching frequency= 400 Hz
Duty Cycle = 70%

Solution: -
Vehicle Output Voltage (V ) is given by: -
V = Battery Voltage (V) * Duty Cycle
Vv = 72 * 0.70=50.4.

........(1)

Thus, Vehicle voltage = 50.4V
Now, Equation for Vehicle torque is given by: -

Tv =((Vv − ω. K∅ ) ⋅ K∅)/Ra

Substituting given values in the above equation...we get,

Tv=((50.4*0.7 - ω.(0.7)^2)/0.5

therefore, Tv=70.56-0.98*ω.......(2)

by Equating equation 1 and 2

70.56-0.98*ω=24.7+(0.0051)ω^2

(0.0051)ω^2 + 0.98*ω - 46.94 =0

by solving the above equation and negleting negative value we get

ω=38.85 rad/s

or

ω=371rpm

Result:

Hence from the above solution we get ω=371rpm with an duty cycle of 70%

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Question.No.3:Develop a mathematical model of a DC Motor for the below equation using Simulink.

ω= V/Kϕ -Ra/Kϕ^2 .T

Thus the above model is simululated using the values that displayed in the above window. the output value o speed=62.

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4. Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

Explain in brief about author’s perspective.

The following points can be concluded from the above topic:

• 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. He explains that all engines were similar and it was up to the user to select according to their requirement. He also speaks about induction motor and brushless DC motors and presents his view that these two technologies will be widely used for the coming years.
• Then he explains the working of both 3-phase induction motor and a brushless DC motor.
• Now the author has done comparison between these two technologies and stated some advantages and disadvantages of
  each.
• Induction motor have some advantages like: it has no magnets. The motor has the ability to start under load. No inverter is
  needed. Some disadvantages of Induction motors are: They cannot operate from DC; AC is a must. Shaft speed is proportionate
  to line frequency. Hence, when used with utility power, they are constant speed machines. When operated from utility power,
  they have limited starting torque and somewhat limited running peak torque capabilities, when compared to DC type machines.
• Brushless DC motor have some advantages like: much less rotor heat is generated with the DC brushless drive. The peak point
  energy efficiency for a DC brushless drive will typically be a few percentage points higher than for an induction drive. Some
  disadvantages of Brushless DC motor are: as machine size grows, the magnetic losses increase proportionately and part load
  efficiency drops. Permanent magnets are expensive and difficult to handle due to very large forces that come into play when
  anything ferromagnetic gets close to them.
• Finally the author 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, and that induction drives will likely maintain dominance
  for the high-performance pure electrics.