Search Results (93)

The high rate of photovoltaic integration poses significant challenges in terms of violations of voltage limits in power grids. Additionally, the operational behavior of PV systems under fault conditions requires thorough investigation in receiving-end grids. This paper analyzes the dynamic coupling characteristics between reactive power and transient voltage in a receiving-end grid with high PV penetration and multiple HVDC infeeds, considering typical AC and DC fault scenarios. Voltage adaptability issues in PV generation systems are also examined. Through an enhanced sensitivity analysis method, the suppression capabilities of transient voltage peaks are quantified in the control parameters of low-voltage ride-through (LVRT) and high-voltage ride-through (HVRT) photovoltaic inverters. On this basis, a hierarchical optimization strategy for PV inverter control parameters is proposed to mitigate post-fault transient voltage peaks and improve the transient voltage response both during and after faults. The feasibility of the proposed method has been verified through simulation on a revised 10-generator 39-bus power system. Following optimization, the transient voltage peak is reduced from 1.263 to 1.098. This validation offers support for the reliable grid connection of the Henan Power Grid. In the events of the N-2 fault at 500 kV and Tian-zhong HVDC monopolar block fault, the post-fault voltage at each node remains below 1.1 p.u. This serves as evidence of a significant enhancement in transient voltage stability within the Henan Power Grid, demonstrating effective improvements in power supply reliability and operational performance. Full article

The reliable joining of dissimilar stainless steel and carbon steel remains a critical challenge in Metal Inert Gas (MIG) welding due to complex thermal–metallurgical interactions and the formation of brittle phases at the weld interface. In this study, a Taguchi-based design of experiments was employed to systematically optimize MIG welding parameters for SUS201/S20C dissimilar joints using a SUS201 filler wire, with particular attention to the welding current, voltage, travel speed, and electrode stick-out. The welding process was performed using an automatic welding robot. Tensile specimens were tested on a universal testing machine. Microstructural analysis was performed using a metallurgical microscope. The microstructure reveals that the development of the carbon side’s large ferrite and the stainless steel side’s δ-ferrite both significantly degrade joint quality. Among all process parameters, electrode stick-out is identified as the most influential parameter governing both tensile and bending performance, highlighting a critical process sensitivity that has received limited attention in prior studies. Optimized parameter combinations are required to maximize tensile and flexural responses. The highest tensile strength is 450.96 MPa. These findings advance the understanding of parameter–microstructure–property relationships in dissimilar MIG welding. Future work applying numerical welding simulations and advanced evaluation techniques is recommended. Full article

The ultra-high frequency (UHF)-based partial discharge (PD) detection technology for gas-insulated switchgear (GIS) has achieved large-scale applications due to its high sensitivity and real-time monitoring capabilities. However, long-term service-induced antenna corrosion in UHF sensors may lead to degraded reception characteristics. To ensure the credibility of monitoring data, on-site sensor calibration under ambient noise conditions is required. This study first analyzes the time–frequency domain characteristics of white noise received by UHF sensors in GIS environments. Leveraging the transceiver reciprocity principle of sensors, a noise reconstruction method based on external sensors is proposed to simulate on-site white noise. Subsequently, CST simulation models are established for both standard and degraded sensors, quantifying the impact of factors like antenna corrosion on performance parameters such as echo impedance S11 and voltage standing wave ratio (VSWR). Finally, the two sensor models are coupled into GIS handholes for comparative simulation analysis. Results show that antenna corrosion causes resonant frequency shifts in sensors, reducing PD signal power by 55.27% and increasing noise power by 64.11%. The signal-to-noise ratio (SNR) decreases from −9.70 dB to −15.34 dB, with evident waveform distortion in the double-exponential PD pulses. These conclusions provide theoretical references for on-site UHF sensor calibration in noisy environments. Full article

High penetration of renewable energy sources complicates static voltage stability assessment, as conventional line-based indices are typically derived under restrictive assumptions, such as neglecting voltage-angle differences or decoupling active and reactive power effects, which may lead to inaccurate proximity signals under RES-rich operating conditions. The proposed research study develops an enhanced voltage stability index (EVSI) from a two-port π line model that explicitly retains line impedance, active and reactive power terms, and voltage-angle difference between the sending and receiving ends; secure system operation satisfies EVSI < 1. Unlike classical indices, EVSI preserves the coupled physical interactions most relevant to voltage collapse while maintaining a closed-form structure suitable for online monitoring. EVSI is evaluated in a coupled transmission–distribution setting with solar photovoltaic-based distributed generation under varying penetration levels and loadings, using PV-curve nose points as collapse references, and benchmarked against classical indices. Across scenarios, EVSI remains closest to unity at the nose point, accurately tracing the collapse boundary and consistently identifying weak buses, whereas the traditional indices exhibit dispersed values and sensitivity to operating assumptions. The proposed results indicate that EVSI offers a reliable and computationally convenient indicator for online assessment and early warning of voltage instability in renewable-integrated, coupled transmission–distribution networks. Full article

