arXiv subjects

Javier Renedo

Publications and source records attributed to Javier Renedo.

16 recordsLinked to original sources

arXiv2026

Impedance-Based Sensitivity Analysis for Stability Enhancement of LCC-HVDC Links Connected to Weak Grids Using Grid-Forming Converters

This paper presents a frequency-domain, impedance-based sensitivity methodology for stability assessment and enhancement of line-commutated converter HVDC (LCC-HVDC) links operating under weak-grid conditions. The methodology integrates frequency-domain identification tailored for black-box systems, the Generalized Nyquist Criterion (GNC) for multivariable stability assessment, and modal impedance decomposition with participation-factor analysis to locate and interpret interaction mechanisms. The approach is validated against a detailed linearized state-space model and nonlinear EMT simulations of an LCC-HVDC benchmark. A sensitivity study varying the grid short-circuit ratio (SCR) reveals a stability limit for the standalone LCC-HVDC link and demonstrates that the integration of a grid-forming voltage source converter (GFM-VSC) substantially increases the stability margin.

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arXiv2026

Guidelines for the implementation of power oscillation damping controllers in power converters

One of the most effective ways to damp electromechanical oscillations in power systems is by means of supplementary controllers attached to the different devices in the power system is by means of power system stabilizers (PSS) in synchronous machines or by means of power oscillation damping (POD) controllers in facilities with power converters. In the recent years, the use of POD controllers in voltage source converters (VSCs) with grid-following (GFL) control has been investigated. Although the potential of POD controllers to help to damp inter-area oscillations in power systems is enormous, their correct implementation is not trivial, because their effectiveness is strongly linked to their settings. This paper provides guidelines for the implementation of POD controllers in power converters for application in real-world power systems. The paper proposes compliance criteria for POD controllers using a synthetic test system and a systematic methodology used in Spanish technical standard for monitoring compliance (NTS), considering practical considerations. The paper also includes numerical examples to illustrate compliance criteria for POD controllers in a synthetic test system. A generic power converter with grid-following (GFL) control is used for the analysis by simulation and POD controllers using modulation of active-power injection (POD-P), reactive-power injection (POD-Q) or both simultaneously (POD-PQ) will be analysed. Results were validated in a large-scale power system. The paper concludes that by using appropriate synthetic systems, methodologies and compliance criteria, POD controllers in power converters could be effective to damp electromechanical oscillation in large-scale power systems.

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arXiv2026

Tests on the POD-P controller of INELFE Spain-France VSC-HVDC interconnector

INELFE interconnector consists of a 2x1000 MW high voltage direct current system based on voltage source converters (VSC-HVDC) interconnecting France and Spain. INELFE VSC-HVDC link is embedded into the high voltage alternating current (HVAC) system. Electromechanical oscillations, also known as power oscillations, are a major concern worldwide. INELFE VSC-HVDC link has specific controllers to damp power oscillations by modulating active (P)- and reactive (Q)-power injections of the VSC converters (POD-P and POD-Q controllers, respectively). The Spanish and French Transmission System Operators (TSOs) carried out a join task force to - Increase the gain of POD-P controller of INELFE VSC-HVDC link. - Make it possible to use the POD-P controller together with angle difference control (ADC) of INELFE VSC-HVDC interconnector. The objective of these modifications is to improve the effectiveness of POD-P controller and, therefore, to increase its contribution to the damping of inter-area oscillations in the Continental Europe (CE) power system. Such changes require (a) extensive simulation studies and (b) extensive tests in different operation modes, in order to ensure the correct behavior of the system. This paper presents simulation studies and field tests on the POD-P controller of INELFE VSC-HVDC interconnector in different modes of operation.

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arXiv2026

Sizing of a grid-forming power converter to improve the small-signal stability of an LCC-HVDC system connected to a weak grid

Line-commutated converter high-voltage direct current (LCC-HVDC) has proven to be a reliable technology for bulk power transmission over long distances. However, the growing penetration of converter interfaced generation (CIG) is resulting in weaker AC grids, rendering the operation of LCC-HVDC systems vulnerable and posing a serious challenge to their stability. Grid-forming (GFM) controlled voltage source converter (VSC) have been shown to provide stabilizing impact in weak grid conditions. However, the impact of GFM controlled VSCs (GFM-VSC) on stability of LCC-HVDC in weak grid conditions has not been studied in depth in the literature. In this paper, a simplified model of LCC-HVDC is proposed and validated. Then a small-signal state-space model of a system consisting of aforementioned LCC-HVDC, a GFM-VSC and an infinite grid is developed to study the interactions between different components. The small-signal stability analysis shows the stabilizing effect of the GFM-VSC on the stability of the LCC-HVDC link in weak grid condition. Furthermore, the study on the sizing of the GFM power converter reveals that even a modest share of the capacity of the GFM power converter relative to the total nominal apparent power (sum of nominal power of LCC-HVDC and the nominal apparent power of GFM-VSC) is sufficient to ensure the stability of the system, in the test system analyzed in this study. This work just focuses in small-signal stability, but it is important to highlight that other stability phenomena should also be taken into account when selecting the final size of the GFM-VSC.

