On Robust Stability Criteria for Nonlinear Voltage Controllers in Electrical Supply Networks

Analysis of Voltage Stability in Terms of Interactions of Q(U)-Characteristic Control in Distribution Grids

“…[2]. A stability assessment based on wind farm (WF) models with focus on medium-and high-voltage levels is introduced in previous work [13]. This approach does not require knowledge of the model parameters, but results in conservative thresholds, i.e.…”

“…Section II introduces DER models with Q(U)-characteristic, which can be expressed by detailed control loops or by approximated models in respect to technical guidelines (VDE-AR-N 4120 [14]). In Section III, a more convenient stability assessment approach based on the so-called circle criteria [15] is presented in addition to previous work [13]. An evaluation of different high-voltage distribution grids is carried out in Section IV.…”

“…Thereby, K Q is a constant n × n matrix that can be computed using the Jacobian obtained during the iterative solution of nonlinear power flow equations, as presented in [13,19]. A more realistic, i.e.…”

“…Preliminary work [13] has introduced the stability criterion from Moylan and Hill to achieve a stability statement for systems with Q(U)-characteristic controlconservative but without the need to know specific transfer function parameters. Furthermore, the so-called Popov criterion for evaluation of a nonlinear single-input single-output (SISO) system with given transfer function parameters was discussed as valuable alternative.…”

“…The introduced stability criterion in section III is applied to four different high-voltage distribution grids. Subsequently, a comparison with the criterion introduced in [13] and stability bounds based on simulations with DIgSILENT PowerFactory 2021 is carried out. The type WF-FRC is used as DER model.…”