Search Results (1,230)

Traditional LLC resonant converters face significant challenges in wide-output-voltage-applications, such as limited voltage gain, efficiency degradation under wide-gain range, and increased complexity in magnetic component design. For example, in electric vehicle charging power modules, achieving wide output voltage typically relies on changing the transformer turns ratio or switching the series-parallel circuit configuration via relays, which prevents real-time dynamic adjustment. To overcome these limitations, this paper proposes a wide-gain-range control method based on a full-bridge T-type three-level LLC resonant converter, capable of achieving a voltage gain range exceeding six times. By integrating a T-type three-level bridge arm with PWM modulation and employing a variable-topology and variable-frequency control strategy, the proposed method achieves synergistic optimization for wide-output-voltage-applications. PWM modulation enables wide-range voltage output by dynamically adjusting both the converter topology and switching frequency. Finally, the proposed method is validated through circuit simulations and experimental results based on a full-bridge T-type three-level LLC converter prototype, demonstrating its effectiveness and feasibility. Full article

Multiple sclerosis (MS) is a chronic disease of the central nervous system that significantly impairs gait and mobility, contributing to a high risk of falls, reduced participation in daily activities, and diminished quality of life. Despite existing interventions such as exercise programs and pharmacological treatments, challenges such as fatigue, pain, and limited accessibility underscore the need for alternative therapies. Focal vibration therapy (FVT) has shown promise in improving gait, reducing spasticity, and enhancing mobility in people with MS (PwMS). However, further research is required to evaluate its long-term feasibility and optimize its parameters. This study examined the feasibility and preliminary efficacy of a home-based four-week wearable FVT device on gait and explored how FVT parameters impact gait and mobility outcomes. In this pilot double-blind randomized controlled trial, 22 PwMS were randomized into control and vibration groups (four FVT groups with varying vibration intensities/durations). Participants wore Myovolt^® vibrators on distal quadricep muscles near the rectus femoris insertion (approximately 2 cm from the medial edge of the patella), gastrocnemius/soleus, and tibialis anterior muscles (10 min/muscle, 3 days/week, 4 weeks). Feasibility was evaluated via adherence and satisfaction (QUEST 2.0, interviews). Gait (3D motion analysis) and mobility (T25FW) were assessed at baseline and post-intervention. Data were analyzed using descriptive/inferential statistics and thematic analysis. Of 22 participants, 17 completed post-intervention (16 intervention, 1 control). Wearable FVT showed promising feasibility, with high satisfaction despite minor adjustability issues. Intervention groups improved gait speed (p = 0.014), stride length (p = 0.004), and ankle angle (p = 0.043), but T25FW was unchanged (p > 0.05). High-intensity FVT enhanced knee/hip moments. This study’s results support the feasibility of wearable FVT for home-based management of mobility symptoms in MS with high participant satisfaction and acceptance. Notable gains in gait parameters suggest FVT’s potential to enhance neuromuscular control and proprioception but may be insufficient to lead to mobility improvements. Subgroup analyses highlighted the impact of vibration intensity and duration on knee joint mechanics, emphasizing the need for personalized dosing strategies. Challenges included participant retention in the control group and burdensome biomechanical assessments, which will be addressed in future studies through improved sham devices and a larger sample size. Full article

The instantaneous AC-side output power of a two-stage single-phase inverter pulsates at twice the output voltage frequency, inducing second harmonic current (SHC) in the front-end DC–DC converter. While conventional SHC mitigation methods mainly focus on controller optimization for PWM-controlled DC–DC converters, LLC resonant converters, which have been widely adopted in two-stage single-phase inverters for high efficiency and soft-switching characteristics, lack tailored solutions due to frequency modulation complexities. To address this gap, this paper first analyzes the propagation mechanism of the SHC in terms of converter output impedance. Then, by simultaneously lowering the open-loop gain and increasing the output impedance of the DC–DC converter at 2f_N, this paper proposes a hybrid SHC mitigation strategy that achieves low SHC and fast dynamic performance for frequency-modulated LLC converters. Finally, a 28 V DC to 220 V/50 Hz AC inverter was developed, and the experimental results verified the effectiveness of the proposed control strategy. Full article

