Understanding Stability of Low-Inertia Systems

Abstract

<p>A large-scale integration of renewable generation,usually interfaced to the network through power electronics,has led to an overall decrease in power system inertia. This paper presents novel insights on the fundamental stability properties of such systems. For that purpose, a uniform set of Differential-Algebraic Equations (DAEs) describing a generic,low-inertia power system has been developed. A full-order, state-of-the-art control scheme of both synchronous and converter-based generators are included, with the latter differentiating between the grid-forming and grid-following mode of operation. Furthermore, the dynamics of transmission lines and loads are captured in the model. Using modal analysis techniques such as participation factors and parameter sensitivity, we determine the most vulnerable segments of the system and investigate the adverse effects of the underlying control interference. Finally, the appropriate directions for improving the system stability margin under different generation portfolios have been proposed.</p>

Frequency Stability of Synchronous Machines and Grid-Forming Power Converters

“…This observation, highlights the importance of the dc dynamics in grid-forming control design as well as the critical need for an ac current limiting mechanism. Furthermore, we reveal a potentially destabilizing interaction between the fast synchronization of GFCs and the slow response of SMs (see [16], [24] for a similar observation on the interaction of GFCs and line dynamics). Lastly, this study shows that an all-GFCs (i.e., no-inertia) system can exhibit more resilience than a mixed SM-GFCs (i.e., low-inertia) system with respect to the large load variations.…”

“…Figure 19 shows i τ and v dc for the converter at node 2. Although the disturbance magnitude affecting the converters is similar to the one in studied in Subsection IV-D, all GFCs remain stable after the loss of the SM without the need to incorporate (24). In particular, due to the absence of the slow turbine dynamics and fast synchronization of the converters i τ exceeds the limit i dc max for around 50ms while it remains above the limit for a prolonged period of time in Figure 14.…”

“…Furthermore, τ g denotes the turbine time constant and p τ denotes the turbine output power. We refer the reader to [24,Fig. 2] for an illustration of the interplay between the SM model, the excitation dynamics, the PSS and governor dynamics.…”

“…dc voltage (top) and dc current demand (bottom) of the converter at node 2 after a 0.9 pu load disturbance when all the limitation schemes i.e., (3),(7) and(24) are active and τ g = 5s.…”

Fundamentals of power systems modelling in the presence of converter-interfaced generation

“…Recent studies (e.g. [69]) discussed the limitations of the time-scale separation associated to the use of a quasi-stationary power grid models relying on phasors when the grid hosts large amount of CIG. In this respect, this section provides a detailed analysis of these limitations.…”