Duty Ratio Research Articles

Microstructural evolution and formability of Ti−6Al−4V alloy sheet during electropulsing-assisted bending

The electropulsing-assisted bending test was carried out on Ti−6Al−4V alloy sheet with the effective current density of 0−3.2 A/mm2 and duty ratio of 10%−70%. The results show that the bending forming displacement increased from 9.15 to 15.60 mm with increasing effective current density from 0 to 2.4 A/mm2. The crack changed to be shallow and small at the same time. Besides, the springback angle decreased as the effective current density increased at the bending displacement of 8 mm. Duty ratio also affected bending angle, where 30% duty ratio led to the lowest bending angle of 135.0°. The thermal stability temperature increased with increasing effective current density and varied non-monotonically with duty ratio. In addition, grain coarsening, {0001} texture strengthening and sub-grain development were observed during electropulsing-assisted bending. The electropulsing decreased dislocation density and accelerated dislocation rearrangement, the rearranged and piled-up dislocation inside α grains promoted sub-grain structure formation, which improved the formability. The contribution of athermal effect made the low-temperature formability of Ti−6Al−4V alloy comparable to that at high temperature.

An Optimized Model Predictive Control Method With Fixed Switching Frequency for Eliminating Common-Mode Voltage of Five-Level Converters

In this paper, an optimized model predictive control (MPC) method with fixed switching frequency (FSF) is proposed to eliminate the common-mode voltage (CMV) and balance the capacitor voltage. Firstly, the zero CMV vector diagram is divided by finite control set MPC (FCS-MPC) to obtain the candidate vectors effectively. Then, in order to control the capacitor voltage and avoid the great computational burden originated from the redundant switching combinations, a piecewise control scheme is proposed to determine the required ones directly. The sequence generated by the selected vectors is further optimized for the purpose of saving switching transitions according to the internal and external parts of the vector diagram. Finally, the duty ratios are evaluated based on the results of the FCS-MPC in dividing sectors so as to avoid any extra complex calculation. The experimental evaluation has been carried out to validate the feasibility and effectiveness of the proposed method.

A High-Efficiency DC-DC Converter Based on Series/Parallel Switched Inductor Capacitors for Ultra-High Voltage Gains

A high-efficiency DC-DC converter employing a modified architecture called the hybrid switched inductor–capacitor series (MHSLCS) is proposed in this paper. The primary goal is to achieve a notably ultra-high voltage gain for renewable energy systems (RESs). Furthermore, the use of only one input capacitor in the MHSLCS eliminates pulsations in the input current at both low and high duty ratios. The proposed converter integrates the MHSLCS with a modified switched capacitor (MSC) that interleaves with the main MOSFET, effectively doubling the voltage transfer gain. Additionally, a modified hybrid switched inductor–capacitor parallel (MHSLCP) is incorporated in parallel with an interleaved auxiliary MOSFET. Both MOSFETs, combined with the MSC, contribute to achieving an ultra-high voltage gain. In addition, the inductors of the MHSLCP operate in a discontinuous conduction mode (DCM), which results in significant stress reductions in the power diodes and switches at high output voltages. The advantages of the proposed converter are multifaceted, demonstrating a high efficiency while minimizing the voltage in power device diodes and MOSFETs. The use of low inductance and capacitance values at high switching frequencies further enhances the performance. Wide-bandgap (WBG) power devices are employed to achieve the desired high voltage gain and efficiency. The proposed converter was designed with a PCB and underwent experimental testing to validate laboratory results. The proposed converter boosted the input voltage from 30 V to a variable output voltage between 325 V and 500 V, with a power output of 325 watts and an efficiency of 95.5%.

Real-Time Implementation for the Robust Controller of the Switched Boost Inverter within an Autonomous Modified Nanogrid

SBI stands for switched-boost inverter and is a single-stage power converter used to connect low-power sources, such as solar photovoltaic (PV) arrays within a modified nanogrid, to loads. Despite its many benefits, such as the fact that it does not require expensive sophisticated dead-time circuitry, its duty ratio is limited to between 0 and 0.5. As a result, this publication is a contribution towards improving the SBI's performance for use in a modified nanogrid. Furthermore, it also presents a revolutionary strategy for a simple closed-loop control technique that overcomes the majority of inverter shortcomings and system nonlinearity. The suggested robust controller uses a metaheuristic optimization technique, called gorilla troops optimization (GTO), to optimize the performance of this controller. The robustness of the suggested controller is tested against the sudden change of the nanogrid input voltage (i.e., PV-voltage), modulation index of the inverter, and the step-change in DC-link output voltage of the inverter. The test results obtained from Matlab/Simulink software are compared with particle swarm optimization (PSO) – as another optimization algorithm. Furthermore, the proposed system is experimentally implemented with OPAL RT-4510v real-time hardware in the loop (HIL), rapid control prototyping, OP-8660 HIL controller and data acquisition platform.

