Search Results (236)

To address the issue of low-frequency oscillations in active power and frequency caused by parameter mismatches among multiple grid-forming energy-storage converters in islanded microgrids—where the fixed damping coefficient of conventional VSG control fails to simultaneously achieve satisfactory dynamic response and steady-state accuracy—this paper proposes a VSG control strategy enhanced by cooperative transient damping. The strategy first introduces active power feedback transient damping (TDP) into the active power loop. Although TDP can effectively suppress low-frequency oscillations in active power, it provides insufficient suppression for frequency oscillations induced by angular frequency coupling. Therefore, angular frequency feedback compensation is further incorporated, forming an active power-angular frequency two-degree-of-freedom architecture. This design flexibly adjusts the system damping without compromising steady-state performance, achieving cooperative suppression of both types of oscillations. Simulation and experimental results demonstrate that the proposed strategy significantly suppresses low-frequency oscillations in active power and frequency, effectively improving both the dynamic response performance and steady-state accuracy of the system. Full article

Trypanosomosis (Surra), caused by the hemoflagellate protozoan Trypanosoma evansi, has a negative impact on animal health and the livestock economy in many countries, including Thailand. Molecular epidemiological data and integrative control approaches for small-scale farms remain limited. This study determined the prevalence of Trypanozoon infection and its associated risk factors in Thai livestock under an integrative control approach. Molecular tools were used to characterize T. evansi typing. A total of 947 blood samples were collected from cattle and buffalo across 123 small-scale farms in 16 provinces covering four regions of Thailand, with diagnostic results and control recommendations communicated to farmers within 14 days. The ITS2-positive samples were then subjected to further molecular characterization, together with two dogs, seven horses, and an in vitro T. evansi isolate, comprising 40 Trypanozoon-positive samples. These were characterized using PCR targeting the TBR primer, maxicircle NADH5, VSG RoTat 1.2, and minicircle B, followed by ITS2-based phylogenetic analysis. Risk factors were assessed using Chi-square and Fisher’s exact tests, logistic regression, a generalized linear mixed model, and Firth’s penalized logistic regression. The overall prevalence of Trypanozoon infection was 3.17% (30/947), detected exclusively in beef cattle in the Northern region (15.30%; 30/196), specifically in Lampang (46.15%, 12/26), Tak (23.08%, 3/13), and Phrae (17.24%, 15/87) Provinces. No infections were reported in the Northeastern, Central, or Southern regions. Male sex, age under one year, and residence in the Northern region were significant individual-level risk factors, while farm-level lacrimation and the presence of Stomoxys were significantly associated with infection. Molecular characterization identified T. evansi type A and type non-A/B, with no type B or maxicircle-positive samples detected. Phylogenetic analysis grouped the Thai isolates with previously reported isolates from Thai deer and cattle, Iranian camels, and Colombian dogs. On follow-up, no Trypanozoon infection was detected in revisited farms. These findings confirmed that T. evansi, comprising types A and non-A/B, continues to circulate in Thai livestock, particularly in beef cattle in Northern Thailand. Data from this study can be used for surveillance and future development of more effective diagnostic systems. Full article

