Harmonic Pulse Research Articles

Comparative Study of Advanced Modulation and Control Schemes for Dual Three-Phase PMSM Drives With Low Switching Frequencies

In this paper, multiple advanced low-switching-frequency modulation and control schemes are investigated for dual three-phase permanent-magnet synchronous motor (PMSM) drives. The modulation schemes under investigation include multisampling space vector modulation (MS-SVM), selective harmonic elimination pulse width modulation (SHEPWM) and synchronous optimal pulse width modulation (SOPWM) while the control schemes include complex vector control, model predictive control (MPC) and flux trajectory control-based model predictive pulse pattern control (MP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C). The difference between three-phase and dual three-phase PMSM drives at low switching frequencies is analyzed. Moreover, an optimal pulse width modulation (PWM)-based MP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C scheme is proposed for the dual three-phase PMSM, where the optimal PWM modulation and MP <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C control are combined such that the optimal steady-state and dynamic control performance is achieved among the modulation and control schemes investigated. Experimental results are given to compare and validate the proposed control scheme.

Nonlinear Frequency Mixing Ultrasound Imaging of Nanoscale Contrast Agents.

Nanoscale ultrasound contrast agents show promise as alternatives for diagnostics and therapies due to their enhanced stability and ability to traverse blood vessels. Nonetheless, their reduced size limits echogenicity. This study introduces an enhanced nanobubble frequency mixing ultrasound imaging method, by capitalizing on their nonlinear acoustic response to dual-frequency excitation. A single broadband transducer (L12-3v) controlled by a programmable ultrasound system was used to transmit a dual-frequency single-cycle wavefront. The frequency mixing effect enabled simultaneous transducer capture of nanobubble-generated sum and difference frequencies in real time without the need for additional hardware or post-processing, by substituting the single-frequency wavefront in a standard contrast harmonic pulse inversion imaging protocol, with the dual-frequency wavefront. Optimization experiments were conducted in tissue mimicking phantoms. Among the dual-frequency combinations that were tested, the highest contrast was obtained using 4&8 MHz. The nanobubble contrast improved with increased mechanical index, and achieved a maximal contrast improvement of 8.4 ± 0.5 dB compared to 4 MHz pulse inversion imaging. In imaging of a breast cancer tumor mouse model, after a systemic nanobubble injection, the contrast was improved by 3.4 ± 1.7, 4.8 ± 1.8, and 6.3 ± 1.6 dB for mechanical indices of 0.04, 0.08, and 0.1, respectively. Nonlinear frequency mixing significantly improved the nanobubble contrast, which facilitated their imaging in-vivo. This study offers a new avenue to enhance ultrasound imaging utilizing nanobubbles, potentially leading to advancements in other diagnostic applications.

Efficient control of three-phase cascaded multilevel Z-Source inverter using SHEPWM technique

This paper presents an enhanced control strategy for three-phase cascaded multilevel Z-source inverters, focusing on the implementation of Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) techniques to improve efficiency. Z-source inverters are gaining prominence in various applications due to their inherent advantages, such as increased voltage boost capability and inherent shoot-through protection. However, achieving optimal control in cascaded multilevel configurations poses challenges that this study seeks to address. The proposed control strategy optimizes the switching patterns of the inverter, thereby enhancing its overall performance. It allows for precise control over the output voltage and reduces harmonic distortion, ensuring the inverter operates efficiently across varying load conditions. The research methodology involves a comprehensive analysis of the proposed technique, including its mathematical modeling and simulation using advanced software tools. Performance metrics such as total harmonic distortion, efficiency, and transient response are evaluated to quantify the improvements achieved. The results obtained demonstrate the efficiency of the proposed control strategy. This method significantly reduces harmonic distortion in the output voltage, leading to improved power quality. Furthermore, the efficiency of the inverter is enhanced, making it suitable for applications demanding high-performance power conversion.

Pulse buildup dynamics in a self-starting Mamyshev oscillator.

