Week-6 Challenge: EV Drivetrain

1)

They are 1. AC-DC converter

2. DC-DC converter

3. DC-AC converter

1. AC-DC Converter:

• AC-DC converter (Onboard charger) is used for charging the vehicle.
• As battery stores energy in the form of DC, so AC-DC power converter is required.
• They are generally used in PHEV and PEV type vehicles.

2. DC-DC Converter(Chopper):

• We know lights, indicators and other signal generators requires only low voltage (12V or 24 V)
• So the battery energy (DC type high range) will converted into Low voltage DC by DC to DC converter (Chopper).

3. DC-AC Converter (Inverter):

• DC-AC converter is used to convert the battery energy (DC type) to AC to supply the motor (AC motor used).
• Therefore, the converted energy (AC) is used for motor operation.

2)

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:-

As the torque formula is given, we need to find the speed in rad/sec. Use the other expression available which is given below:

Rated Armature voltage, V_A = 72 V

Rated armature current= 400 A

Ra= 0.5Ω

KΦ= 0.7 Volt second

Chopper Switching frequency= 400 Hz

For Duty Cycle, δ = 70%

Voltage = V_A × δ

= 72 × 0.7

= 50.4 V

We know,

Torque, T = KΦ/R_A*[ V_A - KΦ*ω]

By Substituting the given values,

Torque, T = (0.70.5)⋅(50.4−0.7w)(0.70.5)⋅(50.4-0.7w)

= 1.4 × (50.4 – 0.7 ω)

= 70.56 – 0.98 ω

T = 70.56 – 0.98 ω and

T_v = 24.7 + 0.0051 ω² (Given)

At T = T_V ;

70.56 – 0.98 ω = 24.7 + 0.0051 ω²

Or, 0.0051 ω² + 0.98 ω +24.7 -70.56 = 0

Or, 0.0051 ω² + 0.98 ω – 45.86 = 0

i.e., ω = 38.915 or −231.072

Since Speed cannot be negative, we will consider that the EV steady-state speed, if the duty cycle is at 70%, is

ω = 38.915 rad. S^-1 or 371 rpm

3)

• In the beginning, author describes the dominance of Internal Combustion Engines (ICE) in the world of automobile industry and also discuss different types of engines. He explains that all engines were similar and it was up to the user to select according to their requirement. He also speaks about induction motor and brushless DC motors and presents his view that these two technologies will be widely used for the coming years.
• Then he explains the working of both 3-phase induction motor and a brushless DC motor.
• Now the author has done comparison between these two technologies and stated some advantages and disadvantages of each.
• Induction motor have some advantages like: it has no magnets. The motor has the ability to start under load. No inverter is needed. Some disadvantages of Induction motors are: They cannot operate from DC; AC is a must. Shaft speed is proportionate to line frequency. Hence, when used with utility power, they are constant speed machines. When operated from utility power, they have limited starting torque and somewhat limited running peak torque capabilities, when compared to DC type machines.
• Brushless DC motor have some advantages like: much less rotor heat is generated with the DC brushless drive. The peak point energy efficiency for a DC brushless drive will typically be a few percentage points higher than for an induction drive. Some disadvantages of Brushless DC motor are: as machine size grows, the magnetic losses increase proportionately and part load efficiency drops. Permanent magnets are expensive and difficult to handle due to very large forces that come into play when anything ferromagnetic gets close to them.
• Finally the author couldn’t choose which drive is better than the other but makes it clear 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.