A framework for development of universal rules for microgrids stability and control

Identifying Parameter Space for Robust Stability in Nonlinear Networks: A Microgrid Application

“…Note that when x(0) = 0 , |x(0) − x 0 (λ, δ)| ≤ ∆ . From (12) it follows immediately that x(0) = 0 implies Ψ(x(0), λ) ≤ ζ * which implies Ψ(x(t), λ) ≤ ζ * for all t ≥ 0 . Applying (12) again, we have |x(t)−x 0 (λ, δ)| ≤ ν * , such that…”

“…Unlike bulk power systems, which have adequate rotational inertia to naturally stabilize fluctuations in the network, the dynamic security of low-inertia microgrids needs to be specifically ensured via design [9], [10]. Identification of droop-coefficients for stability certification of inverter-based microgrids have been investigated in recent works [11], [12]. A centralized approach of identifying the droop-coefficients for a lossless microgrid was adopted in [11], while conditions on droop-coefficients were derived in a distributed approach for small-signal stability in [12].…”

“…Identification of droop-coefficients for stability certification of inverter-based microgrids have been investigated in recent works [11], [12]. A centralized approach of identifying the droop-coefficients for a lossless microgrid was adopted in [11], while conditions on droop-coefficients were derived in a distributed approach for small-signal stability in [12]. However, low-to-medium voltage microgrids typically have significant line resistance-to-reactance ratios, and often operate in a nonlinear regime due to fluctuations from renewable generation, rendering the aforementioned approaches inapplicable.…”

Distributed Control and Optimization for Autonomous Power Grids

“…Other desirable features of droop control are that it induces a frequency consensus (thus grid-forming converters can synchronize with another or with a stiff grid), and it achieves fair power sharing, that is, any load/generation imbalance is picked up equally according to the droop slopes [53]- [55]. Limitations of grid-following control Simplified models of grid-following and grid-forming converters give rise to the same input/output behavior (e.g., a droop specification), but their controllers have different inputs and outputs (which can make a significant difference, e.g., when measuring a brittle frequency), different performance characteristics (e.g., grid-following converters are limited by the accuracy and the bandwidth of their PLLs), and they can function with either only strong or also with weak grids.…”

“…The first and most developed approach is droop control as in (5) and regulation of the terminal voltage kv g k through u mag . While droop control is well-studied and understood, stability characterizations exist only for simplified models [53]- [55] and practical implementation usually demands various extra heuristics such as low-pass filters or virtual impedances inducing damping in the control loop. Finally, droop control closes two independent SISO loops separately for P and !…”