Week-6 Challenge: EV Drivetrain
Q1. Which types of power converter circuits are employed in electric and hybrid electric vehicle?
Power Electronic Converters :-
In electric and hybrid electric vehicles ,the power electronic conveter are considered as the key element that interface their power sources to the drive train of the EVs.
In order to design highly efficient converters for EVs power system, advanced DC/DC and DC/AC convertes are required to adapt the output voltage and current levels with high power qautity.
The 3 types of converters which are widely use in an Electric Vehicle are:-
AC-DC Converter (On Board Charger):-
The electrical circuits that transform alternating current (AC) input into direct current (DC) output are known as AC-DC converters.
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:-
The DC/AC converter is required to convert the dc power to a suitable ac power for the electrical machine.
An inverter is a device that converts DC power from the battery to AC power in an electric vehicle motor.
Reference:-
Q2. 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:-
Input parameters are given:-
Battery pack voltage (V)= 72 V
Rated armature current= 400 A
Armature resistance (Ra)= 0.5Ω
Motor Constant (KΦ)= 0.7
Chopper Switching frequency= 400 Hz
Duty cycle = 70%W
Solution:-
Vehicle output voltage (Vv) is given by:-
Vv=Battery voltage(V)*Duty Cycle
Vv=72*0.70
thus, Vehicle voltage = 50.4V
FORMULA:-
ω = (Vv/K)−(Ra/K^2)×Tv
Now, Equation for Vehicle torque is given by: -
Tv = (Vv-ω *K)*K/Ra................(1)
where;
Tv = Vehicle Torque (N-m)
Vv = Vehicle voltage (Volts)
ω = steady state speed of vehicle (rps)
K = Motor constant
Ra = Armature Resistance
Substituting all these values in eq(1)
Tv = (50.4-0.7*ω )*0.7/0.5
Tv = 70.56 - 0.98*ω ..............(2)
Given vehicle speed-torque ,
.........(3)
Solving these eq (2) & (3)
70.56 - 0.98*ω = 24.7 +0.0051ω^2
0.0051ω^2 + 0.98ω - 45.85 = 0
By taking quadratic Equation, we get two values of,
ω=38.85rad/sec & ω=-230.95 rad/sec
we will take positive value,
ω=38.85rad/sec
Q3. Develop a mathematical model of a DC Motor for the below equation using Simulink.
MATLAB SCRIPT:-
SIMULINK MODEL :-
RESULTS:-
Q4. Refer to the blog on below topic:
Induction Versus DC brushless motors by Wally Rippel, Tesla
Explain in brief about author’s perspective.
According to the blog “Induction versus DC Brushless motor by Wally Rippel, Tesla”, the author wants to highlight topics related to EV technology, especially related to DC brushes and motors.
According to him, DC is replaced by DC Brushless motors or Induction motors. Also, Lead-acid Battery is replaced by lithium ion batteries for EV’s.he said that there will be the future of both the components induction and brushless DC motor depends upon their demands and uses.
DC BRUSHLESS MOTOR :-
The technology behind the DC Brushless motor is that it has more than 2 permanent magnet which generates a DC magnetic field. For better Torque generation in rotor and stator, a current flow in winding and this happen due to magnetic field near the stator. According to him, the brushless motor needs a proper flow of current into rotor and stator if it will be not in proper way then the current will not generate and there will be decrease in torque. To maintain electrical to mechanical conversion there should be smooth flow of current otherwise the brushless motor is not useful. A brushless motor does not create any starting torque.
The advantage of DC Brushless motor is that there is low heat generation in the rotor, its cooling capacity is better as compared to induction motor drive; Also Peak Power efficiency is high. Another difference is that DC Brushless drive can also operate at unity power factor, whereas the best induction drives is about 85%, this means that the peak point energy efficiency for a DC Brushless drive will typically be a Few % points higher than for an Induction drive.
INDUCTION MOTOR :-
The technology behind the induction motor is that it basically uses a 3-phase Induction motor which was Discover by “Nikola Tesla” in 1889. In Induction motor there is the use of steel laminated device instead of Magnets. Currents flowing in the stator windings produce a rotating magnetic field that enters the rotor. In an Induction motor current interacts with the Magnetic field generated by stator to produce a force which is required for rotor torque. The induction motor is compatible with a power source. An induction motor cannot operate from DC voltage it always require AC voltage.
The induction motor does not have any magnets and in this the B field is adjustable. In an induction motor B field is proportionate to V/f (Voltage to frequency). This technology is used to reduce the magnetic losses and conduction losses, due to which efficiency will maintain at maximum peak. This all lead to increase the performance, induction motor is very useful and efficient for high performance. In an induction motor, the peak efficiency is less but it works smoothly better. The controlling of induction motor or mechanism is more complex. Also the Torque generated is low and the motor temperature increases when it works at high speed.
INFERENCE :-
Question is that which one is the best brushless DC motor or Induction motor?
According to Sensors, the DC Brushless motor requires absolute position sensor whereas induction motor only needs speed sensors.
Another factor is related to cost of permanent magnets it is costly in Kg. Also, the permanent magnet rotor needs more careful maintenance and it’s difficult to handle. So the cost of induction motor is less.
conclusion according to the author is that the induction motor drives is only best for Pure High Performance EV whereas, DC Brushless drive are beneficial for all hybrid as well as Plug-In Hybrid Vehicle.