Search Results (718)

Wavelength modulation spectroscopy (WMS) is a representative implementation of tunable diode laser absorption spectroscopy (TDLAS), enabling reliable gas component analysis with concentration-related information derived from harmonic component extraction, while offering enhanced noise immunity for trace gas sensing in open environments. However, due to the strong coupling between laser wavelength and intensity, wavelength modulation inevitably introduces residual amplitude modulation (RAM), which significantly degrades measurement accuracy. To address this issue, this study introduces a RAM suppression algorithm based on multiple harmonic component decoupling (MHCD), using the second-harmonic lateral peak inclination angle (LPIA) as a characteristic indicator. Unit harmonic operators for the first, second, and third harmonics are designed, and an original harmonic reconstruction model is established via linear superposition of harmonic components. The optimal harmonic component ratio is determined at the composite operator with the maximum cross-correlation coefficient, and RAM noise is eliminated through a multi-harmonic decoupling matrix. Repetitive measurements on 22 mm pharmaceutical vials with 4% oxygen concentration demonstrate that MHCD reduces the second-harmonic LPIA from 18.07° to 8.56°. Concentration discrimination experiments conducted on seven groups of 22 mm vials with 2% concentration steps (0–12%) show that MHCD increases the true positive rate by 6–11% and decreases the false positive rate by 4–9%, confirming its effectiveness for pharmaceutical online inspection applications. Full article

Harmonics and interharmonics have a significant impact on the safe operation of power systems, and accurately identifying interharmonics in power systems is the basis of harmonic suppression. The accuracy with which interharmonic components in power systems are detected is easily affected by mode aliasing and noise; to address this issue, a method of detecting them based on an adjusted Fourier-based synchrosqueezing transform (AFSST) and the three-point symmetric difference energy operator (DEO3S) is proposed. First, in order to reduce the influence of endpoint effects on detection accuracy, an improved waveform feature-matching extension method is utilized to reduce endpoint effects generated during the FSST decomposition process. Then, because it is difficult to adaptively determine the number of ridges in the FSST decomposition process, the energy difference and normalized cross-correlation coefficient are utilized as the criterion for determining the number of modal decompositions in the FSST, thereby improving the accuracy of the ridge number. Finally, using AFSST, the harmonic/interharmonic signals are decomposed into a set of intrinsic mode functions (IMFs). The instantaneous frequency and amplitude of each component are extracted using DEO3S, enabling the accurate detection of harmonics and interharmonics in the power system. Experimental analysis was conducted using simulation data, arc furnace experimental system data, and hardware experimental platform data. The results showed that the proposed method can accurately detect harmonic/interharmonic parameters under different levels of noise interference. Compared with the FSST, EMD, EEMD, and CEEMDAN methods, the amplitude detection accuracy of the proposed method is improved by 0.21%, 0.78%, 0.64%, and 0.75%, respectively, and the amplitude detection accuracy is improved by 1.39%, 3.31%, 2.04%, and 3.14%, respectively. Full article

Cylinder–plate combined structures (CPCS) are widely used in aerospace, marine engineering, and offshore platform systems. During service, they are frequently subjected to stochastic excitations induced by turbulent boundary layers, acoustic loads, hydrodynamic disturbances, and broadband operational vibrations. Excessive random vibration responses may significantly reduce structural reliability, accelerate fatigue damage, and compromise operational safety. To address these engineering challenges, a unified stochastic dynamic analysis and vibration suppression framework is established for functionally graded graphene platelet-reinforced composites (FG-GPLRC) CPCS equipped with distributed dynamic vibration absorbers (DVAs). Adopting the First-order Shear Deformation Theory (FSDT), a comprehensive energy functional for the CPCS is established, in which the penalty method is implemented to impose boundary conditions and ensure interface continuity. Subsequently, the Pseudo-excitation Method (PEM) is utilized to convert the stochastic vibration analysis into an equivalent deterministic harmonic problem, and the governing equations are spatially discretized by combining the spectral geometric method (SGM) with the Ritz variational procedure, enabling efficient evaluation of power spectral density (PSD) and root-mean-square (RMS) responses. The reliability of the proposed model is verified through a series of numerical validation comparisons. On this basis, comprehensive parametric investigations are conducted to assess how material properties, structural geometries, and critical DVA parameters influence system behavior. The results demonstrate that the incorporation of distributed DVAs can achieve superior vibration suppression performance. This study provides an efficient and reliable theoretical framework for stochastic vibration analysis and damping design of advanced composite plate–shell coupled structures operating in complex random environments, offering important theoretical support for dynamic optimization design in aerospace and marine engineering applications. Full article

