Width Modulation Research Articles

Membrane III-V/Si DFB Laser Using Uniform Grating and Width-Modulated Si Waveguide

Membrane buried-heterostructure III-V/Si distributed feedback (DFB) lasers with a stopband-modulated cavity on a Si substrate have been developed. The membrane III-V layers with 230-nm thickness enable us to construct an optical supermode with a 220-nm-thick Si waveguide that is used in standard Si photonics platform. We employ a uniform grating and Si waveguide, in which Si waveguide width is modulated to control the center wavelength of the stopband. The cavity can be designed by controlling the modulation width and modulation length of Si waveguide. Therefore, it is easy to engineer and fabricate the laser cavity compared with the cavity using λ/4-phase shift grating. Output light from the cavity is coupled to Si waveguide through InP inverse taper waveguide, and then coupled to SiOx waveguide through Si inverse taper waveguide, which provides the 2-dB fiber coupling loss. We have demonstrated single-mode lasing by using Si waveguide, where its width is increased 80 nm at the center of the cavity. The threshold current and maximum fiber output power are 3 mA and 4 mW, respectively. By extending the active region length to 1 mm, 17-mW fiber coupled output power is obtained. High-temperature operation up to 130 °C is also obtained with a 1-mW fiber output power.

New Topology Multilevel Inverter Type Diode Clamped Five Level Single Phase

Multilevel inverter is a converter that converts DC power sources into AC power sources with the voltage output higher than two levels. Conventional multilevel inverter topology for five levels that is currently developing generally uses eight components of power switches. In this paper, a five-level multilevel inverter topology is proposed by reducing the power switch component to four and aided with two pin diodes and capacitors as voltage couplings. The simulation with MATLAB that has been done shows various advantages of this topology compared to conventional multilevel inverter topologies. Results and discussion This topology compare the switching techniques used between Pulse Width Modulation (PWM) and Sinus Pulse Width Modulation (SPWM) for five-level multilevel inverter. Cohesiveness in switching techniques topology is proposed and validated by using passive filter. The harmonic analysis performed by the proposed topology could reduce the output voltage with the low harmonics.

Simulation of Standalone Three-Phase Photovoltaic System with SPWM and SVPWM Techniques

Maximum power point tracking is a method employed to produce the utmost power available from the photovoltaic module. To date, many algorithms for maximum power point tracking technique had been stated, every with its own capabilities. In this paper, a Luo converter with high-voltage conversion gain is employed to track photovoltaic panels at maximum power and to step up the voltage to a higher level. This work also aims to validate the performance of the maximum power point tracking system with Luo converter which utilizes incremental conductance techniques. Space vector modulation and sinusoidal pulse width modulations are the control techniques employed to control the three-phase voltage source converter. In order to measure the overall performance indices of the proposed system, a simulation is carried out in MATLAB / Simulink environment.

Operation of grid‐connected DFIG using SPWM‐ and THIPWM‐based diode‐clamped multilevel inverters

This paper proposes a WECS based on a back to back diode-clamped multilevel inverter systems (DCMLI) fired comparatively by sinusoidal pulse width modulation (SPWM) and third harmonic injection pulse width modulation (THIPWM) techniques. DFIG performance is compared using these technologies for different wind speed under normal operation condition. The proposed approach shows that the DCMLI systems generate a nearly sinusoidal voltage with reduced total harmonic distortion (THD) thus upgrading the power quality of that produced by DFIG. As SPWM and THIPWM MLI are most common usage techniques in research, we applied them in the system to discuss a comparison of using those techniques to determine the number of levels that achieve the IEEE 519 criteria of THD which is less than 5% for both techniques (5th level for SPWM and 4th level for THIPWM) in all operation wind speed. Compared with simple PWM, and THIPWM have many advantages as lower THD, minimal number of switching to decrease switching losses and the output fundamental voltage is increased. Lastly, the paper investigates the variation of the frequency of induced rotor voltage and the active power flow due to the wind speed change when the rotor speed changes from super-synchronous to sub-synchronous speeds.

