Week-6 Challenge: EV Drivetrain
1) Types of power converter circuits are employed in electric and hybrid electric vehicle?
AC-DC-DC COnverter:
In plug in EV/HEv, Battery can be charged externally through battry charger.
DC-DC Converter:
From the Battery to inverter, DC-DC converter are used to get the required DC input to the inverter. DC DC converter has variuos variety like buck, boost, flyback, forward converter. based upon the requirements, suitable converters will be used.
DC-AC Inverter:
Inverter converts DC input AC voltage as output for the operating Motors. In most cases, inverter may be 3 phase output.
2)
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
Duty Ratio = 70%
Solution:
we know that Speed equation W= V/KΦ -( Ra/(KΦ)2)T
by solving T =((V*KΦ)/Ra)-((KΦ^2*W)/R)
T= torque
V=Armature voltage
Ra=resistance
W=speed rad/sec
by equating the above equations we get
24.7+0.0051*W^2 = ((V*KΦ)/Ra)-((KΦ^2*W)/Ra)
24.7+0.0051*W^2=(72*0.7)/0.5-(0.7^2/0.5)*W
70.56-0.98*W=24.7+0.0051*W^2
W^2+192.15*W-8992.5=0
W=38.95 and W = -231.
speed cannot be negative, so
Steady state speed is 38.96 rad/sec
Steady state speed is 372 RPM
3) Mathematical model of a DC Motor for the below equation:
ω">ω= V/Kϕ">ϕ -Ra/Kϕ">ϕ^2 .T
Speed Torque Characterstics of the DC Motor is simulated and shown below;
4)
| DC Brushless | Indution Motor |
| Require an absolute position sensor | Require an Speed sensor |
| less rotor heat is genereted ,rotor cooling is easier and peak point efficiency higher operate at unity power factor | Power factor is about 85%,peak point efficiency higher compare to DC brushless |
| average efficiency is low | Average efficiency is high |
| Permanent magnets are expensive | No magnet there is advantage in cost |
| They are easy to control | The control laws are more complex and difficult to understand , so difficulties to control |
And finally, both will be alive and both are best as per the requirement ...