Abstract

Stability analysis of power electronicsdominated grids is challenging due to the need of manufacturers to protect the intellectual property of converters control systems. Black-box dq impedance models have been proposed to overcome this challenge in grid stability analysis. However, such models are limited to small-signal analyses and are accurate only around a predefined and pre-computed equilibrium point. Conversely, the recently proposed nonlinear Differential-Algebraic Equations (DAE) models of converter-dominated grids can be used for stability analyses in every operating conditions and additionally for generalized power flow analysis and transient time-domain simulations. Despite these advantages, nonlinear state-space converters models require the full knowledge of their control system. To overcome this limitation, this paper proposes a nonlinear grey-box modeling strategy which uses structured perturbations to represent the converters' control system uncertainties. The stability boundaries and control loops sensitivity are analyzed in a multi-vendor converterdominated grid at different operating points through robust control theory. Hardware-In-the-Loop results are provided.