Week-6 Challenge: EV Drivetrain

1.Power Coverter Circuits

All electric and vehicles are incorporated with power converter circuits in order to supply volatages and currents suitable for the end point of the applications.

AC to DC Convereters or Rectifiers

These converters are used for charging the battery of the vehicle from an AC source as the batteries of the vehicles are generally of DC

DC to AC or Inverters

This is to transform the input battery current to an induction motor where the current for the battery is converted to an alternating current which acts as the input for the motors in EVs

DC to DC or Chopper

These are used as many DC operated applications need different levels of DC voltage from a fixed DC source. This circuits is mainly used in DC drives i.e electric and electric vehicles

2.To find the steady state speed of the vehicle

Given data

Rated Voltage (Vt) = 72 V

Armature Resistance (Ra) = 0.5 Ohm

Motor Constant (KΦ) = 0.7 V-s

Vehicle characteristics T = 24.7 + 0.0051 w^2

Duty cycle (d) = 70%

Motor characteristics T = [ (KΦ*Vt*d)/Ra - (KΦ^2/Ra)*w ]

Substituting the values

T = (0.7*0.7*72 / 0.5) - (0.7^2/0.5)*w

T = 70.56 - 0.98*w

Equating both,

24.7 + 0.0051 w^2 = 70.56 - 0.98 w

Equation,

0.0051 w^2 + 0.98 w - 45.86 = 0

solving the quadratic equation ,

Steady state Speed (w) = 38.9 rps = 2334 rpm

3. Induction Versus DC brushless motors by Wally Rippel, Tesla

There is a lot of changes with the inventions of electrical drives in automotive industry and there is no best machines still now choosed. As each machines has its own advantage over the others based on the application and the user end requirement.

He then compares the major machines DC - brushless and the Induction motors as these are popularly known and used in the automotive sector stating that these machines will be comparitively incorporated in the automobiles i.e the and the fully electric vehicles.

The blog explains the advantages of the DC and the AC machines in detaill over the stability , efficiency , power and the cost. Each has its own pros and cons.

Both the machines almost have the same kind of stator , the only difference is that the rotor and the inverter control differs (as the control code for the DC changes as it requires an position sensor while the induction requires only a speed sensor but these are relativily differences)

Dc brushless has the tendency of peak performance whereas the induction motors are compared to DC but these are better than brushless as these work at constant speed. Due to the eddy current , Hysterisis and the heat losses they have to be controlled and there is no alternative for changing the magnets but in of induction motors the magnetic field is proportional to V/f ( voltage to frequency ) and so the losses are minimum.

Since the DC brushless drives are common in electric vehicles and the induction are common in fully electric vehicles , Both the machines are going to be used side by side in the upcoming future of the automotive industry.