Pole-placement control of 4-leg voltage-source inverters for standalone photovoltaic systems: Considering digital delays

Three leg inverters for photovoltaic systems have a lot of disadvantages, especially when the load is unbalanced. These disadvantages are for example, small utilization of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. A solution for these problems is the four-leg inverter. Most papers dealing with 4-leg inverters ignore the effect of digital delays in control loop and suggest classic controllers, such as PI controller. However, the transient performance of the closed-loop system does not become, accurately, adjustable and acceptable, in most cases. This paper proposes a novel model, considering digital delays, for 4-leg inverters. Then, it applies pole-placement control strategy, via state feedback, to adjust the transient performance of the closed-loop system to a desired second-order system. Simulation results validate theoretical results and proposed control strategy.     

Adaptive pole-placement control of 4-leg voltage-source inverters for standalone photovoltaic systems

Three-leg inverters for photovoltaic systems have many disadvantages, especially when the load is unbalanced. These disadvantages are, for example, small utilization of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. A solution for these problems is the 4-leg inverter. Most papers dealing with 4-leg inverters suggest classic controllers, such as PI controller, for the system. However, the transient performance of the closed-loop system does not become acceptable. On the other hand, adaptive control of 4-leg inverters has not yet been discussed in the literature. This paper proposes pole-placement control strategy, via state feedback, for 4-leg voltage-source inverters to adjust the transient performance of the closed-loop system. In addition, a STR (self-tuner regulator) is introduced to guarantee the adaptive performance of the controller in the presence of time-variant RL loads. Simulation results validate the theoretical results and proposed control strategy.     

Diffusion study of rare-earth oxides into silica layer for environmental barrier coating applications

The effect of exposure temperature and time on the diffusion rate of rare-earth oxides applied on silicon carbide fiber-reinforced SiC ceramic matrix composites (SiC/SiC CMCs) have been investigated. Knowledge on diffusion mechanism between the deposited rare-earth (RE) slurry and silica layer is necessary to understand the process governing EBCs formation and their properties. SEM/EDS analysis were used to study the effect of microstructure on diffusivity. The diffusion coefficient increases with increasing sintering temperature and time. The measured diffusion coefficients of the RE-coating into silica layer were in the order of 10^?15-10^-17 m²/s revealing an overall good adhesion on the SiC/SiC CMCs.     

Kinetic modeling of mass transfer during deep fat frying of shrimp nugget prepared without a pre-frying step

The objective of this study was to evaluate the effect of different batter formulation on mass transfer during deep fat frying of shrimp nuggets prepared without a pre-frying step. The effects of soy and corn flour (5, 10%) addition to the batter formulation, frying temperature and time on mass transfer were determined. The results showed an interaction effect of these processing conditions on mass transfer. The most reduction in fat absorption was observed when samples were coated with batter contained 10% soy flour and fried at 190 °C. The first order kinetic based on the Fick's law were used to describe moisture transfer data. The effective moisture diffusivity ranged between 2.05 × 10⁻⁸ and 5.71 × 10⁻⁸ m²/s with R² between 0.91 and 0.98, and fat transfer rate constant was between 3.5 × 10⁻³ and 7.8 × 10⁻³ s⁻¹ with R² from 0.82 to 0.99. Activation energy obtained from the Arrhenius plot for the effective moisture diffusivity ranged between 18.42 and 23.84 kJ/mol.     

Thermochemical Analysis of Phases Formed at the Interface of a Mg alloy-Ni-plated Steel Joint during Laser Brazing

The thermodynamic stability of precipitated phases at the steel-Ni-Mg alloy interface during laser brazing of Ni-plated steel to AZ31B magnesium sheet using AZ92 magnesium alloy filler wire has been evaluated using FactSage thermochemical software. Assuming local chemical equilibrium at the interface, the chemical activity–temperature–composition relationships of intermetallic compounds that might form in the steel-Ni interlayer-AZ92 magnesium alloy system in the temperature range of 873 K to 1373 K (600 °C to 1100 °C) were estimated using the Equilib module of FactSage. The results provided better understanding of the phases that might form at the interface of the dissimilar metal joints during the laser brazing process. The addition of a Ni interlayer between the steel and the Mg brazing alloy was predicted to result in the formation of the AlNi, Mg₂Ni, and Al₃Ni₂ intermetallic compounds at the interface, depending on the local maximum temperature. This was confirmed experimentally by laser brazing of Ni electro-plated steel to AZ31B-H24 magnesium alloy using AZ92 magnesium alloy filler wire. As predicted, the formation of just AlNi and Mg₂Ni from a monotectic and eutectic reaction, respectively, was observed near the interface.     

