Search Results (615)

The surge in electric vehicles (EVs) in Denmark challenges the country’s residential low-voltage (LV) distribution system. In particular, it increases the demand for home EV charging significantly and possibly overloads the LV grid. This study analyzes the impact of EV charging integration on Denmark’s residential distribution networks. A residential grid comprising 67 households powered by a 630 kVA transformer is studied using DiGSILENT PowerFactory. With the assumption of simultaneous charging of all EVs, the transformer can be heavily loaded up to 147.2%. Thus, a voltage-droop based autonomous control approach is adopted, where the EV charging power is dynamically adjusted based on the point-of-connection voltage of each charger instead of the fixed rated power. This strategy eliminates overloading of the transformers and cables, ensuring they operate within a pre-set limit of 80%. Voltage drops are mitigated within the acceptable safety range of ±10% from normal voltage. These results highlight the effectiveness of the droop control strategy in managing EV charging power. Finally, it exemplifies the benefits of intelligent EV charging systems in Horizon 2020 EU Projects like SERENE and SUSTENANCE. The findings underscore the necessity to integrate smart control mechanisms, consider reinforcing grids, and promote active consumer participation to meet the rising demand for a low-carbon future. Full article

The higher integration of photovoltaic (PV) units is an inevitable component of smart city development. Thanks to smart meter devices that can record the exchange of power between the grid and customers, it is expected that homeowners and businesses will tend to install PV arrays on their rooftops and parking lots to benefit from selling power back to the grid. However, the overvoltage issue resulting from high PV penetration is a major challenge that necessitates the active power curtailment of PV units to ensure power grid stability. Fairness-oriented methods aim to minimize the active power of PV units as much as possible, adopting a fairer approach, and then address the PV owner’s satisfaction with fair profit and loss. Maintaining voltage within a limited standard range under very low load conditions while prioritizing PV inverters’ participation in reactive power contribution and attempting to ensure fairer curtailment of active power presents challenges to existing control design approaches. This paper presents twelve new volt–watt curve design methods to achieve these goals and address the challenges. The methods yield polynomial curves, piecewise linear curves, and single linear curves. A unique voltage sensitivity value for each PV inverter is used to determine the control region area and the slope of the curve at the starting point in certain instances. The effectiveness of the proposed methods is discussed by evaluating their capabilities on the 37-bus IEEE system. Full article

Variable Speed AC-excited Pumped Storage Units (VSACPSUs) demonstrate advantages in flexibility, high efficiency, and fast response, and they play a crucial regulatory role in power systems with increasing renewable energy penetration. Typically connected to weak grids, conventional low-voltage ride-through (LVRT) control methods for these units suffer from single control objectives, poor adaptability, and neglect of electromechanical coupling characteristics. To address these limitations, this paper proposes a multi-objective optimization strategy considering electromechanical coupling under a grid voltage fault. Firstly, a positive/negative-sequence mathematical model of doubly-fed machines is established. Based on stator winding power expressions, the operational characteristics under a grid fault are analyzed, including stator current imbalance as well as oscillation mechanisms of active power, reactive power, and electromagnetic torque. Considering the differences in rotor current references under different control objectives, a unified rotor current reference expression is constructed by introducing a time-varying weighting factor according to expression characteristics and electromechanical coupling properties. The weighting factor can be dynamically adjusted based on operating conditions and grid requirements using turbine input power, grid current unbalance, and voltage dip depth as key indicators to achieve adaptive control optimization. Finally, a multi-objective optimization model incorporating coupling characteristics and operational requirements is developed. Compared with conventional methods, the proposed strategy demonstrates enhanced adaptability and significantly improved low-voltage ride-through performance. Simulation results verify its effectiveness. Full article

This article introduces a high-efficiency, high-voltage-ratio bidirectional DC–DC converter based on the Dual-Active-Bridge (DAB) topology, specifically designed for applications involving low-voltage, high-capacity cells. Addressing the critical challenge of enhancing bidirectional power transfer efficiency under ultra-high step-up ratios, which is essential for integrating renewable energy sources and battery storage systems into modern power grids, an optimized control strategy is proposed. This strategy focuses on refining switching patterns and minimizing conduction losses to improve overall system efficiency. Theoretical analysis revealed significant enhancements in efficiency across various operating conditions. Simulation results further confirmed that the converter achieved exceptional performance in terms of efficiency at extremely high voltage conversion ratios, showcasing full-range Zero-Voltage Switching (ZVS) capabilities and reduced circulating reactive power. Specifically, the proposed method reduced circulating reactive power by up to 22.4% compared to conventional fixed-frequency control strategies, while achieving over 35% overload capability. These advancements reinforce the role of DAB as a key topology for next-generation high-performance power conversion systems, facilitating more efficient integration of renewable energy and energy storage solutions, and thereby contributing to the stability and sustainability of contemporary energy systems. Full article

