---
title: Next Generation Grid Codes
url: https://www.emergentmind.com/topics/next-generation-grid-codes-nggcs
type: topic
---

# Next Generation Grid Codes

Next Generation Grid Codes (NGGCs) denote a paradigm shift in the specification and verification of dynamic ancillary service requirements for power systems with high penetrations of converter-based generation. NGGCs supplant traditional, ad hoc time-domain prescriptions with formal, device-level frequency-domain envelopes for both stability and quantitative performance. They enable plug-and-play interoperability, scalability to large and inverter-based networks, and streamlined compliance testing. The following sections detail the core theoretical underpinnings, specification methodologies, emerging implications for converter design and control, and open challenges in the field.

## 1. Formal Definition and System-Level Objectives

NGGCs are regulatory or framework constructs that specify dynamic-ancillary-service requirements by imposing device-level frequency-domain envelopes on each resource’s transfer function, in place of historical step-response profiles. Their two core system-level objectives are:

- **Guaranteed closed-loop stability**: Ensured for the entire multi-device network under all admissible disturbances by verifying device-local frequency-domain conditions.
- **Explicit performance guarantees**: Achieved via quantitative bounds on critical time-domain metrics such as frequency nadir, rate-of-change-of-frequency (RoCoF), steady-state deviation, and oscillation damping for active-power–frequency (“pf”) dynamics, as well as analogous bounds (voltage peak, steady-state deviation, damping) for reactive-power–voltage (“qv”) dynamics [2601.07090].

These objectives are achieved non-parametrically (model-agnostically): they require no centralized state-space models or system-level parameter sharing, but rather enforce compliance via well-defined, locally testable frequency-domain envelopes.

## 2. Decentralized Stability Certification Framework

Stability within the NGGC framework is certified using per-device frequency-domain passivity inequalities, enforced after suitable loop-shifting of the network and controller transfer functions. Let $D(s)$ denote the block-diagonal stack of device transfer functions in both “pf” and “qv” channels, and $N(s)$ the Kron-reduced network model,

\[
D(s) = \mathrm{diag}(D_i^{\rm pf}(s),\, D_i^{\rm qv}(s))_{i=1}^n,
\quad
N(s) = 
\begin{bmatrix} 
N^{\rm pf}(s) & 0 \\ 
0 & N^{\rm qv}(s) 
\end{bmatrix}
\]

The network $N^{\rm qv}(s)$ is loop-shifted via a diagonal correction $\Gamma^{\rm qv}$: $c_i = \sum_{j\neq i} b_{ij} 0.8/(1+\rho^2)$, resulting in a passive equivalent network $N'(s) = N(s)(I+\Gamma N(s))^{-1}$. The corresponding device transfer functions are shifted to $D'(s)$, which must satisfy:

- **pf-channel (active power/frequency)**: Each $D_i^{\rm pf}(s)$ must be stable, strictly proper, and satisfy $\Re\{D_i^{\rm pf}(\j\omega)\} > 0\,\, \forall \omega \geq 0$.
- **qv-channel (reactive power/voltage)**: Each $D_i^{\rm qv}(s)(1-c_i D_i^{\rm qv}(s))^{-1}$ must be strictly passive, or, equivalently, $\Re\{(D_i^{\rm qv}(\j\omega))^{-1}\} > c_i$.

These conditions are directly verifiable on each device’s Nyquist plot and are independent of other device or network parameters [2601.07090].

## 3. Quantitative Performance Envelopes

NGGCs move beyond stability to deliver explicit performance guarantees aligned with system-level ancillary service metrics.

### Frequency Dynamics

The “average mode” frequency response to aggregated active power disturbances is

\[
\Delta f_{\rm avg}(s) = D_{\rm avg}(s) \Delta p_{\rm d}^\Sigma(s), \quad
D_{\rm avg}(s) = \left(\sum_{i=1}^n (D_i^{\rm pf}(s))^{-1}\right)^{-1}
\]

Spectral constraints on each $D_i^{\rm pf}(s)$ ensure:

- **Nadir bound**: $\|D_i^{\rm pf}(\j\omega)\|_\infty \leq \Delta f_{\max} / (2.5 \Delta p_{\rm d}^\Sigma)$ over all $\omega$.
- **Steady-state error**: $|D_i^{\rm pf}(0)| \leq \Delta f_{\rm ss,max} / \Delta p_{\rm d}^\Sigma$.
- **RoCoF**: $\lim_{\omega \to \infty} |\j\omega D_i^{\rm pf}(\j\omega)| \leq \Delta\dot{f}_{\max} / \Delta p_{\rm d}^\Sigma$.
- **Damping**: $\Re\{(D_i^{\rm pf}(\j\omega))^{-1}\} \geq \rho_{\rm f} > 0$ [2601.07090].

### Voltage Dynamics

Analogous constraints are enforced for each $D_i^{\rm qv}(s)$, guaranteeing peak and steady-state regulation and sufficient damping, with possible high-frequency roll-off to limit bandwidth [2601.07090].

