Search Results (447)

After high-penetration distributed photovoltaics (DPVs) are integrated into AC/DC hybrid distribution networks, stochastic source-load fluctuations, AC-DC coupling, and heterogeneous response characteristics of voltage-regulation devices jointly aggravate voltage violations and rapid voltage fluctuations. This paper proposes a spatio-temporal coordinated hierarchical distributed voltage-optimization framework. Spatially, the AC and DC regions are first separated according to voltage-source-converter (VSC) interfaces, and an electrical-coupling-aware modularity index is then constructed for the AC network by combining normalized bidirectional reactive-power-voltage sensitivities, available fast reactive-power support, and intra-cluster compactness. Temporally, an 1 h day-ahead model coordinates slow, discrete, or intertemporally coupled resources, including on-load tap changers, capacitor banks, energy storage systems, and flexible loads, while a 15 min intra-day rolling model coordinates DPV inverters, static var generators, and VSCs. The synchronous alternating direction method of multipliers (SADMM) is tailored to the resulting AC clusters, DC subnetworks, and VSC boundary variables to enable synchronous regional solution and boundary-consensus coordination. Studies on a modified 50-node AC/DC test system show that, under the investigated operating conditions, the framework mitigates voltage violations and intra-day fluctuations while obtaining favorable network-loss, DPV-curtailment, and solution-time performance. Full article

The development of flexible thin-film transistors (TFTs) is crucial for the advancement of wearable electronics, bendable displays, and the Internet of Things (IoT). A key challenge in this field is the fabrication of high-performance gate dielectric layers that combine excellent electrical properties with mechanical robustness and low-temperature processability. In this work, we report flexible TFTs based on CdS and hybrid PVPh/PMMA-ZrO₂ as semiconductor and gate dielectric layers, respectively. The hybrid gate dielectric films were deposited on flexible PEN substrates via a facile spin-coating process at a low temperature of 150 °C. On the other hand, CdS layers were deposited through photo-assisted chemical bath deposition at room temperature. Both correspond to deposition methods in solutions, fulfilling the low-temperature condition. The electrical properties of the hybrid gate dielectric layers were characterized by using metal–insulator–metal (MIM) capacitors, which presented excellent insulating properties, low leakage current density and suitable gate capacitance for transistor operation. From the analysis of the electrical response of flexible TFTs, reliable device characteristics and key electrical metrics were extracted. Furthermore, the MIM and TFTs were tested under mechanical bending, demonstrating stable performance. The MIM capacitors showed outstanding mechanical stability, retaining low leakage and stable capacitance after 1000 bending cycles, with changes attributed to reversible interfacial charge redistribution rather than bulk degradation. Meanwhile the TFTs kept full electrical functionality under repeated bending and tight bending radii (down to 0.6 cm), demonstrating reasonable mechanical durability. These results validate the solution-processed PVPh/PMMA-ZrO₂/CdS system as a promising, mechanically robust platform for flexible electronics. Full article

Embedded Modular Multilevel Converter-Based Multi-Terminal Direct Current (MMC-MTDC) systems have become an important solution for enhancing transmission capacity and operational flexibility in urban hybrid AC/DC power grids. However, the coexistence of Grid-Following (GFL) and Grid-Forming (GFM) MMC stations introduces complex dynamic interactions through both AC and DC networks. Existing small-signal stability studies often neglect MMC internal dynamics, such as submodule capacitor voltage fluctuations and circulating current-related states, or simplify the AC network as an ideal voltage source, which may lead to inaccurate stability assessment and limited control parameter optimization performance. To address these issues, this paper proposes a coordinated small-signal stability enhancement strategy for an embedded heterogeneous MMC-MTDC system considering AC/DC bilateral coupling. First, a system-level full-order small-signal state-space model is established by incorporating the internal dynamics of both GFL-MMC and GFM-MMC stations, non-ideal AC networks, and DC transmission links. Then, eigenvalue analysis and participation factor-based sensitivity evaluation are performed to identify weakly damped oscillation modes and screen the key variables and control parameters associated with dominant oscillations. Furthermore, a quadratic performance index is constructed by weighting the sensitivities of key control parameters, and particle swarm optimization is employed to obtain coordinated optimized parameters for heterogeneous MMC stations. Comparative case studies and PSCAD/EMTDC time-domain simulations verify the effectiveness of the proposed strategy under different scenarios. The quantitative active-power indices show that, compared with the unoptimized parameters, Strategy 2 reduces the settling time by 49.1% in the power step response, suppresses the power step overshoot from 6.4% to 0%, shortens the settling time by 53.8% under grid-strength variation, and reduces the active-power peak and settling time by 28.0% and 74.8%, respectively, under the fault ride-through scenario. Full article

