InstaSpin promises to “Spin your motor in minutes” but how can I spin my three phase motor in minutes if I do not even know what its parameters are? So let’s start with identifying your machine. InstaSpin offers an automated identification process to find the motor parameter needed for the software encoder. The model behind this is pretty simple, it requires only the following parameters to work properly for synchronous machines:
- Resistance Rs
- Inductance Ls_d/q
- Flux linkage
Now how do we find those values if we have no clue and no datasheet of the machine? I’m pretty sure there are a number of manual ways to find good approximations for those values but you can also connect up the machine and start the identification process so the software will measure the necessary values.
However also this identification process requires some parameter to pass successfully, those are:
- Resistance Estimation Current ~20% of Max Current
- Inductances Estimation Current ~-20% of Max Current
- Maximum Current - Should be known roughly
- Flux Estimation Frequency ~10% rated frequency
These are just some rough recommendations on how to choose those values and dependent on your motor then those values are more or less critical. I will also talk about motors where you will see some issue with this identification but the majority of motors just work from scratch.
Furthermore if you have a “favorable” machine it does not even matter what values you use (as long as you do not destroy it with too much current). I did the following tests with the Anaheim BLY172S which is one of the standard machines TI sells on their eStore for test purpose.
I altered all the identification parameters and noted the outcome of the identification.
The real values from the datasheet are Rr = 0.4 Ohm and Ls = 0.6 mH and compared with any of the identification results you can see that it did not matter what identification parameters you use. Certainly there are number of motors where this will not be true but for the majority of motors it will just take you a minute to find its parameters. Cheers!