Aug 2026· Energies· Vol 19, pp. 3702· 0 citations· 13 references
Abstract
With the integration of renewable energy and power-electronic devices, grid-forming modular multilevel converters (GFM-MMCs) play a critical role in active grid support. An AC grid voltage sag can trigger a large support current, which may cause large voltage fluctuations in submodule capacitors and arm overmodulation, thereby threatening system safety. This paper proposes a multidimensional collaborative method to improve the support capability of grid-forming MMCs under severe grid voltage sags. The multidimensional physical constraints of internal energy fluctuation during fault transients are clarified. The corresponding safe operating boundaries are then established, after which a coordinated optimization strategy is developed. This approach integrates second-harmonic circulating current and zero-sequence voltage injections. Offline optimization utilizes a particle swarm optimization (PSO) algorithm across the full operating range. Expanding the safe P–Q operating region requires no extra hardware costs. A neural network enables a millisecond-level direct mapping control architecture. This architecture addresses the long online computation time of traditional heuristic algorithms by embedding offline optimization data into the network weights. The trained network performs rapid forward computation to generate optimized commands, which is verified by a hardware-in-the-loop (HIL) experiment. The experimental results verify the effectiveness of the proposed method, with clear performance improvements being observed. The strategy suppresses capacitor-voltage peak and prevents overmodulation. This directly improves the MMC support capability during severe faults.
(English) The voltage source converter (VSC) operating in grid-forming (GFM) mode is one of the promising control approaches for the integration of renewable energy sources in future power systems. GFM technology offers numerous advantages due to its inherent voltage-source behavior, enabling improved system stability as well as support for grid restoration services. Technologies capable of providing GFM functionalities include high voltage direct current (HVDC) systems, flexible alternating current transmission systems (FACTS), power park modules (PPMs), and battery energy storage systems (BESS).
In recent years, the GFM control concept has gained significant attention due to its potential benefits in grid stabilization and auxiliary services. Several manufacturers are already offering assets with GFM control capabilities; however, the associated control strategies, limitations, and system-level interactions have yet to be comprehensively addressed in the literature. This work focuses on the application of GFM control to HVDC system and static synchronous compensator (STATCOM) integrated with energy storage.
First, detailed electromagnetic transient (EMT) models and control implementations of STATCOMs operating in both GFM and grid-following (GFL) modes are presented, along with a generic synchronous condenser model for comparison. Different configurations of voltage and current control loops are analyzed. A complete converter control scheme, including grid-side and internal energy controllers for the MMC topology, is developed and tuned according to TransnetBW GFM requirements, including AC current and DC voltage limiting functions.
The system-level performance is evaluated using a developed 9-bus benchmark grid based on the TransnetBW network. Initial time-domain simulations are conducted to improve and refine the GFM-STATCOM control. The impact of different fault locations on the fault ride-through (FRT) performance of the GFM-STATCOM is analyzed and compared using both time-domain simulations and scanning methods.
Finally, based on the experience and results obtained from PSCAD modeling, control tuning, and development of the 9-bus benchmark, a set of conformity tests for GFM-STATCOMs is proposed.
(Català) El convertidor de font de tensió (VSC) que opera en mode de grid-forming (GFM) és un dels enfocaments de control més prometedors per a la integració de fonts d'energia renovable en els futurs sistemes elèctrics. La tecnologia GFM ofereix nombrosos avantatges a causa del seu comportament inherent de font de tensió, la qual cosa permet una estabilitat del sistema millorada, així com el suport als serveis de restabliment de la xarxa. Les tecnologies capaces de proporcionar funcionalitats GFM inclouen els sistemes d'alta tensió en corrent continu (HVDC), els sistemes de transmissió flexibles de corrent altern (FACTS), els mòduls de parc energètic (PPM) i els sistemes d'emmagatzematge d'energia en bateries (BESS).
En els darrers anys, el concepte de control GFM ha guanyat una atenció significativa a causa dels seus beneficis potencials en l'estabilització de la xarxa i els serveis auxiliars. Diversos fabricants ja ofereixen actius amb capacitats de control GFM; no obstant això, les estratègies de control, les limitacions i les interaccions a nivell de sistema associades encara no s'han abordat de manera exhaustiva en la bibliografia. Aquest treball se centra en l'aplicació del control GFM a un sistema HVDC i a un compensador síncron estàtic (STATCOM) integrat amb emmagatzematge d'energia.
En primer lloc, es presenten models detallats de transitoris electromagnètics (EMT) i implementacions de control de STATCOMs que operen tant en mode de control de freqüència i fase (GFM) com en mode de seguiment de la xarxa (GFL), juntament amb un model genèric de condensador síncron per a la comparació. S'analitzen diferents configuracions de bucles de control de tensió i corrent. S'ha desenvolupat i ajustat un esquema de control de convertidor complet, que inclou controladors d'energia interns i de la banda de la xarxa per a la topologia MMC, d'acord amb els requisits GFM de TransnetBW, incloent-hi funcions de limitació de corrent altern i de tensió contínua.
