Lights throbbing or pulsing - 2 Schneider XW Pro Inverters

Good day,

I have been operational with a pair of XW Pros powering my property for just a month. So far, I am impressed. One puzzle I have is throbbing lights. I have about 40 sconce lights with two 7w bulbs around the property. They are dimmable, so at night, I reduce them to 40% brightness. They are not flickering. They are increasing/decreasing in brightness about 3 times per second. I have not calibrated the inverters and with a small load they are producing 118.3V. on L1 and L2. The voltage in both inverters appears to be reporting within 0.1V in Insight Facility. I do have the Schneider Inverter Calibration tool, but they are working so well I do not want to take them offline! The power here is really bad, and no one makes any attempt to set their oven or microwave clocks. They would rarely last a day. Mine have been up for 27 days since I powered up. At night each inverter has under 1kW of load. Under very light loads the master inverter produces about twice as much as the slave. As soon as 3 or 4kW are drawn, they even out to very similar levels of power.

Most modern sinewave inverters use digital PWM chopping, followed by an L-C filter to average and smooth the PWM waveform to a clean sinewave.

The L-C filter rings a bit when lightly loaded and there is sudden current changes in output load. This can be caused by devices that have simple rectifier-capacitor power supplies that draw short current bursts near the peak voltage of AC sinewave to recharge their filter capacitors. This short burst of current can cause some ringing of the inverter's PWM L-C filter. The short period of ringing is usually in the 2 kHz to 4 kHz range which is the corner cutoff frequency of the L-C low frequency filter.

A dimmable light usually uses a triac device to start the conduction at various points in the AC sinewave to accomplish an effective change in output voltage for 'dimming'. Any noise on input AC voltage can cause the triac to trigger a little early or late in the AC cycle causing variation in the effective output voltage.

Even on AC grid, a dimmable light will often blink occasionally when there is small glitches in AC grid voltage due to large loads being turned on or off, like an air conditioner compressor.

Many mini-split air conditioners have significant current spikes at the AC sinewave voltage peaks due to their simple rectifier-filter capacitor AC input to HV DC conversion for their three phase, variable speed inverters. This continuously 'twangs' a sinewave inverter's L-C filter.

I'd start with the calibration. The pulsing may be the inverters fighting for to the load by changing voltage on their outputs.