Motor power measurement using dq-frame

jjjj

Hi,

I am trying to measure the "bus" current consumed by a motor using the power calculated in the dq-frame.
The 'active' dq-power is calculated with the following expression: P = 3/2*(Usq*Isq + Usd*Isd), found in this thesis https://pdfs.semanticscholar.org/3ac0/35f9868961eac064b2e2f1a3fd0a940ee4d4.pdf

Is the power invariant? .i.e the current consume on the bus could be calculated like this: I_bus = P/V_bus?

I have done some testing and found that the calculated and measured power differs with a factor of ~1.33 (P_calc/P_meas ~ 1,33).
I found this tread on the forum http://e2e.ti.com/support/microcontrollers/c2000/f/171/t/406263 where a factor of 1,33 is mentioned.

I am not using the library so it could be something wrong with my code as well:)

over 4 years ago

0 Ramesh Ramamoorthy over 4 years ago

TI__Mastermind 27240 points

Some people may use power invariant vs mag invariant coordinate transformation. I dont know what you used and also dont have a straight answer. Based on your scaling, repeat the experiment again. I suggest to approach the problem starting from the basic principles of co-ordinate transformation. Let us know if you find the solution.

0 jjjj over 4 years ago in reply to Ramesh Ramamoorthy

Prodigy 190 points

Thank you for your reply.
I have used the 'foc' approximation found in http://www.ti.com/lit/an/sprabz0/sprabz0.pdf for controlling the motor. Is this a magnetic invariant transformation?

0 Ramesh Ramamoorthy over 4 years ago in reply to jjjj

TI__Mastermind 27240 points

It is magnitude invariant method.

0 Ramesh Ramamoorthy over 4 years ago in reply to Ramesh Ramamoorthy

TI__Mastermind 27240 points

If your query is resolved, pls close the thread. thanks.

0 jjjj over 4 years ago in reply to Ramesh Ramamoorthy

Prodigy 190 points

I have search through the web and it seems like the 3/2(vd*id + vq*iq) is used to calculate the power in the dq-frame using the magnitude invariant method. Could I use the result to calculate the bus current consumed by the motor? .i.e. I_bus = P_dq/V_bus?

I am still not getting the details right, but if you could confirm that I am using the correct approach, it will then be easier to troubleshoot the problem.

0 Ramesh Ramamoorthy over 4 years ago in reply to jjjj

TI__Mastermind 27240 points

Sure, the approach is valid. If any issues, there could be a scaling error, that you can always reason out why.

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Motor power measurement using dq-frame