Week-6 Challenge: EV Drivetrain
1) a) EV Charger - AC2DC (Rectifier)
b) EV Motor Drive - DC2AC convertor (Invertor) One DC level to another AC voltage and frequency - If AC Induction motor is used.
c) DC2DC Converter - To power infotainment, lights, etc. 100V to 12V converters. They are called step down choppers. Used in auxiliary of an electric car.
d) AC2AC converters are not used in EV, and HEVs because the battery is a DC source.
2) The vehicle speed - torque characteristic is T = ((24.7 + (0.0051)W^2))/(0.7*72)
The motor speed - torque characteristic is T = (d1*Vt/kphi - Wm) * (kphi^2/Ra)
Hence, T = 70.56 - 0.98Wm (after substituting the given values).
Now, at steady-state T vehicle = T motor.
Hence, after solving for steady-state angular velocity, W = 38.91 rad/s or 371.75 rpm.
3) The author's point here is that there is no such thing as a generic 'best option' using the example of an induction motor and BLDC motor. But, the best option is specific to the current scenario. For a specific set of performance criteria, there exists the best choice. To come to the best choice solution too is not an easy choice as far as induction and BLDC motor are concerned.
The author continues to elaborate on why exactly, at first glance, a BLDC motor might seem easily better. But the author breaks that down into pros and cons for either machine.
BLDC Pros and cons:
Pros:
1) Less heat generated, so easier cooling.
2) Higher peak efficiency point.
3)
Cons:
1) Cannot control B value because it has permanent magnets
2) Efficiency drops as machine size increases.
3) PM magnets expensive
4) Rotor is difficult to handle.
Induction Motor Pros and cons:
Pros:
1) B field adjustable.
2) V can be reduced at light loads - reducing magnetic losses
3) Losses need not increase with increasing machine size.
4) Some scenarios - induction motors have higher average efficiency by optimizing eddy, hysteresis and I^2R Losses.
5) Induction machines that are spinning produce little or no voltage when de-excited, they are easier to protect.
Cons:
1) They are more difficult to control.
2) Added development costs..
In conclusion, the author suggests that BLDC drives will continue to dominate in the consumer market. But induction motors will dominate in the niche market of high performance pure electrics.