Week-6 Challenge: EV Drivetrain
1.Power Converters employed in electric and hybrid electric vehicle fall in two categories:isolated converters and non- isolated converters.Half-Bridge,Full-Bridge,Fly-Back,Forward and Push-Pull Converters are examples of isolated converters.They are used when output is needed to be completely isolated from input.On the other hand, Buck,Boost,Cuk,Buck-Boost and Charge-Pump Converters are examples of non-isolated type converters.Boost converter is used for voltage step-up while Buck converter is used for voltage step down.
2.The angular velocity of a DC Motor is given by the expression
w=V/(K(phi))-R/Square of (K(phi))X T
where V is Armature voltage,R is Armature resistance and T is motor torque.
Taking Duty Cycle into consideration and considering the given parameters we find in this case
w=(0.7X72)/0.7-(0.5/(0.7X0.7))XT=50.4/0.7+1.0204T
Substituting the given value of T we get
w=72-1.0204[24.7+(0.0051)w2]
After simplification we find 0.0052w2+w=46.8
On solving we get w=38.94.Hence the steady state angular speed is 38.94 radians/sec.
3.Mathematical model of a DC motor has been developed in Simulink using the given equation vide the file DCmtr attached herewith.This makes use of two no of Adder Blocks,two no of Constant Blocks,two no of Transfer Function Blocks,two no of Gain Blocks,two no of Display Blocks,two no of Scope Blocks and one no of Integrator Block.Simulation was done and speed as well as distance plot and values were obtained after simulation.
4.After studying the prescribed blog the following observations are made:
A:Stator construction of both Brushless DC motor and Induction motor are identical.However,rotor construction is different.While the rotor of Brushless DC motor has two or more permanent magnets rotor of an induction motor is made of stacked steel laminations with buried peripheral conductors.
B. The polarity of stator current needs to be continuously varied in case of a Brushless DC motor and the device that enables this is called an inverter.Without the inverter such motors are useless.Induction motors on the other hand are self starting and only require an utility power supply to get started.They cannot be operated from D.C. and A.C. is a must for their operation.Compared with the Brushless D.C.motors they have limited starting torque and somewhat limited peak torque capabilities.
C. Much less heat is generated in a Brushless D.C.motor compared with an Induction motor and so rotor cooling becomes easier.When inverter is added without feedback to an Induction motor it will be possible tp power such a motor from battery or other D.C.source.Variation of speed is also possible simply by adjusting the inverter frequency.However, even then torque is lower when compared with a Brushless D.C. motor.But if upgraded with an inverter as well as a feedback loop the performance of an induction motor becomes more or less comparable with that of a Brushless D.C. motor.