PWM control techniques for three phase three level inverter drives

In this paper two very efficient pulse width modulation techniques were discussed named Sin pulse width modulation and space vector pulse width modulation. The basic structure of the three-level inverter neutral-point clamped is introduced and the basic idea about space vector pulse width modulation for three-level voltage source inverter has been discussed in detail. Nearest three vectors space vector pulse width modulation control algorithm is adopted as the control strategy for the three phase three level NPC inverter in order to compensate the neutral-point shifting. Mathematical formulation for calculating switching sequence has determined. Comparative analysis proving superiority of the space vector pulse width modulation technique over the conventional pulse width modulation, and the results of the simulations of inverter confirm the feasibility and advantage of the space vector pulse width modulation strategy over sin pulse width modulation in terms of good utilization of dc-bus voltage, low current ripple and reduced switching frequency. Space vector pulse width modulation provides advantages better fundamental output voltage and useful in improving harmonic performance and reducing total harmonic distortion.

Experimental verification of a hybrid multilevel inverter with voltage‐boosting ability

SummaryA new nine‐level natural‐balanced boost hybrid multilevel inverter (BH‐MLI) is proposed in this paper. Each phase of the proposed BH‐MLI is designed with only 11 semiconductor switches and two electrolytic capacitors. Here, the capacitor voltages are balanced by utilizing the series‐parallel and natural balancing techniques effectively. Furthermore, the proposed circuit eradicates the multiple DC sources by introducing a single DC link for single‐ and three‐phase applications. The proposed topology can be easily extendible to obtain higher level output voltage waveform due to its modular‐switched capacitor cells (SCCs). Besides, the higher voltage level generation does not pose high‐voltage stress on any of the topology components, as the blocking voltage of all devices within the source voltage magnitude. Further, a quantitative comparison is conducted among the state‐of‐art switched‐capacitor multilevel inverter (SC‐MLIs) to highlight the superiority of the proposed configuration. Finally, the performance of the proposed BH‐MLI is experimentally validated with phase disposition‐pulse width modulation (PD‐PWM) and round control method at different modulation indices, load conditions.

Study on the evolution of Airy beam in PT symmetric medium

The evolution characteristics of an Airy beam in PT symmetric medium by using split-step Fourier method was investigated. Then the impact of truncation width, modulation depth, and modulation width on the propagation properties of soliton generated from an Airy beam was discussed in detail. The results illustrate that when an Airy beam propagates in a PT symmetric medium, a soliton with periodic variation is shedded at the main peak position and a lateral offset is generated. Moreover, it is demonstrated that with decreasing truncation width a, increasing modulation depth P and modulation factor w, the peak-to-average power ratio of a soliton from Airy beam increases, which causes the beam interference and beam distortion become more and more. With decrement of modulation depth P and increment of modulation factor w, the peak intensity and peak-to-average power ratio of a soliton from an Airy beam jump obviously, leading to decreasing propagation stability of a soliton. However, the shedding soliton can still propagates stably in a long distance.

Comparative Study on Performance Improvement of SPWM/THIPWM based DCMLI Grid Connected DFIG

Multi-level voltage source converter is integrated in various fields in renewable energy power generation technologies such as wind and solar sources for applications that need higher voltage and higher power. In wind power generation market, doubly fed induction generator (DFIG) based on wind power generation is now the leading technology as they are economically feasible, they do offer a variable speed and efficient substitute to the fossil fuel. This paper proposes a DFIG based on a back to back diode clamped multilevel converter systems (DCMLI) fired comparatively by sinusoidal pulse width modulation (SPWM) and third harmonic injection pulse width modulation (THIPWM) techniques. By using these technologies, the DFIG performance is compared for different wind speeds under normal operation condition. The proposed approach shows that the DCMLI systems generate a near sinusoidal voltage with lower values in total harmonic distortion (THD) thus, upgrading the power quality that is produced by DFIG. Lastly, the variation of frequency of induced rotor voltage and the active power flow due to the wind speed changes when the rotor speed changes from super synchronous to sub synchronous speeds is investigated.

