[mrendu43]

hi.
i have single phase PSC induction motor that i wanna run on more speed than its rated
i found aplication note on microchip page
AN967 - Bidirectional VF Control of Single and 3-Phase Induction Motors Using the PIC16F72 - Application Notes - Details
this is for driving that tipe of motor without a capacitor vith variable speed and freqency.
problem is that in few sections in code the freqency is limited from 5-60 hz
so if anyone have time and will to pop the eye in the code and modifey it so freqency can be changed from cca 40-250 hz.
thx alot

sorry about my bad english

[Al_The_Man]

A very interesting concept, although I would have though that a better description would be 2 phase control of a 1 phase motor?
But skimming over the code it would appear that the high speed interrupt Read_ADC_Results is where the limit is placed on 60Hz?
The value stored at FREQUENCY.
I see the Freq pot is centre off and fwd and rev rpm is either side of centre, maybe changing the code to read the the pot from 0 to 5v in one motor direction would help increase the frequency range?
A bit of experimentation would confirm.
Al.

[RomanLini]

Many of these motors are designed so their inductance closely matches their correct operating freq. To run at a higher frequency is generally not advised, you may also need to increase voltage to obtain the higher frequency, and this will start to get very difficult if you need more than a small speed increase as you will run into heating and insulation class issues.

[Al_The_Man]

But Roman, surely then this would apply to any induction motor? VFD's are operating into 3 phase non-vector rated induction motors in applications all over the world?
Al.

[amtekinc]

I will look at it if you still have a need for it. Let me know.

[RomanLini]

But Roman, surely then this would apply to any induction motor? VFD's are operating into 3 phase non-vector rated induction motors in applications all over the world?
Al.

Sorry Al_the_man I missed your question and only saw it now when the thread was bumped.

From what I know about typical induction motors they are quite finely tuned for the magnetics; field strength, iron stauration, number of poles and mains frequency and voltage.

By all means you can run them slower with a VFD, but I don't think you can run them much faster than their standard mains synchronous speed. At light loads you might get some speed increases over the nameplate speed but I would not try to get a lot of speed out of one.

Maybe I misintepreted the OP's question but to me it looked like he has a 50Hz motor and wants to be running it from 40-250Hz.

[Al_The_Man]

Roman I usually run non-vector rated 4 pole motors at up to 120hz (double rpm), the reasoning is that the manufacturer would build the 4 pole to the same rpm rating as the 2 pole.
On a non-vector rated motor I would be hesitant to run a 2 pole over ~60hz due to balance and bearings etc.
Standard induction 4 pole Vector rated motors go up to around 300hz.
The standard induction motor can Never reach synchronism, this would be zero torque.
But it does try.:devious:
Al.

[RomanLini]

Very interesting! Thanks for mentioning that. I get your point about 4-pole and 2-pole (ie RPM mechanical issues) but what about the electrical issues?

Do you get any increased heating running 120Hz into a 60Hz motor, and have you measured the applied AC voltage when it is at double speed? I was taught this is a bit of a no-no although I knew it was safe for a 20% or 30% increase I had never heard of running double RPM (assuming this is a standard induction motor ie squirrel cage or capacitor start motor etc).

[Al_The_Man]

I have never had any issues with heating, I could monitor the voltage as it can be read out on the display instead of frequency.
Vector rated motors are basically the same motor but balanced for higher rpm as well as H.S. bearings.
I only use VFD's with 3 phase motors, 1 ph (split phase cap start) do not do well with VFD type control, they tend to drop out of run at lower speeds.
Al.