The present study investigates the control strategy of a novel doubled-fed induction generator (DFIG) with a series grid-side converter (SGSC) during grid faults. The rotor-side inverter is subject to a control strategy derived from the Model Predictive Current Control (MPCC) theory, which is implemented during periods of fault occurrence; for the series grid-side converter, the positive and negative sequence component control is implemented during both steady state and fault periods to enhance system stability and performance. The proposed coordinated control strategy is implemented on a doubly fed turbine with SGSC, while taking into account different degrees of symmetric and asymmetric faults to further evaluate the efficacy of the proposed method. The results of the simulations demonstrate the efficacy of the model-predictive current control scheme applied to the rotor-side converter under conditions of asymmetric faults. This enables the suppression of a range of phenomena, including rotor overcurrent, stator overcurrent, and overvoltage, electromagnetic torque ripple, and DC bus voltage during low-voltage ride-through (LVRT), among others. The present study confirms the viability of implementing positive and negative sequences of voltage separation control in the SGSC during both grid faults and steady state. This approach is expected to minimize the switching of SGSC control strategies and thereby reduce output power fluctuations. The Rotor Side Converter (RSC) and SGSC can perform coordinated control during faults, and the proposed method is able to improve low-voltage ride-through performance compared to existing methods, thereby preventing damage to the converter under multiple fault conditions. Full article

A grid-connected converter is the interface between renewable energy power generation systems, such as solar power generation, wind power, hydropower, etc., and the power grid, responsible for the stable and efficient transmission of electric energy generated by renewable energy power generation systems to the grid. In order to realize local access for distributed photovoltaic power generation devices and energy storage devices, a composite three-port converter has the advantages of small size, low cost and high power density compared with a combined three-port converter. In view of the current problems of the existing compound three-port (AC/DC/DC) converters, such as DC and AC circulating current in current composite three-port converters and the harmonic control problem, the proposed compound three-port topology consists of a full-bridge inverter with six switching tubes, a zigzag transformer, two sets of filter inductors and two filter capacitors. Among them, the power frequency transformer adopts the zigzag connection method, which can effectively restrain the AC circulation and eliminate the DC magnetic flux of the iron core while introducing the third port. Firstly, the principle of AC/DC and DC/DC power conversion in the composite three-port topology is analyzed, which has higher efficiency than other topologies. Secondly, the topology control strategy is analyzed, and a two-loop hybrid current control method with improved current loop is proposed. When the DC-side voltage fluctuates, the DC offset of the battery can effectively improve the stability of the network side. Through the MATLAB/Simulink simulation experiment platform, the high efficiency of energy conversion and stable grid-connected operation characteristics are verified. Finally, the experiment of integrating into the power grid was carried out. Experiments were used to verify the effectiveness and feasibility of the proposed topology and strategy. The experimental results show that Total Harmonic Distortion (THD) can be controlled below 3%. Full article

The charging station (CS) is generally directly off-grid under a grid fault, which has become a key technical bottleneck that restricts the sustainable development of new energy transportation systems. During a grid fault, the CS under the vehicle-to-grid (V2G) mode experiences a reduction in active power due to the current limitation of the voltage source converter (VSC), which may cause the DC voltage to exceed its limitations under unbalanced power. The effect of the active and reactive power of CS in low- and medium-voltage distribution networks on supporting the PCC voltage under the limitation of DC voltage and VSC current has not been analyzed, and a control method for PCC voltage support for CS has not been established. Therefore, a power boundary that avoids the DC overvoltage and AC overcurrent of the CS is defined. A power feasible region for the CS considering fault duration is established. The characteristic that the power feasible region shrinks with the increase in duration is found, and a calculation method for the critical clearing time of a fault to avoid DC overvoltage is proposed. The relationship between PCC voltage and power injected by the CS is analyzed. The property that the control point of maximum voltage support lies at the boundary of the power feasible region is revealed. A control method of PCC voltage support that considers the limitation of DC voltage and VSC current for the CS is proposed. Simulation verification shows that the support capability of CS for PCC voltage during a fault is significantly enhanced by the proposed method while securing the DC voltage. Full article