Darbo užmokesčio dinamikos viešojoje švietimo įstaigoje analizė

The article investigates the essence, structure of wages, the system of taxation of income received from employment relations. Wage changes for 2015–2024 have been carried out. In a public educational institution, the analysis reveals trends in the salary of academic employees. In 2015 January 1st in Lithuania, instead of the national currency litas, the euro was introduced as the common European currency, a decade full of changes, based on regulated changes. Although the regulation of labor payment in the Republic of Lithuania is assessed ambiguously due to the abundance of laws and other normative acts and their frequent changes, a regulated, moderate, albeit unclear, increase in wages has been identified. Determining the value of an academic employee's work is variable and sensitive, in the absence of a more detailed and reasoned justification of official coefficients. The results of the analysis allow us to make the assumption that when forecasting and strategizing the support of employees' motivation for scientific activities, it is appropriate to adjust job coefficients while maintaining equal gaps between positions. Keywords: academic employee, wage, wage structure, duty ratios, taxation, taxes and tax contributions.

Bidirectional PWM Converter to Interface AC Part to DC Microgrid with Neutral Potential Balancing

This research presents a description of a bidirectional pulse width modulated converter that functions as a rectifier by using the direct power control strategy and space vector modulation technology. In contrast to the voltage-oriented control strategy, this method minimises the number of internal current loops and requires more tuning. While functioning as an inverter, it applies the space vector modulation technique as well. The approach, on the other hand, is not the same as rectifiers since it calculates the duty ratio of the neighbouring voltage vectors in each small triangle that is generated in each sector that has a period of 60 degrees. In both situations, the neutral point potential has been brought back into equilibrium.

Modified direct torque control algorithm for regeneration capability of IM driven electric vehicle by using hybrid energy storage system

The direct torque control (DTC) algorithm of a 3-phase voltage source inverter (VSI) has been implemented to drive induction motor (IM) for EV applications. However, the conventional DTC for IM is distressed due to large torque ripple, high current total harmonic distortion, and variable switching frequency. So, in this manuscript, a modified direct torque control (MDTC) algorithm is proposed to tackle the said challenges. A three-level hysteresis controller is proposed in modified DTC to optimize the duty ratio of the fundamental voltage vector to minimize the error between the reference and final voltage vector imposed on IM terminals. To improve the efficiency of the EVs by developing a system that uses the energy produced during regenerative braking. The proposed method recovers electric energy produced by the EV without using any additional power converter. The switching patterns allow power flow in both directions. Later, a hybrid energy storage system (HESS) is integrated to supply and store the energy in an optimal way. Extensive studies have been performed to show the efficacy of the proposed MDTC technique in IM based EV application with HESS. The key findings indicate that the proposed MDTC provides better dynamic and steady-state performance.

Optimum pulse electrolysis for efficiency enhancement of hydrogen production by alkaline water electrolyzers

Alkaline water electrolysis is considered as the most feasible way to realize large-scale hydrogen production from renewable energy sources. However, the poor efficiency performance in low load limits the wide-range operation of alkaline water electrolyzers. The energy loss caused by the parasitic current is the main reason of the poor efficiency in low load. Based on the electrolyzer internal structure, an improved model of alkaline water electrolyzers is proposed and the inefficiency mechanism is illustrated. It is found that by applying pulse current for electrolysis, the efficiency of hydrogen production in low load can be enhanced greatly. The influence of the pulse current magnitude and duty ratio on the efficiency improvement is studied. Under different operation conditions, they can be regulated to achieve the maximum efficiency of hydrogen production. The electrolyzer parameters also affect the efficiency trend, especially the double layer capacitance. Finally, the results are experimentally verified on a 10 kW alkaline water electrolyzer.

Research on the influence of pulse current parameters on the tooth filling during current-assisted splitting spinning of small module tooth-shaped part

Current parameters are the main factors influencing the tooth filling of small module tooth-shaped parts (SMTSPs) with characteristics of hollow, thin wall-thickness made of difficult-to-deform metal during current-assisted splitting spinning (CASS). A coupled electrical-thermal-mechanical finite element analysis (FEA) model was established based on the ABAQUS software, and the influence of pulse current parameters, such as current density and duty ratio, on the tooth saturation was investigated. The results show that the tooth saturation increases obviously under pulse current comparing without pulse current, and increases rapidly with the increasing of the current density and duty ratio, but the tooth saturation tends to reach a threshold value when the current density greater than 13.5 A/mm2 and the duty ratio greater than 20%. The relative error of the tooth saturation between simulation and experimental result is less than 2%, which indicates that the established CASS FEA model of SMTSPs is reasonable.

