Search Results (689)

In order to adapt to the development trend of large-scale access of distributed resource and power market reform, it has gradually become an industry consensus that multi-agent resources of a distribution network participate in regulation in the form of clusters. Based on the “centralized–distributed” regulation architecture, and relying on the regulation process of cluster partition, external characteristics calculation, command decomposition, and deaggregation, a cluster regulation strategy is proposed considering market factors. Firstly, the behavior characteristics of each agent are analyzed under the market trading mechanism. Then, the model of multi-agents participating in regulation in the form of a single point and a cluster is established. In the process of cluster partition, considering the active and reactive power–voltage coupling characteristics of the distribution network, a Monte Carlo random cluster partition sample generation method and screening mechanism are designed to deal with the problem of insufficient and inapplicable samples in the actual scene. At the same time, in order to reduce the difficulty of solving the cluster’s external characteristics, a multi-agent output range simplification method is proposed for the process of “external characteristics calculation”. Finally, the improved IEEE-33 bus system was taken as an example to verify the accuracy of the cluster regulation method when responding to the Automatic Generation Control (AGC) and Automatic Voltage Control (AVC) scheduling commands of the superior grid under market factors and different cluster partitions. The results show that the relative error of the command tracking of the proposed multi-agents in different cluster forms is less than 5.5%, which verifies the correctness of the proposed method. Full article

The ability to efficiently store raw emulsion and market it as a ready-to-cook convenience meat product would be extremely advantageous to society and the global meat business. With this innovation, consumers may easily make a range of fresh emulsion-based meat products, saving time and labour. The current study was thus designed with the goal of improving the quality and storage stability of meat emulsions by using chitosan-based thyme (Thymus vulgaris) and oregano (Origanum vulgare) essential oil nanoparticles as natural preservatives. The treatments included the following: T0—control; T1—emulsion added with chitosan nanoparticles @ 500 ppm; T2—emulsion added with thyme essential oil nanoparticles @ 500 ppm; T3—emulsion added with oregano essential oil nanoparticles @ 500 ppm; and T4—positive control added with synthetic additive butylated hydroxytoluene @ 200 ppm. TBARS (Thiobarbituric acid reactive substances) values revealed that T2 and T3 exhibited greater oxidative stability throughout storage. Protein carbonyl levels increased at a slower rate during storage in nano-treated essential oil groups. DPPH (2, 2 diphenyl-1-picryl hydrazyl) and FRAP (Ferric Reducing Anti-Oxidant Power) values decreased significantly (p < 0.05) during storage, with T3 having the strongest anti-oxidant activity. T2 and T3 had consistently greater texture values than the other groups. T2 and T3 demonstrated lower values for microbiological parameters, particularly on day 7 and 15. The storage stability period of emulsion was 3 days for T0 and T4, while as it was 6 days for T1 and 9 days for T2 and T3. T2 and T3 showed higher sensory scores, affirming their superior sensory appeal to other treatments. In conclusion, the essential oil nanoparticle treatments resulted in better quality and storage stability of meat emulsions during aerobic refrigerated storage. Full article

Wind energy is essential for promoting sustainability and renewable power solutions. However, ensuring stability and consistent performance in DFIG-based wind turbine systems (WTSs) remains challenging due to rapid wind speed variations, grid disturbances, and parameter uncertainties. These fluctuations result in power instability, increased overshoot, and prolonged settling times, negatively impacting grid compliance and system efficiency. Conventional proportional-integral (PI) controllers are simple and effective in steady-state conditions, but they lack adaptability in dynamic situations. Similarly, artificial intelligence (AI)-based controllers, such as fuzzy logic controllers (FLCs) and artificial neural networks (ANNs), improve adaptability but suffer from high computational demands and training complexity. To address these limitations, this paper presents a hybrid adaptive neuro-fuzzy inference system (ANFIS)-PI controller for DFIG-based WTS. The proposed controller integrates fuzzy logic adaptability with neural network-based learning, allowing real-time optimization of control parameters. Implemented within the rotor-side converter (RSC) and grid-side converter (GSC), ANFIS enhances reactive power management, grid compliance, and overall system stability. The system was tested under a step wind speed signal varying from 10 m/s to 12 m/s to evaluate its robustness. The simulation results confirmed that the ANFIS-PI controller significantly improved performance compared with the conventional PI controller. Specifically, it reduced rotor speed overshoot by 3%, torque overshoot by 12.5%, active power overshoot by 2%, and DC link voltage overshoot by 20%. Additionally, the ANFIS-PI controller shortened settling time by 50% for rotor speed, by 25% for torque, by 33% for active power, and by 16.7% for DC link voltage, ensuring faster stabilization, enhanced dynamic response, and greater efficiency. These improvements establish the ANFIS-PI controller as an advanced, computationally efficient, and scalable solution for enhancing the reliability of DFIG-based WTS, facilitating seamless integration of wind energy into modern power grids. Full article

