Search Results (1,181)

This study proposed a large-target-surface and high-frame-rate display method using multiple Digital Micromirror Devices (DMDs) for high-resolution, high-frame-rate aerospace applications. DMDs offer high frame rates and contrast ratios, but their surface size is constrained. By employing Pulse Width Modulation (PWM) with synchronization signals for grayscale modulation and synchronizing multiple DMDs, this method achieved a target surface four times larger than a single DMD at 400 Hz frame rate, with synchronization errors below 10 ns. This enhances simulation efficiency and provides an effective infrared scene simulation solution. Full article

Two-dimensional transition metal dichalcogenides (TMDs) are key materials in ultrafast photonics. However, the performance of conventional TMDs is limited by their bandwidth and carrier recovery time. The novel Dirac semimetal nickel ditelluride (NiTe₂), with its broad-band response and excellent nonlinear properties, emerges as an ideal candidate for saturable absorber (SA) materials. In this work, we report, for the first time, the application of NiTe₂ in the ytterbium-doped fiber laser, demonstrating stable passive Q-switching operation. The nonlinear transmission curve reveals a modulation depth of 6.82% at 1 µm and a saturation intensity of 2.12 MW/cm². Using an all-fiber ring cavity structure, stable Q-switched pulses with a central wavelength of 1031 nm were achieved at a pump threshold of 94 mW, with a maximum pulse repetition frequency of 30.1 kHz. The minimum pulse width reached 2.3 μs, and the single-pulse energy increased to 3.05 nJ, with an impressive radio frequency (RF) spectral signal-to-noise ratio (SNR) of 58.9 dB. This study demonstrates the potential of NiTe₂ as a high-performance SA in the near-infrared region, providing a solid foundation for its future application in ultrafast laser technologies. Full article

With the increasing integration of renewable energy sources into the grid, power quality at the point of common coupling (PCC)—particularly harmonic distortion introduced by power electronic converters—has become a critical concern. This paper presents a rigorous design and evaluation of a three-phase, fifteen-level cascaded H-bridge multilevel inverter (CHB MLI) with an LCL filter, selected for its superior harmonic attenuation, compact size, and cost-effectiveness compared to conventional passive filters. The proposed system employs Phase-Shifted Pulse Width Modulation (PS PWM) for balanced operation and low output distortion. A systematic, reproducible methodology is used to design the LCL filter, which is then tested across a wide range of switching frequencies (1–5 kHz) and grid impedance ratios (X/R = 2–9) in MATLAB/Simulink R2025a. Comprehensive simulations confirm that the filter effectively reduces both voltage and current total harmonic distortion (THD) to levels well below the 5% limit specified by IEEE 519, with optimal performance (0.53% current THD, 0.69% voltage THD) achieved at 3 kHz and X/R ≈ 5.6. The filter demonstrates robust performance regardless of grid conditions, making it a practical and scalable solution for modern renewable energy integration. These results, further supported by parametric validation and clear design guidelines, provide actionable insights for academic research and industrial deployment. Full article

This article presents the stages of development of a non-dispersive infrared (NDIR) open-type gas analyzer prototype (NGAP-1) with a fundamentally new discrete IR radiation generation scheme using pulse-width modulation for measuring the dynamics of water vapor and carbon dioxide concentrations, with further application in the instrument base of an ecological and climatic station to implement the eddy covariance (EC) method. In addition, selecting the component base for NGAP-1, as well as its calibration and experimental field validation as part of an ecological and climatic station, are described. Full article

Newborns are unable to reliably express changes in their physical condition due to their physiological immaturity and limited capacity for communication; therefore, continuous and systematic monitoring during phototherapy is essential to ensure timely detection of adverse responses and maintenance of therapeutic safety. This study extends our prior work, which introduced an indirect method for measuring light intensity to improve precision in monitoring newborn skin illumination. Light-emitting diode (LED) phototherapy has attracted considerable attention as an effective treatment for neonatal jaundice (NNJ). This study introduces an three-dimensional configuration of blue LEDs. An Arduino Mega 2560 microcontroller with pulse-width modulation (PWM) technology was employed to independently regulate the intensity of LED strips, enabling precise control of light output. The strips were mounted on an arc-shaped structure that can be adjusted mechanically and electronically through pre-programmed instructions embedded in the microcontroller. The results demonstrate that blue light at a wavelength of 460 ± 10 nm aligns with the peak absorption spectrum of bilirubin, thereby optimizing the efficacy of phototherapy for NNJ. Both observed absorption peaks were within the therapeutically effective range. Computer simulations confirmed that stable output contours can be achieved using rapid electronic scanning with a PID control algorithm to dynamically adjust the duty cycle. Experimental data showed that LED radiation output was largely linear. This supports the use of linear control algorithms and confirms the platform’s feasibility for future research. Full article