The Mamyshev oscillator (MO) can generate high-performance pulses. However, due to their non-resonant cavities, they usually are not self-starting, and there is almost no effort to reveal the pulse buildup dynamics of the MO. This paper investigates the dynamic of single pulse (SP) and multi-pulse formation in a self-starting MO. It indicated that both SP self-starting and multi-pulse self-starting can be obtained by adjusting the oscillator parameters. More importantly, increasing pump power could only result in bound state pulses (BSPs) if SP self-starting was formed. With the increase of the pump power, the pulse number in BSPs would increase. However, multiple pulses could not be formed only by increasing the pump power, and the BSPs obtained here underwent SP generated from noise, amplified, and then bounded, which is different from conventional passive mode-locked fiber lasers (CPMLFLs). On the other hand, if multiple pulses were self-initiated, BSPs, pulse bunch, and harmonic mode-locked pulses (HMLPs) could be obtained by adjusting the polarization state and pump power in the cavity. Furthermore, once any of the above states are formed, if the oscillator polarization state and filter interval are unchanged, only increasing the pump power from zero, the original state can still be obtained, which is consistent with the characteristics of the CPMLFLs. These findings will provide new insights into the pulse dynamics of self-starting MO, which will be significant for studying ultrafast laser technology and nonlinear optics.

Control of the spider-like interference structure in photoelectron momentum distributions of a helium atom in a few-cycle nonlinear chirped laser pulse.

We investigate theoretically the photoelectron momentum distributions (PMDs) of the helium atom in the few-cycle nonlinear chirped laser pulse. The numerical results show that the direction of the spider-like interference structure in PMDs exhibits periodic variations with the increase of the chirp parameter. It is illustrated that the direction of the spider-like interference structure is related to the direction of the electron motion by tracking the trajectories of the electrons. We also demonstrate that the carrier-envelope phase can precisely control the opening of the ionization channel. In addition, we investigate the PMDs when a chirp-free second harmonic (SH) laser pulse is added to the chirped laser field, the numerical results show that the interference patterns can change from only spider-like interference structure to both spider-like and ring-like interference structures.

Model verification and vibration analysis of the four-disk hollow flexible shaft rotor system

Rotor unbalances failure due to various factors such as manufacturing defects, mounting errors, and material inhomogeneity is inevitable, and will be aggravated by bearing pulse displacement excitation caused by maneuvering flight. Therefore, the purpose of this paper is to study the vibration of the rotor system under disk unbalance forces and bearing pulse displacement excitation. Firstly, the differential equation of motion for four-disk flexible hollow shaft rotor system modeling with a simple finite element model(SFEM) is established by the Lagrangian method in non-inertial systems, and the shaft is modeled using Timoshenko beam theory. Then, the dynamic characteristics of the four-disk flexible hollow shaft rotor are analyzed and compared with the 3D finite element model(3D FEM) to verify the accuracy of the model. To analyze the effects of different disk unbalanced positions and pulse displacement excitation on the vibration characteristics of the rotor, the characteristic vector method and the Runge–Kutta method are used to obtain the steady-state solution and the transient solution, respectively. In addition, the simulation results show that suitable in-shaft damping has a stable effect on the rotor during the start-up. Disk2 and Disk3 are more sensitive to synchronous harmonic excitation and pulse displacement excitation than Disk1 and Disk4. The research of this paper provides an important basis for vibration monitoring and control, and vibration transmission analysis of aero-engine rotor system.

Comparison of the antimicrobial photocatalytic activities of SiO2 and Au@SiO2 nanostructures in water decontamination.

