At the time I'm writing this, there appears to be about equal (hydro + gas) = (solar + wind). It appears they are running a significant portion of the grid with high inertia generators.
In a control system when you have an actuator that is much more responsive than the load, you can get into instable operating regimes where. On a small scale, when you are setting up servo motors, there is an inertia matching ratio for stability. In some of the systems I set up it was 10:1 load inertia:motor inertia. If you exceed that, you end up with elasticity between the motor and load that the motor can locally be above set point, and the control tells the motor to slow down, while the load has not yet reached set point. The motor is then too slow, and the control tells it to go faster, and you get the motor oscillating around the speed of the load.
On the grid you can have similar elasticity. An inverter many km away can get too far ahead in the AC cycle, then when that signal reaches the local inverter, the local inverter slows down, but the remote inverter has already slowed down, and by the time that slower wave gets to the local inverter, it is already too slow, and so the local inverter starts to speed up. If you get the frequency "right" you can end up with a positive feedback loop. With a high inertia rotating generator, the system is damped and slow enough to respond you don't change set point faster than the signal can propagate.
Seems like a simple cybernetics problem, especially if it's point-to-point. If there's many different inverters on the same circuit, you might need something like a directed graph, but there should be simpler, more local solutions.
I'm sure the inverter manufacturers are working on something.
At the start of solar and wind integration, it didn't matter. Large rotating generators were the main source on the grid, and provided stability. We're in a different world with an all-inverter grid control perspective-wise.
I think there is also still an information issue. The grid is definitely not point-to-point. It also isn't all generators. You also have loads switching on and off at indeterminate times. There is an overall predictability to it, but not at the phase governing resolution. If you have a local inverter and the phase slows down, you don't know if it is a remote inverter that has over-slowed, to which you shouldn't respond as it will fix itself, or a near-by load that suddenly switched on, to which you should respond as demand is now greater, and needs more supply. With big rotating generators, it doesn't really matter, as they are time averaging with the large inertia to stabilize the load/generator balance.
If the response rate is the only problem, you could just add damping to the system with the faster capability (especially when it is already software driven electronics).
Until we start seeing graphs of voltage and frequency, and logs of breaker trips, speculation is futile. All that info is available for major US blackouts.
You have a fundamental misunderstanding of both how a grid in blackout mode appears to a lonely inverter and what means of coordinating inverters that are available to said inverter.
Imagine you're trying to coordinate a choir of ten million singers that are scattered across a radius of a thousand kilometer, that all sing into their individual Ham radio. And you need it to come out in a perfect unison that sounds good for those who tune into the mixed broadcast.
"A problem of coordination" is perhaps correct, but it neglects the difficulties involved
Thing is, it's not ten million - it's several orders of magnitude fewer, particularly if we're starting with just a selected list of generators.
Also we know the locations of the generators, so we can calculate the phase shift and control them accordingly. At thousand kilometres it's around 60 degrees anyway, so not catastrophically huge.
But also, it isn't just generators, it is also the indeterminate loads. If you have nearby loads switching on and off that are similar sized to your local inverters, that is a complicated controls modelling problem.
I'm pretty sure in grid terms, 60 degrees out of sync is catastrophic. I'm pretty sure you'll be disconnected by protection circuits before it gets that far out.
Superluminal information transfer would be more useful for other areas than grid synchronization, but yeah we don't have crazy tech like that. And if we attempt to synch to a 50hz frequency over the internet means a 10ms latency difference results in 180 degree out of phase input.
And even if we did have the superluminal grid sync signal the propagation of electricity itself is slower than C and you'll need to consider perceived phase synchronization over distance.
Microwave, hell, even GPS-based time sources exist.
If I can sync ALL my [important] servers across the globe to the EXACT same time (under 2 microseconds variance in the last 7 days), and all that on the off-the-shelf hardware, surely a NATION can devise something better?
In a control system when you have an actuator that is much more responsive than the load, you can get into instable operating regimes where. On a small scale, when you are setting up servo motors, there is an inertia matching ratio for stability. In some of the systems I set up it was 10:1 load inertia:motor inertia. If you exceed that, you end up with elasticity between the motor and load that the motor can locally be above set point, and the control tells the motor to slow down, while the load has not yet reached set point. The motor is then too slow, and the control tells it to go faster, and you get the motor oscillating around the speed of the load.
On the grid you can have similar elasticity. An inverter many km away can get too far ahead in the AC cycle, then when that signal reaches the local inverter, the local inverter slows down, but the remote inverter has already slowed down, and by the time that slower wave gets to the local inverter, it is already too slow, and so the local inverter starts to speed up. If you get the frequency "right" you can end up with a positive feedback loop. With a high inertia rotating generator, the system is damped and slow enough to respond you don't change set point faster than the signal can propagate.