Model Predictive Control (MPC) is widely employed in three-phase two-level voltage source inverters (2L-VSIs) due to its fast dynamic response and straightforward implementation. However, conventional MPC requires the evaluation of all eight candidate voltage vectors (VVs), which increases computational burden and current prediction time, introduces higher common-mode voltage (CMV), and may degrade steady-state performance. To address these limitations, this paper investigates the effect of reducing the number of candidate VVs on CMV suppression, the reduction in current prediction time, and the enhancement of 2L-VSI performance. First, a five-voltage-vectors MPC approach is developed, achieving noticeable CMV suppression compared with the conventional approach. Although this approach achieved CMV suppression, it still incurred a high computational burden. Therefore, it was further developed into a systematic switching approach based on three VVs, in which only three candidate VVs are selected at each sampling instant. The proposed approach achieves two primary objectives: suppressing CMV and reducing the current prediction time by 50%. Experimental validation is conducted to compare the proposed approach with the conventional MPC in terms of CMV, current prediction time, Total Harmonic Distortion (THD), inductance variation sensitivity, dynamic response, and power loss. The results demonstrate that the proposed approach achieves superior steady-state and dynamic performance while significantly reducing the current prediction time and achieving suppression of the CMV at Vdc/2, thereby enhancing the performance of 2L-VSIs. Full article

Existing model predictive control (MPC) schemes based on virtual voltage vectors (VVVs) for dual three-phase permanent magnet synchronous motors (DT-PMSMs) typically employ a limited set of voltage vectors, which restricts further improvement in steady-state performance. Moreover, the design of switching sequences lacks systematic consideration, focusing mainly on harmonic current suppression while neglecting practical engineering challenges associated with software-layer implementation. This paper proposes an optimized model predictive torque control (MPTC) method for DT-PMSMs using an expanded voltage vector set. First, to enhance steady-state performance, an extended control set of voltage vectors is designed, which introduces not only new directions but also two distinct voltage amplitude levels, resulting in a total of 48 voltage vectors. Second, to alleviate the significant computational burden caused by traversing the extended set for prediction, a candidate voltage vector selection table is constructed based on the sector position of the stator flux linkage and the requirements for torque and flux adjustment. This approach reduces the computational load to only 10 predictive calculations per control cycle, avoiding exhaustive traversal of the extended set. Furthermore, for all VVVs in the control set, a switching sequence combining active voltage vectors with zero vectors is designed to facilitate straightforward digital implementation. Finally, experimental results are provided to validate the effectiveness of the proposed method. Full article

High-resolution microdisplay driver applications impose stringent requirements on the static linearity and dynamic performance of digital-to-analog converters (DACs). To meet these requirements, this paper presents a 200 MS/s 12-bit current-steering DAC. To reduce mismatches among high-weight current sources, a split–sort–symmetric grouping calibration (SSSGC) scheme is introduced, in which each most-significant-bit (MSB) current source is split into sub-cells and reorganized through sorting and symmetric pairing. This approach improves static linearity without complex current measurement or compensation loops. Additionally, a group-domain dynamic element matching (DEM) technique is employed to randomize current-source selection and suppress harmonic distortion. Designed in a 0.18 μm BCD process, the proposed DAC achieves an integral nonlinearity (INL) of 0.79 LSB, a differential nonlinearity (DNL) of 0.42 LSB, and a spurious-free dynamic range (SFDR) of 74.9 dB at an output signal of 4.05 MHz. Full article

To improve the reliability and precision of shunt active power filters (APFs) under disturbances, this paper proposes an enhanced direct deadbeat control strategy requiring only grid-side current sensors. To this end, a sensor-lean yet robust framework is established by integrating PLL-less voltage estimation with online inductance identification. Specifically, the need for AC voltage sensors is eliminated by reconstructing the grid voltage from inverter outputs and consecutive current samples, while a load current feedforward mechanism further obviates the load current sensors. From an algorithmic perspective, the strategy utilizes the grid-side current as the direct controlled variable to minimize error propagation, while an online identification algorithm is incorporated to counteract parameter drift induced by magnetic saturation. Furthermore, system stability is rigorously guaranteed via Lyapunov theory. Validation through both simulation and experiments reveals that the grid current THD is reduced to 2.90% and 3.3%, respectively, with a dynamic response time within 20 ms. Ultimately, these findings confirm that the proposed scheme minimizes hardware dependency without compromising harmonic suppression or transient robustness. Full article