This paper presents the development of a Three-phase Universal Programmable Electronic Load (UPEL) programmed as an unbalanced and distorted current source, highlighting its innovative control strategy and modulation approach. The core contribution is the implementation of Adaptive Sliding Pulse Width Modulation (ASPWM), a novel technique that combines Sliding Mode Control (SMC) with an Adaptive Hysteresis Band (AHB). This methodology eliminates the need for conventional Pulse Width Modulation (PWM), hybrid PI controllers, or cascade control structures, achieving superior robustness, faster response times, and a fixed switching frequency. The proposed ASPWM enhances energy quality by enabling precise control of active and reactive power, harmonic injection, and operation across multiple modes, including AC/DC rectification and DC/AC inversion. Simulation and experimental results validate the effectiveness of ASPWM in improving performance metrics, ensuring operational stability, and demonstrating adaptability for diverse scenarios. This study establishes ASPWM as a transformative control technique for advanced power electronics applications. Full article

This paper presents a comprehensive RMS-based phasorial model of an E-STATCOM with grid-forming (GFM) control, designed to improve power system stability in isolated grids. Unlike previous approaches, this model integrates a governor with an internal power system stabilizer (PSS) and an active current limiter (ACL) to enhance frequency regulation and mitigate oscillations. Additionally, an exciter with a nonlinear modulation function is introduced to optimize voltage regulation and reactive power support. A detailed conventional supercapacitor (SC) model is also incorporated, enabling dynamic DC-voltage control based on active power variations, improving frequency stability. The proposed E-STATCOM RMS model includes algebraic equations, dynamic governor and exciter models, supercapacitor-based energy storage control, and an advanced current-limiting strategy. Simulations are conducted on the Fuerteventura–Lanzarote (Canary Islands, Spain) power system, comparing the E-STATCOM with a synchronous condenser (SynCon) in frequency response, voltage regulation, and fault performance. The results show that the E-STATCOM improves frequency stabilization and energy efficiency while complying with grid codes. This study introduces a novel RMS-based modeling approach for GFM E-STATCOMs, bridging the gap between theoretical phasorial analysis and real-world applications. The findings confirm that E-STATCOMs are a viable alternative to SynCons, enhancing grid stability in high-renewable-penetration systems. Full article

Due to the integration of distributed photovoltaic (PV) into distribution networks, significant challenges have affected voltage regulation and power quality maintenance. To improve the flexibility and stability of system operation, a synergetic optimization operation method based on PV and a flexible interconnection device (FID) is proposed. Both PV and FID hold the capability of controlling active power and reactive power. Besides the active power output of PV, three reactive power output schemes of power factor controlling, direct reactive power output, and night static var generator scheme are defined and analyzed. By adopting different schemes during the day or night, five reactive power output modes were built. FID with four-quadrant power control ability was used to coordinate with PV in system power balance. Different port numbers of FIDs are discussed. An optimization model with the aim of reducing voltage deviation, network loss, and the ratio of PV abandonment was constructed. Three algorithms were used for solving the multi-objective optimization model. Simulation results verify that the proposed synergetic optimization method can obviously improve power quality and decrease network loss. The optimal performance is obtained when PV operates in mode 5 and FID holds four ports. The proposed method shows potential in the coordinated operation of various resources and the flexible interconnection of the distribution network. Full article

