Week-6 Challenge: EV Drivetrain

AIM:- 1) To study types of power converter circuits used in Electric Vehicle ( EV ) & Hybrid Electric Vehicle ( HEV ).

          2) To find EV steady-state speed with using the given data.

QUESTIONS:-

1) Which types of power converter circuits are employed in an electric and hybrid electric vehicles?   

               power electronics is the field to process and control the flow of electric energy by supplying voltages and currents in a form that is optimally suited for user loads.

               In Electric and Hybrid Electric Vehicles (EV/HEV), the power electronic converters play a key role to distinguish the power requirements according to the components need.

               There are mainly 3  types of power convertor are used in HEV & EV-

AC to DC Converter (Rectifier): 

AC to DC converters are most commonly used in Plug-in Hybrid Electric Vehicles (PHEV) & Plug-in Electric Vehicles (PEV). It is also called a rectifier that converts the AC supply and gives DC output. The EV charger (On Board Charger) comes in this category.

                          Above are some sample examples that how it works.

DC – AC  Converter (Inverter):

This type of converter takes a DC supply and converts it to an AC supply. This is also called the inverter. This is mainly used to run the induction motor for driving used in the PHEV & EV

                           In the above figure inverter is used which is shown in the highlighted red color box to run the electric motor.

DC to DC converters (Chopper):

It is also called a chopper cause it converts High voltage to Low voltage & vice versa. But in EV they are mainly used to convert High voltage to low voltage. For Ex, if High battery voltage is of 340V then it converts it into 12V or 48V according to requirements. And this is used to run the auxiliary components like Headlights, Music system, Air conditioning system in the car.

                              Above is the typical power system architecture in EV & HEV.

2) An Electric Vehicle's powertrain with a 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%?

Solution:-

Battery voltage , `Vb = 72V`

The speed of the electric vehicle depends on the speed of the motor.

Hence, 

`Vm=Vb*d`

Where,

        Vm = motor voltage

        Vb  = battery voltage  

          d  = duty cycle

Duty cycle is 70%

Hence the voltage to the motor,  `Vm = 70/100*72 = 50.4V.`

The torque-speed relation for a DC motor is given by,

`T = (V.kphi)/(Ra) – ((kphi)^2.omega)/(Ra)`

Where,

 V = voltage supply,

`kphi` =  motor constant,

Ra = armature resistance, 

w = motor angular speed and 

T = motor torque.

Substituting all values,

 `T = (50.4).(0.7)/0.5 – ((0.7^2).omega)/0.5 = 70.56 – 0.98w`……………………(1)

Now,

Given torque equation 

`T = 24.7 + 0.0051omega^2`………………….(2)

Comparing equation (1) & (2)

Which gives the quadratic equation,

 `0.0051w^2+0.98*w-45.86=0` 

Comaparing with `ax^2 + bx +c`

Solving the above equation byformula,

`(-b+- sqrt(b^2-4ac))/(2a)`

         We get following values

`omega` = 38.85 rad/sec  & -230.98 rad/sec

     Taking +ve value,

Hence the steady state speed of the vehicle is 38.85 rad/sec.

3) Refer to the blog on below topic: 

            Induction Versus DC brushless motors by Wally Rippel, Tesla

            Explain in brief about author’s perspective. 

Answer:-