Variable Frequency Generator Patents: Who Leads, Where the Gaps Are 2026
- 61.4% concentration. The top five assignees together hold 890 of the 1,449 records in scope — 61.4% of the field — with the leader alone accounting for 552.
- Filing cooled from a 2018 peak. Annual filings peaked at 154 in 2018; from 2021 (41) to 2024 (30), the last complete year, volume fell 27%.
- Control and machine classes dominate. H02P (control of motors & generators) and H02K (electric motors & generators) each cover roughly a third of records, well ahead of gas-turbine and engine-starting classes.
Filing growth compares 2021 (41 records) with 2024 (30) — a three-year span. 2024 is the most recent year we treat as complete: publication lags filing by roughly 18 months, so 2025 onwards are still filling in and any growth rate that ends there would understate the field. Top-5 share is the combined record count of the five largest assignees divided by all 1,449 records in scope (CR5), not by the ranked leaders only.
What this dataset covers
This landscape tracks 1,449 published records filed between 2015 and mid-2026 that combine variable frequency generator, integrated drive generator or starter generator claims with control, excitation or rectification subsystems — generator control units, rotating rectifiers, permanent magnet generators, oil-cooled stators, de-excitation circuits and shear sections. The scope is deliberately narrow: it is the electromechanical and control layer of aircraft electrical power generation, not aircraft electrical systems in general.
Filing activity is concentrated in a small number of aerospace primes and their historical subsidiaries, with receiving-office activity led by the United States and Europe. Because publication typically lags filing by around 18 months, the most recent one to two years in any trend understate actual filing activity and should be read as provisional rather than declining.
Filing trend and technology composition
Two views of the same 1,449-record dataset: filings by year, and the IPC subclasses those filings carry. Because a single record can carry several IPC codes, the composition shares add up to more than 100% of the record total.
Filings rose to a 2018 peak, then eased
Annual filings climbed to 154 in 2018 before settling into a lower band; the 2021-to-2024 window shows a 27% decline (41 to 30), the last span both years of which are far enough past the cut-off to be treated as complete.
Control and machine classes lead the field
H02P (control of motors & generators, 32.4% of records) and H02K (electric motors & generators, 29.7%) are the two largest classes, ahead of F02C gas-turbine plants (17.9%), F02N engine starting (12.8%), B64D aircraft equipment (12.3%), F16H gearing (8.8%), H02J power supply/grid (8.6%) and H02M power conversion (7.5%).
Shares are the percentage of the 1,449 records in scope. A patent can carry several IPC classes, so the shares add up to more than 100%.
Go deeper on Variable Frequency Generators and Starter Generators with Eureka
This page is one run against one query. Ask Eureka your own question about variable frequency generators and starter generators and every answer comes back with the patent numbers behind it.
Try EurekaA representative claim architecture
Electric power generation system (EPGS) controller excitation system architecture for variable frequency generators
The claim describes a generator control unit built around two separate rectifiers, each fed by its own permanent magnet generator at a different AC voltage level, controlling excitation for a variable frequency generator. Splitting excitation supply across two PMG-and-rectifier paths at different voltages is the specific architectural choice at the centre of the claim.Filed by Hamilton Sundstrand Corporation, published 2023-07-25.
| # | Publication no. | Patent title | Citations |
|---|---|---|---|
| 1 | US20030093187A1 | PFN/TRAC systemTM FAA upgrades for accountable remote and robotics control to stop the unauthorized use of ai… | 977 |
| 2 | US20050187677A1 | PFN/TRAC systemTM FAA upgrades for accountable remote and robotics control to stop the unauthorized use of ai… | 595 |
| 3 | US6965816B2 | PFN/TRAC system FAA upgrades for accountable remote and robotics control to stop the unauthorized use of airc… | 489 |
| 4 | US4743777A | Starter generator system with two stator exciter windings | 173 |
| 5 | US5587647A | Dual output synchronous-induction starting/generating system | 163 |
| 6 | EP3095989A1 | Accessory apparatus and method of assembling accessories with a turbine engine | 159 |
| 7 | US5555722A | Integrated APU | 159 |
| 8 | US5015941A | Power conversion system with bi-directional power converter having prime mover start capability | 140 |
| 9 | US5068590A | Brushless generator having AC excitation in generating and starting modes | 136 |
| 10 | US20060042252A1 | Engine power extraction control system | 129 |
Citation counts favour older filings inside a searched corpus; treat them as a signal of influence on later filers, not as a measure of which technology matters most today.
Each row carries its publication number; clicking a row searches Eureka by that number.
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Three patterns stand out once the records are broken down by owner, class and geography.
The field is a small owners' club
Five assignees hold 890 of the 1,449 records in scope, and the leader alone holds 552. A newcomer is not entering an open field; it is filing around a small number of dense portfolios that already cover excitation, rectification and control architectures.
Volume has eased from its 2018 peak
Filings peaked at 154 in 2018 and have since declined, down 27% from 41 in 2021 to 30 in 2024, the most recent year that can be read as complete. That is a maturing claim space, not necessarily a shrinking technology — high filing density in earlier years means core architectures are already occupied.
Control claims outweigh pure machine claims
H02P (motor and generator control) narrowly leads H02K (the machines themselves), and both sit well ahead of aircraft-specific class B64D at 12.3%. That ordering suggests control and excitation logic, not the electromechanical hardware, is where the densest recent claim activity sits.
