I'm designing a DTC drive for 500 kW 2300 V induction motor.
The pure integrator is prune to give saturation and drift. So I used a low pass filter to estimate the stator flux vector in the stationary reference frame. How can I determine the cut-off frequency of this filter to obtain an accurate flux estimation over the entire speed range ?
This scheme will be implemented with closed loop PI controllers and the calculated stator voltage will be synthesized using space vector modulation.
hi
1. It will depend on waveform you are using for stator but in any case consider the following.
2. Assuming you are using dq We synchronous reference (see Lipo ,Krause ) .Transform the assumed stator voltage waveform to synch ref Frame for frequency range of interest and choose lowest harmonic at lowest driving frequency as upper limit of filter you are designing.
3. Factors to consider to set below freq obtained in 2. are saturation and stator drop. Perhaps a factor of .5 on 2 above should be adequate.
Good Luck
Cheers
Thank you for the answer ramesh.
I used a pure integrator with a wash out filter to cut out the dc components. The time constant of this filter was set to 0.2.
Now I'm getting the required speed variation but still there is a high ripple in the torque.
The speed ripples may be due to torque ripples which are due to time harmonics. See Hebbar and Robertson (Uof T...long long time ago..)
Cheers
With the help of low pass filter instead of pure integrator you can not eliminate all the ripples of the torque which is a major disadvantage of the DTC technique.
Try using some torque ripple elimination techniques which are available in the literature.
Thank you very much Narasim and Ambrish. I used a modified flux estimator as suggested in the following reference.
Hu, Jun, and Bin Wu. "New integration algorithms for estimating motor flux over a wide speed range." IEEE transactions on power electronics 13.5 (1998): 969-977
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