Modified Phase-Shifted PWM for Cascaded Half-Bridges of Photovoltaic Application

Photovoltaic power plants are generally far away from loads such as cities and industrial zones. Moreover, long-distance power transmission for renewable energy will become an inevitable trend in the future. Cascaded dc-dc converters can reach a high voltage to collect and transport photovoltaic energy, with advantages such as lower costs and larger capacities. However, the input power mismatch may cause a large amount of switching harmonic components, resulting in dc-link voltage fluctuations, which will not only increase the volume of filter components, but also cause unreliable circuit breaker actions. To solve the aforementioned problems, a hierarchical phase-shifted pulse width modulation (HPS-PWM) is proposed. By rationally grouping and layering the modules, low-order harmonics generated by the switching process of the dc-dc converter can be eliminated. The fluctuation of dc-link voltage can be suppressed by HPS-PWM, according to simulation results. When the number of modules is 27 and 81, the weighted total harmonic distortion (WTHD) of the HPS-PWM method can be reduced by more than 60% compared to the phase-shifted tracking pulse width modulation (PST-PWM) and fault tolerant adaptive phase-shifted pulse width modulation (FTA-PS-PWM). Finally, experiments verify the performance of HPS-PWM, agreeing with the simulation results.

Implementation of PWM technique with soft starting algorithm for three-phase induction motor drives

In this paper, a study on issues related to starting of induction motor is carried out. Performance comparisons of various starting methods are also studied. To investigate the performance of ramp soft starting algorithm, sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM) techniques are implemented with voltage source inverter (VSI) fed induction motor. Detailed FFT analysis of stator voltage and current of induction motor is studied under wide range of speed variations. Based on experimental study, few recommendations for implementation of boost start-up and s-curve start-up algorithm in Microcontroller (STM32F407VG) are made for high inertial load. Experimental results are obtained and its performance analysis in view of FFT of motor current is also carried out for aforesaid PWM techniques.

Reliability-Oriented Selection for Grid-Connected Converters: A Low Voltage Direct Current Microgrid Case Study

As the grid-connected AC-DC converter is the key equipment that links the low voltage direct current (LVDC) microgrids and the utility grid, the safe and stable operation of the converter is of great significance to improve the reliability of the LVDC microgirds. Since the converter's reliability is affected by the converter's topological structure and modulation strategy, a civil LVDC microgrid case study is analyzed, and the power losses, thermal stresses, lifetimes and reliability of components in the AC-DC converters with different topologies and modulation strategies are evaluated in this paper. The influence of these two factors on the reliability and efficiency of the converter is discussed, and the normalized weighted total harmonic distortion (NWTHD) with different modulation strategies is analytically determined and compared. The results show that when the converter operates with unity power factor in this application scenario, among the two-level converter, flying capacitor converter, neutral point clamped (NPC) converter and T-type converter, the T-type converter has the highest reliability. The effects of the converter's topology and modulation strategy on the capacitor reliability are relatively small. In view of reliability and power quality, third harmonic injection pulse width modulation (THIPWM) or space vector pulse width modulation (SVPWM) is more suitable for the converter in this microgrid.

Sonlu Eleman Yöntemi İle Düz Dişlilerde Temas Gerilmelerinin İncelenmesi

Gears are one of the most critical elements in power transmission because it plays a significant role in the industry. Spur gear is used to transmit power and rotary motion between parallel shafts. It is one of the simplest types of the gears. Surface failure of the gear tooth is a pitting when contact stress is exceeding the strength of the material to surface fatigue. This paper studies the contact stresses in the contact zone among the spur gear pairs by using finite element method under static conditions. Contact stress among the gear tooth pair’s engagement determines the facility of the gear to transmit the power without harm. The contact stress in gears has played an important role for last years, but an extensive research is still required to understand the several parameters affecting this stress. Among these parameters, the most important factors affecting the surface contact stress are; number of teeth, module and face width. In the present study, the contact stress in spur gear is calculated by changing one of these parameters and keeping remaining constant to obtain the influence of each parameter on contact stress separately based on AGMA's equations and finite element method (FEM). A computer program is used to build up the gears by using homemade software and SolidWorks. The results of the FEM analyses from MSC Software (MARC) are presented. These results are compared with the theoretical results (AGMA’s equations). The contact stress achieved by FEM is lower than the obtained results by AGMA's equations and the corresponding percent difference detected are about 8 %. The results of the contact stress analysis specify that increasing the values of geometrical parameters (number of teeth, module and face width) lead to decrease in the tooth contact stress.

