Week-6 Challenge: EV Drivetrain
Q .1 Which types of power converter circuits are employed in electric and hybrid electric vehicle?
Solution-
On Electric vehicle which include both fuel cell electric vehicle and battery electric vehicle and hybrid electric vehicle the converter , inverter, and ontroller are integrate d in one unit, but each perform different task.
- DC-AC motor-
Convert direct current from the battery to alternating current to be used by other device such as the traction motor.
It is also called Inverter.
This converter are used dc supply and convert variable AC voltage.
- AC-DC Motor-
It is also called for Rectifier.
It Convert AC Source To DC source for supply.
This Converter contain various component like ,transformers, switching unit ,filter and control block.
The supply voltage is adjust to transformer and rectify to dc source.
- DC-DC Motorr-
It is also called chopper.
Many DC application need different level of voltage source from fixed dc source.
The output of the chopper can be high or less and fixed .
The type DC-DC converter-
Step-down
Step –up
Q.2An 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%?
Solution-
Duty cycle=70%=0.7
therefore,
Actual Voltage=0.7*72=50.4V
we have speed - torque euation,
`Tv=24.7+(0.0051)w^2`-----(1)
Torque-Speed characterstics of DC motor-
`T=frac{VKphi}{Ra}-frac{(Kphi)^2){Ra}*w`
=50.4*0.7/0.5-(0.7)^2/0.5*w
T=70.56-0.98w--------------(2)
From Equation (1) and (2)
`24.7+0.0051w^2=70.56-0.98w`
`0.0051w^2+0.98w-45.86=0`
Divide 0.0051 on both side
`w^2+192.156w-8992.156=0`
on soving above quadratic equation
`w=38.915`rad/s or `w=-231.0718`rad/s
Speed of EV(w)=38.915 rad/s
Q.3 Refer to the blog on below topic:
Induction Versus DC brushless motors by Wally Rippel, Tesla
Explain in brief about author’s perspective.
Solution-
- In this article author is mention about advantage and disadvantage side of DC brushless motor and Induction motor explained.
- In DC brushless motor permananet magnet are used which induces a current in conductor.
- In case induction motor the current is supply to the stator which result in generation of emf,when this emf comes in contact with rotor which is use squirell cage type this produce current in rotor.
- In this DC brushless rotor, the induction rotor has no magnets
- In 3-phase induction motor is connected to utility type 3-phase power, torque is produced at the outset; the motor has the ability to start under load. No inverter is needed.
- In brushless DC motor produces no starting torque when directly connected to fixed frequency utility power. They really need the aid of an inverter whose “phase” is maintained in step with the angular position of the rotor.
- While 3-phase induction motors have great utility, they also have some severe limitations.They cannot operate from DC its operate AC is a must.
- Permanent magnets are expensive – something like $50 per kilogram. Permanent magnet (PM) rotors are also difficult to handle due to very large forces that come into play when anything feromagnetic gets close to them.
- while induction motors will likely retain a cost advantage over PM machines.