This study introduces a control strategy that integrates a photovoltaic (PV) array reconfiguration approach into a Three-Level Neutral Point Clamped (NPC) inverter with LCL filtering and Space Vector Pulse Width Modulation (SVPWM) control. The control strategy eliminates multiple local Maximum Power Points (MPP) caused by partial shading in PV systems, thereby reducing mismatch losses and preventing the Maximum Power Point Tracking (MPPT) algorithm from becoming stuck at a local maximum. To achieve this, it utilizes an electrical reconfiguration strategy that dynamically shifts the PV array interconnections. Furthermore, this strategy reduces the system’s Total Harmonic Distortion (THD) by adjusting the DC bus voltage. Consequently, simulation evaluations across four different weather conditions have shown that this control strategy achieves significant power improvements: up to 54.8% in Case 1, 39.4% in Case 2 and 3, 21.3% in Case 4. Furthermore, the proposed approach suppressed DC bus voltage changes (<8.8 V) even under the worst conditions and reduced the THD in the grid current from 10.1% to 3.7%. Full article

Permanent Magnet Linear Synchronous Motors (PMLSMs) are the dominant actuation solution for high-end manufacturing equipment, such as semiconductor lithography systems, owing to their superior force density and direct-drive capabilities. However, the inherent thrust ripple—comprising cogging force, end effects, and harmonics—severely compromises their ability to achieve the nanoscale tracking accuracy required for precision metrology. This paper presents a comprehensive review of structural optimization techniques aimed at suppressing thrust ripple to ultra-low levels suitable for high-precision applications. The optimization methodologies are systematically categorized into Permanent Magnet (PM) modification, core structure optimization, end-effect mitigation, and topological innovations. Beyond analyzing individual techniques, this review critically evaluates the synergistic efficacy of combined optimization strategies, identifying complementary pairings that maximize ripple suppression while minimizing the trade-off with average thrust. Finally, the paper discusses the impact of manufacturing tolerances on optimization robustness, providing a roadmap for designing next-generation, high-fidelity linear motion systems. Full article

This article proposes a parallel current-summing LCC multilevel inverter (MLI) to suppress harmonic distortion of radiated EMI for wireless power transfer. Traditionally, ZVS has been an issue for staircase voltage output multilevel inverters because a shared current output became faster than some of the voltage transitions in staircase voltage output. The other common problem was capacitor voltage imbalance and resultant output voltage distortion if a sophisticated voltage balancing function is not used. The proposed LCC MLI ensures ZVS by separating each voltage transition into multiple bridge legs. Each bridge leg outputs different phases of currents for each voltage transition. The individual output currents are summed at the matching network of wireless power transfer, generating a near-sinusoid output current to suppress harmonic distortions. In this way, each leg achieves ZVS even though the summed output current at the LCC network is faster than some of the voltage transitions. To avoid the capacitor voltage imbalance issue, the proposed MLI eliminated the flying capacitor. Instead, the four parallel legs are supplied by a shared DC input link. Therefore, the four legs can output identical voltages without using a typical DC flying capacitor. The necessity of multiple input voltage sources is, therefore, also eliminated. Measurement demonstrates that the proposed method effectively reduces radiated harmonic EMI by up to 14 dB. Full article

White Mustard (Sinapis alba) seeds contain glucosinolates, mainly sinigrin and sinalbin. Isothiocyanate metabolites, together with flavonoids and tocopherols, present anti-inflammatory, antimicrobial, and antioxidant activities. This narrative review is a result of a literature search in PubMed, Scopus, and Google Scholar, spanning in vitro, in vivo. and clinical studies. The presented data highlight that mustard-derived products suppress pro-inflammatory cytokines such as TNF-α and inhibit a broad spectrum of pathogens at micromolar concentrations. In the largest (n = 113) double-blind dental trial to date, a white-mustard toothpaste reduced the mean value of Silness-Löe plaque index by −2.43 vs. −1.95 placebo and bleeding on probing by 30.6% vs. 26.8% within four weeks, while salivary Streptococcus mutans and Porphyromonas gingival colony counts decreased by 40%. A six-month follow-up study with a sinigrin-rich “Bamberka” extract confirmed these gains and selectively suppressed red-complex periopathogens. Clinical translation is limited by heterogeneous extraction methods, a lack of phytochemical standardization, and an unresolved allergenic risk linked to seed proteins Sin a 1 and Sin a 2. Mustard, therefore, emerges as a promising phytotherapeutic adjunct for controlling inflammation, infection, and oxidative stress, but widespread use awaits harmonized manufacturing guidelines, comprehensive allergological screening, and rigorously designed randomized trials benchmarked against chlorhexidine. Full article

