How about:
"Methods to synchronize AC power sources so they can be interconnected in a grid"
The problem you are trying to solve is how to bring lots of different AC sources together so they can be linked in parallel. AC voltages have three fundamental properties, their voltage, their frequency and their phase. You can assume they are all designed to produce the same voltage (for example 110V or 220V) and nominally the same frequency (50Hz or 60Hz) but their phase may be completely different. You can see the problem if you imagine two generators, both produce 220V 50Hz AC but they are 180 degrees out of phase. Each one on its own if fine but if you link them across each other there would be a huge bang! The reason being that as one was at peak positive in its waveform, the other would be at peak negative. The 'phase' is the time difference between the waveforms. Before they can be connected across each other, the positive and negative cycles from each source have to be brought together so they exactly coincide. In a conventional system, the main source of electricity is a major power station, maybe producing Megawatts of power which dominates the grid, other smaller sources monitor the AC to discover its exact frequency and adjust their phase to match it precisely before connecting. A situation arises when there is no major source of electricity but lots of smaller ones. They all have to connect in synchronism but if there is no timing source except each other, how should they do it? Something has to be a central timing source that they can all adjust to match.
Brian.