Hello all! I have been looking over the code used for the nano and pico inverters in an effort to truly understand what is going on "under the hood/bonnet". I notice that the sine table currently uses

3.14159 /(NPWM - 1)

That puts both zero-degree and 180-degree zero crossings into the same 200-sample half-cycle. The next half-cycle also begins at zero, giving two consecutive zero samples and slightly nonuniform phase spacing. On the scope, that looks like a very tiny flattening at the zero crossing. I haven't noticed any adverse electrical effects, but it would raise the THD. Has anyone else seen any ill effects?

If the math were altered slight so that the half cycle doesn't come around to zero at the end, that would eliminate the double zero at the crossing.

what I wrote works well enough.

But why not give it a go and see if things improve.

I spent a good amount of time working with the area where the PWM changes
from D9 to D10 and also the D10 change to D9.

I found the order of actions that set up the PWM is important and
the code with "perfect_symmetry" in the name is ideal.

pico_2_heavy_filter_bv_better_stop_prefect_symmetry.zip


Possibly removing the extra zero in the sine table will be good.
I expect there will be some other "out by one" mistakes in there
and maybe one of those deals with the extra zero just by accident.

FYI:

  Quote  

but it would raise the THD. Has anyone else seen any ill effects?

HIOKI Power Quality Analyzer.

Power to the property with all normal loads running:

Total Harmonic Distortion:

AC from Mains: 2.5%
AC from Inverter: 2.3%  

Virtually the same first 5 odd harmonics and all below 2.3%.

The Inverter THD when isolated from Property, just Inverter THD, unloaded and loaded with a resistive load..

No Load: 0.9% THD  

 2.3kW:  0.6% THD.

Almost all fundamental frequency, which is exactly what you want, the first and second odd harmonics are tiny, the third barely visible, nothing after the 3rd odd harmonic, and this tester reads out to the 37th harmonic.

From memory, anything under 3% in a typical inverter is considered good enough.

NOTE: This is measured on a 12kW Symmetrical Drive modulated WG Inverter.
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Edited 2026-07-20 11:34 by KeepIS