This paper proposes a fixed frequency pulse width modulation (PWM) for a dual active half-bridge resonant converter. The wide voltage range can be achieved without adding any additional components, and the voltage gain characteristic is independent of the load. Meanwhile, all switches can achieve full range zero voltage switching (ZVS). The driving logic is unified between the primary and secondary sides, allowing for the implementation of both boost and buck modes. Hence, the control logic is simple. In addition, the multiple-order harmonic analysis of the resonant tank is proposed without complex time-domain calculations. Hence, the expression of voltage gain, current characteristics, and soft switching conditions can be conveniently analyzed. Finally, a 500 W experimental prototype was built. The experimental results prove the effectiveness and superiority of the proposed solution. Full article

Field-oriented control (FOC) of induction motors (IMs) is used in railway rolling stock. In such control systems, a fixed frequency of the pulse-width modulation (PWM) inverter is used, which leads to an increase in power losses in the traction drive. To optimize power losses in the locomotive traction drive system, it is proposed to adapt the number of PWM inverter pulses to the frequency of the FOC speed controller, which is proportional to the locomotive speed. To solve this problem, conceptual foundations for adapting FOC to the locomotive speed have been developed, the key aspects of which are algorithms for adapting the PWM inverter frequency, the controller parameters and the parameters of the FOC speed controller frequency filters. The most significant results of the work are the methods for adjusting the maximum of the controllers of the basic FOC IM system, the filter structure and the inverter control scheme, adapted to the locomotive speed. The modeling results have shown the effectiveness of the proposed technical solutions. The proposed approach to developing FOC will allow minimizing the consumption of energy resources by the locomotive in the entire range of changes in its speed. Full article

Nyquist pulses are critical in optical communication networks and signal processing systems. We present, to our best knowledge, the first demonstration of all-optical Nyquist pulse generation using phase-modulated fiber Bragg gratings (PM-FBGs) in transmission. PM-FBGs are a class of fiber gratings that have a nearly uniform coupling strength and a spatially varying grating period. As examples, we have designed and numerically simulated photonic Nyquist pulses with roll-off factors of 0.9, 0.5, and 0.1, respectively. The grating profiles are obtained employing numerical optimization algorithms. Numerical simulations confirm that the generated pulses are in good agreement with ideal Nyquist pulses over a 500 GHz bandwidth and have a good tolerance to the variations in the input pulse width. Full article

Induction motors (IMs) are widely used in variable-speed electric drive systems, where the motor is supplied by a voltage source inverter (VSI). Thus, PWM inverter–IM combination presents several issues that can degrade system performance, particularly overvoltage phenomena when long cables are used. In inverter-fed drive systems, the physical separation between the converter and the motor often requires long motor cables, which can significantly affect voltage stress. As the inverter’s output pulses propagate through the cable, voltage reflections and high-frequency oscillations occur at the motor terminals. We theoretically and experimentally investigate the effect of three PWM methods, namely Space Vector (SVPWM), Selective Harmonic Elimination PWM (SHEPWM), and Random PWM (RPWM) strategies, on overvoltage at the terminals of an induction motor fed by a PWM inverter through a long cable. The simulation results exhibit the validity and efficiency of SVPWM control to reduce overvoltage for different cable lengths. In addition, in order to reduce and eliminate all overvoltage peaks, three filters are proposed and evaluated: an RC filter, an RLC filter, and a compensator. The proposed PWM strategies are assessed using equivalent experimental results obtained on an induction motor fed by a two-level VSI. The experimental tests demonstrate also the efficiency of the SVPWM compared to other strategies. Full article

In this paper, we propose a novel concept of a modular, multiport, single-stage, bidirectional, isolated, three-phase AC-DC converter system. This new system is realized using add-ons to a standard voltage source inverter, including both grid-connected AC-DC converters, like PWM rectifiers, and AC-drive DC-AC inverters. The proposed add-on converters provide isolated DC ports and can be installed into existing inverters of the abovementioned types, with no need for any modification of their topology or control system. Moreover, the add-on converters provide a minimum transistor count and high efficiency. The efficiency of the proposed add-on converters can be further improved by switching the type of pulse width modulation (PWM) scheme based on their operating point. The proposed converter system is validated for a power of 20 kW, an output voltage of 500–800 V DC, and a 40 kHz PWM frequency. Full article

Many methods have been developed for multilevel Space Vector Modulation (SVM), but despite their inherent advantages, all of them have been more complex than the alternative option of using Pulse Width Modulation (PWM) with sinusoidal or modified references. Different axes like g-h at 60° or ja-jb-jc at 120° have been used to simplify the operations to find the three nearest vectors and their duty cycles, but the control signals of multilevel converters are the duty cycles of phases, not the duty cycles of vectors. Moreover, throughout this paper, it was found that local information is not sufficient to compute the duty cycles of the phases: global information should be taken into account to obtain full control on the common mode voltage (CMV), and the selection of the starting vector in the switching sequence is also critical to obtain a balanced CMV. The natural coordinates ab-bc-ca were used in this paper, and a straightforward method is proposed for multilevel SVM: a method that is comparable in complexity to multilevel PWM with modified references and leads to exactly the same control signals. This method can be used as an easy starting point to develop other SVM techniques for multilevel converters. Full article

