{
  "patent_number": "US 8044672",
  "country": "US",
  "title": "How to Measure Stability in Complex Power Grids Using D-Q Impedance",
  "original_title": "Method for measuring D-Q impedance of polyphase power grid components",
  "summary": "A method for testing how electrical components in a power grid react to disturbances to ensure the grid remains stable and doesn't crash.",
  "what_it_does": "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.",
  "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."
  ],
  "filed": "2009-03-23",
  "granted": "2011-10-25",
  "expires": "2029-03-23",
  "status": "active",
  "holder": "Individual",
  "holder_url": "https://patentbrief.org/company/individual",
  "inventors": [
    {
      "name": "Michael Lamar Williams",
      "url": "https://patentbrief.org/inventor/michael-lamar-williams"
    }
  ],
  "times_cited": 7,
  "tags": [
    "energy",
    "mechanical",
    "telecommunications"
  ],
  "abstract": "A method is provided for measuring D-Q impedance of a component of a polyphase power grid connected to a grid node, and evaluating the margin of stability at a node using Nyquist diagrams generated from the measured D-Q impedance data. A generator, coupled to the polyphase power grid, is controlled to induce suppressed-carrier stimulus current into the grid node. Circuitry measures response signals of suppressed-carrier form existing within a bus voltage at the grid node and a branch current of the component being measured. The method includes measuring complex voltage components of the response signals contained in the bus voltage and complex current components of the response signals contained in the branch current to form simultaneous equations that are resolved to determine the D-Q impedance parameters Zqq, Zqd, Zdq and Zdd of the measured component.",
  "url": "https://patentbrief.org/patent/us/8044672/method-for-measuring-d-q-impedance-of-polyphase-power-grid-components",
  "markdown_url": "https://patentbrief.org/patent/us/8044672/method-for-measuring-d-q-impedance-of-polyphase-power-grid-components/md",
  "google_patents_url": "https://patents.google.com/patent/US8044672",
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