# US 2014/0152331 A1 · System and method for detecting a grid event > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0152331 A1 - Document ID: US20140152331A1 - Status: Published application - Kind: A1 - Application number: 13/689,860 - Filed: 2012-11-30 - Published: 2014-06-05 - Earliest claimed: 2012-11-30 - Assignees: General Electric Company - Applicants: General Electric Company - Inventors: Robert Gregory Wagoner; Allen Michael Ritter; Mark Eugene Shepard; Talha Irfanul Haque - Web page: https://patentgrep.com/patent/US20140152331A1 ## CPC - H02J 3/381: {Dispersed generators} - G01R 27/16: Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line - G01R 31/42: AC power supplies - H02J 3/0012: characterised by the contingency detection means in AC networks, e.g. using phasor measurement units [PMU], synchrophasors or contingency analysis - H02J 3/388: Arrangements for the handling of islanding, e.g. for disconnection or for avoiding the disconnection of power - H02J 2101/10: Dispersed power generation using fossil fuels, e.g. diesel generators - H02J 2101/24: Photovoltaics - H02J 2101/28: Wind energy - Y02E 10/56: Power conversion systems, e.g. maximum power point trackers - Y02E 10/72: Wind turbines with rotation axis in wind direction - Y02E 10/76: Power conversion electric or electronic aspects - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract A method for detecting a grid event is provided. The method includes sampling grid voltage and grid current over a fixed period of time; determining grid impedance at one or more frequencies using the sampled grid voltage and the sampled grid current; comparing the grid impedance at the one or more frequencies to a known expected grid impedance at the one or more frequencies; and detecting a grid event based on the comparison. ## Claims ### Claim 1 A method to detect a grid event comprising: sampling grid voltage and grid current over a fixed period of time; determining grid impedance at one or more frequencies using the sampled grid voltage and the sampled grid current; and comparing the grid impedance at the one or more frequencies to a known expected grid impedance at the one or more frequencies; and detecting a grid event based on the comparison. ### Claim 2 (depends on 1) The method of claim 1, wherein determining grid impedance at one or more frequencies using the sampled grid voltage and the sampled grid current comprises calculating a Fourier transform of the sampled grid voltage and sampled grid current at the one or more frequencies and determining the grid impedance at the one or more frequencies using the calculated Fourier transform of sampled grid voltage divided by the calculated Fourier transform of sampled grid current. ### Claim 3 (depends on 2) The method of claim 2, wherein calculating the Fourier transform of the sampled grid voltage and sampled grid current comprises calculating a fast Fourier transform (FFT) of at least one of the sampled grid voltage and sampled grid current. ### Claim 4 (depends on 1) The method of claim 1, wherein determining grid impedance at one or more frequencies using the sampled grid voltage and the sampled grid current comprises filtering the grid voltage and filtering the grid current at the one or more frequencies and determining the grid impedance at the one or more frequencies using the filtered grid voltage divided by the filtered grid current at the one or more frequencies. ### Claim 5 (depends on 1) The method of claim 1, wherein sampling grid voltage and grid current over the fixed period of time comprises sampling grid voltage and grid current over one cycle of a fundamental frequency. ### Claim 6 (depends on 1) The method of claim 1, wherein comparing the grid impedance at the one or more frequencies to the known expected grid impedance at the one or more frequencies comprises comparing the grid impedance at the one or more frequencies to a known expected grid impedance range at the one or more frequencies. ### Claim 7 (depends on 6) The method of claim 6, wherein detecting the grid event based on the comparison comprises detecting the grid event if the grid impedance at the one or more frequencies is outside the known expected grid impedance range at the one or more frequencies. ### Claim 8 (depends on 6) The method of claim 6, wherein detecting the grid event based on the comparison comprises detecting the grid event if the grid impedance at the one or more frequencies is within the known expected grid impedance range at the one or more frequencies. ### Claim 9 (depends on 1) The method of claim 1, wherein detecting the grid event based on the comparison comprises detecting that the grid event comprises islanding of an electrical generator. ### Claim 10 (depends on 9) The method of claim 9, wherein the electrical generator comprises a doubly-fed induction generator (DFIG) driven by a wind turbine or a photovoltaic array. ### Claim 11 A method of detecting a grid event on an electrical grid connected with the one or more electrical machines, said method comprising: connecting one or more electrical machines to an alternating current (AC) electric grid, wherein the AC electric grid is configured to transmit at least one phase of electrical power to the one or more electrical machines or to receive at least one phase of electrical power from the one or more electrical machines; electrically coupling at least a portion of a control system to at least a portion of the AC electric grid; coupling at least a portion of the control system in electronic data communication with at least a portion of the one or more electrical machines; detecting a grid event of the AC electric grid based on one or more conditions monitored by the control system wherein the control system is configured to: sample AC grid voltage and AC grid current over a fixed period of time; calculate a frequency transform of the sampled AC grid voltage and sampled AC grid current; determine grid impedance at one or more frequencies using the calculated frequency transform of sampled AC grid voltage divided by the calculated frequency transform of sampled AC grid current; compare the grid impedance at the one or more frequencies to a known expected grid impedance at the one or more frequencies; and detect a grid event based on the comparison. ### Claim 12 (depends on 3) The method of claim 3, wherein calculating the frequency transform of the sampled AC grid voltage and sampled AC grid current comprises calculating a fast Fourier transform (FFT) of at least one of the sampled AC grid voltage and sampled AC grid current. ### Claim 13 (depends on 11) The method of claim 11, wherein the control system configured to sample AC grid voltage and AC grid current over the fixed period of time comprises the control system sampling AC grid voltage and AC grid current over one cycle of a fundamental frequency. ### Claim 14 (depends on 11) The method of claim 11, wherein the control system configured to compare the grid impedance at the one or more frequencies to the known expected grid impedance at the one or more frequencies comprises the control system configured to compare the grid impedance at the one or more frequencies to a known expected grid impedance range at the one or more frequencies. ### Claim 15 (depends on 11) The method of claim 11, wherein the control system configured to detect the grid event based on the comparison comprises the control system detecting that the grid event comprises islanding of at least one of the electrical machines. ### Claim 16 (depends on 15) The method of claim 15, wherein the at least one electrical machine comprises a doubly-fed induction generator (DFIG) driven by a wind turbine or a photovoltaic array. ### Claim 17 A control system for detecting a grid event on an alternating current (AC) electrical grid connected with the one or more electrical machines, said AC electric grid configured to transmit at least one phase of electrical power to the one or more electrical machines or to receive at least one phase of electrical power from the one or more electrical machines, said control system comprising: a controller, wherein the control system is electrically coupled to at least a portion of the AC electric grid and at least a portion of the control system is coupled in electronic data communication with at least a portion of the one or more electrical machines, and wherein said controller is configured to: sample AC grid voltage and AC grid current over a fixed period of time; calculate a transform of the sampled AC grid voltage and sampled AC grid current; determine grid impedance at one or more frequencies using the sampled AC grid voltage and the sampled AC grid current; compare the grid impedance at the one or more frequencies to a known expected grid impedance at the one or more frequencies; and detect a grid event based on the comparison. ### Claim 18 (depends on 17) The system of claim 17, wherein the controller configured to compare the grid impedance at the one or more frequencies to the known expected grid impedance at the one or more frequencies comprises the controller configured to compare the grid impedance at the one or more frequencies to a known expected grid impedance range at the one or more frequencies. ### Claim 19 (depends on 17) The system of claim 17, wherein the controller configured to determine grid impedance at one or more frequencies using the sampled grid voltage and the sampled grid current comprises the controller configured to calculate a fast Fourier transform (FFT) of the sampled grid voltage and sampled grid current at the one or more frequencies and determine the grid impedance at the one or more frequencies using the FFT of sampled grid voltage divided by the FFT of sampled grid current ### Claim 20 (depends on 17) The system of claim 17, wherein the controller configured to determine grid impedance at one or more frequencies using the sampled grid voltage and the sampled grid current comprises the controller configured to filter the grid voltage and filter the grid current at the one or more frequencies and determine the grid impedance at the one or more frequencies using the filtered grid voltage divided by the filtered grid current at the one or more frequencies.