Hello everyone,

I am a final year electrical engineering student working on my graduation project (PFE), which involves the scalar V/f speed control of a 5.5 kW three-phase squirrel cage induction motor. This is urgent as my project deadline is approaching.

I have successfully implemented the open-loop V/f control in MATLAB/Simulink and obtained good results. However, I am struggling with the closed-loop implementation and would greatly appreciate any help or shared experience from someone who has worked on this topic.

Thank you in advance!

 

You need to show us what you have for us to provide any help.

 

The industrial VFD options available typically use an encoder.

 

Like Max mentioned, for closed loop control, an encoder or tachometer must provide the rotor velocity feedback.
Because induction motors MUST have slip to function, that rotor speed will always be less than the actual magnetic field rotation, and the amount of slip must be included in the algorithm.
However, the slip is not constant but varies with load, and thus a lookup table must be included to determine the actual slip value for precise speed control and, un extreme situations, prevent hunting.
For all those reasons, induction motors are not optimized for tight speed control.

 

For all those reasons, induction motors are not optimized for tight speed control.

A sort of "Fuzzy Logic" perhaps!?

 

Kind of fuzzy, yes.

 

Hello everyone,

I am a final year electrical engineering student working on my graduation project (PFE), which involves the scalar V/f speed control of a 5.5 kW three-phase squirrel cage induction motor. This is urgent as my project deadline is approaching.

I have successfully implemented the open-loop V/f control in MATLAB/Simulink and obtained good results. However, I am struggling with the closed-loop implementation and would greatly appreciate any help or shared experience from someone who has worked on this topic.

Thank you in advance!

Hi,

A quick suggestion would be to first find a spice model of the motor you are dealing with, then go from there. You can work up equations from that too if you need that.
Of course a speed measuring device would be required, and possibly that could come as a shaft position sensor which provides more data as you can get velocity as well as acceleration from that which can help with better overall control.

 

A sort of "Fuzzy Logic" perhaps!?

Well it does seem that the likely non-linear nature of this motor speed control loop would lend itself to the use of Fuzzy Logic rather than PID for feedback.

Edit: See this recent thread on Fuzzy Logic in the Automation, Robotics & Control forum for more info.