Week-6 Challenge: EV Drivetrain

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

Ans.

Power electronic converter is mainly used for to provide desire voltage and current with more efficiency of power to electric and hybrid vehicle. Mainly in electric and hybrid vehicle use DC-DC(chopper), AC-DC(rectifier) and DC-AC(inverter).

In above image see that electric vehicle power electric diagram.

In above image see that hybrid vehicle(parallel) power electric diagram.

In electric and hybrid vehicle mainly used power converter below explained.

1. DC-DC converter:-

DC-DC converter is used for mainly to used step down voltage which is used in auxiliary component and step up for high acceleration. This is done by chopper and boosting. Sometimes is used for regenerative braking for bi-direction in DC-DC.

The most DC-DC converter is follows explained.

• Non isolated converter

This is used when we need to voltage converter into step up or step down with smaller ratio. Here limitation is diode prevent to reverse direction of current flow so this is not bidirectional. Non isolation converter have different types of converter which is below lists.

1) buck

2) boost

3) buck-boost

4) cuk

Now understand all types one by one.

1. Buck

Buck converter is DC-DC converter which is step down voltage from input to output. This types of converter is used for auxiliary component to reduce the operating voltage for that component.

2. Boost

Boost converter is DC-DC converter which is step up voltage from input to output. This types of converter is used when vehicle needs more power to get instant speed so needs more voltage.

3. Buck-boost

Buck-boost converter is DC-DC converter which is step up or step down voltage as per requirement or command of controller.

4. Cuk

Cuk converter is one type of buck-boost converter but here current is zero ripple.

• isolated converter

Galvanic isolation between multi-source systems is required by many standards. Personnel safety, noise reduction and correct operation of protection systems are the main reasons behind galvanic isolation. Isolation converter is two types below list.

1. Half bridge
2. Full bridge

• Half bridge

Half bridge converter is DC-DC converter and it is step up or step down from input to output and it’s provide isolation via transformer.

• Full bridge

This is one type of DC-DC converter and if we add two transformer in half bridge converter then we get full bridge converter.

2. AC-DC converter

This type of converter is known as rectifier that use in electric and hybrid vehicle to providing fast charging AC to DC converter voltage.

basic components in this rectifier is transformer, switching unit, filter and a control block.

This image is full wave rectifier circuit.

3. DC-AC converter

This types of converter is known as inverter that used when via battery AC motor(induction motor) used in electric and hybrid vehicle.

2. 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.

Here we gives,

Rated Armature voltage= 72 V

Rated armature current= 400 A

Ra= 0.5Ω, KΦ= 0.7 Volt second

Chopper Switching frequency= 400 Hz

Duty cycle = 70%

Here we give duty cycle so we can find actual voltage of vehicle,

Actual voltage = 72*0.70

= 50.4 V

For steady state speed of motor we have equation is,

T = V*(k*phai)/Ra – ((k*phai)^2/Ra)*w

Putting the value we have,

T = (50.4*0.7)*0.5 – (((0.7)^2)/0.5)*w

T = 70.56 – 0.98w ----------(1)

As we show in question we give ,

T = 24.7 + (0.0051)w^2 -------(2)

Now we comparing both equation 1 & 2

24.7 + 0.0051w^2 = 70.56 – 0.98w

0.0051w^2 + 0.98w – 45.86 = 0

To solve this quadric equation,

W = 38.89 rad/sec , w = -231.1 rad/sec

Here we take positive for speed value,

W = 38.89 rad/sec

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

ωω= V/Kϕϕ -Ra/Kϕϕ^2 .T

Ans.

In below link DC motor model provide and with variable file is also provide.

matlab version 2021a

https://drive.google.com/file/d/1zti7WCx28r_mjBJbHV-JLVAWKOzcNKnt/view?usp=sharing

in case link is not workin below file is atteched.

For variable torque and velocity we use instead of ramp function to get graph of speed. Here we take constant for that equation of motor mathematical model.

4. Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

Explain in brief about author’s perspective.

Ans.

Here author discuss about two different motor which is very useful in electric and hybrid vehicle first is DC brushless motor and second is induction motor. Also gives idea about all vehicle is alike and it’s up to you that selecting according to the requirement.

• Here both motor is similar with little of different author discuss on it with cost, working, construction between two motor. With the reference of that Author can’t give conclusion of motor which is better in this two motor. In this ripple writes that “there is no one best engine type” this sentence is showing that inn this two motor better is engine compare to these two.
• First we talking about induction motor where instead of permanent magnet we use stacked steel laminated with buried peripheral conductors which is from of shorted structure. this motor has ability to start with load. There is no need to inverter. Induction motor efficiency is less then DC brushless motor but in high power generation DC motor is very costly compare to induction motor and high power generation induction motor efficiency is similar to DC brushless motor. For use in vehicle we not require inverter
• Now we talking about DC brushless motor where use permanent magnet used as rotor. Stator same for both motor. This types of motor start with no load condition. Current flowing in stator winding to produce the rotation magnetic flux. This motor without inverter is useless. This motor torque performance is higher then induction motor.
• We talking about the drives of both motor stator is same, both 3-phase inverter drivees is use with little dissimilarity is induction motor is used speed sensor and DC brushless motor is absolute position sensor these difference is smaller.