Robust nonlinear controller based on control Lyapunov function and terminal sliding mode for buck converter

This paper studies the sliding mode control (SMC) and terminal SMC (TSMC) techniques of output voltage regulation in dc–dc buck converters. In this paper, the conventional terminal sliding manifold (TSM), fast terminal sliding manifold, and adaptive terminal sliding manifold are investigated by using hysteresis‐modulated control. In addition, proportional‐integral‐derivative‐shaped TSM, PI‐shaped TSM, and proportional‐integral‐derivative‐integral‐shaped TSM are proposed in order to overcome the problems of conventional TSMs. Furthermore, a new continuous controller based on control Lyapunov function (CLF), with pre‐settable‐fixed switching frequency, is suggested. CLF‐based controller (CLF‐bC) is also adapted to the discontinuous digital input of the buck converter. In the proposed CLF‐bC, the switching frequency is completely independent and pre‐settable. Stabilization, reference tracking, high performance dynamic response, robustness against parameter uncertainties, and rejection of disturbances (e.g., input voltage changes and load variations) are some advantages of the proposed controllers. Impact of the controllers' parameters on the performance of the system is also summarized. Finite‐time stability of TSMs and proposed CLF‐bC, and the robustness of CLF‐bC against parameter variations and disturbances are mathematically proved. Performance of the proposed Adaptive TSMC (ATSMC), proportional‐integral‐derivative‐TSMC, and CLF‐bC has been verified through matlab simulations and compared with the conventional SMC and TSMC strategies. Copyright © 2016 John Wiley & Sons, Ltd.     

Applying artificial optimization methods for transformer model reduction of lumped parameter models

Detailed R-C-L-M models of power transformers, which are based on lumped parameters, are used extensively not only for transient analysis of power transformers to determine electrical stresses in windings, but also for studying transients in power systems. Models with few elements are generally more practicable for power system studies but at the expense of accuracy. The use of artificial methods to reduce an R-C-L-M model is the main contribution of this paper. Advantages of the suggested method include: (1) a reduced loss of accuracy compared with the original model and (2) the flexibility to choose the number of model elements to achieve the desired model depending on size and accuracy. The ability of three different artificial methods, genetic algorithm, particle swarm optimization, and bacterial foraging algorithm, to model reduction is evaluated using measurements on an actual 400 kV test object and the results are compared with those obtained by common analytical formulae.     

Internal electrical fault detection techniques in DFIG-based wind turbines: a review

The keys factor in making wind power one of the main power sources to meet the world’s growing energy demands is the reliability improvement of wind turbines (WTs). However, the eventuality of fault occurrence on WT com ponents cannot be avoided, especially for doubly-fed induction generator (DFIG) based WTs, which are operating in severe environments. The maintenance need increases due to unexpected faults, which in turn leads to higher operating cost and poor reliability. Extensive investigation into DFIG internal fault detection techniques has been carried out in the last decade. This paper presents a detailed review of these techniques. It discusses the methods that can be used to detect internal electrical faults in a DFIG stator, rotor, or both. A novel sorting technique is presented which takes into consideration different parameters such as fault location, detection technique, and DFIG modelling. The main mathematical representation used to detect these faults is presented to allow an easier and faster under standing of each method. In addition, a comparison is carried out in every section to illustrate the main differences, advantages, and disadvantages of every method and/or model. Some real monitoring systems available in the market are presented. Finally, recommendations for the challenges, future work, and main gaps in the field of internal faults in a DFIG are presented. This review is organized in a tutorial manner, to be an effective guide for future research for enhancing the reliability of DFIG-based WTs.     

A high‐voltage gain nonisolated noncoupled inductor based multi‐input DC‐DC topology with reduced number of components for renewable energy systems

This paper proposes a modular nonisolated noncoupled inductor‐based high‐voltage gain multi‐input DC‐DC converter. Despite the high‐voltage gain of the proposed topology, the average of normalized voltage stress (NVS) on its switches/diodes is low. This property leads to less loss and cost of switches/diodes. Using the same number of components, the proposed topology produces higher voltage gains, in comparison with recently presented high step‐up topologies. Also, the proposed topology utilizes less number of components (capacitors, inductors, diodes, and switches) for producing a desired voltage gain, which can reduce the size, mass, cost, complexity, and losses and improve the efficiency of converter. Continuous current of input sources is another main advantage of the proposed topology. All the abovementioned characteristics have made the proposed topology very suitable for renewable energy systems (or even hybrid/electric vehicles). Design considerations of the proposed topology have also been presented. For better evaluation, the proposed topology has been compared with some of recently presented high step‐up structures, from viewpoints of producible voltage gain, number of components, and normalized voltage stress (NVS) on switches/diodes. Finally, the prototype of 2‐input version has been experimentally implemented. Obtained experimental results confirm appropriate performance of the proposed topology.     

Compensation of voltage disturbances in distribution systems using single-phase dynamic voltage restorer

In this paper, a new topology is proposed for a single-phase dynamic voltage restorer (DVR) using direct ac/ac converter. This topology does not require dc-link energy storage elements. The proposed topology has a simple structure and can compensate several types of voltage disturbances such as voltage sags, swells, harmonics and flickers. This topology will not face any problem in long time compensation due to the fact that it provides the required energy directly through grid. The proposed topology can be easily extended to n-phase systems such as three-phase based on the same principle of the operation. In n-phase systems, the voltage sags and swells can be properly compensated regardless of the balanced or unbalanced operation. A new control method is also proposed for direct ac/ac converter in the proposed topology. The simulation and experimental results verify the effectiveness of the proposed topology and its control method in voltage restoration.     

