Hello,

I'm using ADE7880 and I'm getting AFWATTHR (fundamental active energy) values greater than AWATTHR (total active energy), as AWATTHR includes harmonics that situation shouldn't happen.

This situation arises with several loads and several working settings.

For example for a load of power ~60W cosine ~0.74 I get this values:

AWATTHR = 52

AFWATTHR = 54

To calculate VLEVEL I use this:

Nominal mains voltage = 220V 50Hz

ADC input fullscale = 0x514791 / d5326737 (that would correspond to maximum peak voltage)

peak voltage at ADC input fullscale = 642.55035V

rms voltage at ADC input fullscale = 454.35171V

VLEVEL = 454.35171V/220Vx4000000

VLEVEL = 0x007e0d4c / d8260940

I accumulate for 500ms:

LINECYC = 0x32 / d50

LCYCMODE = 0xe7

Thanks,

Santiago

Hi Santiago

I did some tests in the lab today and observed the following:

1. Set voltage fundamental to 50%FS and current fundamental to 2% FS. Set the harmonics to be positive and equal to 2% FS on both voltage and current channels at 3rd,5th and 7th harmonics. Apply signals at the PF of 1 and set the registers, LCYCMODE to 0x0F and LINECYC to d1000. The result in this case was that the AWATTHR was greater than AFWATTHR.

2. When PF was reduced to 0.5, 0.3 and 0.2, the AWATTHR was still greater than AFWATTHR.

3. Now, I inverted the sign of the harmonics on the current channel and set PF to 1. This time I obtained results similar to what you were seeing. AFWATTHR was larger than AWATTHR.

When thinking about this, it makes sense because the total active power (AWATTHR) is computed as the sum of products of V and I at each of the harmonics over the entire bandwidth. So, if either V or I harmonic is negative, it will multiply with the other non-zero positive component and get subtracted from the fundamental active power. So, AWATTHR can be less than AFWATTHR in that case.

Even if you set the chip in positive only accumulation or absolute accumulation mode, the total power is calculated in the signal path first and then the result is what that is regulated, i.e., if the resultant power is negative, then positive only mode doesn't account that and absolute mode takes just the magnitude into consideration. This regulation does not happen at every harmonic power level.

So, if you wish to do that externally,you can get the fundamental power and all the necessary harmonic powers separately from the chip. But it might take some time for you to do this.The harmonic components can be collected only on a per phase basis and only 3 at a time. It will take 750 ms for the values to settle within rated accuracy.

Hope this helps! Kindly post back with further questions, if you have any.

Regards

hmani