Week-6 Challenge: EV Drivetrain

Q1. Which types of power converter circuits are employed in electric and hybrid electric vehicle?

ans-

Power Electronic Converters: -

1) In Electric and Hybrid Electric Vehicles (EV/HEV), the power electronic converters are considered as the key elements that interface their power sources to the drivetrain of the EVs.

2) In order to design highly efficient converters for the EV’s power system, advanced DC/DC and DC/AC converters are required to adapt the output voltage and current levels with high power quality.

There are three types of converters which are widely used in electric vehicle are:

AC – DC Converter (On Board Charger): -

1)AC to DC converters are most commonly used in Plug-in Hybrid Electric Vehicles (PHEV) & Plug-in Electric Vehicles (PEV).

2)These vehicles get their propulsion power from an external electricity source (charging stations) which is alternating current.

3)The battery needs to be charged using a direct current source. For this purpose, AC to DC converter is employed in a PHEV & PEV.

DC – DC Converter: -

1)DC-DC converters can be used to interface the elements in the electric power train by boosting or chopping the voltage levels.

2)By introducing DC/DC converters one can choose the voltage variation of the devices and the power of each device can be controlled.

3)The power of the DC/DC converter depends on the characteristics of the vehicle such as top speed, acceleration time from 0 to 100 Km/h, weight, maximum torque, and power profile (peak power, continuous power).

DC – AC Converter (Inverter): -

The DC/AC converter is required to convert the dc power to a suitable ac power for the electrical machine. The power output from battery pack (DC current) is converted using inverter to be used in electric motor (AC current).

Q2 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'.

ans-

Given data-

Battery pack voltage (V) = 72V

Rated armature current = 400 A

Armature Resistance (R_a) = 0.5Ω

Motor constant (K_Φ) = 0.7

Chopper Switching frequency= 400 Hz

Duty Cycle = 70%ω">ω

solution

Vehicle Output Voltage (V_v) is given by: -

V_v = Battery Voltage (V) * Duty Cycle

V_v = 72 * 0.70

Thus, Vehicle voltage = 50.4V

Now, Equation for Vehicle torque is given by: -

Tv=(Vv-ω.K∅)⋅K∅Ra">Tv=(Vv−ω.K∅)⋅K∅RaTv=(Vv-ω.K∅)⋅K∅Ra

Where;

Tv">TvTv= Vehicle Torque (N-m)

Vv">VvVv = Vehicle voltage (Volts)

ω">ωω= steady state speed of vehicle (rps)

K∅">K∅K∅= Motor constant

Ra">RaRa= Armature Resistance

Substituting all these values in equation, we get:

Tv=(50.04-0.7⋅ω)⋅0.70.5">Tv=(50.04−0.7⋅ω)⋅0.70.5Tv=(50.04-0.7⋅ω)⋅0.70.5

Tv=70.56-0.98⋅ω">Tv=70.56−0.98⋅ωTv=70.56-0.98⋅ω

Tv=24.7+0.0051⋅ω2">Tv=24.7+0.0051⋅ω2Tv=24.7+0.0051⋅ω2

Solving these two equations,

70.56-0.98⋅ω=24.7+0.0051⋅ω2">70.56−0.98⋅ω=24.7+0.0051⋅ω270.56-0.98⋅ω=24.7+0.0051⋅ω2

We get a quadratic equation:

0.0051⋅ω2+0.98⋅ω-46.94=0">0.0051⋅ω2+0.98⋅ω−46.94=00.0051⋅ω2+0.98⋅ω-46.94=0

Since quadratic equation, we get two values of ;

ω">ωω= 38.85 rad/s and ω">ωω = -230.95 rad/s

We take the positive value;

Steady state speed of vehicle = = 38.85 rad/s

Q4. Refer the blog and Explain in brief about author’s perspective.

ans-

This blog is about the Walley Reppel perspective about brushless DC and induction motor , who is Walley ?

Walley is proponent of Electric Vehicle .He was engineer at AeroVironment,Where is he helped to develop the EV1 for General motor .He also worked in Jet propulsion laboratory on electric vehicle battery research,among other projects ,Proponent means someone who is in favor of something.

In the starting of the blog he said "One Size Does Not Fit All"

he said in that odious world engines are of the different type . He said one would thought that ,year ago ,some was try to figure out which is best engine and that should be in production but his thought got failed .there is no one is best one .with the different requirement there are different type of engine .such a way he said this true for Brushless DC and Induction Motor. He also said about the evolution of batteries DC bush motor ,and contactor controllers

he said the lead acid battery is replaced by the lithium and brush DC motor with Brushless DC motor or Induction motor.

Next he talks a closer look , he gives some closer look of the brushless DC motor and induction motor there technologies ,there working .

also 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 (a core made up of thin, stacked laminations) and interacts with currents flowing within the windings to produce a torque interaction between the rotor and stator. As the rotor rotates, it is necessary that the magnitude and polarity of the stator currents be continuously varied – and in just the right way - such that the torque remains constant and the conversion of electrical to mechanical energy is optimally efficient. The device that provides this current control is called an inverter. He told one thing that Without inverter, brushless motors are useless motors.

Then is told about the induction motor drives. he curiously told that stator of the both DC brushless and induction motor have three sets of “distributed windings” the only difference is in the rotor , induction motor has no magnet it contains steel laminations with buried peripheral conductors .He describe working of induction motor that Currents flowing in the stator windings produce a rotating magnetic field that enters the rotor. In turn, the frequency of this magnetic field as “seen” by the rotor is equal to the difference between the applied electrical frequency and the rotational “frequency” of the rotor itself. Accordingly, an induced voltage exists across the shorted structure that is proportionate to this speed difference between the rotor and electrical frequency. In response to this voltage, currents are produced within the rotor conductors that are approximately proportionate to the voltage, hence the speed difference. Finally, these currents interact with the original magnetic field to produce forces – a component of which is the desired rotor torque.

he said that induction motor not require inverter and the motor has ability to start under the load .

with the fixed utility power dc brushless motor produces no starting torque it needs inverter .

induction motor not operated form the DC source.

Next he is talking with the heading "Brushless or Induction"

He told that back 1990s all EV except one uses the DC brushless drives today all HEV using the DC brushless .Then he gave some comparison between DC brushless and induction motor

DC Brushless	Induction motor
require an absolute position sensor	require an absolute position sensor
less rotor heat is generated ,Rotor cooling is easier and peak point efficiency higher. operate at unity power factor	power factor is about 85 %, peak point efficiency higher compare to DC Brushless
strength of the magnetic field produced by the permanent magnets would be adjustable. to get max torque the magnetic field should max at low speed maintained by the inverter and motor current low	no magnets and B fields are “adjustable,” since B is proportionate to V/f (voltage to frequency).efficiency is maximized due to low magnetic losses
Average efficiency is low	Average efficiency is high
Permanent magnets are expensive	no magnet there is advantage in cost
they are easy to control	The control laws are more complex and difficult to understand, so difficult to control

with saying "Still No Winner",he describe that no one is best DC brushless or induction.

Q3 Develop a mathematical model of a DC Motor for the below equation using Simulink.

ωω= V/Kϕϕ -Ra/Kϕϕ^2 .T

ans-

1) creat a model and substitute value as given.

2) Run the simulation and graph will show.

RESULT-