In the context of global sustainability goals and the integration of renewable energy sources, the efficient and reliable performance of medium- and high-voltage power equipment is critical. This paper presents a high-capacity testing system based on power supply, which significantly enhances the sustainability of power systems by addressing the challenges of low testing efficiency, poor reproducibility, and safety hazards in traditional methods. By proposing a standardized test circuit configuration and an automated monitoring and control system, this study aims to improve the efficiency, safety, and consistency of testing, thereby supporting the reliable operation and integration of renewable energy sources into power grids. The system achieves complete automation in test parameter selection, circuit connection, and data acquisition, reducing human intervention and ensuring the accuracy of test data. Through simulations and physical tests, the feasibility and accuracy of the standardized test circuit design method have been verified. These improvements contribute to sustainable development by reducing resource consumption and environmental impact, and enhancing the reliability and stability of power supply. This research provides a technical foundation for the sustainable operation of power systems, supporting global efforts to achieve carbon neutrality and energy transitions. Full article

To address the issues of cumulative plastic deformation and low-cycle fatigue cracking in ultra-high voltage (UHV) disc spring hydraulic circuit breakers under long-term cyclic high-pressure loads, which lead to internal structural changes and affect closing time stability and phase-controlled closing accuracy, this paper proposes a closing time prediction model considering the low-cycle fatigue of the operating mechanism. First, a Simulink-based simulation model of the 550 kV disc spring hydraulic operating mechanism transmission system was developed to analyze the influence of structural parameter variations on closing time under no-load conditions. Then, an objective function for judging action time stability was constructed, and the stability and influence weights of each structural parameter were calculated under different mechanical dispersion requirements using a combination of adaptive surrogate models and directional importance sampling. Results show that critical parameters such as working cylinder inner diameter, working cylinder stroke, main valve stroke, and working cylinder rod diameter significantly affect closing time, contributing approximately 25%, 20%, 15%, and 10%, respectively. Finally, a dynamic-weighted closing time prediction model was designed based on different phase-controlled accuracy requirements. Compared with no-load closing tests, under mechanical dispersion conditions of ±1 ms, ±1.5 ms, and ±2 ms, the optimized model reduced maximum deviations by 12.8%, 20.4%, and 23.3%, and narrowed fluctuation ranges by 37%, 38.3%, and 38.6%, respectively, significantly improving prediction accuracy. This work is supported by the Science and Technology Project of China Southern Power Grid (No.CGYKJXM20220346). Full article

The insufficient durability of solar energy systems is an important problem in low-voltage situations in the electrical grid. This problem can cause PV systems to become difficult to operate during periods of low voltage and may disconnect PV systems from electrical grids. In this study, a hybrid protection system combining a DC chopper and a capacitive bridge fault current limiter (CBFCL) and based on a machine learning (ML) approach is proposed as a protection strategy to improve the low voltage ride-through (LVRT) capability of a grid-connected PV power plant (PVPP) system. To forecast the best control parameters using real time, including both the fault and normal operation conditions of the grid-connected PVPP system, the ML approach is trained on historical data. Among 20 classifier algorithms, the Coarse Tree classifier and Medium Gaussian SVM classifier have the best accuracy and F1-score for the DC chopper and DC chopper + CBFCL protection systems. The Medium Gaussian SVM classifier has the highest accuracy (98.37%) and F1-score (99.17%) for the DC chopper and CBFCL protection method among the 20 classifier methods. In comparison to another protection system, the simulation results show that a proposed hybrid protection system using SVM offers optimum protection for the grid-connected PVPP system. Full article

Power network codes necessitate that any renewable source aligns with LVRT rules and assists in voltage restoration during voltage dips. This paper focuses on increasing the low-voltage ride through capability of a doubly fed induction generator-based wind turbine. Three different controllers are discussed in this article. The first is based on robust super-twisting sliding mode control, which is a recent robust control technique. The second uses a new metaheuristic optimizer called the Arctic Puffin optimizer (APO), and the third relies on the traditional PI controller. The grid-side converter sustains the potential of the DC converter link and the regulation of both the active and reactive power supplied to the power grid via three controllers. The rotor-side converter regulates the generator’s electromagnetic torque via two controllers. Doubly fed induction generator control is a challenging task as the two converters have five controllers, and it is vital to specify the ideal parameters for each controller. In the case of super-twisting sliding mode control, the APO is utilized to obtain the sliding surfaces needed for the five controllers. Moreover, the APO is exploited to obtain the optimal constants of the suggested PI regulators. The simulation results prove the excellent performance of both super-twisting- and APO-based controllers, with better performance demonstrated with super-twisting sliding mode control, which demonstrates excellent transient performance with the least overshoot among the three controllers. The super-twisting-based controller has a distinct feature, as it has good performance with parameter variations. Full article

