DQ Impedance Modeling and Stability Analysis of SVG with Constant Reactive Power Control

Static var generator (SVG) has been widely applied in modern power systems for reactive power compensation and voltage regulation. In this paper, the dq-frame impedance of SVG with constant reactive power control is built, which includes the dynamics of outer reactive power loop, DC voltage loop, phase-locked loop (PLL), and inner current loop. The impedance model of SVG differs from the common inverter in that its impedance is strongly coupled in the
$d$
. and
$q-\text{axes}$
, since it outputs nearly pure reactive power. The impacts of SVG on system stability is studied by paralleling its impedance with that of the inverter. Through Generalized Nyquist Criterion (GNC), it is observed that after being shunted into the system, SVG will reduce the stability margin and cause oscillations. To avoid this issue, an SVG based damping strategy is proposed. The experimental result verifies the theoretical analysis.