Challenge: EV Drivetrain

AIM:

1. To understand different power convertors found in EV vehicles.
2. To understand duty cycle ratio and Power electronics on he vehicle control
3. Author perpective on Induction motor vs DC brushless motors by Walley Rippel.

OBJECTIVE 1: Which types of power converter circuits are employed in electric and hybrid electric vehicle.

There are 4 main categories of Power converter which are elaborated below:

AC to DC Converter (Controlled Rectifier)

An AC to DC converter circuit can convert AC voltage into a DC voltage. The DC output voltage can be controlled by varying the firing angle of the thyristors. The AC input voltage could be a single phase or three phase.

AC to AC Converters. AC to AC Converter

This converters can convert from a fixed ac input voltage into variable AC output voltage. The output voltage is controlled by varying firing angle of TRIAC. These type converters are known as AC voltage regulator.

DC to DC Converters

These converters can converter a fixed DC input voltage into variable DC voltage or vice versa. The DC output voltage is controlled by varying of duty cycle.

DC to AC Converters or Inverters

These converters are connected between DC source of fixed input, and variable AC load. Most commonly, these DC to AC converters are called as inverters. An inverter is a static device that converts fixed DC supply voltage to variable AC voltage.

OBJECTIVE 2:

An Electric Vehicle's powertrain with 72V battery pack in shown in the diagram below. The duty ratio for acceleration operation is 'd1' and for the braking operation the duty ratio is 'd2'. The other parameters of the electric vehicle is given below, Rated Armature voltage= 72 V Rated armature current= 400 A, Ra= 0.5Ω, KΦ= 0.7 Volt second ,Chopper Switching frequency= 400 Hz

The vehicle speed-torque characteristics are given by the below equation

What is EV steady state speed if duty cycle is 70%?

For dc machine Torque- Speed relation

where V= volatage supply

Km(`phi`)= MOtor constant

Ra = armature resistance

`omega`= angular speed of motor

Voltage(motor) = Voltage of armature * dutycycle

= 72*0.7

=50.4volts

T=`50.4*0.7/0.5-omega*0.7^2/0.5`

T= 70.56-0.98*`omega` .......................... (1)

Tr= 24.7 + 0.0051*`omega^2`.....................(2)

Equating 1 and 2

70.56-0.98`omega`= 24.7 + 0.0051*`omega^2`

`omega^2 + 192.151*omega-8992.156=0`

`omega=38.91 rad//sec`

OBJECTIVE 3 : Induction motor vs DC brushless motor by Wally Rippel

An AC induction motor does not have any magnets on the rotor; instead it has a series of laminations and winding. When 3-phase power is applied to the stator of the motor, a rotating magnetic field is generated. This rotating magnetic field creates a current flow in the rotor via induction. The rotor current creates its own magnet that interacts with the stator field and generates torque.

A BLDC motor replaces the windings on the rotor with a series of permanent magnets. These magnets create a magnetic field that interacts with the stator’s field and generates torque. However, rather than simply relying on the 3-phase power to generate a rotating magnetic field, a BLDC motor requires the stator’s magnetic field to be precisely controlled and aligned with the rotor position and its fixed magnets.

In conclusion Ripples compares advantages and disadvantages of both the motor and in the end states that it depends on the preference of the user. If the user wants high performance with lesser costs, induction drive would be better. Hpwever if it is high peak efficiency, high power factor and easier then DC brushless drive would be better suited.