EV Drivetrain

Uncontrolled Rectifier

Controlled Rectifier

*Usually, the types of Rectifiers are classified based on their output:

• Single Phase Rectifiers
• Three Phase Rectifiers
• Controlled Rectifiers
• Uncontrolled Rectifiers
• Half Wave Rectifiers
• Full Wave Rectifiers
• Bridge Rectifiers
• Center-Tapped Rectifiers

The commonly used rectifier is the bridge rectifier :

As we know that our charge is stored in HEV and EV in the dc form with the help of a Battery. for this battery charging we need a DC supply and this supply is given to the battery from an external supply or from generated supply from the motor of the vehicle. But the generated power supply and external supply is AC and Battery needs DC supply fro this conversion we need REctifer which converts the AV to DC.

* INVERTER:

An inverter converts the DC electricity from sources such as batteries or fuel cells to AC electricity, at any required voltage.

• Sine wave inverters produce good-quality AC power. They use pulse-width modulation (PWM) to produce a true sine wave, which makes them expensive.
• A modified sine wave inverter produces a lower quality of AC power, with strong power system harmonics but is cheaper. The output of a typically modified sine wave inverter is a square wave with a pause between the change in direction.

As we know that our induction motor required an AC power supply but we have a DC power supply in Battery form. This DC supply have to convert in AC form and which is done by the inverter which concerts the DC stored supply into AC supply and also as per our requirement how mush we need supply to get respected speed.

*CHOPPER:

A chopper is a device that converts fixed DC input to a variable DC output voltage directly. The chopper can increase or decrease the DC voltage level at its opposite side.

Step down Chopper :
Step down chopper as Buck converted is used to reduce the i/p voltage level at the output side. Circuit diagram of a step down chopper is shown in the adjacent figure

Step up Chopper or Boost Converter :
Step up chopper or boost converter is used to increase the input voltage level of its output side. Its circuit diagram and waveforms are shown below in the figure.

In-Car there are many applications like radio, Lighting systems, AC, Sencer, Vipers, etc required regulated DC supply and this supply is given by this chopper. The battery has a fixed Dc supply which is converted into a regulated DC supply by using the Chopper.

Q2. An Electric Vehicle's powertrain with a 72V battery pack is 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 the duty cycle is 70%?

ANS:

AIM: Find the steady-state speed if the duty cycle is 70%?

Given data:

1) 72V battery pack

2) Rated Armature voltage= 72 V

3) Rated armature current= 400 A

4) Ra= 0.5Ω, KΦ= 0.7 Volt second

5) Chopper Switching frequency= 400 Hz

6) Speed vs torque given.

solution:

The speed vs torque characteristics at 100% duty cycle is given as:

`t_v=24.7+(0.0051)w^2`.....(1)

The relation between input/output voltage and the duty cycle is given by:

``v_(out)=D*V_(input)``

Therefore, `V_(out)` = 70% of duty cycle*72

= 0.7*72

= 50.4 V

For a DC Motor, the torque produced is given by

`T = (Kphi)/R_a*V-(Kphi)^2/R_a*w_m`

Therefore, `T = (0.7*50.4)/0.5-(0.7)^2/0.5*w_m`

`T = 70.56-0.98w_m` ....(2)

In a steady-state condition, the motor torque is equal to the load torque

Therefore, from equations (1) and (2), we get

`24.7+0.0051w^2 = 70.56-0.98w`

`0.0051w^2+0.98w-45.86 = 0` ...(3)

Solving the above equation using a MATLAB script

From the above script we get the following result:

w1= 38.91 and w2=-231.068

Therefore, taking the positive root as the solution

w = 38.91Rad/sec

Results: The EV steady-state speed when the duty cycle is 70% is 38.91 Rad/sec.

Q3. Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

Explain in brief about author’s perspective.

ANS:

About author:

wally ripple is a long-time proponent of an electric vehicles. Prior to joining Tesla Motors, he was an engineer at AeroVironment, where he helped develop the EV1 for General Motors and was featured in the documentary movie, Who killed the electric car? Wally has also worked for the jet-propulsion on electric vehicle battery research, among other projects. In 1968, as a Caltech undergraduate student, he built an electric car (a converted 1958 Volkswagen microbus) and won the great transcontinental electric car race against MIT.

In this blog authors perspective is:

1) They compared the old and today's technology like a battery, drive machine like motors. he wants to get to know it will get stable this technology any were.

2) they want to know that which motor is better for electric vehicle BLDC or an induction motor.

3) So they compared are these two technologies? How do they work? What differentiates them? And what do they have in common?

4) firstly he goes through the BLDC motor, explained the working principle

5) then he moves on to induction motor drives. A forerunner of the 3 phase induction motor was invented by Nikola tesla. sometime before 1889. 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.

6) After that he informed about the induction motor working principle, advantages, limitation, etc

7) He gives the about power supply to motors.

8) he's main motto is which one is batter for electric vehicle

9) but As per the Application both motors are suitable for cars for more torque BLDC is preferable and induction is for constant speed.

10) So when there is a need for hybrid performance, we could see a completely new combination of drives with these two drives.

11) So he meant there is no winner in the future of EV and HEV for drives, there can always be a new design and combinations.