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arXiv2026

Revisiting angle stability in power systems with grid-forming power converters

This letter presents a comprehensive analysis of the stability phenomenon related to the ability of generators to remain in synchronism when subjected to small or large disturbances, in power systems with both synchronous machines and grid-forming voltage source converters (GFM-VSC). This phenomenon is associated with two stability classes in the IEEE/PES classification, namely, rotor-angle stability (when involving synchronous machines and slow-interaction converter-driven stability (when involving power converters). However, this work shows that this phenomenon is fully characterised with the slow dynamics of the angle difference between the voltage sources connected to the power system, regardless of whether they are synchronous machines (with rotors) or GFM-VSCs. Therefore, we suggest using the term angle stability to refer to this phenomenon, while slow-interaction converter-driven stability should only include slow interactions of different nature involving power converters.

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arXiv2026

Enabling Small-Signal Stability Analysis of Black-Box Voltage Source Converters in Large-Scale Modern Power Systems

Modern power systems increasingly rely on power electronic converters, yet many of these devices are provided as black-box models, limiting the applicability of conventional small-signal analysis (SSA) tools. This work presents a unified multi-variable fitted state-space (SSA-FITSS) methodology that enables accurate small-signal modeling of black-box Voltage Source Converters (VSCs) using frequency-domain (FD) identification, adaptive pole-expansion, and reduced-order realization. The method includes an automated state-interpretation strategy that assigns fitted states to representative control-loop categories based on their dominant frequency ranges, providing an approximate but meaningful physical interpretation of the identified dynamics. This capability allows extensive modal analysis, including eigenvalue sensitivities and participation factors, in systems where internal converter details are unavailable. The methodology is validated on a grid-following (GFL) VSC and applied to the New England system, which contains multiple black-box converters operating in both GFL and grid-forming (GFM) modes. Results show that the SSA-FITSS models accurately reproduce converter and system dynamics, support full eigenvalue-based analysis, and reveal stability limits under varying synchronous generation and GFL penetration levels. The approach overcomes key limitations of existing identification-based techniques by enabling scalable, interpretable, and system-wide stability assessment.

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arXiv2026

Active-power control strategies in grid-forming power converters to improve transient stability in power systems with 100% converter-based generation

Grid-forming voltage source converters (GFM-VSCs) play a crucial role in the stability of power systems with large amounts of converter-based generation. Transient stability (angle stability under large disturbances) is a critical limiting factor in stressed power systems. Previous studies have proposed control strategies in GFM-VSCs to improve transient stability. These approaches typically rely on suitable current-limiting algorithms, voltage/reactive-power and active-power supplementary control strategies. This paper investigates and compares the effectiveness of three active-power control strategies in GFM-VSCs to enhance transient stability in power systems with 100 % converter-based generation: (i) a wide-area control strategy (TSP-WACS) using the centre of inertia (COI) frequency, (ii) a local transient damping method (TSP-TDM), and (iii) a novel local control strategy (TSP-L) proposed in this work. All strategies were implemented and assessed using short-circuit simulations on Kundur two-area test system with 100 % GFM-VSC generators, demonstrating critical clearing time (CCT) improvement. The TSP-WACS strategy achieves the best performance but requires a communication infrastructure, while TSP-L strategy offers a simple-but-robust alternative using local measurements, only.

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arXiv2025

Impact on transient stability of self-synchronisation control strategies in grid-forming VSC-based generators

Grid-forming voltage source converters (GFM-VSCs) are emerging as a solution for integrating renewable energy resources (RERs) into power systems. GFM-VSCs need a self-synchronisation strategy to ensure that all converters and generators in the power system are in synchronism and they reach the same frequency in steady state. The self-synchronisation strategy in GFM-VSCs that has received most attention in previous research is virtual synchronous machine (VSM) control. However, no systematic study of the effects on transient stability of different variants of this strategy has been carried out in previous work. This paper analyses and compares transient stability of four self-synchronisation strategies for GFM-VSCs: VSM without phase-locked loop (PLL), VSM with PLL, VSM without PLL using wash-out filter and integral-proportional (IP) controller. The paper also analyses two different methods that can \color{black} be applied to GFM-VSC self-synchronisation strategies to improve transient stability: the concept of virtual unsaturated active-power controller (VAPC), proposed in previous work, and an algorithm for frequency limitation in the GFM-VSC (FLC), which is proposed in this paper.