El rendiment a nivell de sistema s'avalua mitjançant una xarxa de referència de 9 busos desenvolupada basada en la xarxa de TransnetBW. Es duen a terme simulacions inicials en el domini temporal per a millorar i refinar el control del GFM-STATCOM. S'analitza i es compara l'impacte de diferents ubicacions de fallades en el rendiment de la fault ride-through (FRT) del GFM-STATCOM, utilitzant tant simulacions en el domini temporal com mètodes d'escanneig.
Finalment, basant-se en l'experiència i els resultats obtinguts de la modelització amb PSCAD, la sintonització del control i el desenvolupament del banc de proves de 9 busos, es proposa un conjunt de proves de conformitat per als GFM-STATCOM.
(Español) El convertidor de fuente de voltaje (VSC) operando en modo grid-forming (GFM) es uno de los enfoques de control ms prometedores para la integracin de fuentes de energa renovable en los sistemas elctricos del futuro. La tecnologa GFM ofrece numerosas ventajas debido a su comportamiento inherente de fuente de voltaje, lo que permite una mejora en la estabilidad del sistema, as como el soporte para servicios de restauracin de la red. Las tecnologas capaces de proporcionar funcionalidades GFM incluyen sistemas de corriente continua de alta tensin (HVDC), sistemas de transmisin de corriente alterna flexible (FACTS), mdulos de
parques de energa (PPMs) y sistemas de almacenamiento de energa en bateras (BESS).
En los ltimos aos, el concepto de control GFM ha ganado una atencin significativa debido a sus posibles beneficios en la estabilizacin de la red y los servicios auxiliares. Varios fabricantes ya estn ofreciendo activos con capacidades de control GFM; sin embargo, las estrategias de control asociadas, las limitaciones y las interacciones a nivel de sistema an no se han abordado de manera exhaustiva en la literatura. Este trabajo se enfoca en la aplicacin del control GFM a sistemas HVDC y compensadores sncronos estticos (STATCOM) integrados con almacenamiento de energa.
En primer lugar, se presentan modelos detallados de transitorios electromagnticos (EMT) e implementaciones de control de STATCOMs que operan tanto en modo GFM como en modo grid-following (GFL), junto con un modelo genrico de condensador sncrono para comparacin. Se analizan diferentes configuraciones de bucles de control de voltaje y corriente. Se desarrolla y ajusta un esquema completo de control del convertidor, incluyendo controladores de energa tanto del lado de la red como internos para la topologa MMC, conforme a los requisitos GFM de TransnetBW, incluyendo funciones de limitacin de corriente alterna (AC) y voltaje de corriente continua (DC).
El desempeo a nivel de sistema se evala utilizando una red de referencia de 9 barras basada en la red de TransnetBW. Se realizan simulaciones iniciales en el dominio del tiempo para mejorar y refinar el control GFM-STATCOM.Seanaliza y compara el impacto de diferentes ubicaciones de fallas en el rendimiento de fault ride-through (FRT) del GFM-STATCOM utilizando tanto simulaciones en el dominio del tiempo como mtodos de escaneo.
Finalmente, basado en la experiencia y los resultados obtenidos del modelado en PSCAD, la sintonizacin del control y el desarrollo de la red de referencia de 9 barras, se propone un conjunto de pruebas de conformidad para los GFM-STATCOMs.
The high rate of replacement of synchronous machines by inverter-based resources (IBRs) has increased the role of Dynamic Voltage Support (DVS) during grid disturbances, especially on weak and failed grid conditions. Traditional reactive-current-based grid-support rules can have a poor performance with large R/X ratios, deep voltage sags, and hard inverter current or power constraints. To this end, much research has been done on the development of the best control measures that can help in maximizing positive- sequence voltage, improving low-voltage ride-through capability, and reducing synchronization instability. The review gives a cohesive and thorough evaluation of the best DVS strategies, including analytical global-optimality models, model-driven optimization, sensitivity-based methods, active/reactive power allocation models, and newly developed model-free and real-time optimum-seeking controllers. The review identifies the importance of current limits, active power availability, and synchronization stability limitations in determining inverter behavior, and contrasts the outputs of various approaches to these problems in the presence of varying grid strengths. Aspects in practical implementation of photovoltaic, wind and storage inverters are discussed and also robustness in the face of parameter uncertainties. Future directions in research (such as adaptive optimization, controllers based on learning, multi-inverter coordination, and grid-forming DVS) are determined. This review summarizes the latest knowledge and defines the directions of resilient, optimal, and grid-code-conforming voltage support of next- generation power electronic inverters.
