Hi,

Different overload protection scheme results in different behaviour of an inverter. In case of square wave PWM inverters based on general purpose chips like the SG3525 relies on the principal of pulse by pulse current limitation.

SMPS (notebook adapters mainly without an input PFC stage) converts the incoming AC to DC and there is almost always a NTC in the input side to limit the inrush current while charging the bulk reservoir capacitor.
In case of square wave inverters the current demands while charging the capacitor may be quite steep causing a pulse-by-pulse shutdown of the output stages of the inverter. This results in a lower average output voltage which in turn causes even more currents due to a higher duty cycle of the SMPS operating to keep its output stable. Thus this may drive the inverter protection mechanism nuts.


In case of sinewave the capacitor draws a fairly non-linear current with the input wave-form when no PFC is used. Thus again misleading the overload protection mechanism which almost always relies on a complete cycles current demand to startup heavy loads.

Modern Sinewave inverter firmwares takes care of this by running a separate tight loop on every waveform lookup point to correct distortion and differentiating between steep sustainded overloads and peak current demands. In case of a properly desinged system the system would definately have a softstart and at least 300% overload capability for a period of 15 to 30 seconds. So an AC/Fridge/Compressor connected to such inverters may have starters arranged in a fashion that can be engaged without power and let the inverter startup alongwith the load to take advantage of the soft-start function.

So I think it all depends upon the nature of load and inverter types which should be considered. Only having an equal voltage may not be sufficient for a grid-tied inverter if it is not synchronized with mains. You would not gain energy points rather loose and possibily destroy the inverter if it is not synchronized with the mains and also dynamically adjust the base frequency when the mains frequency varies.