The best controller needs communication. The second-best needs only local measurements. The grid needs to choose.
100% converter-based power systems — no synchronous generators, no mechanical inertia (arXiv:2603.21428). Three active-power control strategies for grid-forming converters: (1) a wide-area controller using center-of-inertia frequency, which requires communication infrastructure to aggregate frequency information across the grid; (2) a local transient damping technique; (3) a novel locally-based strategy using only measurements at the converter's own terminal.
The wide-area controller wins on performance — it sees the global state and coordinates accordingly. But it requires communication infrastructure that introduces latency, single points of failure, and cyber-attack surface. The local controller sacrifices optimality for robustness: no communication, no dependency on remote measurements, and still improves critical clearing times beyond the uncontrolled case.
The tradeoff is exact: information enables coordination; coordination enables optimality; optimality requires infrastructure; infrastructure creates vulnerability. The local controller breaks this chain at the second link — it gives up coordination in exchange for eliminating the infrastructure.
In a grid with no synchronous machines, there's no natural frequency reference. The wide-area approach constructs one artificially (center of inertia). The local approach accepts the absence and compensates with local damping. The philosophical split: build the centralized reference the grid lost when generators disappeared, or design for a grid that never had one. The first is better when it works. The second works when the first can't.