Week-6 Challenge: EV Drivetrain
Q1.Which types of power converter circuits are employed in an electric and hybrid electric vehicle?
Ans:-
A power converter is an electrical or electro-mechanical device for converting electrical energy. A power converter can convert alternating current (AC) into direct current (DC) and vice versa; change the voltage or frequency of the current or do some combination of these.
Types of converters used in the EV and HEV’S
- AC to DC (Rectifier)
- DC to AC (Inverter)
- DC to DC
1.AC to DC (Rectifier):
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification since it straightens the direction of the current.
Uses :
Powering/Charging the vehicle:
- Using a rectifier in the power supply helps in converting AC to DC power supply. Bridge rectifiers are widely used for large appliances, which can convert high AC voltage to low DC voltage.
-In power electronics ,battery management system and other accessories like radio, music system etc.
2.DC to AC (inverter)
An inverter is a device that converts DC power to the AC power used in an electric vehicle motor. The inverter can change the speed at which the motor rotates by adjusting the frequency of the alternating current.
The resulting AC frequency obtained depends on the particular device employed. Inverters do the opposite of "converters" which were originally large electromechanical devices converting AC to DC.
3.DC to DC:
A basic DC-DC converter takes the current and passes it through a switching element, which turns the DC signal into an AC square wave signal. This wave is, then passes through another filter which turns it back into a DC signal of the required voltage.
DC/DC converters are used for the following reasons:
- To step down the voltage from a high voltage source to a lower voltage,
- To match the loads to the power supply,
- To isolate the primary and secondary circuits
-Uses in EV and HEV
Q.2. 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'.
Ans.:
Given:-
Rated Armature voltage (V)= 72 V
Rated armature current= 400 A
Ra= 0.5Ω,
KΦ= 0.7 Volt second
Chopper Switching frequency= 400 Hz
Duty cycle (dc)= 70% = 0.7
Now, we will find the average voltage:
The Average Voltage:
Vs=V×dc
Vs=72×0.7
Vs=50.4
The vehicle speed-torque characteristics are given by the below equation :
.......(1)
motor speed characteristics formula is :
By putting a value of Tv in formula we get :
T = 70.56 -0.98.w ............(2)
if we compare (1) and (2)
70.56 - 0.98.w=24.7+(0.0051).w^2
0.0051.w^2+0.98.w-45.86=0
BY quadratic equation formula:
w = 
w = 
w = 38.92 rad/sec
3. Develop a mathematical model of a DC Motor for the below equation using Simulink.
Ans:
AIM:
To develop a mathematical model of given equation of DC motor using simulink.
Blocks used:
-Constant
-Gain
-Add
-output
Model:
Conclusion :- Thus created the the model for given equation.
Q4. Refer to the blog on below topic:
Induction Versus DC brushless motors by Wally Rippel, Tesla
Explain in brief about author’s perspective.
Ans:-
-In the article writes pointing towards the constantly changing technology he explained about the DC Brushless motors and Induction motors.
- According to him, the rotor has two or more permanent magnets that generate a DC magnetic field. This magnetic field will enter the stator core which interacts with the currents flowing in the windings to produce an interaction between rotor and stator. It needs a proper flow of current into the rotor and stator if it’s not connected properly the current will not generate and the torque decreases. During the Electric and mechanical conversion when the rotor is rotating, the magnitude and polarity of the stator current will continuously vary such that the torque remains constant and optimal efficiency is achieved.
-Unlike the DC brushless rotor, the induction rotor has no magnets. They have just stacked steel laminations with buried peripheral conductors that form a shorted structure. Currents flowing in the stator windings produce a rotating magnetic field that enters the rotor. The frequency of this magnetic field as seen by the rotor is equal to the difference between the applied electrical frequency and the rotational frequency of the rotor itself.
- An induced voltage exists across the shorted structure that is proportionate to this speed difference between the rotor and electrical frequency. The currents are produced within the rotor conductors that are approximately proportionate to the voltage, hence there’s a speed difference. Finally, these currents interact with the original magnetic field to produce forces.
-The motor has the ability to start under load. No inverter is needed. The fact that induction motors are directly compatible with conventional utility power is the main reason for their success. In contrast, a brushless DC motor produces no starting torque when directly connected to fixed frequency utility power.
Difference between induction Motor and DC brushless Machines:
-The Dc brushless requires a position sensor but an induction motor requires only a speed sensor.
- Less rotor heat is generated in DC brushless drive and Rotor cooling is easier and peak point efficiency is generally higher.
- DC brushless drive operates at a power factor of one, whereas the induction drive power factor is 85%.
-Finally writer says that the DC brushless will dominate the Hybrid Electric Vehicle Markets but the Induction drive will maintain dominance in the High performance in the pure electric vehicles. As of now, there is no winner out of the two as each has its own advantages and disadvantages.