Degradation of system strength because of inverter-based resources (IBRs) is a major concern facing the zero-carbon transition. Blackouts like the one in Iberia on April 28 highlight this. They are generally followed by:

- Uninformed conservative voices calling for an end to investment in renewable energy;

- Optimistic solar and wind power advocates claiming that IBRs were not the problem and can totally replace synchronous machines;

- Transmission system operators requiring new investments in synchronous compensators.

This paper will attempt to inform the debate and explain clearly why synchronous machines cannot be totally replaced. At the same time, this does not mean that investment in renewable energy should end, nor are new investments in synchronous compensators the economic way forward.

The author has previously presented work on Type 5 wind turbines, i.e. those that drive a synchronous generator, without inverters, through one of three variants of hydraulic variable speed system. In their 2024 paper he and co-authors presented to this workshop, they explained that the SyncWind Type 5 power-train is the most cost-effective and proven of these three. This paper will detail the various control sub-systems of the power-train, to enable high-level comparison of its control systems with the IBR approach to grid-forming.