Week-6 Challenge: EV Drivetrain
Q.1 ANSWER
There are four types of power converters are used in electric and hybrid electric vehicle.
1.AC to DC Converter (Controlled Rectifier)- This rectifier basically converts ac to dc by using rectifier circuits.
2.DC To DC converter (DC chopper)- It basically converts fixed dct supply for example 220V to required dc supply like 20V. This operation is basically called as Chopper.
3.AC to AC Converter (AC voltage regulator)- This is basically used to regulate the value of AC voltage like different type of operation
4.DC to AC Converter (Inverter)- In the case of DC to AC i.nverter if in electric vehicle if we are using DC battery and wants to use AC motor like induction motor then in that case we need an inverter circuit to convert DC to Ac .
Mostly used Converter are - CHOPPER AND INVERTER.
Q.2
rated voltage voltage =72 V
Ia=400 A
Ra=0.5
K_phi=0.7 v s
f of chopper =400
so torque euqtion is
T=V*(k_phi)/Ra-w*(k_phi^2)/Ra
at duty cycle of 70 %
the value of voltage which will be applied V= 72*0.70 = 50.4 V
so on sustituting the value in above equation we get
Torque T = 70.56-w*(0.98)
and value of torque given in equation as
Tv=24.7+(0.0051)*w^2
so on equateing both two torque we get
70.56-w*(0.98)=24.7+(0.0051)*w^2
the value of w in quardatic equation as
(0.0051)*w^2+(0.98*w)-45.86=0
so on solving we get two values
on considering positive value of speed
w=38.9 rps
so on changing in rpm
w= 38.9*60 =2334 rpm
Q.3
on taking the above values as for given model as
V=50.4
k_phi =0.7
Ra=0.5
Torque as Ramp function
so
model as well as scope result is attached.
Q.4
Authors prospective
With brushless machines, the rotor includes two or more permanent magnets that generate a DC magnetic field (as seen from the vantage point of the rotor). In turn, 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.
observations are
1The device that provides this current control is called an inverter Without it, brushless motors are useless motors.
2.Curiously, the stators for the 3-phase induction motor and the DC brushless motor are virtually identical. Both have three sets of “distributed windings” that are inserted within the stator core. The essential difference between the two machines is with the rotor.
3.Unlike the DC brushless rotor, the induction rotor has no magnets – just stacked steel laminations with buried peripheral conductors that form a “shorted structure.
4.When a 3-phase induction motor is connected to utility type 3-phase power, torque is produced at the outset; the motor has the ability to start under load. No inverter is needed.
5.In contrast, a brushless DC motor produces no starting torque when directly connected to fixed frequency utility power.
6.The only differences are the rotors and the inverter controls. And with digital controllers, the only control differences are with control code.
7.One of the main differences is that much less rotor heat is generated with the DC brushless drive. Rotor cooling is easier and peak point efficiency is generally higher for this drive.
8.induction machines have no magnets and B fields are “adjustable,”
9.Thus, the induction machine when operated with a smart inverter has an advantage over a DC brushless machine – magnetic and conduction losses can be traded such that efficiency is optimized.
10.With DC brushless, as machine size grows, the magnetic losses increase proportionately and part load efficiency drops.
11.Permanent magnets are expensive – something like $50 per kilogram. Permanent magnet (PM) rotors are also difficult to handle due to very large forces that come into play when anything ferromagnetic gets close to them.
12.Dc need inverter but induction do not need inverter
13. Dc not able to start under load but induction does.
Conclusion
My conclusion is that DC brushless drives will likely continue to dominate in the hybrid and coming plug-in hybrid markets, and that induction drives will likely maintain dominance for the high-performance pure electrics.