This study presents the design of a high-efficiency pulse width modulation (PWM) power amplifier for marine biological sound reproduction. Due to the capacitive nature of underwater transducers and step-up transformers, output LC filter design is constrained, making it difficult to achieve a flat frequency response and low total harmonic distortion (THD). To address this, the electrical characteristics of these components were measured and modeled to construct equivalent circuits for the PSPICE simulator. Based on these models, an optimized LC filter was designed, and its performance was validated through simulation and experiments. The cause of THD occurring in specific frequency bands was analyzed, and two types of notch filters were applied to improve THD and switching signal attenuation. The proposed methodology offers a practical approach to improving PWM amplifier performance in underwater acoustic systems, supporting the development of compact, efficient, and reliable SONAR transmitters. Full article

This paper proposes a small-signal model of a DC–DC parallel resonant converter operating in continuous conduction mode based on asymmetric pulse-width modulation (APWM) under light-load conditions. The parallel resonant converter enables soft switching and no-load control over a wide load range because the resonant capacitor is connected in parallel with the load. However, the resonant energy required for soft switching is already sufficient, and the current flowing through the resonant tank is independent of the load magnitude; therefore, as the load decreases, the energy that is not delivered to the load and instead circulates meaninglessly inside the resonant tank increases. This results in conduction loss and reduced efficiency. To address this issue, APWM with a fixed switching frequency is required, which reduces circulating energy and improves efficiency under light-load conditions. Precise small-signal modeling is required to optimize the APWM controller. Unlike PFM or PSFB, APWM includes not only sine components but also DC and cosine components in the control signal due to its asymmetric switching characteristics, and this study proposes a small-signal model that can relatively accurately reflect these multi-harmonic characteristics. The proposed model is derived based on the Extended Describing Function (EDF) concept, and the derived transfer function is useful for systematically analyzing the dynamic characteristics of the APWM-based parallel resonant converter. In addition, it provides information that can systematically analyze the dynamic characteristics of various APWM-based resonant converters and control signals that reflect various harmonic characteristics, and it can be widely applied to future control design and analysis studies. The validity of the model is verified through MATLAB (R2025b) and PLECS (4.7.5) switching-model simulations and experimental results, confirming its high accuracy and practicality. Full article

Inter-turn short-circuit (ITSC) faults in motor drives can induce substantial circulating currents and localized thermal stress, ultimately degrading winding insulation and compromising torque stability. To enhance the operational reliability of open-winding (OW) five-phase fault-tolerant fractional-slot concentrated-winding interior permanent-magnet (FTFSCW-IPM) motor drive systems, this paper proposes a real-time fault-tolerant control strategy that provides current suppression and torque stabilization under ITSC conditions. Upon fault detection, the affected phase is actively isolated and connected to an external dissipative resistor, thereby limiting the fault-phase current and inhibiting further propagation of insulation damage. This reconfiguration allows the drive system to uniformly accommodate both open-circuit (OC) and ITSC scenarios without modification of the underlying control architecture. For OC operation, an equal-amplitude modulation scheme based on carrier-based pulse-width modulation (CPWM) is formulated to preserve the required magnetomotive-force distribution. Under ITSC conditions, a feedforward compensation mechanism is introduced to counteract the disturbance generated by the short-circuit loop. A principal contribution of this work is the derivation of a compensation term that can be estimated online using zero-sequence voltage (ZSV) together with measured phase currents, enabling accurate adaptation across varying ITSC severities. Simulation and experimental results demonstrate that the proposed method effectively suppresses fault-phase current, maintains near-sinusoidal current waveforms in the remaining healthy phases, and stabilizes torque production over a wide range of fault and load conditions. Full article

We experimentally demonstrate an 80 Gbit/s Nyquist-dense wavelength division multiplexed (Nyquist-DWDM) transmission system operating in a simulated atmospheric turbulence channel. The system utilizes eight wavelength-tunable lasers with 100 GHz spacing, modulated by cascaded Mach–Zehnder modulators, to generate phase-locked Nyquist pulse sequences with a 10 GHz repetition rate and a temporal width of 66.7 ps. Each channel is synchronously modulated with a 10 Gbit/s pseudo-random bit sequence (PRBS) and transmitted through controlled weak turbulence conditions generated by a temperature-gradient convection chamber. Experimental measurements reveal that, as the turbulence intensity increases from $C_n^2=1.01\times {10}^{-16}$ to $5.71\times {10}^{-16} {\mathrm{m}}^{-2/3}$, the signal-to-noise ratio (SNR) of the edge channel (C29) and central channel (C33) decreases by approximately 6.5 dB while maintaining stable Nyquist waveform profiles and inter-channel orthogonality. At a forward-error-correction (FEC) threshold of $3.8\times {10}^{-3}$, the minimum receiver sensitivity is −17.66 dBm, corresponding to power penalties below 5 dB relative to the back-to-back condition. The consistent SNR difference (<2 dB) between adjacent channels confirms uniform power distribution and low inter-channel crosstalk under turbulence. These findings verify that Nyquist pulse shaping substantially mitigates phase distortion and scintillation effects, demonstrating the feasibility of high-capacity DWDM free-space optical (FSO) systems with enhanced spectral efficiency and turbulence resilience. The proposed configuration provides a scalable foundation for future multi-wavelength FSO links and hybrid fiber-wireless optical networks. Full article