A new quasi Z-source embedded network capable of producing DC-side voltage gain even without shoot-through state for efficient operation

The conventional quasi-z-source inverter (QZSI) is not capable of producing DC-side voltage gain without shoot-through operation. This restricts freedom of control and performance. The decoupled control between modulation index (MI) and duty ratio for producing DC-side voltage gain at MI = 1 is not permitted. In this context, this paper proposes a novel active-switched impedance network. This is capable of producing DC-side voltage gain either in shoot-through mode or in the absence of shoot-through state. In effect, variable DC-side voltage gains are achieved at a fixed value of MI, even at MI = 1 (without the dead-time requirement of the inverter bridge). For low-gain operations (up to 2.5), the DC-side voltage gain is achieved by the proposed active-switched QZSI by restricting the shoot-through duty ratio to a low value (0-0.1). In high-gain (>2.5) operations, the variable-boosting operations of the proposed QZSI are achieved without shoot-through operation (MI = 1) by controlling its active switch. This increases efficiency by discarding the shoot-through state at high gain. The suggested closed-loop control logic of the proposed QZSI is also provided to meet the load voltage. The simulation work is conducted in versatile operating conditions to highlight its diversified performances. The experiments also verify its operations under different conditions.

Device characteristics of alternating-current-driven colour-tunable phosphorescent organic light-emitting diodes

We demonstrate alternating-current (AC)-driven colour-tunable organic light-emitting diodes (OLEDs) with vertically stacked green and red phosphorescent OLED units. Optically optimized thicknesses of hole and electron transporting layers were investigated through optical simulation. In addition, two types of red host materials were used for the red OLED unit, and the red OLED unit with 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl showed higher current efficiency compared to that of the red OLED unit with 2,6-Bis(3-(9H-carbazol-9-yl)phenyl)pyridine. The fabricated colour-tunable exhibited red and green colours when the duty ratio was 1% and 99%, respectively. Furthermore, the device can produce various colours that are a mixture of green and red by adjusting the AC-driving duty ratios.

Investigation of enhancing EDM machining performance of INCONEL alloy using composite electrodes

In this research, an attempt was made to reinforce aluminium with graphite particles and use it as a tool material with the objective of combining the properties of aluminium and graphite. The micrograph confirms that the graphite particles were uniformly distributed over the aluminium matrix, density reduces and thermal conductivity increases with the addition of graphite particles. Material Removal Rate (MRR) peaks at 12 A current before declining due to plasma channel expansion, an optimal Ton of 8 μs ws observed, with 4 μs Toff yielding higher MRR. Copper electrodes excel due to thermal conductivity, while 5% graphite in aluminum boosts MRR to 31.89 mm3 min−1, additional graphite decreases MRR. TWR rises with shorter Toff until 6 μs, then decreases. Gap control impacts TWR, with lower spark gaps causing higher TWR due to intense material removal, and higher gaps leading to increased TWR due to incomplete flushing. Copper electrodes have the lowest TWR due to their high melting temperature. The addition of graphite in aluminum reduces TWR at low currents but is less effective at higher currents. Surface roughness (Ra) decreases with higher current, reaching a minimum of 7.02 μm at 12 A. Optimal Ton is 8 μs (7.56 μm), while shorter Toff at 4 μs and a 3 mm gap yield the best Ra of 7.36 μm with A4 composite tool. Copper electrodes result in higher Ra at higher currents, while graphite in aluminum improves surface quality, especially at 5% content. Arcing, an undesirable electrical discharge phenomenon in EDM, adversely affects machining. Experiments revealed a strong correlation between high duty cycles, duty ratios, and arcing propensity, with composite tools being more susceptible due to their variable conductivity. In contrast, non-composite tools, exemplified by copper, withstand higher duty ratios without arcing.

