Nah - it's pretty simple. Have your inverter measure it's own load - for example by measuring the current through the main switching element. Compare that to the max current that switching element can handle. That is your percentage load that you are under. (negative if current goes backwards)

Then use that to decide what frequency you will output, using the formula.

There is one extra element to this... At startup, to avoid large transient currents, you need to start with the 'max switching element current' for the formula at zero, and then increase it smoothly only while the calculated load figure is under 100%. Within a few seconds you will get sync with any existing network. Such a scheme also works for blackstarting an isolated grid, or with many other inverters with the same strategy.

This scheme has a big benefit that there is no need to measure the grid frequency precisely - which is actually a fairly hard thing to do on noisy small grids.

And it turns out thats all thats required to maintain grid sync. As long as supply capacity exceeds demand at all times, this grid will be stable.