Week-6 Challenge: EV Drivetrain
1Q
Which types of power converter circuits are employed in electric and hybrid electric vehicles?
Types of the converter:
1. AC to DC(Rectifier)
2. DC to DC(Chopper)
3. DC to AC (Invertor)
4. AC to AC (Cycloconverters)
AC to DC(Rectifier):
This converter is built inside the car. It is called the onboard charger through it really is a converter. It converts power from AC to DC and then feeds it into the car battery. this is the most common charging method for electric vehicles today.
DC to DC(Chopper):
It is used in EV as to output the required voltage supply. In the case of interfacing the fuel cell, the DC/DC converter is used to boost the fuel cell voltage and to regulate the DC-link voltage.
A DC charger has a converter inside the charger itself. That means it can feed power directly to the car battery and does not need the onboard charger to convert it. DC chargers are bigger,faster, and exciting breakthroughs when it comes to EVs.
DC to AC (Invertor):
On-Board AC/DC converters are connected to the ground to prevent electric shock. TO ensure the insulation between input and output ports, power de-vices with 1kv or higher withstanding voltage are applied to the insulation circuit.
It converts DC to AC and controls the signal frequency and sends it to an electric motor which essentially means it can control the speed of the vehicle.
AC to AC Converter:
AC to AC converter is used for converting the AC waveforms with one particular frequency and magnitude to the waveform with another frequency at another magnitude. This conversion is mainly required in case of speed controlling of a machine, for low frequency and variable voltage magnitude application.
We require a particular voltage and particular frequency for operating some special devices or machines. For speed control of induction motor, AC to AC converters(Cycloconverters) is used majorly. For obtaining a desired AC power supply from the actual power supply, we need some converters called AC to AC converters.
Types
1. Cycloconverters
2. AC to AC converters with DC link
3. Matrix converters
4. Hybrid Matrix Converters.
Q2. An Electric Vehicle's Drivetrain with a 72V battery pack shown in the diagram below. The duty ratio for acceleration operation is d1 and for the braking operation the duty ratio is2'. The other parameters of the electric vehicle are given below,
Motor and Controller Parameters:
Rated Armature voltage= 72 V
Rated armature current= 400 A
Ra= 0.5Ω,
KΦ= 0.7 V-s
Chopper Switching frequency= 400 Hz
The vehicle characteristics are given by the equation
TTR=24.7+0.0051w2
Given:
DC machine Torque speed relation:
`T=(V.Km(phi))/(Ra)-(Km(phi)^2)/(Ra).omega`
Where,
T- Motor Torque
V- voltage supply
Ra- Armature Resistance
Km(`phi`)- Motor constant
`omega`- Angular speed of the motor
Solution:
Voltage(motor)= voltage of armature*dutycycle
Voltage =72*0.7=50.4volts
`T=(V.Km(phi))/(Ra)-(Km(phi)^2)/(Ra).omega`
Motor_T= (50.4*(0.7))/0.5-((0.7)^2/(0.5))*w (Eq 1)
Given,TTR=24.7+0.0051w2(Eq 2)
(50.4*(0.7))/0.5-((0.7)^2/(0.5))*w=24.7+0.0051w2
We solve the equation to get w by using the auadratic formula;
Where,
a=0.0051
b= 0.98
c= -45.89
The 2 solution are w=-230.06 rad/sec and 38.95rad/sec
The vehicle mving in forward direction we take w as38.95rad/sec
Q3. Refer to the blog on the below topic:
Induction Versus DC brushless motors by Wally Rippel, Tesla
Explain in brief about the author’s perspective.
He starts with the headline of 'One size does not fit all' he feels extremely unpleasant about this world of a gas-powered vehicle engine are not all alike and there is no best engine type rather there are different types of engine to suit personal requirements and it is true for electric vehicle drives. He feels like he is missing the version of mechanical components from which he was grown like lead-acid batteries, DC brushed motors, and contractor controllers he said none of there remain including his hair. He guesses that we will see both induction and brushless machines in the future.
There is a explains about the brushless machine and points out without inverter brushless motors are useless motors. Moving on to induction motor drives the 3-phase induction motor was invented by Nikola Tesla sometime before 1889. the stator for the 3-phase induction motor and the DC brushless motor are virtually identical both have three sets of distributing windings that are inserted within the stator core. the essential difference between the two machines is with the rotor.
Now moving on to Brushless or Induction The main difference is that much less rotor heat is generated with the DC brushless drive Rotor cooling is easier and peak point efficiency is generally higher for the drive. the best power factor for the induction drive is about 85 percent. This means that the peak point energy efficiency for DC brushless drive will typically be a few percentage points higher thank for an induction drive.
The conclusion is that DC brushless drive will likely continue to dominate in the hybrid and coming plug-in hybrid markets, and that induction drives will likely maintain and dominance for the high-performance pure electrics. He has a question that what will happen as hybrids become more electrically intensive. and as their performance levels increase? the author says there are lots of hardware that is common for both drives could mean that we will see induction and DC brushless life and work side by side during the coming golden era of hybrid and electric vehicles.