Week-6 Challenge: EV Drivetrain
1) Which types of power converter circuits are employed in an electric and hybrid electric vehicles?
There are dour types of power converter circuits used inan electric and hybrid electric vehicle are:
1) AC - DC converter( Rectifier)
2) DC - AC converter(Inverter)
3) DC-DC converter ( Chopper)
(i) Step up chopper
(ii) Step down chopper
4) AC - AC converter
AC - DC converter( Rectifier)
These are the converter used while charging electric and hybrid electric vehicle where it converts the ac supply source to dc supply to a battery othe f vehicle while charging.
DC - AC converter(Inverter)
These are the converter used in a vehicle to convert dc supply to ac supply, for example, to run a motor in the electric and hybrid electric vehicle it needs ac supply but the source from the battery is dc supply so in those place this type of inverter is used.
DC-DC converter ( Chopper)
These are the converter used in the vehicle to convert one level of DC supply to another level of DC supply. If they increase the DC supply then they are called Step up Chopper, when they decrease the DC supply they are called Step Down Chopper.
AC - AC converter
These converters are used to one level of voltage and frequency in AC supply to another level of voltage and frequency in AC supply they are similar as a chopper, example for this converter is fan regulator.
2) What is EV steady-state speed if the duty cycle is 70%?
An Electric Vehicle's powertrain with a 72V battery packs 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 vehicleares 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
`T_υ=24.7+(0.0051)×ω^2` --- 1
The torque equation of DC motor is
`T=((V×K∅)/R)-((K∅^2×ω)/R)`---- 2
By equating equation 1 and equation 2
`24.7+(0.0051)×ω^2 = ((V×K∅)/R)-((K∅^2×ω)/R)`
By substituting the values of voltage, Resistance, constant we get the equation
`24.7+(0.0051)×ω^2 = ((72×0.7×0.7)/0.5)-((0.7^2×ω)/0.5)`
`24.7+(0.0051)×ω^2 = (70.56)-(0.98×ω)`
By rewriting the above equation we get
`ω^2 + (192.15×ω) - 8992.15 = 0`
The above equation is the quadratic equation by solving that equation we will get the value of steady-state speed ifthe duty cycle is 70%
ω = 38.95 rad/sec
3)Develop a mathematical model of a DC Motor for the below equation using Simulink.
`ω = ( V/K_ϕ) -(R_a/K _ϕ ^2 .T)`
The model is made in Simulink it consists of a constant block, Ramp block, square block, divide block, addthe block, scope block and the stimulation time is 100 Seconds
After running the model we get this plot
4) Refer to the blog and Explain in brief the author’s perspective.
In the above blog, the author first explains himself and then discussed normal commercial vehicles and then about the changes which happened in new vehicles and also about the electrical vehicle. Then the main topic he discussed in the blog is about Brushless Dc motor and Induction Motor which is used in Hybrid electrical vehicle and Electrical vehicle. Then he discussed the basic concept and working of Brushless DC motor and Induction Motor and then discussed efficiency, positive and negative of both Brushless DC motor and Induction Motor.
Brushless DC motor:
Brushless DC motor consists of two or more permanent magnets which are present in the rotor that generates a magnetic field that reaches with current flowing in winding which produces torque. All the electrical energy produced is then converted to mechanical energy with good efficiency.A Brushless DC motor produces no starting torque when it is connected to fixed frequency utility power. Since the brushless dc motor has a rotor cooling system the heat produced by the motor is low so there is less loss of energy in form of heat which in turn works more efficiently. A Brushless dc motor will also operate with unity power which gives more efficiency than an induction motor. In a brushless dc motor, the strength of the magnetic field produced is hard to adjust so there will be more loss compared to the induction motor. The cost of a permanent magnet present in a brushless dc motor costs more so it may require more cost to build.
Induction Motor:
The 3 phase induction motor looks similar to the brushless dc motor, they have the same type of winding within the stator but the difference between both is with in rotor. The induction motor does not use magnets they only have steel laminations with the buried peripheral conductors, Current flowing in stator windings produce a rotating magnetic field that enters the rotor.If a there-phase induction motor is connected to three-phase power it will produce torque. The main reason for induction motor success is because it can directly compatible with conventional power. The induction motor cannot operate in dc it must require AC. If we add an inverter and feedback loop it will be in equal efficiency to a brushless dc motor. In induction motor magnetic field strength is adjustable and it is preferable forhigh-performancee operation. The average efficiency of induction motor is better than brushless dc motor. The cost of this motor is less when compared to the brushless motor but it requires more control than a brushless dc motor.
Finally, the author concludes that both Brushless DC motor and induction motor has some advantages and disadvantages in the future we can see the working of both Brushless dc motor and induction motor in life by working it side by side and we can see the performance of both.