Modular multilevel converter–high-voltage direct current (MMC-HVDC) systems are a key technology for integrating large-scale offshore wind farms due to their flexibility, controllability, and decoupled active and reactive power characteristics. However, offshore wind farms rely on power electronic converters, resulting in low inertia, which can worsen frequency fluctuations and affect system stability during major disturbances. Additionally, the decoupled power control of MMC-HVDC systems limits wind farms’ inertia contribution to the AC grid, exacerbating inertia deficiency. To address this, a coordinated inertia support strategy is proposed, utilizing a DC voltage–frequency mapping method that enables wind farms to perceive frequency variations without communication and rapidly provide inertia response. This strategy coordinates wind farms and MMC-HVDC systems to enhance frequency support. Simulations demonstrate that the proposed strategy overcomes MMC-HVDC’s decoupling effect, accelerates frequency recovery, and improves the inertia response speed, achieving faster power support and higher peak power output, thereby enhancing frequency stability. Furthermore, PSCAD/EMTDC simulations were conducted to analyze the transient characteristics of MMC-HVDC under AC-side faults, verifying that braking resistors (BRs) effectively suppress DC overvoltage, reducing wind farm power curtailment and improving system security. This study provides a new approach for frequency stability control in MMC-HVDC-based offshore wind integration and serves as a reference for further optimization of inertia support and fault protection strategies. Full article

The growing demand for electricity, integration of renewable energy sources, and recent advances in power electronics have driven the development of HVDC systems. Multi-terminal HVDC (MTDC) grids, enabled by Voltage Source Converters (VSCs), provide increased operational flexibility, including the ability to reverse power flow and independently control both active and reactive power. However, fault propagation in DC grids occurs more rapidly, potentially leading to significant damage within milliseconds. Unlike AC systems, HVDC systems lack natural zero-crossing points, making fault isolation more complex. This paper presents the implementation of a wavelet-based protection algorithm to detect faults in a four-terminal VSC-HVDC grid, modelled in MATLAB and SIMULINK. The study considers several fault scenarios, including two internal DC pole-to-ground faults, an external DC fault in the load branch, and an external AC fault outside the protected area. The discrete wavelet transform, using Symlet decomposition, is applied to classify faults based on the wavelet entropy and sharp voltage and current signal variations. The algorithm processes the decomposition coefficients to differentiate between internal and external faults, triggering appropriate relay actions. Key factors influencing the algorithm’s performance include system complexity, fault location, and threshold settings. The suggested algorithm’s reliability and suitability are demonstrated by the real-time implementation. The results confirmed the precise fault detection, with fault currents aligning with the values in offline models. The internal faults exhibit more entropy than external faults. Results demonstrate the algorithm’s effectiveness in detecting faults rapidly and accurately. These outcomes confirm the algorithm’s suitability for a real-time environment. Full article

Background: This study aimed to evaluate the impact of different set volumes and durations of isometric conditioning activity (ICA) (a single 9 s set vs. three 9 s sets, totaling 27 s) on countermovement jump (CMJ) performance in highly trained male volleyball players. Understanding these effects is essential for optimizing warm-up protocols, particularly before competitions or high-intensity training sessions, to maximize performance outcomes. Methods: The 14 participants completed three conditions: one set of ICA (9 s) and three sets of ICA (27 s), each involving maximal isometric contractions in the half-back squat position, as well as a control condition without ICA. Approximately 3 min pre-ICA and at 3, 6, and 9 min post-ICA, the CMJ performance was assessed. Results: The results showed a significant interaction between CMJ height (p = 0.002) and relative peak power (p = 0.004) with the three-set condition. Post hoc comparisons indicated a significant increase in CMJ height at 3 min (p = 0.018; effect size [ES]: 0.868) and 6 min (p = 0.044; ES: 0.808), and a relative peak power output at 3 min (p = 0.005; ES: 0.874) and 6 min (p = 0.034; ES: 0.745) post-ICA compared to pre-ICA. No significant interactions or main effects were found for the modified reactive strength index or CMJ contraction time. Conclusions: The findings suggest that a three-set ICA with a total duration of 27 s may acutely improve CMJ height and relative peak power output in highly trained volleyball players. Full article