Rydberg atoms are neutral atoms excited to high principal quantum number states, which endows them with exaggerated properties such as large electric dipole moments, long lifetimes, and extreme sensitivity to external electromagnetic fields. These characteristics form the foundation of Rydberg atom-based sensors, an emerging class of quantum devices capable of optically detecting electric fields across frequencies from DC to the terahertz regime. Rydberg-based electrometry operates through both Autler–Townes (AT) splitting of resonant Rydberg transitions and Stark-shift measurements for high-frequency or far-detuned fields, enabling broadband field sensing from DC to the THz regime. Using ladder-type electromagnetically induced transparency (EIT) and AT splitting, these sensors enable non-invasive, SI-traceable measurements of field amplitude, frequency, phase, and polarization. Recent developments have demonstrated broadband electric field probes, voltage calibration standards, and compact RF receivers based on thermal vapor cells and integrated photonic architectures. Furthermore, innovations in multi-photon EIT, superheterodyne readout, and multi wave mixing have expanded the dynamic range and bandwidth of Rydberg-based electrometry. Despite challenges related to environmental perturbations, linewidth broadening, and laser stabilization, ongoing advances in atomic control, hybrid photonic integration, and EIT-based readout promise scalable, chip-compatible sensors. This review summarizes the physical principles, experimental progress, and emerging applications of Rydberg atom-based sensing, emphasizing their potential for next generation quantum metrology, wireless communication, and precision field mapping. Full article

To address the critical issue of low reliability caused by fault impacts in large-scale wind farms transmitting power over long distances via flexible DC transmission systems, this study proposes a collaborative solution. First, a new protection scheme integrating variable quantity differential protection, steady-state quantity differential protection and zero-sequence differential protection is proposed. By establishing a refined model of a wind farm with a flexible DC system, the adaptability of the differential protection for the outgoing lines is checked. Simulation results show that the sensitivity of metallic faults within the protection zone is better than 3.0, and the protection reliably remains inactive for faults outside the protection zone. Second, an innovative fault ride-through strategy combining self-regulating resistor circuits with wind farm MPPT load reduction is proposed. During faults on the receiving grid, the DC voltage fluctuation is controlled within 1.05 p.u. through graded switching of resistor modules and dynamic power regulation. This solution offers both rapid response and smooth fault ride-through characteristics, significantly improving the feasibility and economic viability of wind farm integration via flexible DC transmission. Full article

There are various non-destructive techniques for determining the internal properties of materials in fluids, semi-solids, solids, and biological tissue. One of these techniques is low-intensity ultrasonic testing. In this proceeding paper, a study on the architecture of a piezoelectric acoustic detector (PAD) is presented, from which an analysis for the design, development, and construction of an acoustic wave detector in the ultrasonic spectrum has emerged. Its purpose is to be applied to soft matter and tissue. The 110 μm thick polyvinylidene fluoride (PVDF) piezoelectric element was used as the active element in the thickness mode configuration. Piezoelectric constitutive equations were applied to a one-dimensional model for the analysis. A cylindrical iron–nickel backing was used, and the parts were bonded with conductive silver epoxy glue. The results are presented. The equation for the output voltage of the piezoelectric acoustic detector is described. Functional testing of the PAD is demonstrated using the pulse-echo technique, in which an acoustic wave generator excites an ultrasonic immersion sensor in emission configuration and the DAP is connected to a digital oscilloscope to observe the received signal. Finally, pulsed photoacoustic spectroscopy was applied to a biological tissue emulator and yielded significant results in the detection of a ruby sphere embedded in the emulator. It is proposed to further investigation the DAP models in multilayer structural configurations to increase their sensitivity. Full article