Biodegradation of natural and synthetic estrogens in moving bed bioreactor

Estrogen hormones as a group of endocrine disruptive compounds(EDC) can interfere with endocrine system in humans and animals. The goal of this study was to investigate the elimination rate of Estrone(El), 17β-estradiol(E2) and 17α-ethinyl estradiol(EE2) in Moving Bed Bioreactor(MBBR). These analytes extracted by Dispersive Liquid-Liquid Microextraction(DLLME) technique, followed by derivatization, and detected by GC/MS. Estrogen removal efficiency in MBBR improved at high solid retention times(SRTs), which notion is owing to development of nitrification. Estrogen specific removal rate was between 0.22-1.45 μg·(g VSS)~(-1)·d~(-1) for natural and synthetic hormones. The adsorption rate was 0.9%-3.2%, 0-1.3%, and 0.7%-5.7% for El, E2, and EE2, respectively. In addition, the biodegradation rates were more than 95% for these compounds. These results illustrated that in MBBR,the biodegradation and the adsorption to biomass are considered as two significant routes for elimination of estrogenic compounds. As a whole, the deterioration rate of estrogens enhanced by MBBR compared to other biological wastewater treatment processes such as conventional activated sludge.     

Effect of seed layers on low-temperature,chemical bath deposited ZnO nanorods-based near UV-OLED performance

Low-temperature wet chemical bath deposition (CBD) method is one of the most efficient and least hazardous solution-based techniques which is widely employed to grow ZnO NRs. In CBD method, a seed layer is usually deposited on the substrate. In this paper, high quality ZnO and aluminum doped ZnO (AZO) seed layers are sputtered on the indium tin oxide (ITO) coated glass. In continue, aligned ZnO NRs are grown on the AZO and ZnO seed layers via CBD technique. The effect of the growth time and seed layer on the physical properties of as-grown ZnO NRs are investigated. According to the results, the seed layer plays an essential role on the growth orientation and growth rate of the ZnO NRs. The ZnO NRs grown on AZO seed layer are more aligned rather than ZnO seed layer due to their higher texture coefficients. The relative photoluminescence (PL) intensity ratio of near band emission (NBE) to deep level emission (DLE) (I_NBE/I_DLE) for the ZnO NRs grown on AZO and ZnO seed layers are calculated as 7.45 and 2.62, respectively. To investigate the performance of the as-grown ZnO NRs, near ultraviolet organic light-emitting diodes (UV-OLEDs) using ZnO NRs array as n-type material and poly [2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) conjugated polymer as p-type material have been fabricated. The total concentration of traps ($N_t$), the characteristic energies ($E_t$) and the turn-on voltages for the devices with the structures of ITO/AZO/ZnO NRs/MEH-PPV/Al (device A) and ITO/ZnO/ZnO NRs/MEH-PPV/Al (device B) are attained 7.65 × 10¹⁶ and 7.75 × 10¹⁶ cm^?3, 0.232 and 0.206 eV, 23 and 21 V, respectively. Moreover, based on the electroluminescence (EL) spectra, the NBE peaks for device A and B are obtained nearly in the wavelengths of 382 and 388 nm, respectively. Finally, various charge carrier transportation processes of prepared UV-OLEDs have been studied, systematically.     

Preformed particle gels of sulfonated polyacrylamide: preparation,characterization, and application as permeability modifier

In this study, a preformed particle gel (PPG) was synthesized from sulfonated polyacrylamide and chromium metal cross-linker with specific concentration. The main characteristics of PPG, such as gelation time, gel fraction, swelling properties and salt sensitivity factor were investigated. The gel fraction of 94.1% practically indicated an appropriate conversion of gelant to the gel. The equilibrium swelling ratios of particle gels in distilled water and formation water at 80 °C were 470.49 and 12.61, respectively. Additionally, the rheological properties of gel were studied by a dynamic rheometer. The ultimate storage modulus of gel was measured 35.4 kPa. The linear viscoelastic behavior was observed at strain between 1 and 82.6% and gel structure was stable up to strain of 1120% with small reduction of storage modulus. The kinetics of gelation were also studied at different temperatures and tested against Avrami equation to determine the kinetic parameters. The Avrami exponents for two kinetic steps were about 2.29 and 0.80, respectively, indicating the rapid formation of the gel network at first step due to nucleation and two-dimensional growths of gel nuclei. Furthermore, a core flooding experiment was conducted to study PPG performance in porous media. The residual resistance factor of water and oil was 41.58 and 12.91, respectively. A value of 3.22 for the ratio of these two factors indicated the ability of the synthesized PPG to decrease water-effective permeability compared to oil-effective permeability in porous media.

     

Heterogeneous Catalytic Polymerization of Ethylene in Microtubular Reactor Systems

The feasibility of using a microtubular reactor for heterogeneous polymerization of ethylene was investigated experimentally. Chemically inert polymer tubing of 800–2300 μm in inner diameter was fabricated and used as a polymerization reactor. Nonporous silica nanoparticles with a diameter of 400 nm were synthesized and used as support for the high‐activity rac‐ethylene(indenyl)₂ZrCl₂ catalyst with methylaluminoxane as cocatalyst and toluene as diluent. Large‐diameter microtubular reactors were also successfully used to conduct heterogeneous polymerization of ethylene in continuous reaction operations. High initial catalyst activity was obtained and the overall polymerization activity per volume or reactor length was quite high. No particle fragmentation occurred and the polymer particles were covered with small subgrains or nanofibrils with a diameter of 30 nm.