Subsynchronous oscillation (SSO) is a critical stability issue in grid-following direct-drive wind farms connected to weak grids. To mitigate this issue, this paper proposes a phase-shift subsynchronous damping control strategy based on grid-forming energy storage (GF-ES). First, a small-signal state-space model of a grid-connected wind-storage system incorporating GF-ES is established, and eigenvalue analysis is conducted to examine the effects of GF-ES capacity share, virtual synchronous control parameters, and grid strength on the dominant SSO mode. The results show that, under weak-grid conditions, the coupling among point of common coupling (PCC) voltage disturbances, the wind turbine Phase-Locked Loop (PLL), and grid-side current control reduces system damping, causing the dominant SSO mode around 22.1 Hz to exhibit weak or even negative damping. To enhance damping under low-capacity conditions, a phase-shift subsynchronous damping controller (PS-SDC) is designed, and its additional damping voltage signal is superimposed onto the q-axis voltage command of the GF-ES inner current control loop. Eigenvalue analysis shows that, under conventional virtual synchronous generator (VSG)-controlled GF-ES, increasing the GF-ES capacity share from 2% to 20% shifts the dominant SSO eigenvalue from 1.0128 ± j138.8370 to −1.7111 ± j138.8097, and increases the damping ratio from −0.0073 to 0.0123. At the baseline 10% GF-ES capacity share, the proposed PS-SDC further shifts the dominant eigenvalue from −0.4780 ± j138.8223 to −1.5691 ± j138.8224, increasing the damping ratio from 0.0034 to 0.0113. The small-signal stability boundary is also improved from between 6.5% and 10% GF-ES capacity share to between 4% and 6.5%, demonstrating that the proposed PS-SDC provides enhanced damping capability for the 22.1 Hz dominant SSO mode under weak-grid and low-capacity GF-ES conditions. Full article

With the increasing penetration of renewable energy sources (RESs) in the power grid, the active support capability of power conversion systems (PCSs), which serve as the critical link between RESs and the grid, has become increasingly vital. In this paper, an optimized control strategy for frequency regulation of response speed in grid-forming energy storage converters based on adaptive mode-switching is proposed. When power fluctuations are detected, the system switches to droop control, and reverts to virtual synchronous generator (VSG) control when frequency stability is nearly restored. Experimental results demonstrate that during load transients, the proposed control strategy significantly improves the frequency regulation response speed of the energy storage converter compared to conventional VSG and droop control, achieving a reduction in regulation time within the range of 40% to 70%, while also reducing overshoot, as validated by both simulation and hardware-in-the-loop experiments. Full article

Conventional soft open points (SOPs) suffer from limited transfer capacity during distribution network faults. To address this issue, this paper proposes an integrated energy storage system and soft open point (ES-SOP) along with a power path dynamic reconfiguration method. The device consists of an M × N AC switch matrix, N AC/DC converters, and a common DC bus with energy storage. This structure provides three distinct power paths: a mechanical direct path, a third-party grid path, and an energy storage path. A seamless reconfiguration technology is developed to eliminate inrush currents during mechanical switching. It combines multi-unit virtual synchronous generator (VSG) pre-synchronization with a DC bus voltage droop coordination mechanism. The overall control follows a two-time-scale strategy. On a long time scale, a heuristic rule selects the most suitable healthy grid as the mechanical source. On a short time scale, the droop parameters of the converters are optimized to autonomously share the remaining power between the third-party grid path and the energy storage path. This allocation minimizes losses and requires no fast communication. Hardware-in-the-loop experiments verify the performance: the proposed method completely suppresses inrush current, keeps DC bus voltage fluctuation below 20 V during mode transitions, and achieves a transfer efficiency of approximately 98.5%. Full article

Large-scale photovoltaic (PV)–hydrogen production systems are increasingly regarded as a promising solution for mitigating renewable energy curtailment and supporting the transition toward low-carbon energy systems. However, when connected to weak grids, such systems often suffer from insufficient voltage–frequency support capability and pronounced Direct current (DC) bus voltage fluctuations, which limit their operational stability and practical deployment. To address these challenges, this paper proposes a dual virtual motor coordinated control strategy for PV-based hydrogen production systems, integrating a grid-forming virtual synchronous generator (VSG) with a virtual DC motor (VDCM). By exploiting the complementary dynamic characteristics of grid-side converters and hydrogen production loads, the proposed approach enhances grid support capability while simultaneously providing inertia and damping to the hydrogen production DC bus without relying on additional physical energy storage. Dynamic response analysis is conducted to investigate the influence of virtual inertia and damping parameters on system stability. Simulation results under weak-grid conditions demonstrate that the proposed strategy effectively improves frequency and voltage support performance and significantly suppresses DC bus voltage fluctuations during load and power disturbances. The proposed control framework offers a practical and scalable solution for improving the operational robustness of PV–hydrogen production systems, contributing to the reliable integration of renewable energy and the development of green hydrogen infrastructure. Full article