This paper proposes a dynamic intelligent method for voltage violation management in high-renewable-penetration distribution networks. The method employs a dual-agent architecture: DERMS_Agent coordinates task scheduling, data management, and computational resource allocation, while Solution_Agent performs three-phase unbalanced power flow calculation and MIQP-based voltage violation joint optimization. Four key technical contributions are presented. (i) An asymmetric nodal admittance matrix is developed to incorporate transformer tap-phase-shift and capacitor branches within a unified formulation. (ii) Five categories of analytical sensitivities are systematically derived, covering transformer tap, phase shift, and capacitor compensation effects for both voltage regulation and harmonic suppression. (iii) A three-parameter MIQP joint optimization model is constructed with voltage deviation minimization as the objective and three-phase unbalance and resonance avoidance as constraints. (iv) A two-stage hybrid solution strategy combining Ipopt continuous relaxation with Gurobi neighborhood enumeration is designed to achieve real-time solvability. Validation on a real 10 kV feeder with 91 transformer areas over 768 time sections (8 days) demonstrates a 95.6% voltage violation resolution rate within the first three polling cycles and an average single-section solution time of 0.83 s, satisfying the real-time requirements of 15 min operational control cycles. Full article

Increasing demand in radial distribution systems intensifies active power losses, voltage drops, and power factor deterioration, leading to reduced network efficiency and increased annual operating costs. Shunt capacitor banks can mitigate these effects by supplying reactive power locally; however, determining their locations and discrete ratings constitutes a nonlinear optimization problem governed by the radial network structure, nonlinear load flow equations, reactive power compensation limits, power factor requirements, and commercially available capacitor sizes. This paper presents a hybrid methodology that combines Loss Sensitivity Factors (LSFs) for candidate-bus screening with the Flower Pollination Algorithm (FPA) for discrete capacitor sizing. The LSF stage ranks buses according to the local sensitivity of active power losses to reactive power variations and applies a voltage-based screening criterion to reduce the number of decision variables. The FPA subsequently explores the reduced search space through global and local pollination, while a projection-and-repair procedure maps every continuous trial vector onto admissible capacitor ratings in 50 kVAr increments. The objective function minimizes the annual cost of active power losses, capacitor bank installation, and installed reactive power capacity. The method is evaluated on the IEEE 33-bus, 69-bus, and 141-bus radial distribution systems. For the IEEE 33-bus system, active power losses decrease from 202.7 to 133.5 kW and the power factor increases from 0.8502 to 0.9827. For the IEEE 69-bus system, losses decrease from 225.0 to 145.9 kW and the power factor increases from 0.8159 to 0.9705. For the IEEE 141-bus system, losses decrease from 632.7 to 453.7 kW and the power factor increases from 0.8500 to 0.9876. The corresponding cost savings in terms of annual loss are USD 36,371.52, USD 41,574.96, and USD 94,082.40. The compensation configurations improve the voltage profiles in all three systems; nevertheless, the resulting minimum voltages of 0.939, 0.932, and 0.948 p.u. remain below the 0.95 p.u. lower reference because voltage deviation is evaluated as a performance indicator rather than enforced through a hard constraint or penalty term. The results demonstrate that the proposed LSF–FPA framework provides effective loss reduction, power factor correction, and voltage profile improvement, while the economic comparison shows that the solution with the greatest loss reduction benefit does not necessarily produce the lowest total annual cost. Full article

