Week-6 Challenge: EV Drivetrain

AIM:- To develop a proper insight of a EV Drivetrain

OBJECTIVES:-

1. To describe about different types of power converters used in Hybrid ev's and EVs

2. To find the steady state speed of motor by using the given characteristic equation.

3. To write the summary on a article of Wally Rippel.

PART-01

Power Converters are defined as the devices assigned to process and control flow of electric energy by supplying voltages and currents in a form that is optimally suited for user loads.

The purpose of its usage is to convert one characteristic of electrical signal to another. With context to electric and hybrid electric vehicles, they are used to convert DC to AC signals or vice-versa. Moreover they are also used to regulate voltage.

We will be discussing about four power converters that are used in electric vehicles.

(i) AC to DC Converter:- This power converter is commonly known as Rectifier. Its working is to convert AC signal to DC signal.

Various devices work on DC signal moreover charging is done by dc signals. So as its application suggest its useda s EV charger.

(ii) DC to AC Converter:- it is used to convert DC signals to AC one. The power supplied by the battery packs are primary in DC signals . To convert them in usable AC form inverters are used. It allows us to convert the DC to AC in the required frequency variations.

(iii) DC to DC converter:- commonly known as chopper. It is used to vary voltage of a DC signal according to our needs.

this could easily be understood from an example, let us consider we have 100 v supply of DC from availabel battery, but we need a voltage of 12v to run the info-tainment sysytems of a vehicle. So here the chopper will be used to convert 100v to usable 12 v.

(iv) AC to AC Converter:- it used to regulate the ac signals into required voltage and frequency. the most commmon example in our household is fan regulator which rsults into speed variation of fans.

PART-02

By referning to given conditions we have following specifications:-

d1= 70%
Rated Armature Voltage,(Va)=72 V
Armature Resistance,(Ra)= 0.5 ohm
Rated Armature Current,(Ia)= 400 A
Motor Constant,(`K*phi`)= 0.7

V= Va*d1

We Know the Torque-angular velocity relation is given by

`T=(V*(K*phi)/(Ra))-((K*phi)^2*omega/(Ra))`

Also we have been provided with the vehicle speed characteristic equation which is

`T=24.7+0.0051*omega^2`

Since to provide proper running conditions, same omega value must have to satisfy both equations.

therefore

`(V*(K*phi)/(Ra))-((K*phi)^2*omega/(Ra))=24.7+0.0051*omega^2`

substituting the respective values we will get.

`omega=38.23 (rad)/(s)`

Therefore steady state speed will be 38.23 rad/s.

PART-03

Walley Rippel , is a profound mind in the field of Electric Vehicles. He has done various works in the field of EV.

From past time onwards it has been a matter of value which engines or motors would be suitable for a particular purpose. Whether it is IC engine or electric motors , the demands have not been fulfilled with just one type of there. Various developments are being done to enhance the performances of thes machines but till date none of them have satisfied human needs completely and hence, always paved the path of future developments.

Same scenario can be observed in the case of batteries. In the intial era, lead was popularly used in battery manufacturing which is now been replaced by lithium and will be replaced by some better substitutes.

Different types of motors:-

Brushless DC motors - In these devices 2 or more permanent magnets are attached to the rotor part of the motor whose magnetic fields are crossing all over the stator windings. when the rotor rotates it provides a fluctiating magnetic field which leads to the torque generation, due to the current flow in the stator windings.
The current in the stator is controlled with the help of inverter.

Induction Motor:-

As the name suggests its working is based on the principle of induction. Due to rotating magnetic field of stator, a voltage is induced in the conductor racks of rotor which ultimately induces curent. And these currents will produce a required tor torque. The main difference of induction motor fom dc motor is the absence of magnets.

Three phase induction motor has an edge over DC brushless motor in presence of great starting torque on the threshold of its utility, when connected with 3 phase supply. moreover 3 phase motor doesn't even require a inverter which increses its acceptance in present times.

Having major advantages they still have some drawbacks that don't let the popularity of DC motors go completly vanish.
AC power supply is a major compulsion for its application and moreover its speed depends directly on the frequency of the utility signal, which makes it a constant speed motor.
By making use of an inverter we can tackle this problems and can be as par as dc motors.

From the beginning of the eras of motors there would have always been a competetion to develop a more efficient motors. With the coarse of time, differnt designs have been introduced. To face this competetion DC brushless and induction motors were always been a tough oponents of each other. But the judgement of time has never decided the true winner. Till present times these two machines are seen much of a same level.
It can be assumed there mutual supremacy will lead the future industry of HEV's and EV's until and unless a more efficient motor will not be introduced but then also it would be tough a judge a true hero as with time human needs will also change and demand a more efficient machine which will be motivation for future developments.