I had replaced 2 Multiplus 48/5000 running in parallel (no problem in this configuration) with 1 Quattro 48/10000.
After I keep hearing an annoying buzz from the Quattro when in inverter mode, I started to check in the problem. The noise is not the standard trafo sound that rises at high loads, but like a harmonic oscillation. It happens only alt low power loads < 800W-1kW. Above 1kW it disappearing. No meter what type of load the noise is present.
The washing machine is struggling to spin, the audio amplifier is humming (and is dead quiet normally), basically the noise is transferred in any equipment with a transformer/motor.
I have tested the output with the oscilloscope and the sine wave is very distorted. See the pictures/movie IMG_3407.MOV
480W load1.6kW load
Any one noticed this? Looks like a glitch in MOSFETS timing