An Impedance-Based Stability Analysis for Constant Power Load with Line Failure

Modeling the grid-side converter (GSC) in detail while simplifying the machine-side converter (MSC) as a constant power load (CPL) is beneficial for voltage stability analysis at the load bus. On the ac side of GSC, Nyquist-based stability analyses are typically performed due to the presence of multiple eigen-loci. However, DC side Nyquist stability criteria lead to computing the input admittance at the ac side of GSC. This input admittance behaves as a negative incremental for the CPL operation of the connected induction motor load; thus leads to voltage instability at the load bus. This paper also addresses the voltage stability issue corresponding to double-circuit line failure. This analysis is conducted through detailed impedance modelling of the system. The feasibility of designing a phase-locked loop (PLL) for such a scenario of grid disturbances are investigated in this paper through MATLAB/Simulink environment.