Week-6 Challenge: EV Drivetrain

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

Ans:

The power converters are used to process and control the flow of electric energy by supplying and currents in a form that is optimally suited for the user loads,The power converters present in electric and hybrid electric vehicle are

• AC to DC power converters called Rectifiers
• DC to AC power converters called inverters
• DC to DC power converters called choppers(step down and step up)

Rectifiers:

• The recifier is present in charging system of electrical and hybrid electrical vehicles.We charge electric vehicle from home or from a charging station there supply is ac voltage and this ac supply is converted to dc using rectifier and stored in batter.

• A rectifier may b of half wave type or full wave type ,A half wave rectifier is one in which current in any on line ,connected to the source is unidirectional ,However , a full wave rectifier has bidirectional current in any one line connected to ac surface

Inverters:

• Battery power of electrical and hybridic electrical vehicle is given to ac induction motor through inverters
• The inverters convert dc power from battery to ac so that it can used by ac induction motor
• So inverters are present in motor drive of electrical and hybrid electrical vehicles
• Inverters are also called AC Drives, or VFD (variable frequency drive). They are electronic devices that can turn DC (Direct Current) to AC (Alternating Current). It is also responsible for controlling speed and torque for electric motors.

Choppers:

• A chopper is a static circuit that converts fixed dc inputs voltage to a variable dc output voltage directly
• A chopper may be thought of as dcequivalent of an ac transformer since the behave in an identical manner
• Choppers involve one stage conversion,these are more efficient
• choppers are of two type

1)step up choppers: output dc voltage of this chopper is greater than input dc voltage

2)step down choppers:output dc voltage of this chopper is lesser than input dc voltage

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,

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%?

ans:

d=70%=0.7

we have V average=d*Vrated

V=.7*72

=50.4V

T=KΦ/Ra*V -KΦ^2*w/Ra

on subsituting value

T=.7/.5 -.7^2*w/.5

T=70.56-0.98w

at steady state

Tv=T

24.7+(0.0051)^2=70.56-0.98w

on solving above quadratic equation we get

w=38.915 rad/sec and w=-231.072 rad sec

By choosing positive value we get

w=39.915 rad/s

=371rpm.

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

w=V/k*phi-Ra/(k*phi)^2

Ans:

Develope the model of Torque speed equation and block diagram is shown below

We used constant block ,addition block,square,sum ,product ,xy graph and scope for modeling the above equation

Output:

Speed torque plot of dc motor is shown below

plot of speed with respect to time is shown below

4.Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

Explain in brief about author’s perspective.

Ans:

• In this blog author comparing Induction and DC brsuhless motor,The author analysing the construction of each motor and discussing advantages and disadvantages of each motor and their differece is giving in this blog

• In DC brushless machine rotor had permanent magnet to generate a DC magnetic field,This magnetic field interact current flowing through the stator windings and produces torque effect,Magnitude and polarity of stator current must be varied continuously in the right way,we should get constant constant torque and there should be a efficient conversion of electrical to mechanical energy.The device used for this is Inverter without inverters these motors are useless

• In Induction motors rotors has no magnet ,In this stator current produces a rotating magnetic field that enters the rotor,In this rotor frequency is different from rotor frequency,These frequency difference is responsible for the production of voltage and current,hence speed difference Then interaction of these currents with original magnetic field results forces.a component which desiring rotor torque.

• While using 3pase induction motor torque is produced at the outset,this motor work under no load and no inverter needed,Induction motor is directly compatible with conventional utility power is the main reason of their success where as Dc motor require inverter to connect to conventional utility power

• By using inverter we can power induction motor from dc supply and we can varry the speed by varying the inverter frequency,we can improve its torque performance by adding feedbacks

• Both brushless and inductuon drives use motors having similar stator,Both drive uses 3 phase modulating conveters,the only diffrence is rotor and inverter control and digital controllers and control codes

• Comparing with induction motor ,dc motor produce less heat ,rotor cooling is easier,peak point efficiency is generally higher

• Induction motors are operated with smart inverters has advantage over dc brushless machine ie magnetic and conduction losses can be traded such that efficiency is optimized,so when size of induction machine increases loss doesnt grow ie compared to dc overall efficiency is better

• Permanent magnets are costlier so Induction motor become less costlier than dc brushless motor

• Controlling of induction motor is difficult and there is over temperature issue is in induction motor

• Author concluded that DC brushless drives will dominate over hybrid and plug in hybrid market and Induction motor will likely dominant in pure electric market,so many hardware are common iin dc brush less and induction but both drives live and work side by side during the coming golden era of hybrid and electric vehicle.