As the proportion of renewable energy sources integrated into the power grid increases, it imposes significant volatility on the grid, leading to uneven load distribution across certain transmission lines. Rotating Power Flow Controllers (RPFCs) based on Rotating Phase-Shifting Transformers (RPSTs) offer a viable solution to such issues in lines rated at 10 kV and below. This paper begins with a brief introduction to RPFCs, followed by the modeling of their topology for a single-circuit line and the derivation of active and reactive power flow formulas. Notably, this paper introduces intelligent optimization algorithms to this field for the first time, employing an improved hybrid particle swarm optimization (HPSO) algorithm to control the active power while keeping the reactive power constant and subsequently adjusting the reactive power while maintaining the active power steady, thereby achieving power regulation. Using Matlab/Simulink simulations, this strategy was compared with adaptive adjustment strategies, verifying that it exhibits reduced power fluctuations and overshoots during the adjustment process, thus confirming the effectiveness of the adjustment scheme. By leveraging this algorithm in conjunction with simulations, a Q-P operating range diagram for transmission lines was plotted, determining the adjustable range of actual power. Full article

With the widespread integration of renewable energy into distribution networks, energy storage systems are playing an increasingly critical role in maintaining grid stability and sustainability. Hydrogen, as a key zero-carbon energy carrier, offers unique advantages in the transition to low-carbon energy systems. To facilitate the coordination between hydrogen and renewables, this paper proposes a flexible on-grid and off-grid control method for an electric–hydrogen hybrid AC-DC microgrid which integrates photovoltaic panels, battery energy storage, electrolysers, a hydrogen storage tank, and fuel cells. The flexible control method proposed here employs a hierarchical structure. The upper level adopts a power management strategy (PMS) that allocates power to each component based on the states of energy storage. The lower level utilises the master–slave control where master and slave converters are regulated by virtual synchronous generator (VSG) and active and reactive power (PQ) control, respectively. In addition, a pre-synchronisation control strategy which does not rely on traditional phase-locked loops is introduced to enable a smooth transition from the off-grid to on-grid mode. The electric–hydrogen microgrid along with the proposed control method is modelled and tested under various operating modes and scenarios. The simulation results demonstrate that the proposed control method achieves an effective power dispatch within microgrid and maintains microgrid stability in on- and off-grid modes as well as in the transition between the two modes. Full article

Grid-forming (GFM) converters face significant challenges in low-voltage ride-through (LVRT) due to their limited overcurrent capacity. Various transient current-limiting methods have been proposed to address this issue. However, simple current-limiting settings during grid faults can severely compromise the transient stability and reactive power output of GFM, thereby affecting compliance with grid codes. To align with the global push for sustainable energy systems, this study proposes a virtual impedance tuning method (CL-TS VI) that simultaneously considers current-limiting and transient stability requirements, addressing the dual demands of high efficiency and reliable integration of renewable energy. By combining this method with an inner-loop control design based on balanced currents, an enhanced low-voltage ride-through (E-LVRT) scheme is developed. The proposed scheme achieves the coordinated fulfillment of both current-limiting and transient stability requirements by quantitatively analyzing the applicable range of virtual impedance parameters. Specifically, under the constraint of current-limiting conditions, fault scenarios are classified into two categories, with and without equilibrium points, depending on the severity of voltage sag. Then, based on the Lyapunov stability theory, separate virtual impedance design criteria are proposed for these two scenarios, ensuring that the GFM maintains both current-limiting capability and transient stability during fault ride-through while minimizing active power losses. Additionally, the proposed scheme enhances reactive power support capability in the post-fault phase, ensuring compliance with grid code requirements while promoting sustainable grid operation. The proposed strategy is validated through time-domain simulations and hardware experiments. The results demonstrate that the proposed scheme significantly improves the transient stability of GFM and provides a reliable solution for its efficient operation under complex grid conditions. Full article