Pulse width modulation (PWM) allows for the real-time flow rate adjustment of spray nozzles without changing system pressure, indicating that PWM is a promising technology for improving the quality of pesticide applications. However, its effect on the droplet formation process is not yet fully understood. In this study, the effects of a PWM system on the droplet spectrum and velocity generated by different flat fan hydraulic nozzles were evaluated. The experiment was conducted via a spray simulator to test the impact of PWM technology under various operational conditions and flat fan nozzle types (standard, pre-orifice, and air inclusion). With the aid of a real-time particle analyzer and high-resolution imaging, the following variables were analyzed: volume median diameter (VMD), relative span, droplet velocity, and the percentage of volume composed of droplets with a diameter smaller than 100 µm. Four simulated working speeds (1.1, 1.7, 2.8, and 3.9 m s⁻¹), which were equivalent to four PWM valve duty cycles (35%, 42%, 71%, and 100%), respectively, were evaluated. The PWM system altered the droplet size, generally reducing the VMD in comparison to the conventional system. The relative span was not influenced by the PWM system’s duty cycle, although system activation increased droplet size heterogeneity in some nozzle types. The droplet velocity was generally slower using the PWM system in comparison with the conventional system, but higher duty cycles increased this parameter. Overall, the results of this study suggest that spray patterns are altered by PWM activation, and the traits of this behaviour depend on the spray nozzle type. Full article

This paper presents a small-signal model of a series resonant converter under continuous conduction mode, based on asymmetric pulse-width modulation, which is commonly used under light-load conditions. When controlled using conventional pulse-frequency modulation, the series resonant converter (SRC) suffers from insufficient resonant current under light loads, leading to degraded soft-switching performance, increased switching losses, and reduced efficiency due to the need for higher switching frequencies to maintain output regulation. To address these issues, the asymmetric pulse-width modulation with a fixed switching frequency is required to improve efficiency. In this study, a small-signal model is derived using the Extended Describing Function method. Based on this model, transfer functions are obtained and verified through MATLAB(R2024a), switching model-based PLECS(4.7.5) simulations, and experimental results. Full article

This paper presents modeling for an external rotor permanent magnet generator (PMG) with fractional-slot concentrated windings working with a power electronic converter in the rotor magnetic field coordinate—the model is also called the DQ model. The model is needed to synthesize controllers of the PMG. Additionally, modeling for an active rectifier of the PMG is also investigated. The models of PMG and the active rectifier with two closed loops, namely the current loop and dc voltage loop, are verified by simulation in Matlab/Simulink. By modeling PMG in the rotor magnetic field coordinate, vector current can be decomposed in two independent currents, namely active current and reactive current. By controlling the active current, active power or electromagnetic torque or DC bus voltage can be controlled. By setting a relevant reactive current, the power factor or reactive power or rotor magnetic flux of PMG can be controlled. Simulation results of control PMG working with an active converter, such as pulse width modulation voltage, current, DC voltage, or power, are reported. The simulation helps to synthesize controllers and improve performances of the PMG working with the converter in wind applications. Full article

In wheat pest and disease control methods, pesticide application occupies a dominant position, and the use of UAVs for precise pesticide application is a key technology in precision agriculture. However, it is difficult for existing UAV spraying systems to accurately achieve variable spraying according to crop growth conditions, resulting in pesticide waste and environmental pollution. To address this issue, this paper proposes a LiDAR-assisted UAV variable-speed spraying system. Firstly, a biomass estimation model based on LiDAR data and RGB data is constructed, LiDAR point cloud data and RGB data are extracted from the target farmland, and, after preprocessing, key parameters including LiDAR feature variables, canopy cover, and visible-light vegetation indices are extracted from the two types of data. Using these key parameters as model inputs, multiple machine learning methods are employed to build a wheat biomass estimation model, and a variable spraying prescription map is generated based on the spatial distribution of biomass. Secondly, the variable-speed spraying system is constructed, which integrates a prescription map interpretation module and a PWM control module. Under the guidance of the variable spraying prescription map, the spraying rate is adjusted to achieve real-time variable spraying. Finally, a comparative experiment is designed, and the results show that the LiDAR-assisted UAV variable spraying system designed in this study performs better than the traditional constant-rate spraying system; while maintaining equivalent spraying effects, the usage of chemical agents is significantly reduced by 30.1%, providing a new technical path for reducing pesticide pollution and lowering grain production costs. Full article