Hybrid systems integrating grid-following (GFL) and grid-forming (GFM) inverters are increasingly deployed in renewable-energy-dominated power systems. However, impedance coupling between the two inverter types may induce low-frequency oscillations and high-frequency resonances, particularly under weak-grid conditions and varying power injections. This paper clarifies the stability mechanism of a hybrid GFL/GFM inverter system and develops a frequency-segmented active damping strategy. Small-signal impedance models are first derived for the GFL inverter, the GFM inverter, and the overall hybrid system, incorporating the control loops, digital delay, LC filters, interconnection branch impedances, and external grid impedance. Impedance decomposition, Bode plots, and Nyquist criteria are then employed to quantify the influence of power operating points and grid strength on system stability. The results indicate that increasing the GFL inverter output power weakens the stability margins in both low- and high-frequency ranges, whereas variations in the GFM inverter output power provide only limited impedance reshaping in the targeted oscillation bands. On this basis, a low-frequency damping loop is designed on the GFM inverter side, while a high-frequency damping loop based on capacitor-current feedback is implemented on the GFL inverter side. Simulation results confirm that the proposed strategy suppresses low-frequency oscillations and high-frequency harmonic components, maintains stable operation in the hybrid system under high GFL power injection, and reduces the THD of the PCC current from 14.52% to 0.62%. Full article

High-efficiency and high-power-density point-of-load (POL) converters are critical for data center power supplies. Although hybrid resonant switched-capacitor (ReSC) converters can substantially reduce the volume of passive components, they often suffer from severe efficiency degradation when the switching frequency mismatches the resonant frequency due to component tolerances. To address this challenge, this paper proposes a parameter-mismatch insensitive cascaded POL converter by integrating a BUCK stage with a cascaded voltage divider (CVD). By introducing an auxiliary resonant branch, a multi-resonant operation is established, enabling the residual inductor energy caused by component variations to be transferred to the output during the dead time with virtually eliminated hard-switching losses. Consequently, precise matching between the switching frequency and the resonant frequency is no longer mandatory. A 12 V-to-1 V/30 A GaN-based prototype was developed to validate the theoretical analysis. Experimental results demonstrate that the proposed converter maintains high efficiency under a ±10% component variation and achieves robust voltage regulation and fast transient response, making it highly suitable for high-current data center applications. Full article

This paper proposes a new hybrid switched inductor and switched capacitor (HSISC) buck–boost DC–DC converter. For the duty ratio above 28%, the proposed converter operates as a boost converter; otherwise, it acts as a buck converter. Compared with conventional buck–boost converters, incorporating the hybrid switched inductor and switched capacitor (HSISC), the network yields a substantial voltage gain at lower duty ratios. Being a non-isolated topology, high-frequency transformers and the associated issues are absent. Additionally, the proposed topology has the merits of continuous input current, making it suitable for renewable energy integration and vehicle-to-grid (V2G) applications, a wide range of duty ratio for boost operation, and ease of control as there are only two modes of operation with switches operating in a complementary manner. Operational analysis for the two modes, necessary mathematical derivations for component design, and a steady-state analysis of the converter are reported. The experimental findings for the converter, which were conducted at a duty ratio of 0.05 to 0.5 at a switching frequency of 10 kHz, are reported. The presented results provide proof-of-concept validation based on analytical and simulation studies, demonstrating the feasibility and operational characteristics of the proposed converter. Full article