Photocatalytic disinfection of Escherichia coli suspension by silicon dioxide nanoparticles and silicon dioxide/gold nanocomposite in a batch reactor is investigated experimentally and results are compared. Silica nanoparticles were synthesized by Stöber method and pulsed laser ablation method was employed to prepare gold nanoparticles in distilled water. Composition of two nanoparticles species was carried out, using the second harmonic pulse of Nd:YAG laser, whose wavelength is in the absorption spectra of gold nanoparticles. Results confirm a decrease in the bandgap energy of silica nanoparticles after composition. Escherichia coli were selected as an indicator of the microbial water contamination. Disk diffusion method was used to evaluate the antimicrobial potential of SiO2 and Au@SiO2 nanostructures. Photocatalytic activities of both nanostructures were examined in dark, and under the irradiation of UV and visible light. In all conditions, the performance of Au@SiO2 nanocomposites was higher than SiO2 nanoparticles. In dark condition the higher biocidal nature and activity of Au nanoparticles and for the case of UV radiation, decreasing the bandgap energy and recombination rate of SiO2 nanoparticles after composition with Au increased the efficiency. For the case of visible light radiation, surface plasmon resonances effects, and local heat of Au nanoparticles were responsible for increasing the efficiency. RESEARCH HIGHLIGHTS: Doping large bandgap semiconductors nanostructures, such as silica with metal nanoparticles, such as gold will improve their photocatalytic activity to work in visible light. In this mechanism, gold nanoparticles act as effective traps to prevent the recombination of photogenerated electron-hole pairs. Other mechanisms, such as Schottky barrier formation, surface plasmon resonance absorption of gold nanoparticles, and biocidal nature of the gold nanoparticles are effective in increasing the efficiency of Au doped silica nanostructures.

Application of soft computing algorithms for hybrid modular multilevel inverters

This study utilized Harris Hawk optimization to analyze the harmonic distortions of a symmetric capacitor based multilevel converter. The proposed multilevel converter uses identical and symmetric DC sources in its input. The proposed topology for a multilevel converter uses fewer switches than typical cascaded designs. It can output 9-level outputs and can be scaled up to higher levels. The proposed multilevel converter can be improved by implementing a low frequency pulse width modulation technique to reduce the stress on the switches. The optimization of the switching angles using Harris Hawk was able to solve the non-linear aspects of the Selective Harmonic Elimination Pulse Width Modulation. The output voltage's THD was compared with that of other optimization methods, such as ant colony and particle swarm. The comparison shows that the output THD of the Harris Hawk optimizer is lower than that of other methods, which is about 5 %, according to the standards of IEEE-519.

Generation of millijoule-level sub-5 fs violet laser pulses

AbstractWe demonstrate the generation, spectral broadening and post-compression of second harmonic pulses using a thin beta barium borate (BBO) crystal on a fused-silica substrate as the nonlinear interaction medium. By combining second harmonic generation in the BBO crystal with self-phase modulation in the fused-silica substrate, we efficiently generate millijoule-level broadband violet pulses from a single optical component. The second harmonic spectrum covers a range from long wave ultraviolet (down to 310 nm) to visible (up to 550 nm) with a bandwidth of 65 nm. Subsequently, we compress the second harmonic beam to a duration of 4.8 fs with a pulse energy of 0.64 mJ (5 fs with a pulse energy of 1.05 mJ) using chirped mirrors. The all-solid free-space apparatus is compact, robust and pulse energy scalable, making it highly advantageous for generating intense second harmonic pulses from near-infrared femtosecond lasers in the sub-5 fs regime.

Modelling and design of grid voltage oriented vector control scheme for DC railway recuperating system

The braking energy harvested by a railway vehicle can be restored to the utility grid with a power recuperating system. A grid connected voltage source inverter (VSI) is commonly used as a grid-feeding converter in the recuperating system. This paper proposes to integrate grid voltage oriented vector control (GVOVC) and third harmonic voltage injection pulse width modulation (THVI-PWM) technique for the VSI to ensure grid voltage and frequency synchronization. A simulation study is carried out to evaluate the feasibility of the proposed control and modulation schemes using MATLAB/Simulink. The results show that the proposed controller may reach steady-state operating mode within 7 ms by producing good quality AC voltages and currents waveforms. With the independent control of voltage quantities in dq reference frame, the regulation of active and reactive power could be realized.

