Induction motor equivalent circuits

[Antti]

Hello folks!

Kicking off the discussion with an old yet difficult topic: numerically determining the equivalent circuit of an induction machine. Any approaches that you prefer?

My latest approach is based on defining the dq-transformation for the rotor cage, and then using the standard inductance computation approaches to compute the self- and mutual inductances between the rotor and the stator windings. But, I'd be interested in any other approaches.

[Push14]

Not a preferred method of mine as I use the same method you prescribed , but what is your opinion on using the stored energy method ?
If we can calculate total stored energy and we assume that we know the current (assuming current source) self and mutual inductance can be calculated to calculate reactance .

[alex333]

The thing to consider is what you need the equivalent circuit for.
If you're after the "Steinmetz" T-type equivalent circuit, then the approach outlined in the OP is appropriate. Or simulate no-load / locked-rotor tests (which I believe is equivalent).

For an approached based on stored energy a lot of simulations are needed. Is the equivalent circuit used often enough to justify it?

[alex333]

I found another possible approach in:
https://www.femm.info/wiki/RapidIMAnalysis.

Summary:
1. replace squirrel cage rotor with equivalent 3ph winding
2. Analysis is carried out in synchronous dq-frame
3. Iterativeley determine rotor current. Start with i_dr = 0; i_qr = -iq_s
3. Calculate stator androtor flux linkage lambda_{s,r}d, lambda_{s,r}q
4. New rotor current: i_r' = i_rd' + j*i_rq' = j*(i_sq + lambda_rq/lambda_qd*i_sd)
5. GOTO 3

Then calculate equivalent circuit parameters for the converged stator and rotor currents.