As global power systems transition toward increasing penetration of renewable energy sources (RESs), such as solar and wind, maintaining frequency stability in converter-dominated low-inertia grids has become a critical challenge. This review examines the role of inertia in power system dynamics, emphasising the consequences of reduced mechanical inertia, the resulting increase in the rate of change of frequency (RoCoF), and the associated stability risks in grids with high inverter-based penetration. Inertial, primary, and secondary frequency response mechanisms are discussed alongside potential cascading failures, protection system triggering, and pathways toward fully renewable grids are assessed. Virtual inertia techniques, including synchronverters, swing-equation-based methods, virtual synchronous generators (VSGs), droop control, Virtual Oscillator Control (VOC), and matching control, are evaluated in terms of benefits, limitations, implementation complexity, and Technology Readiness Levels (TRLs). A key contribution is a multi-criteria evaluation framework that classifies these methods by control adaptability, scalability, and communication requirements, providing system operators with a structured basis for strategy selection. A comparative assessment of Phase-Locked Loop (PLL) synchronisation methods, including SRF-PLL, DDSRF-PLL, FLL-PLL, and Kalman filter-based approaches, is presented under weak-grid, unbalanced, and harmonic-distorted conditions. The integration of virtual inertia with energy storage technologies, such as batteries, supercapacitors, and flywheels, is also discussed, along with its role as an ancillary service within evolving electricity markets and grid codes. Collectively, this study provides a unified reference to advance intelligent, scalable, and deployment-ready frequency control in low-inertia renewable power systems, offering both theoretical insights and practical guidance for future high-RES grid architectures. Full article

Variations in wind-turbine rotor speed and converter power margin under different operating conditions constrain the frequency-support power output of wind turbines, thereby affecting the controllability and stability of the frequency-support response. To address this problem, this paper proposes a dual virtual synchronous generator (VSG) coordinated control method for energy-storage doubly fed induction generator wind turbines based on frequency-support power-response equivalence. First, frequency-support power-response models are established for the VSGs implemented at the rotor-side converter and the grid-side converter to describe the active-power dynamic characteristics of the two frequency-support channels. Second, using the target inertial-support power response as the reference, the dual-VSG parameter configuration is transformed into a power-response consistency optimization problem. Furthermore, considering rotor speed, state of charge (SOC), and the grid-side converter upward power margin, the inertia-support and primary frequency regulation power contributions are assigned between the stator and grid-side converter channels. Hardware-in-the-loop validation results show that the proposed method coordinates the dual-channel frequency-support power output under four typical operating conditions with high/low wind speeds and high/low SOC levels, maintains a consistent frequency-support power response, and achieves controllable and stable frequency support over a wide operating range. Full article

Aiming at the problems of the severe active–reactive power coupling, insufficient adaptive inertia–damping regulation, and degraded dynamic performance of virtual synchronous generators (VSGs) under the operating conditions of a weak grid, high resistance-to-reactance ratio, and large power angle, this paper proposes a cooperative control strategy that combines reactive power feedforward decoupling with adaptive damping–inertia regulation. First, a small-signal power model of the VSG is established, and a dynamic relative gain array is employed to quantitatively analyze the effects of the resistance-to-reactance ratio and power angle on power coupling characteristics, revealing that large power angles and high resistance-to-reactance ratios significantly aggravate active–reactive power coupling. Based on this analysis, a reactive-power-oriented feedforward decoupling strategy is designed to suppress the cross-coupling between reactive power and power angle while preserving the intrinsic inertia support characteristics of the active power loop. Eigenvalue migration analysis further demonstrates that the proposed reactive-power-oriented decoupling provides higher damping ratios and larger stability margins than conventional full active–reactive power decoupling. Furthermore, a deep deterministic policy gradient-based adaptive damping–inertia control method is developed by incorporating frequency deviation, power fluctuation, voltage deviation, and coupling degree into the state space, enabling the online coordinated optimization of virtual inertia and damping coefficients. The hardware-in-the-loop experimental results verify that the proposed strategy effectively suppresses active–reactive power coupling, reduces power overshoot and oscillation, enhances frequency support capability and dynamic response speed, and maintains superior stability under weak grid conditions. Sensitivity analysis under grid impedance estimation errors further confirms its strong robustness against parameter uncertainty, while tests under composite disturbance scenarios demonstrate excellent transient performance. The proposed strategy provides an effective solution for improving the grid-connected operation performance and adaptability of VSGs in low-inertia power systems. Full article