FC-PV-battery-Z source-BBO integrated unified power quality conditioner for sensitive load & EV charging station

The proposed integrated system combines of fuel cell (FC), photovoltaic (PV), battery, Z-source and Biogeography-Based Optimization (BBO) based Unified Power Quality Conditioner (UPQC) compensator aims to provide a high-quality power supply to sensitive loads, such as electrical, electronics, medical equipment, Electrical Vehicles (EV), or critical industrial processes. It can regulate voltage, mitigate power disturbances (e.g., voltage sags, swells, flicker, voltage interruption, harmonics, reactive power etc.), and ensure a stable power supply. Additionally, it can facilitate EV charging stations by managing the power flow and optimizing charging processes. The PV or FC based Z-source inverter can control and regulate power flow in both directions. It operates with a unique impedance network, allowing for voltage boosting or bucking. The Z-source inverter enhances the flexibility and control of power flow in the system. The fuel cell generates electricity through an electrochemical process, typically using hydrogen as a fuel source, while the PV array converts sunlight into electrical energy. The FC-PV system provides a renewable and clean energy source. The battery serves as an energy storage device within the integrated UPQC system. It stores excess energy produced by the FC-PV system or from the grid during off-peak hours and releases it when needed, contributing to load balancing and stability. Biogeography-Based Optimization (BBO)-based Selected Harmonic Elimination Pulse Width Modulation (SHE-PWM) technique calculate the proper inverter switching angles and control the total harmonic distortion (%THD). Grid connected EV charging station produce nonlinear current and pollute the DC-link system. The proposed FC-PV-Z source-BBO based UPQC and its control strategy can enhance the EV-charging induced PQ (power quality) issues, eliminate the voltage and current harmonic or reduce overall voltage and current %THD control the proper reactive power, improve the power factor, restoring the flicker, transient, swells and sags of the micro grid, grid or smart grid and completely moderate the fluctuations of DC-link voltage.

Routes from stationary dissipative solitons to chaos in a Mamyshev oscillator

Mamyshev oscillators (MOs), a new type of femtosecond fiber laser, can produce not only high-performance stationary dissipative solitons (SDSs), but also exhibit chaotic dynamics. Since chaotic behavior may lead to dramatic degradation of the performance, it is particularly important to investigate chaotic dynamics in MOs. Here, using numerical simulation and experimental research methods, we systematically investigate different routes from SDSs to chaos in an MO. Specifically, by simply increasing the gain saturation energy under different polarization states, we obtained different routes from SDSs to chaos, including via a cascade of period-doubling bifurcations (CPDB), via a quasi-cascade of period-doubling bifurcations, and via a double CPDB. In addition, the evolution from dissipative soliton molecules to chaos via CPDB was also observed by increasing the gain saturation energy with a small filter wavelength separation. This finding shows that the evolution from SDSs to chaos is a generic property of laser systems and can appear in various pulse patterns such as single pulse, dissipative soliton molecules, and harmonic mode-locking pulses, which may be beneficial for better understanding chaotic dynamics in MOs.

10 Hz Stable Mode-locked Er-Fiber Laser

Abstract: In this paper, a stable output at the reduction repetition rate from 80 MHz mode-locked Er-doped fiber laser (EDFL) was demonstrated by adjusting the operating point for external LiNbO3 Mach-Zehnder‎ electro-optic intensity modulator to suppress harmonic mode-locked pulses. More than 70% of the laser beam was launched into the external pigtail Mach-Zehnder intensity modulator using single mode fiber with collimating lens and fiber (ferrule connector) FC adapter. The optimum values of Mach-Zehnder modulator bias voltages V0 and Vπ (half wave voltage) which resulted in maximum and minimum laser output power to leave the modulator were found at 6.5 and 0.29 V, respectively. The best modulation was achieved for the RF modulating signal with an opening time of about 8 ns. For driving voltage equal to Vπ, a clean mode-locked pulse train was generated with a pulse shape and energy similar to the input pulse, albeit with a low repetition rate. The minimum repetition rate reached as low as 10 Hz, resulting in pulse energy and peak power of 0.32 nJ and 1.5 kW, respectively. Second-harmonic generation of the low repetition rate pulse train was also produced by using a PPLN crystal. This opens up the potential for using this laser in single photon detection experiments and as a seed laser for many applications. Keywords: Er-fiber laser, Passively mode-locked fiber laser, Nonlinear polarization rotation, Mach-Zehnder modulator, Fast electro-optic modulator. PACS: Fiber lasers, 42.55.Wd, Mode locking, 42.60.Fc.

