Stability Region Analysis of Grid-Tied Voltage Sourced Converters Using Variable Operating Point Impedance Model

The interactions between voltage-sourced converters (VSCs) and the grid may trigger unstable electromagnetic oscillations. Impedance model-based analysis is widely utilized for investigating such emerging stability issues, mainly due to its capability to model black/gray-box VSC-based devices without complete knowledge of their internal control structures and parameters. It is well known that the characteristics of the triggered oscillation are determined by the operating conditions. However, most of the existing impedance-based methods are operating point specific, i.e., the impedance model of VSC-based devices has to be re-measured upon variations in the operating point. Thus, it is quite cumbersome and hectic to reconstruct the impedance model of a VSC-based device for all possible operating points and establish a stable or unstable region. This paper develops a novel method to determine the oscillatory stability region of a grid-tied VSC. First, a variable-operating point impedance model (VOPIM) of a VSC is derived. Next, the VOPIM is used to determine the frequency and damping of the oscillation modes for varying operating points. Finally, the oscillatory stability region is determined according to the damping of each oscillation mode. The accuracy of the oscillatory stability region and the effectiveness of the proposed method is verified through time-domain electromagnetic simulations.