It's actually pretty simple on the control side. The "smart" generator's brain only really needs to know two things: how much power is going to the load from the generator it controls, and what is the phase/frequency of the inverter with respect to the line?If the inverter is outputting a frequency based on an oscillator it would be a constant frequency and should act like an isochronous non inverter set (steady frequency with no droop). It seems to me the only way to couple them would be to parallel them with the inverter set at full load, then add throttle on the non inverter set to share that load. Possibly add more load until both sets are st or near full output. Problem now is when you shed ANY load from the “grid” the mechanically governed set will try to raise the grid frequency above the oscillator frequency (basically a reverse current situation”. I have no idea how the inverter could deal with that other than having a frequency droop option as it cannot control the mechanical governor which is now attempting to raise frequency :shrug:
All the generator's brain is really doing is the following:
1 - Match the frequency of the line
2 - Measure the output kw of the smart generator
3 - Advance or retard the phase of the output sinewave until the kw measured in step (2) is whatever is desired.
Phase control of an inverter is REALLY simple. Numerically controlled oscillators have some similarities, so this link might provide more info as to how it can work: https://en.wikipedia.org/wiki/Numerically_controlled_oscillator
Most of those inverters are going to be PWM based, so a microprocessor is already under complete control of the waveform. Phase can be controlled by simply changing the timing of the PWM modulator a little bit (wider pulses sooner means a leading phase angle, for example). Its really easy to implement. Since the phase of the generator with respect to the line is what controls how much power the generator puts into the line, all you need to do is adjust the output phase until you see the load you want on the generator. There's not a whole lot more to it.