Generation and periodic evolution of third harmonics carrying transverse orbital angular momentum in air-plasma filaments.

Spatiotemporal optical vortex (STOV) pulses, possessing inherent transverse orbital angular momentum (OAM) and exhibiting phase singularity and intensity null in the spatiotemporal (ST) domain, have received increasing attention in recent years. Here, we investigate theoretically the third harmonic generation and evolution properties of STOV pulses via the interaction of 800-nm-STOV pulses with air-plasma filaments. We show that beautiful third harmonic STOV pulses are generated at a propagation distance of several millimeters. During further propagation, the ST intensity profiles of the third harmonics undergo variations in a periodic way, leading to the distortion and subsequent restoration to the initial ring pattern. The periodic evolution is a result of the interference effects between the third harmonics generated with different phases. Consequently, the evolution period is roughly twice the dephasing length of the third harmonics. Meanwhile, additional singularities emerge in the intensity patterns due to destructive interference occurring at specific dephasing lengths for the specific frequency components. The high-frequency components experience destructive interference earlier than the low-frequency components during each evolution period because the dephasing length decreases with frequency. This results in the sequentially appearance of the additional singularities from top to bottom in the ST intensity patterns. The proposed scheme demonstrates a way for higher-order STOV generation and manipulation in air-plasma filaments, which can be of interest for experiments related to vortex light science.

Active Optimization Method for Power Loss Distribution in T-Type Three-Level Converter Under Half-Wave Symmetry SHEPWM

For high-power converters, it is an important task to optimize the power loss in switching devices. The total power loss affects the efficiency and cooling design of converters, and the uneven power loss distribution causes the switching devices with the highest power loss to age prematurely and shorten the lifespan. Although some low switching frequency modulation strategies can decrease the total power loss, they are not able to balance the power loss distribution. On the contrary, some approaches can balance the power loss distribution by the software and hardware redundancy states of converters only under a high switching frequency. It results in an inability to reduce the total power loss. Therefore, this article proposes an active optimization method for T-type three-level converters to deal with the uneven power loss distribution under a relatively low switching frequency. By analyzing the inner connection between the power loss distribution and 3-order component, the constraint equations of half-wave symmetry selective harmonic elimination pulse width modulation (SHEPWM) are actively redesigned. Thus, both optimization objectives of the power loss can be achieved simultaneously under the proposed SHEPWM. Some numerical analysis and experimental results are given to demonstrate the correctness and feasibility of the proposed method.

A single source five-level switched-capacitor based multilevel inverter with reduced device count

Nowadays, multilevel inverters (MLIs) are widely used for integration with renewable energy (RE) resources and in industrial applications. Among different RE sources, photovoltaic (PV) energy is generally used for the generation of power. For accumulating more power from PV systems, the Fuzzy Logic Controller (FLC) technique is used to trace the maximum power (MPP). The FLC computes the reference PV voltage guarantee to ensure optimal power transmission between the PV system and the MLI's connected load. In this paper, a novel 5L (five-level) PV-based switched-capacitor MLI topology (PV-SC-MLI) has been projected with the target of reducing the number of switches and boosting the input voltage without any bulky transformer. A selected harmonic elimination pulse width modulation technique (SHEPWM) based technique is used to remove the harmonic for 5L-PV-SC-MLI. The projected technique is appropriate for all levels of MLIs, including non-equal and equal DC sources. The SHEPWM technique is used to solve the non-linear transcendental equations and obtain the optimal values of switching angles. The obtained switching value is used to reduce the total harmonic distortion (THD) of 5L-PV-SC-MLI. The THD at the output voltage of proposed inverter has been obtained value is 8.72% without filter and with filter 4.20%, which lies within the limits of IEEE 519 standards.

