Week-6 Challenge: EV Drivetrain

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

POWER ELECTRONICS :

Power electronic technology deals with processing and controlling the flow of electrical energy in order to supply voltages and currents in a form that optimally suited for end user’s requirements.

The type of converters:

Depending on the type of function performed, power electronic converters are categorized into following types.

• AC to DC = Rectifier: It converts AC to unipolar (DC) current
• DC to AC = Inverter: It converts DC to AC of desired frequency and voltage
• DC to DC = Chopper: It converts constant to variable DC or variable DC to constant DC
• AC to AC = Cycloconverter, Matrix converter: It converts AC of desired frequency and/or desired voltage magnitude from a line AC supply.

1.AC to DC Converters or Rectifiers :

(1).uncontrolled Diode Rectifiers :

• Single phase half wave rectifier
• Single phase center-tapped full-wave rectifier
• Single phase full-wave bridge rectifier
• Three-phase half-wave diode rectifier
• Three-phase full-wave diode rectifier

(2).Phase controlled rectifiers:

• Single phase half wave rectifier
• Single phase full wave mid-point rectifier
• Single phase full-wave bridge rectifier
• Three-phase half-wave converter
• Three-phase full-wave converter

2. DC to DC Converters :

• Step-down chopper or buck converer
• step-up chopper or boost converter
• buck/boost converter

3. AC toAC Converters :

• AC to AC Voltage Converters
• AC to AC frequency converters
• Cyclo converters
• Matrix converter

4. DC to AC converters or inverters

2. What is the steady state of an EV if duty cycle is 70% for the below given data of an electic vechicle ?

GIVEN DATA:

Battery = 72V

Rated Armature voltage= 72 V

Rated armature current= 400 A

Ra= 0.5Ω,

KΦ= 0.7 V-s

Chopper Switching frequency= 400 Hz

The vehicle characteristics are given by the equation

TTR=24.7+0.0051w2

EV steady state speed if duty cycle is 70%

SOLUTION:

The vehicle characteristics are given by the equation

TTR=24.7+0.0051w2

and we know that,

Speed-Torque Equation for dc motor,

`omega=(V/k_phi)-((T.R)/(k_phi)^2)`

by rearranging the above equation we need torque equ,

`T=((V*K_phi)/R)-((omega*(K_phi)^2)/R)`

substuting the coressponding values,

and in the question that duty cycle is given as 70%,

so, finding the voltage at duty cycle at 70%,

V = 72*0.7 =50.47V

T =(50.4*0.7/0.5)-(`omega`*0.7^2)/0.5

motor torque equation is T_motor =70.56 -(`omega`*0.98)

At steady state condition of Ev,

`T_TR = T_M`

now substutng the values in the vehicle characteristic equation

24.72+0.0051*`omega^2`=70.56-(`omega`*0.98)

(0.0051*`omega^2`)+(`omega*0.98`)-45.84 = 0

by calculating the quadratic equation, we get,

`omega`=38.91 rad/sec

therefore at the steady state of the duty cycle for 70% the omega is 38.91 rad/sec.

3. Induction Versus DC brushless motors by Wally Rippel, Tesla

BRUSHLESS DC MOTOR:

1. in this dc motor rotor has 2 or more permanent magnets, that generates dc magnetic field,then the magnetic field enters the core.
2. core is made up of thin stacked laminators.
3. currents flowing within the windings to produce a torque interaction between the rotor and stator
4. as stator rotates its magnitude and polarity of stator curent varied continously.
5. torque remains constant.
6. device that provides current control is called inverter.
7. Without inverter, brushless motors are useless motors.
8. the magnetic field produced by the permanent magnets would be adjustable.
9. When maximum torque is required, especially at low speeds, the magnetic field strength (B) should be maximum so that inverter and motor currents are maintained at their lowest possible values.
10. mean by the losses(hystersis,eddy current) are small.

INDUCTION MOTOR:(INVENTED BY TESLA,1889)

1. stators for the 3-phase induction motor and the DC brushless motor are same,three sets of “distributed windings” that are inserted within the stator core.
2. difference between the two machines is with the rotor.
3. the induction rotor has no magnets its made up of steel laminations with conductors.
4. Currents flowing in the stator windings produce a rotating magnetic field that enters the rotor.
5. frequency of this magnetic field of the rotor is equal to the difference between the applied electrical frequency and the rotational frequency.
6. induced voltage exists across the shorted structure that is proportionate to this speed difference between the rotor and electrical frequency.
7. Finally, these currents interact with the original magnetic field to produce forces.
8. induction machines have no magnets and B fields are adjustable, since B is proportionate to V/f (voltage to frequency).
9. This means that at light loads the inverter can reduce voltage such that magnetic losses are reduced and efficiency is maximized.
10. as machine size grows, the magnetic losses increase proportionately and part load efficiency drops. With induction, as machine size grows, losses do not necessarily grow.

SIMILARITIES :

• Both DC brushless and induction drives use motors having similar stators.
• Both drives use 3-phase modulating inverters.
• The only differences are the rotors and the inverter controls.
• And with digital controllers, the only control differences are with control code.
• DC brushless drives require an absolute position sensor, while induction drives require only a speed sensor; these differences are relatively small.

CONCLUSION :

Here by the author conclude that brushless dc motor and induction motor is likely same(more are less same) and according to the utility the motors are decided i.e., hybrid and plug in hybrid are continues DC brushless motor and for the high performance of electic cars are induction motors are maintain dominance nowadays.

so, much of harwares parts/equipments are more or less same in the drives,so in future both hybrid , plug in hybrid and pure electric will participate equally with both the induction and dc bushless motors.