In a prior question it was established that any string or microinverter that is grid tied must put out sinusodial power. But there is also the task of being in sync with the grid. It seems from apperances that task for a single string inverter is far simpler than for an arrary of 28 microinverters on a 10kwh solar system to stay in step with each other let alone the grid. I can only imagine the analog nightmare of trying to cue 28 phonographs to play the same lp in unison and with variations in drive components and lp pressings. So what is the microinverter problem and solution to this symphonic nightmare of phase variance?
A baseline grid-tie inverter samples the line voltage and produces current that is in phase with it and proportional to the maximum power it can squeeze out of the source (typically photovoltaic). So it's actually the grid itself that the inverters are synchronizing to.
This can actually burden the grid with power it doesn't need, or make the job of regulating voltage at remote spots more difficult. This can have a direct impact on the stability of the power grid.
Do a search on "smart grid tie inverters" or "advanced grid tie inverters". There's a movement afoot in areas that are seeing a lot of alternative power sources to encourage or require power providers to have inverters that can be managed or otherwise be provisioned to be an assist to grid stability, rather than a burden.