A core loss estimation method based on improved waveform coefficient Steinmetz equation for asymmetric triangular flux density waveform

Accurate estimation of high frequency magnetic core losses under non-sinusoidal excitations is critical to the design of solid-state transformers. This paper proposes a waveform transformation principle, termed the equal derivative transformation (EDT), for piecewise linear flux density waveforms. Under the same maximum flux density, an asymmetric triangular flux density wave can be transformed into a symmetric one with a different frequency in terms of the calculation of core losses, hence the introduction of the improved waveform coefficient Steinmetz equation (iWcSE). The magnetic characteristics of three different toroidal samples (nanocrystalline alloy FT-3KL, amorphous alloy 1K101, ferrite N87) under square excitation at different duty ratios and certain frequencies are measured. Core losses predicted by the model are in good agreement with the measurement.

Study of PLL less DSGTP System using band-pass filter and APC (active power coefficient) control

This paper represents a study on a grid-tied photovoltaic (PV) system connected to a non-linear load. The system includes a PV array, a boost converter, a voltage source inverter (VSI), and a coupling inductor for grid connection. The maximum power point tracking (MPPT) mechanism based on Perturb and Observe (P&O) method which is used to control the duty ratio of the boost converter. Synchronization is achieved through a second-order band-pass filter instead of a Phase Locked Loop (PLL). However, the non-linear load causes poor current quality, leading to a high Total Harmonic Distortion (THD) in the grid current, which may affect the sinusoidal nature of the grid current and other connected loads. To address the harmonics problem, an Active Power Coefficient (APC) control technique is implemented to control the PV inverter gate pulse. The proposed model has been simulated in Matlab/Simulink, and system output parameters are analysed graphically. The simulation results indicate that the proposed approach maintains the total harmonic distortion (THD) of the grid current below 5% even in changing weather conditions, which satisfies the IEEE 519 standard.

Maximizing solar photovoltaic system efficiency by multivariate linear regression based maximum power point tracking using machine learning

Introduction. In recent times, there has been a growing popularity of photovoltaic (PV) systems, primarily due to their numerous advantages in the field of renewable energy. One crucial and challenging task in PV systems is tracking the maximum power point (MPP), which is essential for enhancing their efficiency. Aim. PV systems face two main challenges. Firstly, they exhibit low efficiency in generating electric power, particularly in situations of low irradiation. Secondly, there is a strong connection between the power output of solar arrays and the constantly changing weather conditions. This interdependence can lead to load mismatch, where the maximum power is not effectively extracted and delivered to the load. This problem is commonly referred to as the maximum power point tracking (MPPT) problem various control methods for MPPT have been suggested to optimize the peak power output and overall generation efficiency of PV systems. Methodology. This article presents a novel approach to maximize the efficiency of solar PV systems by tracking the MPP and dynamic response of the system is investigated. Originality. The technique involves a multivariate linear regression (MLR) machine learning algorithm to predict the MPP for any value of irradiance level and temperature, based on data collected from the solar PV generator specifications. This information is then used to calculate the duty ratio for the boost converter. Results. MATLAB/Simulink simulations and experimental results demonstrate that this approach consistently achieves a mean efficiency of over 96 % in the steady-state operation of the PV system, even under variable irradiance level and temperature. Practical value. The improved efficiency of 96 % of the proposed MLR based MPP in the steady-state operation extracting maximum from PV system, adds more value. The same is evidently proved by the hardware results.

Total harmonic distortion analysis of inverter fed induction motor drive using neuro fuzzy type-1 and neuro fuzzy type-2 controllers

Introduction. When the working point of the indirect vector control is constant, the conventional speed and current controllers operate effectively. The operating point, however, is always shifting. In a closed-system situation, the inverter measured reference voltages show higher harmonics. As a result, the provided pulse is uneven and contains more harmonics, which enables the inverter to create an output voltage that is higher. Aim. A space vector modulation (SVM) technique is presented in this paper for type-2 neuro fuzzy systems. The inverter’s performance is compared to that of a neuro fuzzy type-1 system, a neuro fuzzy type-2 system, and classical SVM using MATLAB simulation and experimental validation. Methodology. It trains the input-output data pattern using a hybrid-learning algorithm that combines back-propagation and least squares techniques. Input and output data for the proposed technique include information on the rotation angle and change of rotation angle as input and output of produced duty ratios. A neuro fuzzy-controlled induction motor drive’s dynamic and steady-state performance is compared to that of the conventional SVM when using neuro fuzzy type-2 SVM the induction motor, performance metrics for current, torque, and speed are compared to those of neuro fuzzy type-1 and conventional SVM. Practical value. The performance of an induction motor created by simulation results are examined using the experimental validation of a dSPACE DS-1104. For various switching frequencies, the total harmonic distortion of line-line voltage using neuro fuzzy type-2, neuro fuzzy type-1, and conventional based SVMs are provided. The 3 hp induction motor in the lab is taken into consideration in the experimental validations.