This study addresses the issues related to the inaccurate assessment of transient voltage stability margins and the limited participation of resources involved in regulation during high-voltage direct current (HVDC) receiving-end grid faults under high-penetration new energy integration. This paper proposes a method for transient voltage emergency control at the HVDC receiving-end grid, utilizing a multi-resource approach based on transient voltage similarity partitioning with a multiple-two-element notation criterion. First, the transient voltage stability margin and the new energy transient off-grid margin index, based on the multiple-two-element notation criterion, are introduced. Second, a grid partitioning scheme is employed, which clusters nodes based on the similarity of their transient voltage features, and the impact of multiple resources on the transient voltage stability of the HVDC receiving-end system is analyzed using trajectory sensitivity. On this basis, a multi-resource optimization model for transient voltage emergencies is established with the aim of minimizing the control cost, considering the transient voltage stability, off-grid new energy, and other safety evaluation constraints, in order to coordinate multiple resources participating in transient voltage control until the stability requirements are met. Finally, the validity of the proposed control scheme is verified using the improved frequency stability benchmark test system (Chinese Society for Electrical Engineering—Frequency Stability, CSEE-FS). The research results demonstrate that the scheme proposed in this study can be utilized to accurately assess the transient voltage stability and off-grid potential of renewable energy units following failure at the HVDC receiving-end system. Additionally, it can reasonably partition the grid based on transient operating conditions while fully exploiting the potential of multiple resources within the faulted partition to control transient voltage emergencies in the grid. Full article

Flextensional transducers are widely utilized as underwater acoustic transducers with broadband and high-sensitivity characteristics in low-frequency ranges. In this study, we have developed an equivalent circuit to facilitate the design of a class IV flextensional hydrophone. The end-plate of the class IV transducer is essential for sustaining the structure while keeping the hydrophone waterproof in underwater environments, and the presence or absence of the end-plate changes the hydrophone’s receiving performance. Previous studies have not included the end-plate in their equivalent circuit configurations, but this study proposes a new equivalent circuit model that incorporates an elastic boundary condition representing the constraint imposed on the shell by the compressive force of the end-plate. The receiving voltage sensitivity, calculated using the proposed equivalent circuit model, shows a high degree of agreement with the finite element analysis results, confirming that the mechanical influence of the end-plate significantly affects the hydrophone’s acoustic receiver characteristics. The proposed equivalent circuit approach offers faster computation while maintaining sufficient accuracy compared to the finite element analysis, making it a useful tool for future hydrophone design. Full article

This study investigates a non-destructive, compact pulse-echo ultrasonic method that combines an external transmitter with a single receiving sensor to identify different surface treatments applied to cementitious materials. The primary objective was to evaluate whether treatment-induced acoustic changes could be reliably quantified using time-domain signal parameters. Three types of surface conditions were examined: untreated reference specimens (R), specimens treated with a standard lithium silicate solution (A), and those treated with an enriched formulation containing hexylene glycol (B) intended to enhance pore sealing via gelation. A broadband piezoelectric receiver collected the backscattered echoes, from which the maximum amplitude, root mean square (RMS) voltage, signal energy, and effective duration were extracted. Receiver operating characteristic (ROC) analysis was conducted to quantify the discriminative power of each parameter. The results showed excellent classification performance between groups involving the B-treatment (AUC ≥ 0.96), whereas the R vs. A comparison yielded moderate separation (AUC ≈ 0.61). Optimal cut-off values were established using the Youden index, with sensitivity and specificity exceeding 96% in the best-performing scenarios. The results demonstrate that a single-receiver, one-sided pulse-echo arrangement coupled with straightforward amplitude metrics provides a rapid, cost-effective, and field-adaptable tool for the quality control of silicate-surface treatments. By translating laboratory ultrasonics into a practical on-site protocol, this study helps close the gap between the experimental characterisation and real-world implementation of surface-treatment verification. Full article

Capacitive micromachined ultrasonic transducers (CMUTs) have been widely applied in fields such as air-coupled ultrasonic nondestructive testing, gesture recognition, and 3D imaging. However, most current CMUTs struggle to simultaneously achieve both low power consumption and high performance, which limits their application in relevant fields. In this paper, a dual-layer CMUT is proposed, and its structural optimization design is also analyzed. The dual-layer CMUT consists of a top-layer circular CMUT cell and a bottom-layer annular CMUT cell. A movable pillar connects the top and bottom cells of the double-layer CMUT. This design increases the total deflection and reduces the stiffness, making the membrane more susceptible to deformation under external forces, thereby achieving low power consumption and high reception performance. The finite element method (FEM) results showed that, compared with conventional CMUTs, the structural optimization design of the dual-layer CMUT had a 13.7% reduction in collapse voltage. The improvements in the maximum deflection, average deflection, electromechanical coupling coefficient, transmitting sensitivity, and receiving sensitivity were 41.2%, 68.0%, 84.6%, 17.7%, and 101.6%, respectively. Therefore, the dual-layer CMUT has low power consumption and high reception performance while maintaining transmission performance, and it has potential for applications in portable, low-power devices and air-coupled ultrasonic nondestructive testing. Full article