To address the low-voltage fault issue in doubly fed induction generator-motor (DFIGM) systems, this paper proposes a practically implementable cooperative control strategy that integrates an improved current reversely tracking control (CRTC) scheme with an enhanced IGBT-based active crowbar topology. The proposed method optimizes the current-tracking coefficients under rotor voltage and current constraints during LVRT operation. Meanwhile, the enhanced active crowbar provides reactive power support, thereby suppressing negative-sequence current components, mitigating harmonic distortion, and improving the power quality at the point of common coupling (PCC). A 10-MW DFIGM model is developed, and comparative studies are conducted with the conventional inductance emulating control (IEC) and the crowbar structure. The experimental results show the feasibility and effectiveness of the proposed method. Full article

The acoustic technique emerges as a highly promising, cutting-edge solution that can be effectively employed for extinguishing flames in locations where the access to classical fire-protection measures is limited, the available extinguishing agent is severely restricted, or the burning materials are difficult to suppress using currently known methods. The results of the experimental attempts confirmed that low-frequency acoustic waves containing higher even harmonics from the tenth to the sixteenth order (inclusive) can successfully extinguish flames, demonstrating both the feasibility and the novelty of the acoustic technique for fire protection. Moreover, statistical analysis was applied to identify operational boundary values and assess their variability, supporting the optimal selection of system parameters required for rapid and effective flame extinguishing. By integrating an acoustic extinguisher with optional intelligent sensors, including artificial vision, it becomes possible to rapidly detect flames at much greater distances than with conventional smoke and temperature sensors, as well as to automatically extinguish them. In this context, an integrated solution combining acoustic waves with an artificial intelligence module (smart sensor) may be employed for comprehensive fire management, encompassing both fire detection and flame extinguishing. Full article

Harmonic resonance challenges have intensified in modern power grids, primarily due to the high penetration of converter-based offshore wind energy. Traditional modal analysis methods conducted in the abc reference frame are often constrained by complex coordinate transformations and laborious analytical procedures. Therefore, research into dq-domain modal analysis and mitigation techniques is essential. This paper first elucidates the limitations of conventional modal analysis and outlines the fundamental principles of the dq-domain approach, validating its effectiveness through a three-bus test system. Subsequently, a resonance analysis model for offshore wind systems is established to derive the complete nodal admittance matrix. A dq-domain resonance analysis is then performed, and resonance is mitigated by optimizing the control parameters. Finally, the proposed dq-domain modal analysis method and suppression strategy are validated using a laboratory-scale experimental testbed. The results indicate that the proportional gain of the power control loop (K_PP) significantly influences the system’s resonance modes. Fine-tuning controller parameters via modal analysis provides an active, flexible, and cost-effective solution for resonance suppression. Full article

Based on the dilemma of analyzing the resonance stability of AC power grids using impedance models, it is demonstrated that the “negative resistance” mechanism of wideband oscillation is untenable. A general method for describing power electronic devices using wideband voltage-source converter models and wideband current-source converter models is proposed, thereby representing the nonlinear characteristics of power electronic devices with harmonic voltage sources and harmonic current sources. This allows the renewable energy power system to still be described by a linear system, and interprets the mechanism of wideband oscillation as a “harmonic amplification” phenomenon caused by network resonance, thus establishing a new framework for explaining the mechanism of wideband oscillation in renewable energy power systems. Through the analysis of two basic resonant circuits, the relationship between the damping ratio of resonant modes and the harmonic amplification factor is derived, laying a theoretical foundation for the analysis and suppression of wideband oscillation based on the s-domain nodal admittance matrix method and C-type damping filters. Based on the maximum damping criterion, a design method for C-type damping filters is proposed. The designed C-type damping filters exhibit strong broadband damping effects. Full article