RHP Poles Trajectory Study for D–Q Impedance-Based Stability Monitoring Using a Power-Hardware-in-the-Loop Testbed

Using impedance-based stability analysis for ac grids has become an extensively accepted method. Online impedance-based stability monitoring, which requires assessing system stability in real time, is crucial for various tasks in the grid. While many previous studies have disregarded the presence of right-half-plane (RHP) poles in the minor loop gain when applying forbidden-region-based stability criteria, this article has found that these poles may appear in a microgrid’s open-loop impedance if certain conditions are met, such as when grid-tied inverters power or their phase-locked-loop (PLL) bandwidth exceeding a certain value. The presence of these poles can significantly alter the characteristic loci in the complex plane, rendering many traditional stability-margin criteria inapplicable. As such, this article suggests an alternative stability margin index for these scenarios. A power-hardware-in-the-loop (PHIL) testbed with a converter featuring impedance measuring functions was established to confirm the findings of the study. The accuracy of the PHIL model emulation is verified by the modeled and measured impedance.