Voltage source converter-based high-voltage direct current (VSC-HVDC) systems integrated into weak AC grids may exhibit oscillation-induced instability, posing significant threats to power system security. With increasing structural complexity and diverse control strategies, the stability characteristics of VSC-HVDC system require further investigation. This paper focuses on the stability of a receiving-end VSC-HVDC system consisting of a DC voltage-controlled VSC parallel-connected to a power-controlled VSC, under various operating conditions. First, small-signal models of each subsystem were developed and a linearized full-system model was constructed based on port relationships. Then, eigenvalue and participation factor analyses were utilized to evaluate the influence of control strategy, asymmetrical grid strength, power flow direction, and tie line on the system’s small-signal stability. A feasible short-circuit ratio (SCR) region was established based on joint power–topology joint, forming a stable operating space for the system. Finally, the correctness of the theoretical analysis was validated via MATLAB/Simulink time-domain simulations. Results indicate that, in comparison to the power control strategy, the DC voltage control strategy was more sensitive to variations in the AC system and demands a strong grid, and this disparity was predominantly caused by the DC voltage control. Furthermore, the feasible region of the short-circuit ratio (SCR) diminished with the increase in the length of the tie-line and alterations in power flow direction under the mutual-support power mode, leading to a gradual reduction in the system’s stability margin. Full article

In Wireless Power Transfer Systems (WPTS), variations in a load connected to a receiver can cause instability in the waveforms of output voltage and current due to their sensitivity to changes in load impedance. To overcome such drawbacks, this paper presents a control scheme for regulating voltage and current at the output of a WPTS system with the Double-LCC topology. The proposed method is based on estimating secondary-side parameters while assuming a constant coupling coefficient that remains close to its intended value during operation. The methodology begins with the mathematical modeling of the primary and secondary resonant circuits. By measuring the input voltage and current, the system estimates the load impedance, which is then used to derive the expected output voltage and a reference for the input voltage. To maintain a stable output, the system dynamically adjusts the input voltage, ensuring that it aligns with the theoretical reference value. Analytical calculations and simulations were performed using the MATLAB/Simulink platform to validate the proposed approach. Simulations confirmed the theoretical predictions for a wireless system operating at 120 kHz with a power transfer of 100 W. The results demonstrated that the load voltage remains stable at 32 V, even under varying load conditions, while the output current remains at 3 A despite fluctuations in battery voltage. Full article

We demonstrated that focusing an ultrasonic beam on the eardrum can overcome the high-frequency sensitivity limitations and acoustic distortion of conventional hearing aid receivers. Multilayer PZT was used for an ultrasonic receiver that operates at low voltage and enters the external auditory canal, and a 3 mm radius radiator was designed to radiate the focused parametric acoustic signal to the center of the eardrum based on an acoustic analysis according to the frequency. To this end, an ultrasonic earphone consisting of a radiator attached to multilayer PZT and a 130 kHz parametric ultrasonic modulator was implemented; vibration and sound pressure were measured using a laser vibrometer and a tube-type microphone. The proposed parametric ultrasonic receiver generates an average sound pressure of 70 dB SPL at a frequency of 1~10 kHz with a 10 V_peak applied voltage; this was implemented to provide a higher output in the range of 5 kHz and above, which is difficult to cover with existing receivers. Full article

Series–series (SS) wireless power transfer (WPT) systems are used in many applications because of their simple circuit structure. Compared with higher-order complex compensation topology, they are suitable for more demanding applications, such as rail trams with high power requirements but limited space for the coupling mechanism. However, the characteristics of their voltage source also put forward higher requirements for the control strategy. Improving the dynamic response performance of an SS compensation WPT system without any communication between the primary and secondary sides is the key issue. This paper proposes an improved variable step-size maximum power point tracking control strategy with the mutual inductance identification. Compared with the conventional P&O control, it can achieve a faster response and more accurate tracking, which are very important to the WPT for rail transit. A method of the mutual inductance identification based on the weight of parameter sensitivity is proposed. Based on the results of the identified mutual inductance, to make the system transfer the maximum power, the duty ratio of the receiver is adjusted to approach the corresponding equivalent load. To deal with the change of the mutual inductance, a condition of terminating the searching process of the maximum power point and re-identifying the mutual inductance is proposed. A simulation and experimental platform is built for verification. The results show that the proposed control strategy can quickly respond to the variation of the mutual inductance and load and achieve accurate maximum power point location, which improves the performance of the SS compensation WPT system. Full article