Week-6 Challenge: EV Drivetrain
1. Which types of power converter circuits are employed in electric and hybrid electric vehicle?
Power Conveter is a device which transfers the power from source side to the load side efficiently with minimum amount of losses.The type of power converters used in the electric and hybrid vehicles are
a. AC to DC Converter which also known by the name Rectifiers. For example For EV battery charger is charged by using the rectifier because the power available in the grid is AC and battery needs DC supply.
b. DC to AC Converter which also known by the name Inverter. For example if we have employed ac machine in the EV than this machine has to be supplied with ac power,that is done through inverter.
c. DC to DC Converter known by popular name Choppers. When the autoinfotainment systems in the vehicles,head light and some auxiliary equipments require small amount of DC power these are powered by the choppers. it is again classified into two types Step up dc-dc converter also known as Boost converter (more output voltage) and the Step down dc-dc converter also known as Buck converter (less out put voltage).
d. AC to AC Converter also called as Cyclo converters. They convert fixed ac voltage and frequency into variable ac voltage and the frequency.Example is the stepless fan regulator.
2. Calculation of Steady state Speed
Given Parameters
Armature voltage=72V
Ia= 400A
Ra=05 ohm
Kɸ= 0.7 V-s
fs= 400Hz
T= 24.7+(0.0051)ὠ^2
Duty ratio is 0.7
We know that Vo= D*Vs
Vo= 0.7*72= 50.4V
ὠ= V/Kɸ -Ra/Kɸ^2 .T--------------------(1)
T=(V*Kɸ/Ra)-(ὠ*Kɸ^2/Ra)
T=(50.4*0.7/0.5)-(ὠ*0.7^2/0.5)
T=70.56-0.98ὠ------------------(2)
Solving equation 1 and 2
24.7+0.0051ὠ^2 = 70.56-0.98ὠ
0.0051ὠ^2+0.98ὠ-45.89=0
solving the quadratic equation we get
ὠ= -231.07 rad/s and 38.92 rad/sec
There fore EV steady state speed is the 38.92 Rad/sec
3. Mathematical model of a DC Motor for the below equation using Simulink.
ὠ= V/Kɸ -Ra/Kɸ^2 .T
4. Authors View on the Brushless DC Motors and the Induction Motors
The Author has compared the BLDC and Induction motors with respect to construction,operation, reliability and the friedliness in using them.
The BLDC Motors have the permanent magnets embedded in the rotor and when the motor is powered the PM magnet produce the dc magnetic field which interacts with the stator magnetic field,which results in the production of the torque.BLDC Motor requires the inverter which is conneted to the stator.
Now coming to the Induction motor,here both stator and rotor does not contain any permanent magnets, both stator and rotor are laminated to reduce the eddy current losses,compared to the BLDC construction the induction motors are simple in construction and cost is reduced due to the absence of the permanent magnets.In case of the induction motor torque is produced due to the interaction of rotating magnetic field and the field produced by the current carrying rotor conductors.Supose if we want to operate the induction motor for variable speed than it should be fed by the variable frequency drive which is nothing but Inverter. some of the draw backs associated with IM Motor are that they cannot operate from DC supply and when used with utility power, they are constant speed machines and they have limited starting torque and somewhat limited running peak torque capabilities, when compared to DC type machines.
Which is the better choice BLDC or Induction Motor??
Earlier days the DC brushless motors were used in the EV applications,later these motors were replaced by the AC induction motor.DC brushless drives are 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 vehicles.