Prashant Kumar, Y. Singh· 2026 International Conferenc...· 0 citations
High penetration levels of renewable energy and power electronic apparatus create prominent obstacles for novel power grids, which mainly manifested as inadequate system inertia and a deteriorated stability margin. To overcome such drawbacks, this research develops an operational control method to maintain safe and steady grid operation with large-capacity grid-forming energy storage connected to the system. This paper first builds a dynamic voltage model covering grid-forming energy storage, distributed renewable generators, and distribution network frameworks. Then it explores how different control parameter settings of grid-forming storage affect dynamic voltage regulation capabilities under distinct R-L ratio scenarios. Since the correlation between energy storage control variables and voltage regulation features is highly nonlinear and complicated, trajectory sensitivity analysis is adopted to linearize these coupling constraints, which are further embedded into the power system security operation mathematical model. A chaotic particle swarm optimization (PSO) algorithm is used to solve the constructed optimization model. Simulation tests on a modified IEEE 33-bus test system ultimately prove that the proposed method is reliable and practically applicable. Simulation results on the modified IEEE 33-bus test system demonstrate that the proposed strategy restricts grid voltage fluctuation rate to only 2.41%, raises renewable energy accommodation rate up to 98.4%, and achieves a 30.6% reduction in overall system operation cost compared to traditional energy storage configuration schemes, which fully verifies the outstanding effectiveness and practical engineering feasibility of the proposed method.
Grid-forming (GFM) virtual synchronous generators are critical for stabilizing inverter-dominated power grids, yet their low inertia necessitates robust fault ride-through (FRT) and overcurrent protection strategies. While finite-set model predictive control (FS-MPC) provides optimal transient management, its practical deployment is heavily hampered by an exhaustive online computational burden. To overcome this limitation, this paper proposes a novel sequential neural network (SNN) based FRT control strategy for GFM converters. Leveraging a long short-term memory architecture, the proposed SNN is trained offline via imitation learning to approximate the optimal nonlinear control law of an FS-MPC model. This approach fundamentally shifts the heavy optimization process offline, reducing online execution to deterministic, microsecond-level inference. An adaptive virtual resistance mechanism is integrated to dynamically constrain the voltage reference, enabling the SNN to strictly limit the converter fault current to a safe threshold of 1.5 per unit. Extensive time-domain simulations demonstrate that the SNN intrinsically manages unbalanced sequence components during severe asymmetrical faults without requiring complex sequence extraction filters. Comparative analysis reveals that the proposed data-driven strategy not only minimizes computational latency but also enhances grid-compliant power quality, achieving a current total harmonic distortion of less than 2%, thereby outperforming the FS-MPC baseline.
A. Aliyu, Ramani Kannan, E. Ho· Engineering Research Express· 0 citations
In grid- connected applications featuring a large share of renewable generation, the output fluctuations of photovoltaic (PV) generation deteriorate the power quality of grid-connected systems, and the improper power allocation within the hybrid energy storage system (HESS) further degrades the operational performance. With these concerns in mind, this study develops a grid-connected PV configuration that incorporates a battery–supercapacitor HESS. In terms of energy storage converter control, an improved voltage–current dual closed-loop strategy based on Model Predictive Control (MPC) is proposed for the bidirectional DC/DC converter, in which the outer PI loop stabilizes the DC bus voltage while the inner MPC loop achieves accurate tracking of the inductor current. Compared with the conventional PI-based dual closed-loop control, the maximum voltage deviation is reduced by 2.1 V, and the recovery time is shortened by up to 0.32 s. With respect to power sharing, considering that the conventional low-pass filter (LPF) approach suffers from difficulties in determining the time constant and ignores the state of charge (SoC) of the storage units, an alternative scheme governed by the supercapacitor SoC is proposed, in which the battery compensation coefficient is varied adaptively in accordance with the SoC. The simulation results demonstrate that the proposed strategy markedly reduces the count of charging and discharging cycles of the battery, and effectively prevents the supercapacitor from entering over-charged or overdischarged conditions, thereby ensuring the safe operation of the storage devices.
Yuyan Liu, Yihua Zhu, Chao Luo et al.· International Conference on...· 0 citations
To address voltage fluctuations, low renewable energy permeability, and high power loss in low-voltage distribution networks (LVDNs) integrated with photovoltaic (PV) and energy storage systems (ESSs), a Chaotic Particle Swarm Optimization (PSO)-based hierarchical optimal operation method is proposed. Firstly, the mathematical model for grid-forming control (GFM)-based PV and ESSs in LVDNs is developed. Then, the multi-objective optimization problem is formulated to: (1) minimize voltage deviation, (2) maximize PV generation power, and (3) minimize power losses. Next, the objectives are ranked based on priority, and the multi-objective optimization problem is split into several single-objective sub-problems, each solved with the chaotic PSO algorithm. Several test studies confirm that the proposed strategy achieves faster convergence (68 iterations vs. 142, reducing total computation time by 36.9%), along with a marginal accuracy improvement over standard PSO. Finally, both simulation and hardware-in-the-loop (HIL) experimental results demonstrate the effectiveness and reliability of the proposed operation scheme in LVDNs.
Xuguang Zhou, Jian Han, Bo Chen et al.· Energies· 0 citations