Next-Generation Grid Codes: Toward a New Paradigm for Dynamic Ancillary Services

TL;DR

The paper tackles the lack of guaranteed stability and explicit performance in current grid codes for dynamic ancillary services by introducing Next Generation Grid Codes (NGGCs) that rely on loop-shifting and passivity to yield decentralized stability certificates and quantitative time-domain bounds. It formulates a model-agnostic, decoupled pf/qv framework using a Kron-reduced small-signal network with transfer matrices $N(s)$ and $D_i^{\mathrm{pf}}(s),D_i^{\mathrm{qv}}(s)$, enabling per-device design rules that ensure global stability and performance via Nyquist-envelope constraints. The key contributions are the per-device stability and performance criteria, the decentralized certification methodology, and the interpretation of compliance through Nyquist-plot envelopes, all aimed at guiding future grid-code implementations. The findings suggest that ensuring each device meets the proposed conditions yields guaranteed closed-loop stability and bounded frequency- and voltage-dynamics, with practical validation in two-node simulations indicating how device choice impacts nadir, RoCoF, and damping. This framework has significant potential to influence practical grid-code development by providing principled, model-agnostic guidelines for dynamic ancillary services in modern power systems.

Abstract

This paper presents preliminary results toward a conceptual foundation for Next Generation Grid Codes (NGGCs) based on decentralized stability and performance certification for dynamic ancillary services. The proposed NGGC framework targets two core outcomes: (i) guaranteed closed-loop stability and (ii) explicit performance assurances for power-system frequency and voltage dynamics. Stability is addressed using loop-shifting and passivity-based methods that yield local frequency-domain certificates for individual devices, enabling fully decentralized verification of the interconnected system. Performance is characterized by deriving quantitative bounds on key time-domain metrics (e.g., nadirs, rate-of-change-of-frequency (RoCoF), steady-state deviations, and oscillation damping) through frequency-domain constraints on local device behavior. The framework is non-parametric and model-agnostic, accommodating a broad class of device dynamics under mild assumptions, and provides an initial unified approach to stability and performance certification without explicit device-model parameterization. As such, these results offer a principled starting point for the development of future grid codes and control design methodologies in modern power systems.

Figures (7)

• Figure 1: Multi-device transmission system with SGs and grid-forming VSCs connected by resistive–inductive transmission lines.
• Figure 2: Closed-loop power system with active and reactive power disturbances $\Delta p_\mathrm{d}$ and $\Delta q_\mathrm{d}$, and frequency and voltage disturbances $\Delta f_\mathrm{d}$ and $\Delta |{v}|_{\mathrm{d}}$.
• Figure 3: Qualitative graphical illustration of the eight frequency-domain conditions \ref{['cond:1i_short']} to \ref{['cond:1viii_short']} for each $D_i^\mathrm{pf}(\mathrm{j}\omega)$ in the complex plane.
• Figure 4: Qualitative graphical illustration of the six frequency-domain conditions \ref{['cond:2i_short']} to \ref{['cond:2vi_short']} for each $D_i^\mathrm{qv}(\mathrm{j}\omega)$ in the complex plane.
• Figure 5: Superposition of NGGC conditions \ref{['cond:1i_short']} to \ref{['cond:1viii_short']} in \ref{['fig:nyquist_pf_elements']}. The gray shaded region indicates the feasible set for all $\omega\in(0,\omega_\mathrm{bw})$, and the black curve depicts an exemplary feasible Nyquist plot of $D_i^\mathrm{pf}(\mathrm{j}\omega)$.