Encoder Realted
Hi,
I am trying to understand the implemented logic in altair Motor control modules. Currently I am referring "Applied Control of electric Drives" , From that book >>3 Module 1: Lab Sessions>>3.3 Laboratory 1:3: FOC Sensored Control of PM.
I am using Teknic M-2310P-LN-04K motor
In this module, Main motor Control>>Encoder Speed/Angle module>>what is significance if 200Hz ?
and Main motor Control>>Encoder Speed/Angle module>>Encoder to elec Angle>>
1. what is significance of theta offset ?
2. why Gain value 2 is used ?
I have attached below module of the same. Can anyone please solve my doubts ?
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Hi Swapnil,
Thanks for writing to us.
Here are some answers to your queries:
1. '200Hz' as the encoder base frequency is multiplied by invF_fs to incorporate the number of ticks the encoder has. The encoder in use can have different resolutions which actually affects how fast can the speed be measured. Sometimes poor encoders with less tick counts limit the response time of attaining faster speed. However, in newer diagrams (attached below), you will see that this method is not used and the speed is actually calculated inside FOC block using a different approach.
2. 'thetaOffset' - This offset is introduced so as to make the d axis vector align with the encoder. For FOC, it is important that the PM vector is aligned with the d-axis and to do that encoder position is necessary. For a particular sequence of motor wires (Va - Red, Vb-Black, Vc-White), the enoder position may need some starting offset. For convenience and better understanding you can see the effect of theta_offset in the debug diagram attached below.
3. Gain of 2 multiplied - That was done to correctly reflect the encoder tick counts. Earlier the diagram used half of the values and a gain of 2 is used to update it. However, that has been simplified and fixed in the newer diagrams
Hope this was helpful.
Do keep tuned in to see a new and complete library of motor control examples and tools to be released as a part of 2022 eDrives add on accompanied with a step by step documentation to make life easier.
Try out the new examples attached here
Best
Mayank