Eureka can read the same corpus for gaps instead of for coverage: under-claimed branches adjacent to variable frequency generators and starter generators, with the prior art for and against each one.
Who holds the portfolios, and where they are not filing
The ranked leaders are aerospace primes and their historical subsidiaries rather than a broad supplier base, and recent-year momentum has slowed across nearly all of them.
One assignee holds well over a third of the field
The leading assignee's 552 records dwarf the fifth-place holder's 71, a gap that signals a long-established, defensively maintained portfolio rather than an actively expanding one.
A steep drop-off after the top ranks
Filing counts fall from 71 at fifth place to 24 at tenth, and the ranking runs to 100 companies in total — most of them holding a handful of records each. That pattern points to a core group defending established architectures and a much larger group filing narrow, specific improvements.
Recent-year activity has gone quiet even among leaders
Several of the most active historical filers show zero or one filing in the latest tracked year, with year-on-year changes ranging from flat to a full drop-off. Read this alongside the publication lag: the true 2025-2026 picture is still filling in, but the slowdown from 2021 to 2024 is already measurable.
| Assignee | Recent year | YoY |
|---|---|---|
| GE Aviation Systems LLC | 1 | 0% |
| Yamaha Motor Co., Ltd. | 1 | -50% |
| Hamilton Sundstrand Corporation | 0 | — |
| Honeywell International Inc. | 0 | — |
| Sundstrand Corporation | 0 | — |
| The Boeing Company | 0 | -100% |
| General Electric Company | 0 | -100% |
| Rolls-Royce plc | 0 | — |
Where to take this from here
A landscape snapshot answers where the field stands; the next questions are usually specific to one architecture or one competitor.
Model a specific excitation architecture
Take a dual-PMG rectifier configuration like the featured 2023 record and map exactly which claim elements are already covered versus open for a design-around.
Explore in EurekaTrack a single assignee's filing behaviour
Follow year-by-year filing and citation activity for one of the concentrated top-five portfolios to see whether its slowdown is defensive maintenance or a genuine pivot.
Explore in EurekaCheck white space before drafting claims
Run a freedom-to-operate pass against the under-claimed sub-areas — oil-cooled stator thermal management and shear-section failsafe design in particular — before committing claim language.
Explore in EurekaCommon questions about this landscape
The field is highly concentrated: the top five assignees together hold 890 of the 1,449 records in scope, 61.4% of the total, and the single leading assignee accounts for 552 of those on its own. This is typical of aerospace power electronics, where a small number of primes and their historical subsidiaries have filed continuously since well before this dataset's 2015 start. A new entrant should expect to be filing around, not into, open space held by these portfolios.
Filings peaked at 154 in 2018 and have since eased; from 2021 (41) to 2024 (30), the last year that can be treated as complete, volume fell 27%. Because publication lags filing by roughly 18 months, 2025 and 2026 figures in any raw chart will look artificially low and should not be read as a continuation of the decline. The honest read is a maturing claim space rather than a shrinking one — high filing density in earlier years already occupies much of the core architecture.
Control-related claims lead: IPC class H02P (control of motors and generators) covers 32.4% of the 1,449 records, narrowly ahead of H02K (electric motors and generators themselves) at 29.7%. Gas-turbine plant integration (F02C) and engine starting (F02N) follow at 17.9% and 12.8%. Because records often carry multiple IPC codes, these percentages overlap rather than sum to 100%, but the ordering is a reasonable proxy for where recent claim activity is densest.
It claims a generator control unit built from two separate rectifiers, each connected to its own permanent magnet generator supplying a different AC voltage, used to control excitation for a variable frequency generator. Filed by Hamilton Sundstrand and published in 2023, it is a recent example of the excitation-architecture claims that sit inside the dominant H02P and H02K classes. Anyone designing a dual-source excitation path for a variable frequency generator should review this claim's specific voltage-differential structure before assuming a design-around is clean.
Sub-areas adjacent to the dense control and machine classes carry noticeably fewer records, including oil-cooled stator thermal management, de-excitation fault response, shear-section mechanical failsafe design, and rotating rectifier fault tolerance. These are not proven-empty spaces, but their lower density relative to H02P and H02K suggests less claim crowding. A freedom-to-operate check against the concentrated top-five portfolios is still the right first step before filing there.
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Disclaimer. This page is generated from Patsnap Eureka data drawn from a limited snapshot of global patent and scientific-literature records, and is provided for general information and reference only.
Patent data carries inherent limitations: recent filings (typically the most recent 18–24 months) are under-counted due to standard publication lag; counts may be reported at either a patent-family or a patent-record basis and are not always directly comparable; classification, applicant-name, and citation data may contain errors, duplicates, or omissions; and the underlying search query defines and constrains the scope shown. As a result, the analysis may be incomplete or inaccurate and may not reflect the full technology landscape.
Nothing on this page constitutes an exhaustive prior-art, novelty, freedom-to-operate, or validity search, nor does it constitute legal, financial, investment, or professional advice, and it should not be relied upon as such. Any patent, commercial, or strategic decision should be verified independently and reviewed with qualified patent, legal, and domain professionals. Patsnap makes no warranties, express or implied, as to the accuracy, completeness, or fitness for any particular purpose of the information presented.
Machine translation. Assignee and organisation names originally recorded in Chinese, Japanese or Korean have been rendered into English by an AI translation step so that the tables stay readable. These renderings are best-effort and may not match a company’s registered English name; the original name is what the underlying patent record carries, and it is what any Eureka query launched from this page uses.