Week-6 Challenge: EV Drivetrain

The different configurations of EV power supply show that at least one DC/DC converter is necessary to interface the FC, the Battery or the Supercapacitors module to the DC-link. In electric engineering, a DC to DC converter is a category of power converters and it is an electric circuit which converts a source of direct current (DC) from one voltage level to another, by storing the input energy temporarily and then releasing that energy to the output at a different voltage. The storage may be in either magnetic field storage components (inductors, transformers) or electric field storage components (capacitors).DC/DC

converters can be designed to transfer power in only one direction, from the input to the output. However, almost all DC/DC converter topologies can be made bi-directional.A bi-directional converter can move power in either direction, which is useful in applications requiring regenerative braking.

in an elctric machine DC to AC power converter is used to convert DC to suitable AC power.Electric motor required AC current so power output from dc battery is converted using this converter to get ac current to motor.

The other parameters of the electric vehicle is given below,

Motor and Controller Parameters:

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%?

Solution

Battery pack voltage=72V

Rated armature current=400A

Armature resistance=0.5Ω

Motor constant=0.7

Chopper switching frequency=400Hz

Duty cycle=70%

Vv=Battery voltage=72*0.70=50.4V

Equation for vehicle torque is

Tv=(Vv−ω.K∅)⋅K∅/Ra

Tv=(50.4-0.7*w)*0.7/0.5

Tv=70.56-0.98*w--1

Tv=24.7+0.0051⋅ω^2--2

By solving the above two equations into quadratic form we get

w=38.8rad/s and w=-230.9 rad/s

so steady state speed of vehicle is taken as positive so w=38.8 rad/s

Question 3

Develop a mathematical model of a DC Motor for the below equation using Simulink.

ω= V/Kϕ-(Ra/Kϕ)^2 .T

V=50.4; %Voltage
Ia=400;  %armature current
Ra=0.5;  %armature resistance
K1=0.7;   %motor constant

Result

Question 4

wally rippel is a long time proponent of electric vehicles.he helped to develop the ev 1 vehicle of general motors.

at the starting of the blog wally says that no one is the best engine he says different type of engine is used for different requirement.he also said about evolution of batteries dc motor and lead acid type of batteries is replaced by lithium batteries.lso he speak about what differentiate them ? in that he told about DC brushless machine that rotor generate the magnetic field with two or more permanent magnet and this magnetic field enters the stator core

in conclusion wally found elaborated different aspects for dc brushless and induction motor

Dc brushless motor

• dc brushless motor require absolute position sensor.
• heat produced in rotor side is less .
• rotor cooling is easy in dc brushless motor.
• it can operate at unity power factor.
• the torque generated due interaction of rotor and stator magnetic field
• The rotor requires two or more permanent magnet to generate a magnetic field
• power factor upto 100% can be reached
• permanent magnets are costliest and ferromagnet cannot be brought near the magnet
• when size increases losses increases and also load efficiency also got decreases
• The magnetic field strength cannot be adjusted thus only single torque output can be obtained
• Preferred for ev

Induction motor

• AC supply
• induction motor requires speed sensor
• Stators rotating magnetic field induces a current in rotor laminations, which interact with the stator magnetic field and produce torque
• rotor cooling is difficult maximum efficiency is upto 85%
• complex control laws for inverter
• as size increases losses also approximately as same.
• The magnetic field strength can be varied as a function of voltage supply and frequency for optimized torque output.
• preferred for pure ev