Week-6 Challenge: EV Drivetrain

1,

There are mainly three types of Power converters are used in Hev or Ev.

• AC to DC converter (rectifier) :
  • These type of converter converts the ac voltage into the dc voltage. Ev Charger is an example.

• DC to AC converter (Inverter) :
  • These type of converters convert the DC voltage into AC voltage. In Ev it is used in case of Induction motor inverter to convert dc voltage from the battery to ac voltage to the motor supply.

• DC to DC converter (Chopper) :
  • A chopper is a dc to dc converter. It may be step down (reduces voltage) or step up (increase voltage) type.

Step down DC chopper (Buck converter) ;

Step up DC chopper (Boost converter);

• AC to AC converter.
  • These type of converter are usually not used in the Electric vehicle. It is used in the applications like stepless fan regulator. Here voltage and frequency level changes to obtain new AC voltage.

2,

Given that,

Rated Armature voltage= 72 V

Rated armature current= 400 A

Ra= 0.5Ω

KΦ= 0.7 Volt

Chopper Switching frequency= 400 Hz

Given that vehicle speed-torque characteristics ,

We need to find out the steady state speed of the Electric vehicle if the duty ratio is 70%.

we know that average voltage = rated voltage * duty cycle

ie, Vav = V * d = 72 * 0.7 = 50.4 v.

We have T = (V*kϕ)/Ra - ((kϕ)^2*w)/Ra)

= (50.4*0.7) / 0.5 - 0.98*w = 70.56 - 0.98*w = T.

By comparing both equations of torque we get,

24.7 + (0.0051)w^2 = 70.56 - 0.98*w

ie, w^2 + 192.156 w + 8992.15 = 0

By solving the quadratic equation ,

we get w = 38.91 rad/s or -231.07 rad/s

Taking the positive value the staedy state speed will be = 38.91 rad/s.

3,

ω= (V/Kϕ) - ((Ra/(Kϕ)^2))*T

The dc motor model for given equation is created using simulink. The simulink file is attached below.

4,

• Brush less DC motor (BLDC)
  • In BLDC there are more than two permenent magnets which are generates dc magnetic field. Permenent magnets are costly. According to the author the BLDC needs a proper flow of current into rotor and stator. If it will be not in proper way the current will not generates and the torque will reduces. If there is smooth current flow then the BLDC is usefull otherwise useless. BLDC motors does'nt create any starting torque.
• Induction Motors (IM)
  • 3 Phase IM are discovered by Nikola Tesla in 1889. Induction motors uses steel laminations instead of magnets. Current through the stator winding produces the rotating magnetic flux, which rotates the rotor with a speed of less than synchronous speed. Induction machines have no magnets and B fields are “adjustable,” since B is proportionate to V/f (voltage to frequency). This means that at light loads the inverter can reduce voltage such that magnetic losses are reduced and efficiency is maximized. Induction machines are more difficult to control. The control laws are more complex and difficult to understand.
• Conclusion
  • The conclusion of the author is that the DC brushless drives will 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.