Week-6 Challenge: EV Drivetrain

Power converters are used in electric/hybrid vehicles to manipulates the form and magnitude of voltage and current fed from and to the vehicle.

- DC/DC converter - This converts one value of DC voltage into other value of DC voltage ( increase/ decrease) .

AC/DC converter ( rectifier) - These convert AC voltage into regulated DC voltage. The form and magnitude are regulated. Used to get back regen power from vehicle to the battery.

DC/AC converter (inverter) -These convert DC voltage into regulated AC voltage. Form and magnitude are regulated. Usually emplyed when AC motor is used to dirve the vehicle.

AC/AC converter - Regulated AC out put from AC input.

The above converters either increase the magnitude of the output voltage ( boost converters) or reduce the output voltage ( buck converter) .

2) As the duty cycle is 0.7, the effective voltage to the motor is 72 * 0.7 = 50.4 V

The equation representing characteristics of DC motor is

`T = (V.k phi)/R - (Kphi^2. w)/R`

Comparing this with the given equation

gives ---

`(V.k phi)/R - (Kphi^2. w)/R = 24.7 + (0.0051).w^2`

`(50.4 * 0.7)/0.5 - (0.7 ^2 *w)/0.5 = 24.7 + 0.0051.w^2`

Solving for w gives -

`0.0051 w^2 +0.98 w - 45.86 = 0`

w= 38.95 rad/s --- steady state speed.

3) The blog gives a breif description of Motors used in electric vehicles in the recent years and focuses on two types of motors -

• DC brushless motor
• Induction motor

The author compares the two motors based on their working, performance characteristics, efficency points, and suitability for the EV application.

DC brushless motor	AC Induction motor
Uses permannet magnet as rotor, to produce magnetic field.	Uses alternating current in a stator to produce rotating magnetic field.
Stator core involves current flowing within the windings to produce torque interaction between stator and rator. Requires inverter for operation.	The stators for the 3-phase induction motor and the DC brushless motor are virtually identical. It has no magnets. Does not require inverter for operation but integrating it with one gives a smoother operation of this motor for EV.
Requires angle position sensor for operation	requires speed sensor for operation
Does not produce much heat . Cooling is easier	Has heating issues and efficiency depreciation as an effect.
Has higher peak efficieny point	Comparitively lower efficiency point compared to DC Brushless motor.
Permanent magnets are expensive and the motor cost increases as a result. Handling becomes difficult because of the strong magnetic forces between ferromagnetic materials and magnets.	Requires just coils to make the motor and is inherently cheaper to produce and easier to handle as coils need to be excited to produce any magnetic field.
Easier to control for lower to medium performance ranges.	Achieving stability over the entire torque-speed range and over temperature is more difficult with induction than with DC brushless.
difficult to alter motor parameters such as field strenght because of permanent magnets.	induction machines have no magnets and B fields are “adjustable,” since B is proportionate to V/f (voltage to frequency).
Speed is controlled by PWM method.	Speed is controlled by altering RMS speed by altering frequency of fed in voltage.
As the motor size increases, magnetic losses inrease proportionately and loead efficiency drops .	induction motors do not follow the same trend and are thus desired for high performance applications as average efficiency is better than DC machine counterpart.