## 4. Transfer Function–Based Specification and Implementation

A central innovation of NGGCs is the formal mapping of historic piecewise-linear, time-domain service requirements into rational transfer-function templates for converter control.

- **Piecewise step-response curves** (e.g., FCR, FFR) are decomposed into Laplace-domain segment representations, assembled, and approximated as rational transfer functions using Padé approximations for time delays.
- The resulting transfer function

\[
G(s) = \frac{a_n s^n + \ldots + a_0}{b_m s^m + \ldots + b_0}
\]

is directly embeddable in converter outer-loop PI or robust MPC architectures via matching control schemes [2310.01552].
- Compliance is validated both in the time-domain (by verifying step responses against profiles) and frequency-domain (by checking $G(s)$ magnitude and phase envelopes) [2310.01552].

| Specification Step              | Description                                                                             | Reference      |
|---------------------------------|-----------------------------------------------------------------------------------------|----------------|
| Time-domain curve extraction    | Define breakpoints $(t_i, y_i)$ for the needed response curve                          | [2310.01552]   |
| Transfer function synthesis     | Map curve to $G(s)$ via Laplace segment construction, Padé delay approx.                | [2310.01552]   |
| Controller integration         | Insert $G(s)$ in outer PI/robust control loop                                           | [2310.01552]   |
| Compliance test                | Enforce frequency and time-domain matches to $G_{\rm req}(s)$                           | [2310.01552]   |

## 5. NGGCs and Grid-Forming Converter Control

The NGGC framework is compatible with advanced GFM designs, such as Emulated Synchronous Condenser (ESC) plus current-source architectures, which inherently satisfy both stability and advanced grid code requirements including:

- Severe phase jumps,
- Balanced and unbalanced fault ride-through (FRT),
- Main grid disconnection (islanding),
- Black start capability.

A unified control structure (ESC with virtual swing equation, parallel active power current source, virtual impedance, and inner-loop elliptical saturation) enforces NADIR, ride-through, and steady-state metrics without explicit mode switching or PLLs [2303.00391]. In time-domain simulations of a 2-MW BESS, such architectures meet or exceed voltage and frequency ride-through envelopes, provide firm inertial support, and maintain stability under worst-case events, aligning with NGGC objectives [2303.00391].

## 6. Field Size and Coding Requirements for Distributed NGGCs

For data and distributed control applications, NGGCs interface with grid-like code topologies where robust erasure recovery is critical. Maximally recoverable (MR) codes for $T_{m\times n}(1, b, 0)$ topologies have polynomial upper and lower field size bounds. Recent results establish:

- **Upper bounds**: $q > C_0(m, b) n^{2b(m-1)} + n(b-1)$ for general $m, b$, with explicit improvements for $m=3,4$.
- **Lower bounds**: $q = \Omega(n^2)$ or $q = \Omega(n)$ for small $m$, via Sidon set arguments [1901.06915].
- Polynomial field-size requirements render scaling to large $n$ (long codes, large system instances) practical and resource-efficient, supporting NGGC data anchoring and recovery under correlated failures.

| MR Code Topology                  | Sufficient Field Size $q$                                | Necessary Field Size $q$             | Reference    |
|-----------------------------------|---------------------------------------------------------|--------------------------------------|--------------|
| $T_{m\times n}(1, b, 0)$ general | $q > C_0(m, b) n^{2b(m-1)}$                             | ---                                  | [1901.06915] |
| $T_{4\times n}(1,2,0)$            | $q > C_1 n^5\log n$                                     | $q \ge (n-3)^2/4 + 2$                | [1901.06915] |
| $T_{3\times n}(1,3,0)$            | $q > C_2 n^5\log n$                                     | $q \ge \sqrt{n^2-11n+34}$            | [1901.06915] |

## 7. Implications, Open Questions, and Future Directions

NGGCs constitute a rigorous, scalable foundation for dynamic ancillary service specification and device-level compliance in inverter-dominated and low-inertia grids. Principal implications and open problems include:

- **Implications**: Unified passivity-plus-performance envelopes enable manufacturers to offer plug-and-play resources and system planners to obtain explicit performance metrics. Automation of certification and compliance testing is facilitated by transfer-function-based specifications [2601.07090, 2310.01552].
- **Open questions**: Sharper combinatorial characterization of erasure patterns for distributed code topologies, explicit deterministic MR code constructions at minimal field sizes, and generalization to $T_{m\times n}(a, b, h)$ topologies remain outstanding [1901.06915]. For converter control, integrating parameter-varying transfer function templates to adapt to real-time grid conditions and formalizing higher-layer supervisory frameworks are fertile areas for future research.

NGGCs unify local device-level, frequency-domain certification with global system performance, recasting ancillary service regulation for the era of high renewable and inverter penetration [2601.07090, 2310.01552, 2303.00391, 1901.06915].

Source: https://www.emergentmind.com/topics/next-generation-grid-codes-nggcs