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arXiv2024

Power Oscillation Damping Controllers for Grid-Forming Power Converters in Modern PowerSystems

Inter-area oscillations have been extensively studied in conventional power systems dominated by synchronous machines, as well as methods to mitigate them. Several publications have addressed Power Oscillation Damping (POD) controllers in grid-following voltage source converters (GFOL). However, the performance of POD controllers for Grid-Forming voltage source converters (GFOR) in modern power systems with increased penetration of power electronics requires further investigation. This paper investigates the performance of GFORs and supplementary POD controllers in the damping of electromechanical oscillations in modern power systems. This paper proposes POD controllers in GFORs by supplementary modulation of active- and reactive-power injections of the converter and both simultaneously (POD- P, POD-Q and POD-PQ, respectively). The proposed POD controllers use the frequency imposed by the GFOR as the input signal, which has a simple implementation and it eliminates the need for additional measurements. Eigenvalue-sensitivity methods using a synthetic test system are applied to the design of POD controllers in GFORs, which is useful when limited information of the power system is available. This paper demonstrates the effectiveness of POD controllers in GFOR converters to damp electromechanical oscillations, by small-signal stability analysis and non-linear time-domain simulations in a small test system and in a large-scale power system.

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arXiv2024

Addressing intra-area oscillations and frequency stability after DC segmentation of a large AC power system

In the last decades, various events have shown that electromechanical oscillations are a major concern for large interconnected Alternating Current (AC) power systems. Segmentation of AC power systems with High Voltage Direct Current (HVDC) systems (DC segmentation, for short) is a method that consists in turning large AC grids into a set of asynchronous AC clusters linked by HVDC links. It is a promising solution to mitigate electromechanical oscillations and other issues. In particular, an appropriately placed DC segmentation can stop a selected inter-area electromechanical oscillation mode. However, without supplementary controllers, DC segmentation will not contribute to the damping of the intra-area oscillation modes in the remaining AC clusters and will deteriorate the frequency stability of the power system. This paper aims at filling this gap and proposes the use of DC segmentation with HVDC systems based on Voltage Source Converters (VSC-HVDC) with supplementary controllers in the converter stations: (a) active-power supplementary controllers for frequency support among the asynchronous AC clusters and (b) a reactive-power supplementary controllers for Power Oscillation Damping (POD-Q), in order to damp the intra-area oscillation modes. The proposed supplementary controllers and their design will be presented, and their efficiency will be demonstrated on the Nordic 44 test system with DC segmentation by means of non-linear time-domain simulation and small-signal stability analysis.

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arXiv2024

Impact of current limiters and fast voltage boosters in grid-forming VSC-based generators on transient stability

Transient stability is a complex phenomenon presented in multi-machine and multi-converter systems, and it is still considered a key limiting factor for stressed power systems. The increasing integration of non-synchronous generation further emphasises the need to address the challenges of improving the transient stability faced by these power systems. Several studies have focused on developing control strategies for GFM-VSCs to improve transient stability. These strategies include the use of current limiting algorithms and/or control of active/reactive power injections. This paper investigates the impact of fast voltage boosters (FVBs) and hybrid current limiters (HCLs) on transient stability of power systems with 100% grid-forming VSC-based generators. Short-circuit simulations and critical clearing time analysis are performed to evaluate the effectiveness of HCLs and FVBs in improving transient stability. The simulation results demonstrate the effectiveness of these approaches in avoiding the loss of synchronism. This research contributes to the current studies on transient stability in power systems and provides valuable insights into the potential of HCLs and FVBs as effective approaches to improve system stability.

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arXiv2023

An algorithm for DC segmentation of AC power systems to mitigate electromechanical oscillations

In the last decades, various events have shown that electromechanical oscillations are a major concern for large interconnected Alternative Current (AC) power systems. DC segmentation - a method that consist in turning large AC grids into a set of asynchronous AC clusters linked by Direct Current (DC) links - is a promising solution to mitigate this and other issues. However, no systematic segmentation procedure for a given AC power system exists so far. This paper aims at filling this gap and proposes an algorithm for DC segmentation for a given AC power system to mitigate electromechanical oscillations. In this proposal, DC segmentation is implemented with High Voltage Direct Current links based on Voltage Source Converters (VSC-HVDC). The algorithm uses small-signal stability techniques and the concept of dominant inter-area oscillation paths to stop the main inter-area mode of the power system. The algorithm will be explained using a six-generator test system and it will then be used on the Nordic 44 test system. The proposed algorithm for DC segmentation has been validated by means of non-linear time-domain simulation and small-signal stability analysis (SSSA).