Flywheel energy storage systems (FESSs) offer millisecond-level response speed, making them highly suitable for providing system inertia/frequency support in emergency grid scenarios. However, the FESSs often have limited energy capacity due to their high capacity cost, which necessitates a comprehensive consideration between remaining stored energy and sustained support capability. Thus, this paper proposes a virtual synchronous generator (VSG) control strategy based on a multi-time-step model predictive control (MPC) that considering flywheel’s state of charge (SOC), which provides both emergency frequency support and autonomous flywheel energy recovery within a single integrated framework. First, a multi-time-step MPC with the objective function aiming for both fast frequency response and smooth power output is introduced to compensate the reference power generated by the VSG strategy. Second, an SOC-adaptive frequency weight function is designed and incorporated into the objective function to balance the frequency deviation and the inertia/frequency support duration. Furthermore, an SOC self-recovery strategy is developed, allowing the flywheel to autonomously adjust its SOC to the desired range when the FESS is not participating in frequency regulation. Finally, the proposed strategy is verified through comprehensive simulations on various scenarios, demonstrating that it can efficiently and rapidly meet the frequency regulation demands when the SOC is sufficient, as well as achieve the balances between the frequency regulation performance and the support continuity when the SOC is insufficient. Full article

Parallel grid-forming energy storage converters based on virtual synchronous generator (VSG) control are prone to active power oscillation and interphase circulating current under load disturbance, unit switching, and parameter mismatch conditions. To address these problems, this paper proposes a dual-layer damping control strategy that combines adaptive virtual damping in the power loop with capacitor current feedback damping in the current loop. First, the small-signal models of the LCL filter, VSG power loop, and parallel converter system are established, and the dominant oscillation modes are analyzed using eigenvalue and participation factor methods. Then, an adaptive damping coefficient is designed according to the active power deviation and frequency dynamic response to suppress low-frequency power oscillation, while a capacitor current feedback branch is introduced to reshape the LCL filter’s resonant poles and attenuate circulating current resonance. Compared with the conventional fixed-damping VSG control, the proposed method reduces active power overshoot and accelerates power redistribution under load step and unit switching conditions. In the traditional control case, the active power peaks of VSG1 and VSG2 reach approximately 30 kW and 40 kW, with an oscillation period of about 1.8 s, whereas the proposed strategy suppresses the oscillatory process and enables the output powers to rapidly reach the preset sharing ratio. In addition, the system frequency can recover to the rated value of 50 Hz without obvious steady-state deviation, and the high-frequency component of the grid-connected current and the interphase circulating current are significantly attenuated. MATLAB/Simulink simulation results verify that the proposed dual-layer damping strategy provides better power oscillation suppression, circulating current mitigation, and frequency dynamic performance than the conventional VSG control. Full article

This paper presents the modelling and dynamic analysis of a Virtual Synchronous Generator (VSG) operating under three representative load models: constant impedance (Z), constant power load (CPL), and composite ZIP (constant impedance, constant current, and constant power) loads. The VSG control strategy enables voltage-source converters to emulate the inertial behavior of synchronous machines. However, load characteristics strongly affect the stability of such systems, and CPLs can be particularly destabilizing because of their negative incremental impedance. This study provides a theoretical and simulation-based analysis of VSG performance under Z-, CPL, and ZIP load conditions. A swing-equation-based control model is linearized to obtain a reduced-order small-signal stability model. The incremental impedance properties of the load types are evaluated analytically, showing that CPL behavior reduces effective damping and can destabilize the system. The resulting analytical stability condition provides a practical basis for selecting virtual inertia and damping parameters. Practical DC-side energy storage and current-limiting constraints associated with inertia emulation are also discussed. The analysis is supported by simulation studies that quantify the influence of load dynamics on frequency stability and transient response. In contrast to current research, this paper offers a single comparative framework in which all load types are analyzed under the same operating conditions and derives analytical stability conditions that inform the selection of virtual inertia and damping parameters. Full article

