Week-6 Challenge: EV Drivetrain

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

We know generally there are three types of Electrical vehicles.

1. Hybrid Electric vehicle
2. Plugin Hybrid Electric vehicle
3. Battery Electric vehicle

Hybrid Electric vehicle:

• Hybrid Electric Vehicles, or HEVs, have both a gas-powered engine and an electric motor to drive the car.
• All energy for the battery is gained through regenerative braking, which recoups otherwise lost energy in braking to assist the gasoline engine during acceleration.
• In a traditional internal combustion engine vehicle, this braking energy is normally lost as heat in the brake pads and rotors
• Regular hybrids cannot plug into the grid to recharge and cannot charge with EVgo.

Plug-in Hybrid Electric vehicle:

• Plug-in Hybrid Electric Vehicles, or PHEVs, have both an engine and electric motor to drive the car.
• Like regular hybrids, they can recharge their battery through regenerative braking.
• They differ from regular hybrids by having a much larger battery, and being able to plug into the grid to recharge.
• While regular hybrids can (at low speed) travel 1-2 miles before the gasoline engine turns on, PHEVs can go anywhere from 10-40 miles before their gas engines provide assistance.
• Once the all-electric range is depleted, PHEVs act as regular hybrids, and can travel several hundred miles on a tank of gasoline.
• All PHEVs can charge at an EVgo L2 charger, but most PHEVs are not capable of supporting fast charging

Battery Electric vehicle:

• Battery Electric Vehicles, also called BEVs and more frequently called EVs, are fully electric vehicles with rechargeable batteries and no gasoline engine.
• BEVs are zero emissions vehicles, as they do not generate any harmful tailpipe emissions or air pollution hazards caused by traditional gasoline-powered vehicles.
• All energy to run the vehicle comes from the battery pack which is recharged from the grid.
• Some popular EV models are pictured here and a full list of available fast charging EV models is available in the chart above.

But in all these types of vehicles, we use basically 3 types of power converters.

They are

1. AC-DC converter

2. DC-DC converter
3. DC-AC converter
4. 

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.

Q2.An Electric Vehicle's powertrain with 72V battery pack in shown in the diagram below. The duty ratio for acceleration operation is 'd1' and for the braking operation the duty ratio is 'd2'.

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)(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. Develop a mathematical model of a DC Motor for the below equation using Simulink.

ωω= V/Kϕϕ -Ra/Kϕϕ^2 .T

Ans:-

Output:-

4. Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

Explain in brief about author’s perspective

Objective: To brief about the blog written by an author from Tesla.

Main Points:

1. There is no such thing called the best engine. According to the personal requirements, we need to adapt the engine type.
2. In the course of time, Lead-acid batteries are replaced by Lithium-ion batteries.
3. In the course of time, DC brush motors are replaced by DC Brushless or Induction Motors.
4. In the course of time, Contactor Controllers are replaced by Modulating Inverters.
5. There is a bigger concern regarding the stable use of these elements mentioned above over the next few decades.
6. The author discusses the two technologies such as: 1. DC Brushless Drives and 2. Induction Motor with it's feature of operation.
7. He says brushless motors are useless motors without the inverter.
8. He also mentioned that the 3-phase induction motor has great utility but with several limitations.
9. The major limitation being, the Induction Motor can not operate from DC, and AC is a must.
10. Further, he compares the future trends which may occur in DC Brushless as well as in Induction motor.

Conclusion:

He concludes 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.