Influence of saturable absorber parameters on the hybrid mode-locking performance of fiber lasers

In this paper, we numerically study the influence of saturable absorber parameters, namely, modulation depth, recovery time, and saturation energy, on the performance of an ultrafast fiber laser that is mode-locked by a hybrid scheme of a saturation absorber (SA) and a nonlinear polarization rotation (NPR). Maps of mode-locked states related to intracavity wave-plates are created to evaluate the operation of hybrid mode-locking under different modulation depths of the SA. Along with the improvement of modulation depth of the SA, the mode-locked pulse results from a combination effect of the SA and NPR. The numerical analysis reveals that the SA parameters can significantly impact the pulse profile, peak power, and operation state. Moreover, they can also impact the selection of NPR mode-locked points, resulting in variation in stable single pulse output. A higher modulation depth can suppress the unstable multiple pulses’ operation and convert them into harmonic mode-locked pulses. The obtained results indicate that the selection of appropriate SA parameters can effectively improve the output characteristics of hybrid mode-locked fiber lasers.

Control technique for power quality improvement of isolated wind power generation system

Power quality (PQ) problems for renewable energy system (RES) is major challenge for using these systems. Amplitude, frequency, and waveform is important PQ parameters especially for standalone or isolated systems. In this paper we propose RES with wind turbine (WT) and permanent magnet synchronous generator (PMSG) to feed different loads (liner, non-liner) through AC-DC-AC converter. The PMSG operate with fuzzy logic inertia controller, to convert turbine torque form PU to Nm. The inverter stage in the converter operate according to proportional integral derivative (PID) controller with 3rd harmonic injection pulse width modulation (PWM) to regulate the AC voltage in load side. For the same case study and operating condition, we compared the result for system parameters when using ordinary PWM and using PID with 3rd harmonic injection. Voltages total harmonics distortion (THD) was less than 2% with liner loads, and 3.5% with non-liner load and the same was for current load, the voltage amplitude was between (1-1.03) PU under different wind speed by using the proposed controller.

Control technique for power quality improvement of isolated wind power generation system

Power quality (PQ) problems for renewable energy system (RES) is major challenge for using these systems. Amplitude, frequency, and waveform is important PQ parameters especially for standalone or isolated systems. In this paper we propose RES with wind turbine (WT) and permanent magnet synchronous generator (PMSG) to feed different loads (liner, non-liner) through AC-DC-AC converter. The PMSG operate with fuzzy logic inertia controller, to convert turbine torque form PU to Nm. The inverter stage in the converter operate according to proportional integral derivative (PID) controller with 3rd harmonic injection pulse width modulation (PWM) to regulate the AC voltage in load side. For the same case study and operating condition, we compared the result for system parameters when using ordinary PWM and using PID with 3rd harmonic injection. Voltages total harmonics distortion (THD) was less than 2% with liner loads, and 3.5% with non-liner load and the same was for current load, the voltage amplitude was between (1-1.03) PU under different wind speed by using the proposed controller.

Efficient (2N+1) selective harmonic elimination in modular multilevel converters using an evolutionary many-tasking approach with prior knowledge

(2N+1) selective harmonic elimination pulse with modulation (SHE-PWM) is an important technique for a modular multi-level converter (MMC) to enhance the control ability and improve the fundamental wave amplitude accuracy of the output waveform. While finding optimal switch angles by solving the complex non-linear equation system is one of its main challenges. A current popular solution is to run a metaheuristic or evolutionary algorithm repeatedly on various modulation indexes. These methods ignore the fact that some of the optimization tasks are similar, and the optimization experiences could be shared among these similar tasks. To fill this gap, this study proposes an evolutionary many-tasking approach with prior knowledge (EMT-PK). EMT-PK facilitates positive knowledge transfer between similar tasks and is capable to solve all the sub SHE-PWM problems simultaneously through a single run. Numerical results on 7-, 9- and 11-level MMCs show that EMT-PK provides superior results for the (2N+1) SHE-PWM in comparison with 8 other widely used metaheuristics/evolutionary algorithms in this field including differential evolution (DE), ant colony optimization (ACO), teaching and learning-based optimization (TLBO), bee algorithm (BA), genetic algorithm (GA), particle swarm optimization (PSO), generalized pattern search (GPS) and asynchronous particle swarm optimization-genetic algorithm(APSO-GA). The superior performance of EMT-PK is further validated by the MATLAB Simulink simulation and the laboratory experiment on a 7-level MMC.