Grid-forming converters (GFMCs) have emerged as enablers in modern power systems. However, they face the transient stability problem, which hinders them from successful fault ride-through (FRT) and potentially results in the system’s collapse. These problems have drawn increasing attention, leading to a rise in related research. To capture the advancements in the field, this paper reviews studies on the transient stability analysis and enhancement of GFMCs. In particular, the transient stabilities of GFMCs with first- and second-order power control modes are reviewed, and a comprehensive comparison of the two modes is provided. Additionally, this paper classifies the transient stability enhancement methods of GFMCs into six types: active power, reactive power, voltage amplitude, virtual impedance, inertia and damping regulations. Moreover, this paper summarizes the effects and limitations of each method from the perspective of practical application. Based on the analysis, this paper further discusses future research directions for the transient stability of GFMCs. Full article

Sodium benzoate, a common food preservative, has been linked to oxidative stress, inflammation, and potential damage to various organs, including the kidneys. Aged black garlic (ABG) offers significant potential in supporting body health through its powerful antioxidant and anti-inflammatory properties, which can help reduce cellular damage and inflammation and, thus, improve organ functions. The purpose of this investigation is to investigate the ameliorative effect of aged black garlic extract (ABG extract) on the nephrotoxicity and oxidative stress induced by sodium benzoate. A total of thirty-two adult male albino rats were divided randomly into four groups: Group 1: control; Group 2: orally given ABG extract (200 mg/kg bw) daily for 4 weeks; Group 3: administrated orally by sodium benzoate daily for 4 weeks; Group 4: cotreated with both ABG extract and sodium benzoate for 30 days. This included histological examinations, a histochemical demonstration of DNA contents, and an immunohistochemical demonstration of pro-apoptotic protein caspase-3, as well as a biochemical evaluation of renal MDA, CAT, SOD, GPx, and IL-1β levels. Moreover, serum and urinary urea, uric acid, creatinine, sodium, and potassium levels were also determined, as well as serum C-reactive protein. FI (30 days), FER, and BWG% were calculated as well as urinary volume and protein being measured. The findings revealed that ABG extract significantly improved all histopathological and physiological changes (p < 0.05) induced by SB as renal tissue was significantly improved, DNA contents were restored, and capase-3 immunoreactivity was diminished. Additionally, oxidative and inflammatory markers, and renal function parameters, were significantly improved. These results showed that ABG extract possesses significant ameliorative effects against the nephrotoxicity induced by sodium benzoate; this may be mediated by its antioxidant activity. Full article

The issues of low inertia, overvoltage, and wide-frequency oscillations in high-proportion renewable energy systems have become prominent, posing major challenges to renewable energy integration and threatening grid stability. Currently, many wind-rich areas ensure grid safety and stability by reducing wind farm output. To enhance the active power delivery capability of wind farms, this paper proposes a hybrid solution of a small synchronous condenser (SC) and static var generator (SVG) within wind farm stations to optimize reactive power and voltage at the point of grid connection. First, it was analyzed that the low short-circuit ratio (SCR) is a key factor affecting the stable operation of wind farms, and the sub-transient reactance of the SC can increase the SCR. Based on this, a method for configuring the capacity of the SC was developed. Next, simulation models for both the SC and the SVG were established, and their reactive power compensation capabilities were verified. The hybrid control approach combined the advantages of both devices, providing comprehensive voltage support across sub-transient, transient, and steady-state conditions for renewable energy stations. Furthermore, based on a practical 50.5 MW wind farm, which has been operating with a power delivery consistently limited to 60% of its capacity, a simulation model and scenarios were set up. A comparison of the simulation results shows that, with only the SVG in operation, the wind farm is prone to oscillations after a grid fault. However, after adopting the hybrid control of the SC and SVG, the wind farm operates stably. Therefore, installing a small SC within wind farms can effectively address the limitations of voltage stability and a low short-circuit ratio, thereby supporting higher levels of renewable energy integration. Full article