A grid-forming inverter sets its own voltage and frequency reference and behaves like a voltage source, whereas a grid-following inverter tracks an existing grid reference using a phase-locked loop. Patent claims in this space tend to center on the control model that generates the voltage or current instruction — for example virtual admittance, virtual impedance, or synthetic-inertia loops — rather than on the power hardware itself, which is often shared with conventional inverter designs. That is why this landscape's IPC composition is dominated by H02J (power supply and grid systems) rather than H02M (power conversion hardware): the differentiating claim language sits in the control layer, not the converter topology.

This 42-family dataset includes filings from major grid and energy equipment names such as General Electric, GE Renewable Energy Spain, Hitachi Energy, and State Grid Corporation of China, alongside university and research-institute filers such as Tsinghua University and the Colorado State University Board of Governors. None of the assignees tracked for recent-year momentum show filings in the latest year, which given typical publication lag is more likely a pipeline effect than a sign that these organisations have stopped filing. The dataset is too small for a single company to claim clear dominance; activity is spread across utility-side research institutes and equipment vendors rather than concentrated in one leader.

The clearest under-claimed areas sit outside the dense H02J core: communication and coordination protocols for fleets of grid-forming inverters (H04L and H04W each appear only twice in 42 records), and the overlap between grid-forming control and wind-turbine power trains (F03D, 9 records) or multi-terminal HVDC systems. High filing density in the core control loop does not mean those adjacent branches are technically solved — it means the basic single-converter control claims are occupied, while multi-asset coordination and specific renewable-source integrations remain comparatively open for new claims.

Filing activity rose from zero in 2017 to a peak of 20 records in 2022 and has not exceeded that level in the years since. Part of this is a data artefact: publication lags filing by roughly 18 months, so the most recent one to two years in any patent trend are always undercounted and should not be read as a real decline yet. But the plateau at the 2022 midpoint, combined with the concentration of filings in H02J, is consistent with the core grid-forming control architectures having already been staked out by early movers, with newer activity shifting toward specific applications rather than foundational claims.

US20260142471A1, filed by Tsinghua University, claims a multi-terminal flexible direct-current adaptive grid-forming control system that sets power values for adaptive grid-forming converters based on the loss of an HVDC line, builds an adaptive grid-forming control model to derive the AC voltage instruction, and constrains the current inner loop using virtual admittance and current clamping. Anyone designing a multi-terminal HVDC system with adaptive grid-forming behavior on line loss should map their control architecture against this filing's specific combination of loss-detection, adaptive model, and current-clamping constraint, since a design that avoids one of those three elements is less likely to fall within its claim scope. Given the filing's 2026 date, prosecution is still active and claim scope may narrow or shift during examination.