Tooth wear prediction of crowned helical gears in point contact

A tooth wear prediction methodology for helical gears in point contact is developed to evaluate their wear resistances using a lead crown. The load distribution coefficient is proposed in accordance with the elastic approach of each contact tooth pair being equal, and contact pressure are determined, and the sliding distance is obtained by adopting a generalized moving distance model. Then, the wear depth is computed in accordance with Archard’s wear equation, and the differences in tooth wear on standard and crowned helical gears are analyzed comparatively. The effects of crowned amount, fundamental geometry, and operating parameters on the wear resistance of the crowned helical gear pair are investigated. The results reveal that the tooth wear is lower on the gear surface with a moderate crowned amount than on the standard one, and that wear depths decrease with the increase in the helix angle, normal pressure angle, normal module, tooth number, or tooth width but increase with input torque rises. Furthermore, the rational lead crown, the geometric, and operating parameters optimization can be applied to wear resistance in the gear design.

Transformer based NPC multilevel inverter using reduced number of components

This paper revolves around the reduction of a number of switches and the sources for a multilevel inverter, for this, we have proposed a transformer-based topology which has helped us in reducing the number of switches from twenty-four to sixteen and also in the reduction of sources from eight to one. The circuit consists of two H-Bridges which are coupled by a single-phase transformer, the topology gives us a liberty of changing the number of levels in accordance to the number of turns in the secondary side of the transformer for example if our ratio is 1:1 the number of levels will be five subsequently if it is changed to 1:2 the number of levels will be changed to seven. As the number of switches is reduced the size and complexity of the circuit is also decreased. In order to improve on the part of switching efficiency, we have used space vector pulse width modulation which is a better method as compared to its counterpart switching methods such as sinusoidal pulse width modulation and multiple pulse width modulation techniques.

Investigation on positioning control strategy and switching optimization of an equal coded digital valve system

This article concerns high accuracy positioning control with switching optimization for an equal coded digital valve system. Typically, pulse number modulation control cannot realize micro-positioning due to the characteristics of step-wise flow variation, therefore, a new position controller consisting of a model-based pulse number modulation and a differential pulse width modulation strategy is proposed to control the position of a hydraulic cylinder at high and low velocity cases, respectively. In addition, in order to solve several problems caused by the pulse number modulation and differential pulse width modulation, such as increased number of switchings and large difference among number of switchings of valves, a switching optimization consisting of a switching cost function, a circular buffer and a circular switching method is proposed. An adaptive weight of the switching cost function is proposed for the first time to reduce the total number of switchings under different pressure differences and its design criterion is presented. A circular buffer and a new circular switching method are used to improve the degree of equal distribution of switchings when the pulse number modulation and differential pulse width modulation are used, respectively. Comparative experimental results indicated that the average and the minimum positioning error for the proposed controller are only 10 and 1 μm, respectively. The number of switchings and the degree of equal distribution of switchings are significantly optimized. Moreover, the pressure fluctuations caused by the proposed controller remain acceptable.

Performance Analysis of Control Techniques for Micro Power System using Hybrid Approach

The hybrid combination (Photovoltaic, Fuel Cells, and Battery) has found to be best energy resources which provide a reliable micro-power system. The single-phase inverter is modelled using appropriate gate pulses and the three-phase systems are modelled by control techniques such as Sinusoidal Pulse Width Modulation (SPWM) and State Vector Pulse Width Modulation (SVPWM) for attaining AC power. In this paper, the modular approach and Multiple Input Single Control (MISC) is applied to single-phase and three-phase systems with SPWM and SVPWM respectively to achieve better output efficiency. The modular approach is introduced for the power quality problem in the micro system, and MISC maintains the constant dc-link voltage. Furthermore, the proposed method maintains the State of Charge (SOC) of the battery by controlling the converter switches. The proposed research methodology is executed in MATLAB/Simulink-R2014a (Version 8.3) tool. The simulation results demonstrate that the MISC-based three-phase AC system with SVPWM achieves better results with reduced distortion level than SPWM.

