How to Measure Stability in Complex Power Grids Using D-Q Impedance
A method for testing how electrical components in a power grid react to disturbances to ensure the grid remains stable and doesn't crash.
Original patent title: “Method for measuring D-Q impedance of polyphase power grid components”
A method for testing how electrical components in a power grid react to disturbances to ensure the grid remains stable and doesn't crash. Granted to Individual in 2011 with 16 claims and 7 forward citations, and it is expected to expire in 2029.
Coverage
What does this patent actually cover?
This patent describes a way to measure the 'D-Q impedance' of electrical components in a power grid, which helps engineers understand how those components interact with the grid's stability. It uses a generator as a probe, injecting specific 'suppressed-carrier' signals into the grid through its speed and field inputs. By measuring how the grid's voltage and current respond to these signals, the system solves a set of four simultaneous equations to calculate the D-Q impedance parameters (Zqq, Zqd, Zdq, and Zdd). These parameters allow engineers to create Nyquist diagrams, which are visual tools used to check if a power system is stable or prone to dangerous oscillations.
The gap
What does this patent NOT cover?
- Does not cover measuring impedance using external hardware probes or non-generator stimulus sources.
- Does not cover standard steady-state impedance measurements that do not utilize D-Q coordinate transformations.
- Does not cover stability analysis methods that do not rely on the specific four-equation resolution process described.
- Does not cover grid components that cannot be stimulated via speed or field excitation inputs.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
Instead of building a separate, expensive testing device, the method turns an existing generator into a precision instrument by using its own control inputs (speed and field) to 'ping' the grid and measure the response.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Utility-scale power grid stability testing
Wind farm integration analysis
Large-scale synchronous generator performance monitoring
Why it matters
The bigger picture
Modern power grids are increasingly complex due to the integration of renewable energy sources and power electronics, which can cause unpredictable interactions. This method provides a systematic way to diagnose potential instability before it leads to equipment damage or blackouts. It is particularly relevant for utility-scale grid operators who need to ensure that new hardware, like wind or solar farms, will play nicely with existing infrastructure.
Filed
March 23, 2009
Granted
October 25, 2011
Market context
Who's building on this
Companies in this space
Large power equipment manufacturers like Siemens, GE Vernova, and ABB utilize similar concepts of small-signal stability analysis and impedance-based modeling to certify grid-connected hardware. These companies rely on these mathematical frameworks to ensure that power converters do not cause sub-synchronous oscillations in the grid.
Market impact
This patent formalizes a diagnostic approach that has become increasingly critical as grids move away from purely passive, rotating-mass-based systems toward active, inverter-dominated systems. It provides a standardized framework for stability verification, which is now a common requirement in grid interconnection studies for new power plants.
Claim 1 — Plain English
What this patent covers
This patent describes a way to measure the 'D-Q impedance' of electrical components in a power grid, which helps engineers understand how those components interact with the grid's stability. It uses a generator as a probe, injecting specific 'suppressed-carrier' signals into the grid through its speed and field inputs. By measuring how the grid's voltage and current respond to these signals, the system solves a set of four simultaneous equations to calculate the D-Q impedance parameters (Zqq, Zqd, Zdq, and Zdd). These parameters allow engineers to create Nyquist diagrams, which are visual tools used to check if a power system is stable or prone to dangerous oscillations.
The clever bit
Instead of building a separate, expensive testing device, the method turns an existing generator into a precision instrument by using its own control inputs (speed and field) to 'ping' the grid and measure the response.
What it does not cover
- Does not cover measuring impedance using external hardware probes or non-generator stimulus sources.
- Does not cover standard steady-state impedance measurements that do not utilize D-Q coordinate transformations.
- Does not cover stability analysis methods that do not rely on the specific four-equation resolution process described.
- Does not cover grid components that cannot be stimulated via speed or field excitation inputs.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
PatentBrief Score
Impact Score
Early stage
Citation count
18/40
Early citations
Claim breadth
11/20
Broad claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
5/20
Granted 10–20 years ago
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$31K – $100K
Midpoint $62K · 2.7 yr remaining · industry ×1.5
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
16 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Williams, M. L. (2011). How to Measure Stability in Complex Power Grids Using D-Q Impedance (U.S. Patent No. 8,044,672). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/8044672/method-for-measuring-d-q-impedance-of-polyphase-power-grid-components
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How to Measure Stability in Complex Power Grids Using D-Q Impedance cover?
A method for testing how electrical components in a power grid react to disturbances to ensure the grid remains stable and doesn't crash.
Who owns patent US 8044672?
Individual owns this patent, granted in 2011.
When does this patent expire?
This patent is expected to expire on March 23, 2029, when the invention enters the public domain.
What is patent US 8044672 cited by?
This patent has been cited by 7 later patents that build on its ideas.
What problem does this patent solve?
Modern power grids are increasingly complex due to the integration of renewable energy sources and power electronics, which can cause unpredictable interactions. This method provides a systematic way to diagnose potential instability before it leads to equipment damage or blackouts. It is particularly relevant for utility-scale grid operators who need to ensure that new hardware, like wind or solar farms, will play nicely with existing infrastructure.
What does this patent NOT cover?
Does not cover measuring impedance using external hardware probes or non-generator stimulus sources.
Same assignee
More from Individual
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