Method for small-signal stability assessment of power systems using source side and load side perturbations
View Patent ↗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 by injecting a current of about 0.5 to 1 percent of a nominal current of the power system at the source side and perturbing the load side of the power electronic-based component by injecting a voltage of about 0.5 to about 1 percent of a nominal voltage of the power system at the load side and varying the voltage at the load side. 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 Generalized Nyquist Criterion or unit circle criterion.
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 using a Hardware-in-the-Loop (HIL) simulation system, the power system comprising a source side and a load side from a perspective of the power electronic-based component, wherein the power electronic-based component is selected from a solid state transformer (SST), a machine drive and an inverter;
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, and perturbing the load side of the power electronic-based component by injecting a voltage of about 0.5 to about 1 percent of a nominal voltage of the power system at the load side, wherein perturbing the power system comprises perturbing the source side and the load side of the power electronic-based component simultaneously;
measuring a current and a voltage at the source side to generate a measured source side current and a measured source side voltage and measuring a current and a voltage at the load side to generate a measured load side current and a measured load side voltage;
determining a phase of the power system using single-phase Phase Lock Loop;
transforming the measured source side current and the measured source side voltage and the measured load side current and the measured load side voltage to a d-q reference frame using the determined phase of the power system, to generate a transformed time-domain source side current value and a transformed time-domain source side voltage value and a transformed time domain load side current value and a transformed time-domain load side voltage value;
transferring the transformed time-domain source side current value to a frequency-domain source side current value, transferring the transformed time-domain source side voltage value to a frequency-domain source side voltage value, transferring the transformed time-domain load side current value to a frequency-domain load side current value and transferring the transformed time-domain load side voltage value to a frequency-domain load side voltage value using Fourier transforms;
calculating a frequency-domain return-ratio matrix in the d-q reference frame using the frequency-domain source side current value and the frequency-domain source side voltage value and the frequency-domain load side current value and the frequency-domain load side voltage value;
plotting a Nyquist contour of a component using the frequency-domain return-ratio matrix;
evaluating small-signal stability of the power system using stability criteria; and
preventing instabilities of the power system based upon the evaluation of small-signal stability of the power system using stability criteria.
2. The method of claim 1 , wherein a frequency of the perturbations range from about 0.1 Hz to about 1000 Hz.
3. The method of claim 1 , wherein perturbing the source side of the power electronic-based component comprises varying a current of the power system.
4. The method of claim 1 , wherein perturbing the power system comprises more than one independent perturbation.
5. 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.
6. 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.
7. The method of claim 1 , wherein using Fourier transforms further comprises defining a phase and magnitude of the current of the load side and defining a phase and magnitude of the current of the source side of the power system.
8. The method of claim 1 , wherein the stability criteria comprises unit circle criterion or Generalized Nyquist criterion.
9. The method of claim I, 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.
10. The method of claim 1 , wherein evaluating the small-signal stability of the power system further comprises utilizing Nyquist immittance criterion.