Optimization of Modulation Methods for Solenoid Valves to Realize an Odor Generation System.

An artificial olfactory system coupled with an odor generation system is herein reported. The artificial olfactory system is composed of four chemical sensors consisting of quartz crystal microbalances (QCMs) coated with room temperature ionic liquids (RTILs). The sensors are interrogated by four vector network analyzers, which are used to measure the series resonant frequency and motional resistance. The odor generation system can generate eight different odors and mix them in any composition. Solenoid valves are used to switch the path and control the concentration of the different odors before blending. Two algorithms to control the solenoid valves, delta-sigma modulator, and simple pulse width modulation (PWM) are studied, optimized, and compared. Finally, the uncertainty of the odor generating system is calculated.

Investigation of Bragg gratings in planar hybrid metal–insulator–metal plasmonic waveguide using graded profile

The design of integrated components using hybrid plasmonics is attracting a widespread interest in the recent years. This work proposes a consistent approach to design Bragg gratings employing the concept of graded profile in a planar hybrid metal–insulator–metal plasmonic waveguide. A comparative study of various width modulations such as triangular, parabolic and rectangular profiles is presented. The most striking observation is that Bragg gratings with parabolic profile offer best performance in terms of compact track length (3.48 μm), wide stopband (168 nm) and good transmission characteristics with fewer side lobes. Additionally, a nanocavity analysis is performed by introducing a defect length of 140 nm in the Bragg grating structure with parabolic profile. A peak transmission of 89% is observed at the resonance wavelength of 1550 nm.

Sector Subdivision Based SVPWM Strategy of Neutral-Point-Clamped Three-Level Inverter for Current Ripple Reduction

This paper presents a sector subdivision based space vector pulse width modulation (SVPWM) strategy with reduced current ripple for a three-level inverter. Using the output current ripple theory, closed-form expressions of average current ripple vectors for both continuous and discontinuous switching sequences are derived. Based on the sector and triangle distributions of conventional SVPWM strategy, each triangle is further divided into three small-regions. Then the switching sequence with the lowest magnitude of the average current ripple vector is applied in every small-region, so that the advantages of continuous pulse width modulation (CPWM) and discontinuous pulse width modulation (DPWM) under different modulation index conditions are combined to reduce the current ripple in the whole modulation range. The output performance of the proposed strategy is compared with the conventional CPWM and DPWM strategy, and experimental results verify that the proposed strategy could reduce the current ripple of three-level inverters effectively.

진폭 변조 절대거리측정을 위한 마이크로컨트롤러 기반의 고안정도 RF-주파수 생성

In this paper, we describe high-stable RF-frequency generation using a low-cost 8-bit microcontroller for amplitudemodulation based distance measurement, which is one of the indispensable technologies for cost-effective Lidar application. The RF frequency generator using the microcontroller was implemented by externally referencing to an atomic clock and 8- bit timer/pulse width modulation (PWM) functions, which are embedded in a microcontroller. The microcontroller we used was ATmega128 of Microchip with 16 MHz clock and 8-bit timer, which generates the maximum frequency of up to 62.5 kHz, enabling 2.4-kilometer ranging without phase ambiguity. The stability of RF-frequency generated from the implemented system was evaluated in terms of Allan deviation using a commercial frequency counter. The stability indicated 10<SUP>-11</SUP> at 1-s averaging time and 10<SUP>-12</SUP> at 100 s averaging time, which represents a 1/10 degradation compared to the stability of the commercial function generator. Along with the stability evaluation, we interrogated frequency tunability, which extends a measurable range without phase ambiguity.