The LLC converter achieves the highest efficiency in resonant operation. Conventionally, the input DC-link voltage is controlled to operate the LLC converter at resonance for the given operating point. However, the DC-link capacitor voltage shows a low-frequency voltage ripple (typically the second harmonic of grid frequency) in cascaded converters so that the LLC has to adapt its switching frequency within the grid period. Conventionally, the LLC converter operates 50% of the time above the resonant frequency of 40 kHz and 50% below resonance. Both operating conditions cause additional losses. However, experimental measurements indicate that the below-resonance operation causes significantly higher losses than above-resonance operation due to much higher primary and secondary transformer currents. It is better to increase the DC-link voltage by 30% of the peak-to-peak low-frequency voltage ripple to mostly avoid below-resonance operation (i.e., from 650 V to 680 V in this case). With the proposed control, the LLC converter operates about 75% of time over resonance and only 25% of time below resonance. The overall efficiency increases from 97.66% to 97.7% for the average operating point with an 80% load current. This corresponds to a 2% total loss reduction. Finally, the peak resonance capacitor voltage decreases from 910 V to 790 V (−13%). Full article

The aim of this paper is to develop a self-adaptive control methodology capable of optimizing in real-time the operation of PV-powered microgrids by dynamically managing both the output powers of battery energy storage systems (BESSs) and power exchanges with the utility grid. Control actions are evaluated by solving a constrained multi-objective optimization problem that integrates the optimal state-of-charge (SoC) management of BESSs within a broader economic dispatch framework. In this way, the SoC is continuously optimized alongside other economic objectives, such as minimizing operating costs and maximizing revenues from energy sales to the grid, while maintaining the microgrid’s energy balance. This ensures that BESSs operate efficiently within their optimal ranges, preventing premature depletion or overload and thereby safeguarding overall microgrid performance. To enable real-time adaptability, the methodology employs a Lyapunov-based optimization algorithm combined with a sensitivity analysis, ensuring rapid convergence to optimal solutions, even under rapidly changing conditions. Computer simulations performed on a low-voltage PV-BESS-based microgrid under different operating conditions confirm the effectiveness of the proposed methodology in enhancing real-time economic performance, operational efficiency, and microgrid reliability. Full article

The transformation of low-voltage distribution grids toward decentralized, user-centric models has increased the need for advanced metering infrastructures capable of ensuring both visibility and control. This paper presents a self-diagnostic advanced metering solution based on power-line communication deployed in a segment of the Spanish distribution network. The proposed infrastructure leverages the existing power network as a shared-media communication channel, reducing capital expenditures while enhancing system observability. A methodology is introduced for integrating smart metering data with topological and operational analytics to improve network monitoring and energy management. This study details the proposed metering infrastructure, highlighting its role in enhancing distribution network resilience through asynchronous energy measurements, event-driven analytics, and dynamic grid management strategies. The self-diagnostic module enables the detection of non-technical losses, identification of congested areas, and monitoring of network assets. Furthermore, this paper discusses the regulatory and technological challenges associated with scaling metering solutions, particularly in the context of increasing distributed energy resource penetration and evolving European Union regulatory frameworks. The findings demonstrate that a well-integrated advanced metering infrastructure system significantly improves distribution network efficiency, enabling proactive congestion detection and advanced load management techniques. However, this study also emphasizes the limitations of PLC in high-noise environments and proposes enhancements such as hybrid communication approaches to improve reliability and real-time performance. The insights provided contribute to the ongoing evolution of metering infrastructure technologies, offering a path toward more efficient and resource-optimized smart grids. Full article

The full-size converter-based variable-speed pumped storage unit (FSC-VSPSU) is widely regarded as the future direction of variable-speed pumped storage technology due to its wide operating range and fast switching capabilities. However, previous studies often assume a constant DC-link voltage, which is not applicable to FSC-VSPSU, as fluctuations in grid-side active power can affect the DC-link voltage, thereby threatening system stability. To address this issue, this article proposes a crowbar-less low-voltage ride-through (LVRT) control strategy for FSC-VSPSU. The proposed approach effectively mitigates the elevated system costs inherent in conventional crowbar circuit implementations by harnessing the significant energy storage potential of the rotor to absorb power imbalances during LVRT. Furthermore, a novel parameter design methodology for the DC-link voltage controller is introduced to guarantee that the DC-link voltage consistently remains within the allowable threshold range during LVRT. The effectiveness of the proposed control strategy and the accuracy of the parameter design methodology have been validated through MATLAB(R2023a)/Simulink. Full article