The increasing penetration of renewable energy sources and converter-interfaced loads has intensified the need for fast and reliable grid-support services. Although electric vehicle (EV) battery chargers have emerged as promising resources for Vehicle-to-Grid (V2G) applications, existing solutions typically focus on individual services such as virtual inertia or frequency regulation, while limited attention has been given to the coordinated provision of multiple ancillary services within a unified framework. Furthermore, the use of batteries alone for fast frequency support may accelerate battery degradation due to frequent high-power transients. To address these challenges, this paper proposes a hybrid energy storage-based EV battery charger architecture and a coordinated multi-timescale control strategy capable of simultaneously providing virtual inertia support, long-term frequency regulation, reactive power compensation, and harmonic mitigation. The proposed approach utilizes a DC-link capacitor to deliver fast inertial response while the battery supplies sustained frequency support, thereby reducing battery stress and improving energy management efficiency. An enhanced frequency estimation method based on a phase-locked loop combined with a low-pass filter is also introduced to improve dynamic performance. Simulation results demonstrate the effectiveness of the proposed strategy under various grid disturbances. The system achieves an equivalent virtual inertia constant of approximately 1.85 s and delivers up to 786 W of transient inertial support within 80 ms during frequency events. The enhanced frequency estimation method significantly reduces transient overshoot, while harmonic compensation limits the grid current and voltage total harmonic distortion to 1.50% and 3.23%, respectively. In addition, the controller provides up to 400 VAR of reactive power support during voltage disturbances while maintaining stable battery operation. These results demonstrate that the proposed EV battery charger can function as a multifunctional grid-support resource, enhancing frequency stability, voltage regulation, power quality, and overall V2G capability in future smart grids. Full article

Two semiflexible piezoelectric composite plate structures were developed, incorporating 1 × 9 and 2 × 9 arrays of PZT elements mounted on brass discs and mechanically secured by pop rivets within a thin plastic foil spacer positioned between two copper-clad PCB layers. This configuration provides reliable electrical contact, adequate mechanical compliance, and efficient conversion of mechanical vibration energy into electrical energy. In addition, a multifunctional thermoelectric device was realized, consisting of four cubic modules arranged around a rectangular tube and enabling both handheld operation and coupling to hot or cold surfaces. Each cube is equipped with optimized finned heat sinks and integrates four thermoelectric elements on each face. Experimental results show that each cube generates approximately 6 mW, when handheld and with icy water injected into the central tube, demonstrating its suitability as a compact and versatile thermal energy harvester. Under low-light conditions, a solar panel is supplemented by this hybrid piezoelectric–thermoelectric energy harvesting system that combines the output of a piezoelectric composite plate with the dual outputs of a thermoelectric device using an electronically isolated summing block to ensure source decoupling. Energy storage and management are implemented using a capacitor buffer for the piezoelectric device, two voltage boosters for the thermoelectric outputs, and an automatic ultra-low-power pulse width modulation buck regulator for charging supercapacitors at 5 V. Full article

Power system operators globally face an ongoing challenge of maintaining a balance between electricity supply and load demand. This is a task which has been made increasingly complex by variability inherent in both generation sources and consumer loads. The balancing act is resource intensive, costly, and is critical for preventing frequency deviations that could destabilize the entire network, which can lead to blackouts and equipment damage. The intermittent nature caused by unpredictable wind speeds adds more challenges by introducing rapid fluctuations that system operators may struggle to mitigate. Energy storage systems (ESSs) have shown potential in addressing these challenges by offering flexible buffering capabilities to smooth out imbalances and enhance frequency stability. In this research, the impact of fluctuating wind speeds on power system frequency stability was analyzed. Subsequently, a hybrid energy storage system that integrates batteries for sustained energy discharge and super capacitors for rapid high-power responses was added. This enabled the system to handle mismatches effectively. The results show a 66% reduction in frequency deviations during wind fluctuations compared to baseline scenarios without storage. This improvement facilitates improved integration of renewable energy sources by allowing higher penetration levels without compromising stability. Full article

In hybrid-series-converter-based LCC-HVDC systems, controllable capacitor modules can provide additional voltage–time area during commutation, thereby improving inverter-side fault tolerance under AC faults. However, their switching behavior makes the commutation path impedance state-dependent, while most existing commutation-failure prediction methods still rely on fixed-reactance assumptions. To address this problem, this paper proposes a reactance-corrected predictive control and coordinated switching method. First, a capacitor switching coefficient is introduced to describe the insertion state of the controllable capacitor modules, and an equivalent commutation reactance of the HSC valve arm is derived. Then, the corrected reactance is incorporated into an extinction-angle margin index and an energy-margin index to quantify the influence of reactance variation on commutation capability. A segmented firing-angle controller with smooth compensation is further designed, and energy-margin feedback is coordinated with capacitor insertion control. PSCAD/EMTDC simulations verify that the proposed method reduces prediction error, provides a prediction lead time of 0.7–4.5 ms, and improves fault ride-through capability. Full article

