• A generalized Kron-reduction method to accurately derive the exact characteristic equation. • Theoretical proof on merits of magnitude-angle criterion in low-frequency oscillation analysis. • Proposed framework assessing low-frequency oscillations with limited system observability. Compared with damping torque analysis and eigenvalue-based methods, the impedance method demonstrates its superiority in power system oscillation studies when detailed models are unavailable. However, existing impedance methods used in wide-frequency oscillation have modeling and stability criterion limitations in analyzing low-frequency oscillations. Therefore, this paper proposes a generalized Kron-Reduction based stability estimation method (GKRSME), which aims to accurately estimate low-frequency oscillatory stability margin and tackle the above-mentioned limitations. Firstly, it is mathematically proved in the paper that existing π–type circuit-based lumped impedance (LIM) cannot derive characteristic equation accurately. A generalized Kron-Reduction is hence proposed to replace existing modeling method. Secondly, a comparative analysis is conducted between two stability criteria to elucidate their applicability to low-frequency oscillation analysis. It is revealed that stability criterion based on real and imaginary parts of LIM determinant (RIC) has nonnegligible errors in studying oscillations in low-frequency range due to inaccurate assumption, i.e., the imaginary part is much larger than the real part of the mode. In contrast, a stability criterion based on magnitude and angle of LIM determinant (MAC) is a more suitable alternative for low-frequency oscillation analysis, which can accurately estimate the stability margin. Additionally, modified IEEE-39 and IEEE-68 bus power systems with converters are used to validate the proposed GKRSME.
Fang et al. (Sun,) studied this question.