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arXiv2022

Coordinated control in multi-terminal VSC-HVDC systems to improve transient stability: Impact on electromechanical-oscillation damping

Multi-terminal high-voltage Direct Current technology based on Voltage-Source Converter stations (VSC-MTDC) is expected to be one of the most important contributors to the future of electric power systems. In fact, among other features, it has already been shown how this technology can contribute to improve transient stability in power systems by the use of supplementary controllers. Along this line, this paper will investigate in detail how these supplementary controllers may affect electromechanical oscillations, by means of small-signal stability analysis. The paper analyses two control strategies based on the modulation of active-power injections (P-WAF) and reactive-power injections (Q-WAF) in the VSC stations. Both control strategies use global signals of the frequencies of the VSC-MTDC system and they presented significant improvements on transient stability. The paper will provide guidelines for the design of these type of controllers to improve both, large- and small-disturbance angle stability. Small-signal stability techniques (in Matlab) will be used to assess electromechanical-oscillation damping, while non-linear time domain simulation (in PSS/E) will be used to confirm the results. Results will be illustrated in Nordic32A test system with an embedded VSC-MTDC system. The paper analyses the impact of the controller gains and communication latency on electromechanical-oscillation damping. The main conclusion of the paper is that transient-stability-tailored supplementary controllers in VSC-MTDC systems can be tuned to damp inter-area oscillations too, maintaining their effectiveness for transient-stability improvement.

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arXiv2021

Fast voltage boosters to improve transient stability of power systems with 100% of grid-forming VSC-based generation

Grid-forming voltage source converter (GF-VSC) has been identified as the key technology for the operation of future converter-dominated power systems. Among many other issues, transient stability of this type of power systems remains an open topic of research because it is still a key limiting factor for stressed power systems. Previous studies have proposed control strategies for GF-VSC to improve transient stability of this type of systems by suitable current-limitation algorithms and/or control of active-power injections. As an alternative, this paper proposes two fast voltage boosters to improve transient stability of power systems with 100% of GF-VSC-based generation with virtual synchronous machine (VSM). One control strategy uses local measurements, whereas the other one uses global measurements of the frequency of the centre of inertia (COI). Both strategies improve transient stability of this type of systems significantly. The advantage of using fast voltage boosters for this purpose is that the set points linked to frequency/active-power injection (i.e set points linked to the primary energy source of the VSCs) will not be modified. Furthermore, strategies such as current-limitation, active-power control and fast voltage controllers for transient stability improvement are compatible and complementary.

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arXiv2021

Impact on power system transient stability of AC-line-emulation controllers of VSC-HVDC links

High voltage direct current links based on voltage source converters (VSC-HVDC) embedded in alternating current (AC) systems are receiving a great deal of attention recently because they can contribute positively to the flexibilisation of modern power systems. Among several possibilities, AC-line-emulation control has been highlighted as an simple-but-useful alternative for these type of systems. With this strategy, the power flow through the link is controlled proportionally to the angle difference between its two AC terminals and this provides self-adaptation of the power flow in case of contingencies in the parallel AC lines, naturally. Although this controller is mainly concerned with steady state, it can also have an impact on the dynamic behaviour of the system, which has not been sufficiently analysed. Along this line, this paper analyses the impact of AC-line-emulation controllers of VSC-HVDC on power system transient stability. Nonlinear time-domain simulations were carried out by using PSS/E on a small test system with an embedded point-to-point VSC-HVDC link. The critical clearing time (CCT) of a test fault has been used to assess transient-stability margins of the whole system. The paper provides recommendations for the design of AC-line-emulation controllers in order to ensure that transient stability is not jeopardised.

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arXiv2016

Symmetry of surface nanopatterns induced by ion-beam sputtering: the role of anisotropic surface diffusion

Ion Beam Sputtering (IBS) is a cost-effective technique able to produce ordered nanopatterns on the surfaces of different materials. To date, most theoretical studies of this process have focused on systems which become amorphous under irradiation, e.g. semiconductors at room temperature. Thus, in spite of the large amount of experimental work on metals, or more recently on semiconductors at high temperatures, such experimental contexts have received relatively little theoretical attention. These systems are characterized by transport mechanisms, e.g. surface diffusion, which are anisotropic as a reflection of the crystalline structure not being overruled by the irradiation. Here, we generalize a previous continuum theory of IBS at normal incidence, in order to account for anisotropic surface diffusion. We explore systematically our generalized model in order to understand the role of anisotropy in the space ordering properties of the resulting patterns. In particular, we derive a height equation which predicts morphological transitions among hexagonal and rectangular patterns as a function of system parameters and employ an angular correlation function to assess these pattern symmetries. By suitably choosing experimental conditions, it is found that one might be able to experimentally control the type of order displayed by the patterns produced.

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