The increasing global demand for high-performance, reliable, and sustainable energy storage systems has accelerated the development of supercapacitors as technologies capable of bridging the performance gap between conventional capacitors and batteries. Supercapacitors combine rapid charge–discharge capability, high power density, and exceptional cycle life through charge storage mechanisms based on ion adsorption and fast surface redox reactions at the electrode–electrolyte interface. This review examines the fundamental operating principles, charge storage mechanisms, electrode materials, mechanical and functional properties, fabrication methods, and engineering applications of modern supercapacitors. Carbon-based materials, metal oxides, conducting polymers, MXenes, sulfides, nitrides, borides, and emerging hybrid systems are critically compared in terms of capacitance, energy density, cycling stability, and mechanical robustness. Additionally, recent advances in scalable manufacturing approaches, including thin-film deposition and printing technologies, are discussed alongside key challenges such as limited energy density, interfacial instability, mechanical degradation, electrolyte compatibility, and large-scale processing. By consolidating recent developments across materials science, electrochemistry, and device engineering, this review provides insight into future directions for next-generation high-performance supercapacitor technologies. Full article

Some previous studies argue that under the conditions of a double line to ground fault at the point of common coupling at the inverter end, the AC grid voltage of phases A and B will decrease along with the same level while the phase C will maintain at a stable steady state and this will lead to an excess increase in the voltage level of the high voltage direct current (HVDC) link. Presented in this paper is a model that comprises the hybrid multiterminal line commutated converters and the voltage source converter HVDC system. This model was mathematically modelled and implemented on Matlab/Simulink software in order to investigate the fault behavior, with a particular emphasis on double line to ground fault at different fault resistances. The system under study consists of a fault switch timer, photovoltaic solar array, wind energy conversion system, inverter control for the voltage source converter, Inductor–capacitor–inductor (LCL) filter and PI section line. The findings of this study indicated that during the double line to ground fault at varying fault resistances, the AC grid voltage in phase A will experience a more pronounced decrease compared to phase B. In contrast, phase C will exhibit only a slight reduction in voltage at the inverter end. Similarly, at the inverter end of the hybrid system, it was observed that the AC grid currents for the affected phases, specifically phases A and B, will experience an increase. It is further discovered that phase C will maintain relatively stable condition without increasing or decreasing during a double line to ground fault event. In addition, it is noted that the HVDC link voltage will decrease while the HVDC link current will increase depending on any fault resistance values. Thus, the inferences as a result of this study are presented in this paper. Full article

To address the insufficient frequency-support capability, the difficulty of multi-terminal power coordination, and the constraints on DC-voltage fluctuations in flexible DC transmission systems under weak-grid interconnection, this paper conducts a simulation-based control strategy study. First, based on the coupling relationship between AC frequency and DC voltage, an inertia-enhanced grid-forming/VSG control method is proposed, enabling converter stations to use DC-link capacitor energy to provide transient frequency support during the initial stage of a disturbance. Second, for multi-terminal flexible DC systems, an adaptive U-P-f dual-droop distributed control strategy is designed to coordinate unbalanced power sharing among multiple converter stations and to limit the DC-voltage deviation generated during frequency support. In this paper, a hybrid half-bridge/full-bridge MMC is adopted as a fixed-converter simulation platform, rather than being treated as an object of systematic topology optimization. Finally, a four-terminal MMC-HVDC simulation model is established in MATLAB/Simulink, and the proposed control strategy is evaluated under weak-grid step-load disturbances, different short-circuit-ratio conditions, and continuous pseudo-random load disturbance scenarios. Simulation results show that, under the tested operating conditions, the proposed method can reduce the maximum frequency deviation, suppress DC-voltage fluctuations, and improve the power-sharing process among multi-terminal converter stations compared with conventional VSG control and fixed-droop control. Full article