Week-6 Challenge: EV Drivetrain
1.
There are many kinds of power converter circuits.
Fast switching is employed in many motor control elctronics.
Chopper DC to DC is used to control DC machines to vary the duty cycle voltage with fast switching.
VFD (variable frequency drive) is used to control AC machines by varying the frequency of AC current.
AC to DC converter is also known as a rectifier, mostly used in charging devices. DC to AC converter is known as inverter used in Electric vehicles with AC motor, where DC current from battery has to be converted in to AC.
2.
By substituting the given values in the motor torque equation
we get T = 71.4-0.98w, and the vehicle torque is given as T = 24.7+0.0051w^2
with these two equations we get a quadratic equation as 0.0051w^2+0.98w-46.7=0
by solving the above quadratic equation we get w= -231, 39.5
taking w= 39.5 rad/sec = 377 RPM, assuming wheel RPM = motor RPM.
taking wheel radius as 0.35m, vehicle velocity will be 50 Kmph.
3.
According to the author both DC and Induction motors have their own advantages.
induction motors when used in utility can only be constant speed machines.
but Induction motors have fewer parts and easier to maintain, there is no positioon snesor needed.
where as permanent magnet DC brushless motors can always be variable speed.
but permanent magnet DC machies have position sensors and may need maintenance.
Development cost of Induction motors is high, Cost of Permanent magnet DC motors is less but they need rare earth metals for the magnets, for induction motors rotor only uses a conductive material.
average efficiency of Induction motor is higher, in low loads for a variable speed induction machine, the voltage input can be reduced which reduces the eddy current losses, but for PM DC motors the magnetic field strength from magnets is constant and can not be varied.
even though average efficiency of BLDC motors is lower, peak efficiency is always higher for the PM DC motors.
induction motors are generally prefered in cars with high power and performance requirements. But most generally for all the hybrid cases PM DC motor is used.
so there is no winner as such but it depends on the requirements, costs and strategy.