The treatment of chronic wounds and pressure sores is an important challenge in the context of public health and the effectiveness of patient treatment. Therefore, new methods are being developed to reduce or, in extreme cases, to initiate and conduct the wound healing process. This article presents an innovative smart bandage, programmable using a smartphone, which generates small amplitude impulse vibrations. The communication between the smart bandage and the smartphone is realized using BLE. The possibility of programming the smart bandage allows for personalized therapy. Owing to the built-in MEMS sensor, the smart bandage makes it possible to monitor work during rehabilitation and implement an auto-calibration procedure. The flexible, openwork mechanical structure of the dressing was made in 3D printing technology, thanks to which the solution is easy to implement and can be used together with traditional dressings to create hybrid ones. Miniature electronic circuits and actuators controlled by the PWM signal were designed as replaceable elements; thus, the openwork structure can be treated as single-use. The smart bandage containing six actuators presented in this article generates oscillations in the range from about 40 Hz to 190 Hz. The system generates low-amplitude vibrations, below 1 g. The actuators were operated at a voltage of 1.65 V to reduce energy consumption. For comparison, the actuators were also operated at the nominal voltage of 3.17 V, as specified by the manufacturer. Full article

The following article aims to implement a hybrid modulation methodology based on the Selective Harmonic Elimination Pulse Width Modulation (SHE-PWM) technique to work with the fundamental frequency of the system and find the optimal firing angles using the PSO optimization algorithm, capable of reducing the voltage THDv present in the output signals of three-phase multilevel inverters. To develop this approach, three case studies are proposed, developed in MATLAB/Simulink software, which feature three-phase inverters with five, seven, and nine levels, respectively, of the CHB topology. The impact of adequate modulation is assessed, resulting in a voltage output signal with reduced distortion. The national regulation ARCERNNR 002/20 will be used as a reference point to evaluate the results before and after implementing the methodology. It was verified that the developed methodology can effectively eliminate the selected harmonics, especially those of lower order (3rd, 5th, 7th, 9th, 11th, 13th, and 15th), achieving an improvement of up to 17.93% in the voltage THDv concerning the standard S-PWM modulation present in the CHB-MLI. Full article

This study investigates the thermal performance of induction motors powered by multilevel H-bridge inverters using a novel pulse-width phase shift triangle modulation (PSTM-PWM) technique. Conventional PWM methods introduce significant harmonic distortion, increasing copper and iron losses and causing overheating and reduced motor lifespan. Through experimental testing and comparison with standard PWM techniques (LS-PWM and PS-PWM), the proposed PSTM-PWM reduces harmonic distortion by up to 64% compared to the worst one and internal motor losses by up to 5.5%. A first-order thermal model is used to predict motor temperature, validated with direct thermocouple measurements and infrared thermography. The results also indicate that the PSTM-PWM technique improves thermal performance, particularly at a triangular waveform peak value of 3.5 V, reducing temperature by around 6% and offering a practical and simple solution for industrial motor drive applications. The modulation order was set to M = 7 to reduce both the losses in the power inverter and to prevent the generation of very high voltage pulses (high dV/dt), which can deteriorate the insulation of the induction motor windings over time. Full article

(1) Background: The COVID-19 pandemic presented unprecedented challenges for people with multiple sclerosis (PwMS) in Oman, necessitating targeted healthcare planning and patient support. This study aimed to investigate the impact of COVID-19 on MS management and disease course, incidence, and outcomes of COVID-19, psychosocial and mental health effects of the pandemic, and demographic and clinical predictors of the effects related to COVID-19 among Omani PwMS. (2) Methods: This cross-sectional study was conducted from January to April 2021. Adult (18–60 years) Omani PwMS completed a structured interview along with the Expanded Disability Status Scale (EDSS) and World Health Organization Well-being Index (WHO-5). Clinical data on relapses and disease-modifying therapies and adherence were analyzed. The data was statistically analyzed. (3) Results: Of 104 PwMS (73.1% female), 22.1% contracted COVID-19, with fatigue being the most reported symptom (87%). Female sex (p = 0.042), younger age (18–34 vs. 35–45 years; p = 0.014), diagnosis of COVID-19 (p = 0.037), and low current mental well-being scores (p = 0.021) predicted greater COVID-19-related effects. (4) Conclusion: These findings highlight the need to study the mental resilience of this subgroup of PwMS and provide them with targeted support during crises. Full article

