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STPM10: Reactive and Total Harmonic Distortion

Question asked by germino.santiago on Mar 23, 2016
Latest reply on Mar 24, 2016 by germino.santiago
Hi, first of all I'm sorry for the offtopic, but there is no smart meter IC section on the entire forum, which is odd.

I've a functional prototype of a Smart Meter running on a STM32-F0/STPM10 platform. Before entering pre-production we'll need to solve this issues:

1) Sometimes the active power register goes DOWN by a little amount, generally decrementing by 2 (7,6 microWatt) when it does. We managed to count for this, but is it normal?

2) Active and Apparent energies are being measured well, we calculate cos fi and all. But Reactive as read is always not exact or even closer compared to the power triangle resulting from given P and S to get R. From the datasheet we have interpreted that the KAW constant should be multiplied by two to get the amount of Wh consumed, I mean:
ReactivePowerConsumed = ReactiveRegisterRead * 2 * KAW

For Type1 energy, we shold multiply by 4:
ActiveFundamentalPowerConsumed = Type1RegisterRead * 4 * KAW
Is this right?

3) Since Type1 energy is Active with noise and harmonics filtered, is there some way to calculate THD using this given data? or, what is the recommended method? is it possible to reliably sample iMOM and uMOM several times higher than the line frequency to do a FFT?

Thanks in advance,