Week-6 Challenge: EV Drivetrain

Student of EV LIVE BTACH 16:

Soltion for Question 1:

We usually use THREE types of POWER CONVERTERS in Electric and Hybrid Electric vehicles:

1. AC-DC CONVERTER

2. DC-DC CONVERTER

3. DC-AC CONVERTER

AC-DC converter: Elctric power is transferred through cables as a direct current (DC) in one direction at a oscillating constant voltage, or as alternating current(AC) flowing backwards and forwards due to an oscillating voltage with some frequency. This converter converts the AC into DC and it is also known as rectifier.

• This converter is used for Charging of the Vehicle.
• As battery stores energy in the form of DC, hence AC-DC power converter is required.
• AC-DC converters are generally used in Plug-in Hybrid Electric vehicles(PHEV) and Electric vehicles(EV).

DC-DC Converter: A DC to DC conveter is an elctronic circuit that converts DC voltage from one level to another level.

• Lights,Indicators,Electronic devices and other signal generators requires low voltage ( 12 volts to 24 volts)
• Hence we need to convert the high DC voltage to low level DC voltage by using DC-DC converter.

DC-AC Conveter: DC to AC conveters are designed to change a DC power supply to an AC power supply.DC is relatively stable and positive voltage source and AC oscillates around a 0V base level, usually in a square or sinusoidal function.

• It is used to convert the Battery energy (DC) to AC to supply to motor (Induction Motor)
• Thus converted AC power is used for MOTOR operation.

Solution for Question 2:

Given data

Rated Armature voltgage, Va=72 V

Rated Armature Current, Ia=400 A

Armature resistance,Ra=0.5 Ω

Kϕ=0.7

Chopper switching frequency=400 Hz

Speed torque characterstics equation, Tv=24.7+(0.0051)ω^2 -------eqn 1

thn for duty cycle of 70 % i.e.. 0.7

Voltage = Va* duty cycle

=72*0.7

50.4V

We know that

Torque, T = (V-ωKϕ)*Kϕ/Ra

= (50.4-0.7ω)*0.7/0.5

=(50.4-0.7ω)*1.4

T=70.56-0.98ω -------- eqn 2

Equate eqn 1 and 2

T=Tv

70.56-0.98ω=24.7+(0.0051)ω^2

0.0051ω^2+0.98ω+24.7-70.56=0

By solving the above quadratic equation

we will get ω= 38.915 and -231.07

Speed can not be negative , so take the positive value

Therefore, EV steady state speed at duty cycle of 70 % is 38.915 rad/sec or 371 RPM

Solution for Question 3:

Simulink model:

Result:

Solution for Question 4:

Induction motor versus DC brushless motors

• Author emphasis on electric motors and how do they work. He mentioned that difference between Three phase Induction motor and the DC Brushless Motor.
• He preffered the Induction motor as it has No magnets, the motor has the ability to start under the loaded condition.
• No Inverter is needed.
• With Induction,as machine size increases, losses are not much increasing.
• Thus the Induction motor may be the favoured approach where high perfomance needs.
• He also mentioned the drawbacks of Induction motor like they can not operate DC and when operated from utility power , they have limited starting torque.
• limited Peak torque capabilties as shaft speed is proportionate to line frequency.
• He mentioned some advantages of DC brushless motor like less less rotor is generated.
• it will high starting torque and can operate at Unity Power Converter.

Conclusion:

In case of Hybrid and Plug in Hybrid vehicle DC brushless Motors will dominate. However, Induction motor drive always dominate for high performance.