A guided tabu search/path relinking algorithm for the job shop problem

The job shop scheduling problem with makespan criterion is valuable from both practical and theoretical points of view. This problem has been attacked by most of the well-known meta-heuristic algorithms. Among them, tabu search has emerged as the most effective approach. The proposed algorithm takes advantages of both N1 and N6 neighborhoods. N1 neighborhood is used as a path relinking procedure while N6 neighborhood with its guideposts is applied in a tabu search framework. In addition, a method is presented for updating the topological order, heads and tails in N6 neighborhood. The algorithm is tested on standard benchmark sets, outperformed all previous approaches (include i-TSAB) and found six new upper bounds among the unsolved problems. Furthermore, we have tried to collect the newest upper bounds for the other problems.     

A fast and reliable multi-sender algorithm for peer-to-peer networks

Due to special constraints in peer-to-peer (P2P) networks (such as bandwidth limitation) and because of their highly dynamic characteristics, a single node cannot provide a reliable multimedia stream to the receivers. Several multi-sender algorithms are proposed to reliably deliver a media stream to the receiver through the intrinsically unreliable P2P networks. Based on upload bandwidths and availability of peers as well as the bandwidths of the links connecting the senders and the receiver, PROMISE selects a set of active senders to maximize the expected bit-rate delivered to the receiver. By careful investigation of PROMISE, in this paper, we present why and how it deviates from finding the optimal solution. The proposed algorithm, we call IPROMISE, consistently provides a higher media quality to the receiver, with a computational complexity similar to PROMISE. We also introduce FastIPROMISE which provides the same quality as IPROMISE but requires much less computations. That is achieved by shrinking the search space.     

The Use of Plasma Actuators in Narrowband Active Noise Control

The analysis of narrowband active noise control systems for single-tone input signals is considered. The narrowband active noise control (ANC) system with FX-LMS algorithm is described. Then the narrowband ANC system via plasma actuators is investigated. Experiments were conducted using plasma actuators to control narrowband noise generated by speaker in a duct. The motivation behind the study was to explore the potential of plasma actuators to reduce noise.     

Synthesis and Biological Screening of New Lawson Derivatives as Selective Substrate-Based Inhibitors of Cytochrome bo3 Ubiquinol Oxidase from Escherichia coli

The respiratory chain of Escherichia coli contains two different types of terminal oxidase that are differentially regulated as a response to changing environmental conditions. These oxidoreductases catalyze the reduction of molecular oxygen to water and contribute to the proton motive force. The cytochrome bo₃ oxidase (cyt bo₃) acts as the primary terminal oxidase under atmospheric oxygen levels, whereas the bd-type oxidase is most abundant under microaerobic conditions. In E. coli, both types of respiratory terminal oxidase (HCO and bd-type) use ubiquinol-8 as electron donor. Here, we assess the inhibitory potential of newly designed and synthesized 3-alkylated Lawson derivatives through L-proline-catalyzed three-component reductive alkylation (TCRA). The inhibitory effects of these Lawson derivatives on the terminal oxidases of E. coli (cyt bo₃ and cyt bd-I) were tested potentiometrically. Four compounds were able to reduce the oxidoreductase activity of cyt bo₃ by more than 50 % without affecting the cyt bd-I activity. Moreover, two inhibitors for both cyt bo₃ and cyt bd-I oxidase could be identified. Based on molecular-docking simulations, we propose binding modes of the new Lawson inhibitors. The molecular fragment benzyl enhances the inhibitory potential and selectivity for cyt bo₃, whereas heterocycles reduce this effect. This work extends the library of 3-alkylated Lawson derivatives as selective inhibitors for respiratory oxidases and provides molecular probes for detailed investigations of the mechanisms of respiratory-chain enzymes of E. coli.