For Modular Multilevel DC-Link T-Type Converter (MMDTC)-based STATCOMs, under identical operating conditions, the submodule (SM) capacitor voltage ripple is inversely proportional to its capacitance value. A configuration with a lower capacitance will inevitably result in significant capacitor voltage ripples. During the PWM modulation process, these ripples can lead to distortions in the output voltage waveform. To address this issue, this paper proposes an innovative carrier reconfiguration method that not only compensates for the output voltage pulse deviation caused by SM capacitor voltage ripples but also achieves effective balancing of the SM capacitor voltages. Finally, the validity and performance of the proposed carrier reconfiguration method are verified through both simulations and experimental results. Full article

The growing need for high-efficiency and reliable propulsion systems in naval applications, particularly within the evolving landscape of submarine warfare, has led to an increased interest in multiphase Permanent Magnet AC motors. This study presents a modelling and simulation approach for a 3MW, seventeen-phase Permanent Magnet AC motor designed for submarine propulsion, integrating an AI-based drive control system. Despite the advantages of multiphase motors, such as higher power density and enhanced fault tolerance, significant challenges remain in achieving precise torque and variable speed, especially for externally mounted motors operating under deep-sea conditions. Existing control strategies often struggle with the inherent nonlinearities, unmodelled dynamics, and extreme environmental variations (e.g., pressure, temperature affecting oil viscosity and motor parameters) characteristic of such demanding deep-sea applications, leading to suboptimal performance and compromised reliability. Addressing this gap, this research investigates advanced control methodologies to enhance the performance of such motors. A MATLAB/Simulink framework was developed to model the motor, whose drive system leverages an AI-optimised dual fuzzy-PID controller refined using the Harmony Search Algorithm. Additionally, a combination of Indirect Field-Oriented Control (IFOC) and Space Vector PWM strategies are implemented to optimise inverter switching sequences for precise output modulation. Simulation results demonstrate significant improvements in torque response and control accuracy, validating the efficacy of the proposed system. The results highlight the role of AI-based propulsion systems in revolutionising submarine manoeuvrability and energy efficiency. In particular, during a test case involving a speed transition from 75 RPM to 900 RPM, the proposed AI-based controller achieves a near-zero overshoot compared to an initial control scheme that exhibits 75.89% overshoot. Full article

This paper presents a microcontroller-based technique for accurately measuring resistive sensors over a wide dynamic range using an adaptive constant current source. Unlike conventional voltage dividers or fixed-current methods—often limited by reduced resolution and saturation when sensor resistance varies across several decades—the proposed system dynamically adjusts the excitation current to maintain optimal Analog-to-Digital Converter (ADC) input conditions. The measurement circuit employs a fixed reference resistor and an inverting amplifier configuration, where the excitation current is generated by one or more pulse-width modulated (PWM) signals filtered through low-pass RC networks. A microcontroller selects the appropriate PWM channel to ensure that the output voltage remains within the ADC’s linear range. To support multiple sensors, an analog switch enables sequential measurements using the same dual-PWM current source. The full experimental implementation uses four op-amps to support modularity, buffering, and dual-range operation. Experimental results show accurate measurement of resistances from 1 kΩ to 100 kΩ, with maximum relative errors of 0.15% in the 1–10 kΩ range and 0.33% in the 10–100 kΩ range. The method provides a low-cost, scalable, and digitally controlled solution suitable for embedded resistive sensing applications without the need for high-resolution ADCs or programmable gain amplifiers. Full article

The aim of the article is to determine the control range of a multiphase squirrel cage induction generator with more than three stator phases, operating in a wide range of driving speeds. The generator produces an output DC voltage using a multiphase converter operating as a PWM rectifier. The entire speed range is divided into intervals in which the sequence of stator phase voltages and, in effect, the number of pole pairs, is changed. In each interval, the output voltage is regulated by the frequency and amplitude of the stator voltages causing the highest possible power efficiency of the generator. The system can be scalar controlled or regulated using field orientation. Generator characteristics are calculated based on the set of steady-state equations derived from differential equations describing the multiphase induction machine. The calculation results are compared with simulations and with the steady-state measurement of the vector-controlled nine-phase generator. Recognizing the reliability of the obtained results, calculations are performed for a twelve-phase generator, obtaining satisfactory efficiency from 70% to 85% in the generator speed range from 0.2 to 1.0 of the assumed reference speed of 314 rad/s. The generator producing DC voltage can charge an electrical energy storage system or can be used directly to provide electrical power. This solution is not patented. Full article