Grid-forming (GFM) converters enhance power system stability by emulating synchronous generators, but their limited overcurrent capability under grid faults poses a critical challenge to transient stability. Existing current-limiting methods often force a trade-off between fault current suppression and voltage support. To address this, a direct internal voltage control (DIVC)-based fault current-limiting strategy is proposed. The DIVC framework eliminates inner control loops and directly regulates the internal voltage amplitude and phase by leveraging measurements at the point of common coupling (PCC) and the converter output, enabling fast, accurate current control within a virtual synchronous generator (VSG) architecture. Under mild faults, the strategy prioritizes maintaining the terminal voltage to preserve voltage source behavior; under severe faults, it smoothly transitions to a current-limiting mode that preserves the terminal voltage phase angle to support transient synchronization. The scheme incorporates compensation-enabling criteria, dual-mode amplitude/phase compensation, and power reference modification. Experimental results under an 80% voltage sag demonstrate that the proposed method limits the transient current peak to 1.1 p.u. and ensures oscillation-free recovery within 0.1 s, significantly outperforming conventional current saturation and virtual impedance techniques. The proposed approach also exhibits strong current-limiting capability under unbalanced faults. Full article

Virtual synchronous generators (VSGs) are prone to transient power angle instability and short-circuit current overshoot under symmetrical short-circuit grid faults. To address the limitation that existing transient control strategies fail to simultaneously guarantee power angle stability and fault current limiting, a coordinated control strategy combining dynamic active power reference regulation and adaptive virtual impedance is designed. Specifically, the active power reference is dynamically adjusted in accordance with the voltage sag magnitude at the point of common coupling (PCC), which effectively narrows the acceleration area of the virtual rotor and maintains the transient power angle near its rated value to prevent the risk of system loss of synchronism. On this basis, an adaptive virtual impedance control scheme is designed to accurately calculate and implement the optimal current-limiting impedance on demand, confining the steady-state fault current within the allowable threshold. Finally, the effectiveness of the designed strategy is verified on the Matlab/Simulink simulation platform. Simulation results demonstrate that the designed strategy achieves the coordination between transient power angle stability and fault current limiting, thus improving the operational stability of the VSG grid-connected system under symmetrical short-circuit grid faults. Full article

To address the increasingly prominent challenges of “low inertia” and “weak damping” in modern power systems, grid-forming (GFM) control technologies with inertia and damping support capabilities are being extensively adopted. However, distributed generation units interfaced with GFM inverters are highly susceptible to overcurrent phenomena during grid short-circuit faults. Existing research primarily focuses on current-limiting control strategies for virtual synchronous generators (VSGs), while investigations into their fault current characteristics remain insufficient. Given this, this paper proposes a short-circuit current calculation methodology for VSG-based PV-storage grid-connected systems. First, a model of a grid-forming PV-storage grid-connected system based on virtual synchronous control is established. Subsequently, the virtual impedance is solved within the timescale of current inner-loop stabilization, and the virtual internal electromotive force (EMF) equation for the VSG is formulated. This leads to the derivation of an analytical expression for the VSG short-circuit current, accounting for variations in the virtual internal potential. Furthermore, the impacts of diverse control parameters and fault severities on the short-circuit current are investigated based on this expression. Finally, simulations are conducted on the MATLAB/Simulink(R2024b) platform to validate the accuracy of the proposed short-circuit current calculation method and the correctness of the analysis regarding the influencing factors. Full article