Induction Motor Vector Control
Induction Motor Vector Control
(OP)
Hello
I am trying to model an induction motor in Simulink and have come across a few problems.
The model is a 3 phase induction motor based around a rotating reference frame on the rotor.
problem:
1- When starting from zero rpm, the id current is 0. This means the flux is 0, thus my starting torque is 0 and has to ramp up. Therefore i dont get full load torque from 0 rpm
2- The flux doesn't reach its desired value until base speed.
3- Since i am using a limited voltage source (300V), the torque dramatically drops off to 0 at base speed. (Flux weakening IS being considered)
The torque graph looks like the left hand side of a bell curve up to base speed, then drops to 0 soon after.
The vector control scheme i am using matches all the others in research papers.
Any advice would be appreciated
Thanks!
I am trying to model an induction motor in Simulink and have come across a few problems.
The model is a 3 phase induction motor based around a rotating reference frame on the rotor.
problem:
1- When starting from zero rpm, the id current is 0. This means the flux is 0, thus my starting torque is 0 and has to ramp up. Therefore i dont get full load torque from 0 rpm
2- The flux doesn't reach its desired value until base speed.
3- Since i am using a limited voltage source (300V), the torque dramatically drops off to 0 at base speed. (Flux weakening IS being considered)
The torque graph looks like the left hand side of a bell curve up to base speed, then drops to 0 soon after.
The vector control scheme i am using matches all the others in research papers.
Any advice would be appreciated
Thanks!





RE: Induction Motor Vector Control
Is this DOL or VFD control?
Are you modelling applied frequency or rotor slip frequency?
You must have a difference between applied frequency and rotor frequency. This is called the slip frequency. Without a slip frequency there is no current induced in the rotor and no torque.
Take a look at the torque graphs on pdf page 7 of the Cowern papers:
http://www.baldor.com/Shared/manuals/PR2525.pdf
These graphs are for DOL starting. To use for VFD control, use 100% on the graph as the applied frequency. At full load the slip frequency will be about 2% or 3%, or 97% or 98% based on rated speed.
You can see that the curves pass the full load torque line at less than but very close to 100% speed.
The curves are accurate for evaluating slip frequency and torque at various different applied frequencies, but if the applied frequency is changed, the percentages become meaningless.
That is at 50% of rated frequency the slip frequency for a given torque will be the same as at rated frequency in Hz or in RPM, but the percentage base will have changed. That is 3% slip at 1500 RPM will be 6% slip at 750 RPM but in both cases the slip at full load will be 45 RPM slip and a rotor frequency of 1.5 Hz.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Induction Motor Vector Control
Is what you are calling "base speed" really the no-load speed, where the back EMF matches the supply voltage so there is no "head room" to apply torque-producing current?
Curt Wilson
Omron Delta Tau
RE: Induction Motor Vector Control
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.