# US 9,519,032 B1 · Method for small-signal stability assessment of power systems using shunt current injection source side and series voltage injection load side perturbations > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,519,032 B1 - Document ID: US9519032B1 - Status: Granted - Kind: B1 - Application number: 15/131,720 - Filed: 2016-04-18 - Granted: 2016-12-13 - Earliest claimed: 2014-05-06 - Assignees: The Florida State University Research Foundation, Inc. - Applicants: The Florida State University Research Foundation, Inc. - Inventors: Mohamadamin Salmani; Chris S. Edrington - Web page: https://patentgrep.com/patent/US9519032B1 ## CPC - G01R 31/40: Testing power supplies (testing photovoltaic devices H02S50/10) - G01R 19/2506: {Arrangements for conditioning or analysing measured signals, e.g. for indicating peak values (G01R19/003 takes precedence); Details concerning sampling, digitizing or waveform capturing (displaying waveforms G01R13/00; analog sampling G01R19/0053)} - G01R 19/2513: {Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging} - G01R 27/00: Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom - G01R 27/02: Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant (by measuring phase angle only G01R25/00) - G01R 27/16: Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract A novel method for real-time small-signal stability analysis for power electronic-based components in a power system. The method may be used to monitor a power system in real-time by perturbing the source side of an electronic-based component of the power system of about 0.5 to 1 percent of a nominal current of the power system at the source side using shunt current injection, and perturbing the load side of the power electronic-based component by varying the voltage at the load side using series voltage injection. Time-domain results of the perturbations may be transferred to frequency-domain results and the stability of the power system may be monitored by obtaining a Nyquist contour and employing unit circuit criterion or Generalized Nyquist Criterion. ## Claims ### Claim 1 A method for real-time analysis of small-signal stability of a power system, the method comprising: providing non-transitory computer readable media having computer-executable instructions for performing a method of running a software program on a computing device, the computing device operating under an operating system, the method including issuing instructions from the software program comprising; observing the power system in a real-time operational mode, the power system comprising a source side and a load side from a perspective of the power electronic-base component; perturbing the source side of the power electronic-based component by injecting a current of about 0.5 to about 1 percent of a nominal current of the power system at the source side using shunt current injection and perturbing the load side of the power electronic-based component by varying a voltage of the power system using series voltage injection, wherein perturbing the source side of the power electronic-based component using shunt current injection and perturbing the load side of the power electronic-based component using series voltage injection occurs simultaneously; measuring currents and voltages at the source side and at the load side; determining a phase of the power system using single-phase Phase Lock Loop; transforming the measured source side current and voltage and the measured load side current and voltage to a d−q reference frame using the determined phase of the power system; transferring time-domain source side current and voltage values and time-domain load side current and voltage values to frequency-domain current and voltage values using Fourier transforms; calculating a frequency-domain return-ratio matrix in the d−q reference frame using the frequency-domain source side current and voltage values and the frequency-domain load side current and voltage values; plotting a Nyquist contour of a d−d component of the frequency-domain return-ratio matrix; and evaluating small-signal stability of the power system using stability criteria. ### Claim 2 (depends on 1) The method of claim 1, wherein a frequency of the perturbations range from about 0.1 Hz to about 1000 Hz. ### Claim 3 (depends on 1) The method of claim 1, wherein perturbing the source side of the power electronic-based component comprises varying a current of the power system. ### Claim 4 (depends on 1) The method of claim 1, wherein perturbing the source side of the power electronic-based component and perturbing the load side of the power electronic-based component comprises one or more independent perturbations. ### Claim 5 (depends on 4) The method of claim 4, wherein the one or more independent perturbations occur over a range of frequencies other than a fundamental frequency of the power system. ### Claim 6 (depends on 4) The method of claim 4, wherein the one or more independent perturbations are based on responses of the power system to one or more previous perturbations. ### Claim 7 (depends on 1) The method of claim 1, wherein using Fourier transforms further comprises defining a phase and magnitude of the current of the load side and the source side of the power system. ### Claim 8 (depends on 7) The method of claim 7, wherein the one or more independent perturbations are based on responses of the power system to one or more previous perturbations. ### Claim 9 (depends on 1) The method of claim 1, wherein evaluating the small-signal stability of the power system further comprises defining a relative stability of the power system and comparing the relative stability to instability borders of the power system. ### Claim 10 (depends on 1) The method of claim 1, wherein evaluating the small-signal stability of the power system further comprises utilizing Nyquist immittance criterion. ### Claim 11 (depends on 1) The method of claim 1, wherein perturbing the load side of the power electronic-based component comprises injecting a voltage of about 0.5 to about 1 percent of a nominal voltage of the power system.