A Small-Signal Stability Analysis Method for DC Microgrids Based on Immittance Phases

Immittance-based small-signal stability analysis methods are frequently employed in dc microgrids. However, most existing methods either suffer from right-half-plane (RHP) pole issues or depend on complete amplitude and phase information of all frequencies. To address these limitations, this letter constructs a novel immittance transfer function that combines the impedance/admittance of all converters, with introduced left-half- plane (LHP) zeros to satisfy the prerequisites of the Argument principle. Then, we rigorously prove that this immittance transfer function contains no RHP poles when each converter remains stable under standalone operating conditions. The stability of dc microgrids can therefore be determined by checking whether the immittance transfer function contains RHP zeros. Furthermore, this letter demonstrates that the immittance phases at zero and infinity frequencies directly indicate system stability, without counting the net number of times that the Nyquist contour encircles the origin. Finally, the proposed method is validated by case studies and experiments.