Week-6 Challenge: EV Drivetrain
ans 1).
the most commonly use convertors in the ev sectors mainly in hybrid and fully electric vehicle are
"ac to ac" , "ac to dc" , "dc to ac" , "dc to dc
why do we require convertors ?
We require a particular voltage and particular frequency for operating some special devices or machines. For speed control of induction motors, AC to AC converters (Cycloconverters) is used majorly. For obtaining a desired AC power supply from the actual power supply, we need some converters called AC to AC converters.and rather than that there are many diffrent area in which diffrent types of convertor are required as per use ,as per the voltage type ,application etc etc
starting with ac to dc which we also know as "rectifier"
the major use of ac to dc convertor are in power electronic circuit based devices and a vide range of products from satellite till charger ac to dc convertor are used to transform alternating current input into direct current output. They are used in power electronic applications where the power input a 50 Hz or 60 Hz sine-wave AC voltage that requires power conversion for a DC output.
ac to ac convertors we can call it as voltage regulators because all it does is convert one value of alternating current to another value of ac quantity
there are types of ac to ac convertors such as
- Indirect AC-AC
- Cycloconverters.
- Hybrid matrix converters.
- Matrix converters
Matrix converters are used for converting AC to AC directly without using any DC link for increasing the reliability and efficiency of the system by reducing the cost and losses of the DC-link storage element.
Matrix converter consists of the bidirectional switches that practically don’t exist at present but can be realized by using the IGBTs and these are capable of conducting current and blocking voltage of both polarities.
hybrid convertor The matrix converters that convert AC/DC/AC are termed as Hybrid matrix converters and similar to the matrix converters these hybrid converters also don’t use any capacitor or inductor or DC link If the voltage and current are converted in two different stages, then that converter can be called a Hybrid Indirect Matrix Converter.
A cycloconverter is a device that converts AC, power at one frequency into AC power of an adjustable but lower frequency without any direct current, or DC, stage in between and again cycloconvertor are divided in many types according to their construction and component used in it as well as number of phases it serves for
.
dc to ac convertor also known as "inverter"
the most common known example for a dc to ac convertor are the power backup system or inverter system that is used to provide backup to a house in case of power outage
another example we can take for power inverter is in case of solar system fixed on roof top there inverter is used for serving a purpose of converting dc output from solar panel to usable ac quantity DC to AC converters is also used in a vehicle to charge their batteries
dc to ac convertor uses
Adjustable-speed ac motor drives,Uninterrupted power supplies (UPS),Running appliances of ac used in an automobile battery, power transmission industry such as reactive power controllers and adaptive power filters.
dc to dc convertor
dc to dc convertor is same as ac to ac the diffrence is the mode of voltage ac to ac convertor steps up or step down the ac voltage where as dc to dc convertor is used to convert ,step down or step up the dc voltage
the more common name for this convertor are
buck convertor ,boost convertor and there 3rd which can do both which is buck boost convertor
buck convertor :The buck converter is a DC-DC converter that efficiently converts a high voltage to a low voltage efficiently. Efficient power conversion extends battery life, reduces heat, and allows for smaller gadgets to be built. The buck converter can be used in lots of cool applications.
boost convertor:The boost converter is used to "step-up" an input voltage to some higher level, required by a load. This unique capability is achieved by storing energy in an inductor and releasing it to the load at a higher voltage.
buck-boost convertor :while in case of buck boost convertor it is a type of DC-to-DC converter that has an output voltage magnitude that is either greater than or less than the input voltage magnitude. It is equivalent to a flyback converter using a single inductor instead of a transformer.
ans 2).
we have the following data
Rated Armature voltage= 72 V, Rated armature current= 400 A, Ra= 0.5Ω, KΦ= 0.7 Volt second Chopper Switching frequency= 400 Hz
average velocity=voltage*duty cycle
=72*0.7
=50.4v
now as we know the equation for ω = v/kØ – Ra / (Kø)^2 X T
Ra = armature resistance ohms ,ω = angular velocity in rad/sec, Kø = motor constant, V = rated battery voltage, T = torque
w = 50.4 / 0.7 – 0.5 / (0.7)^2 x T
kepping the value and after evaluating it we get
w = 50.4 / 0.7 – 0.5 / (0.49) x T
here we got
w = 35.28 – 0.5 T / 0.49
0.49 = 35.28 – 0.5 T
0.49 w + 0.5 T – 35.28 = 0
0.5T + 0.49 w– 35.28 = 0
0.5T = 35.28 – 0.49 w
T = 35.28 – 0.49 w /0.5
Substituting the value of T in the given equation
now we have
(35.28-0.49)/0.5=24.7+0.0051w^2
35.28-0.49w=(24.7+0.0051w^2)0.5
35.28-0.49w=12.35+0.00255w^2
0.00255w^2+0.49w+12.35-35.28=0
0.00255w^2+0.48w-22.93=0
x={-b±√(b^2-4ac)}/2a
therefore as per the above equation we can take a=0.00255 ,b=0.49, c=-22.93 and x=w(omega)
w=[-0.49±√{(0.49)^2-4(0.00255-22.93)}]/2*0.00255
=-0.49±√0.4739/0.0051
=-0.49±0.6884/0.0051
w=-0.49+0.6884/0.0051
38.901rad/sec
now we have negative value
w=-0.49-0.6884/0.0051
=-231.05rad/sec
which is actually not possible in real life unless the car is moving backward i guess!
rough notes attached below
ans 3 ). wally rippel a long-time developer and advocate of battery electric vehicles. Wally has a prominent role, labeled as himself, "Research Engineer, AeroVironment," in this biography or blog he has discrimation the future of electric vehicle and within the first paragraph he want to explain that as he grew up things changed and technology also changed and he had seen upgrades here he want to tell us that no one knows what will be the future of ev
in second para he explains that nothing is perfect and nothing is best everthing has its own advantage and everything has its limitation and everything dosent fit well in all the situation by this he concluded with an example of car which has diffrent engine type and drive performance but it depends on a person who buys it and which one is more suitable for him in every ways .
in next part he starts with dc motor in which a permenent magnet is used and a varying field is generated in the stator core then he brings a major fact about this motor that is .in order to maintain the torque the magnitude and polarity of the stator must be varied continiously and in just the right way so that the conversion is efficient enough and to do this inverter is used and he states that without it brushless motor are useless
next he explains and diffrentiate the induction motor which was invented by nikola tesla and he explains the diffrence in rotor of induction motor which has no magnet instead of magnet rods of coppor steel or aluminium is shorted in the rotor
next comes the torque capacity of an induction motor that if connected at load it still consist enough capacity to run at full load and the fact thgat induction motor was success ful at that time was mainly due to this quality that it can run directly through the main 3 phase power supply
in case of dc motor torque is not produced immediately it need the support of an inverter whose “phase” is maintained in step with the angular position of the rotor
the cons
of an induction motor is that it can run only on ac quantity
as it is depended on frequency it can run only at constant speed unless frequency is varied
they have limited starting torque and somewhat limited running peak torque capabilities, when compared to DC type machines
through all this we can come to an conclusion that dc brushless motor will lead the market of electric vehicle sector unless and untill something more effective and efficient is been invented but the type of motor will depend on the vehicle higher torque motor like induction motor will lead the pure electric vehicle and hybrid cars will likely to rely on dc brushless motor for now a conclusion can not be made concrete but it can be said for sure that days aint too far when we will see more efficient drives in this vast field of electric vehicle .