Hybrid PV and Fuel Cell Generating System for Shipboard Applications Based on Optimal Dispatch Evaluator Algorithm

The construction of an Energy Management System (EMS) for ships has been designed to improve the electrical performance of cruise lines. According to the target requirement, the specified electrical plant is an integrated power system characteristic of contemporary electric ships. Battery backup, low performance, and voltage instability are the drawbacks of the existing method. To overcome the limitations of the proposed method-based Photovoltaic (PV) renewable source using SEPIC DC–DC converters and a bidirectional fuel cell as an additional input power source. Power generation from the two different input sources is controlled through a DC bus and conversion through a centralized high-gain DC–DC converter. In this conversion, Pulse Width Modulation (PWM), which is the maximum power obtained using the optimal dispatch evaluation algorithm using an Artificial Neural Network (ANN), is obtained by adjusting the duty ratio of the Single-Ended Primary Inductance DC–DC converters (SEPIC). The electrochemical power source is a fuel cell. Hydrogen and oxygen are combined in fuel cells to create electricity, along with the consequences of heat and water being transformed into mechanical energy; in the battery management system, the battery is employed as an energy storage system to regulate any power imbalance or excess while taking the battery’s state of charge into account Electric Ships (AESs). The outcomes of the MATLAB Simulink output, fuel cell and battery storage performance analysis, efficiency, and THD analysis are summarized as follows.

Characteristics of high-repetition-rate bipolar pulse DBD under various electrical conditions in atmospheric-pressure air

Numerous studies have been conducted on pulse dielectric barrier discharge (DBD) because it can produce powerful discharges uniformly at atmospheric pressure with a fast rise time. Although much research has been conducted on pulse DBD below 10 kHz, relatively little has been conducted on pulse DBD at high pulse repetition rates (PRRs). Therefore, in this study, the ozone generation and discharge characteristics of bipolar pulse DBD in atmospheric-pressure air at a high PRR of 10 kHz or above were investigated. According to the results of this study, with the exception of electron temperature, most discharge characteristics need for practical applications—like transfer charge, electron density, and discharge uniformity—improved as the voltage and duty ratio increased at high PRR. On the contrary, increasing the PRR exhibited trade-off features like low electron temperature, low discharge uniformity, and a high number of discharges per unit time. Ozone generation demonstrated good results at high voltage, appropriate PRR, and low duty ratio, but applying suitable electrical conditions is crucial considering ozone generation speed and power consumption. The findings of this study will be very beneficial for high-PRR pulse DBD applications that require quick and effective processing. Additionally, they will be useful for researching the characteristics of pulse DBD at high PRR.

Stability and reliability analysis of a non‐isolated high gain DC‐DC converter

AbstractThis paper investigates the stability and reliability analysis of a non‐isolated high‐gain DC‐DC converter. The proposed DC‐DC converter produces a high gain output voltage with a lower duty ratio and reduced voltage stress on the semiconductor switch. A reliability analysis is performed to predict the failure rate and lifetime of the individual components using the military handbook (MIL‐HDBK‐217F). A state space equation and small signal modeling of the proposed converter are derived to elucidate the performance of the proposed converter through stability analysis. A closed‐loop using PID controller is incorporated to attain the constant regulated output voltage during sudden parameter changes. The validation of the closed‐loop using the PID controller is verified with the wide range of variations in the different parameters, such as input voltage, load value, and reference voltage value. The laboratory‐based prototype is developed for the proposed converter and validated the performance with 250 W. The power density and efficiency of the proposed converter are 1.360 kW/L and 93%, respectively.

The influences of light scattering on digital light processing high-resolution ceramic additive manufacturing

Digital light processing (DLP) has emerged as a highly promising 3D printing technology, which is due to its ability to fabricate components and structures with low cost and high precision. The DLP is, therefore, applicable in a wide range of fields. The phenomenon of light-scattering plays a dominant role in the DLP manufacturing process, but the specific impact of ceramic particles on the distribution of incident light remains unclear. The present study has, therefore, focused on studying the effect of ceramic particles on light-scattering by performing extensive theoretical finite element simulations. The aim was then to improve the curing quality of the DLP 3D printing process. More specifically, spherically shaped particles with a uniform distribution, lower duty ratios, or materials with lower refractive indices were necessary conditions for enhancing the printing precision due to the mitigated lateral light scattering effects. The overall results of this study have provided valuable guidance for the control of the light-induced curing in the 3D printing process of ceramics, thereby facilitating advancements in ceramic-based fabrication techniques.