Modified dual active bridge DC/DC converter with improved efficiency and interoperability in hybrid LCC/VSC HVDC transmission grids

DC transmission grids are the promising electrical networks in the near future especially with the high penetration of large scale renewables. This paper proposes a modified version of the dual active bridge (DAB) DC/DC converter with AC link capacitors generating reactive power to compensate for non-active power consumption; hence mitigating current stresses and losses to improve efficiency. The proposed topology also enables the connectivity of current source line-commutated HVDC and voltage source HVDC technologies particularly during power reversal; a feature which conventional DAB is incapable of doing. Analysis and detailed design of the proposed converter are addressed and a comparative performance analysis is carried out with conventional DAB. Converter principle of operation is explained and Matlab/Simulink simulations are carried out to verify converter operation particularly under adverse conditions such as rated power reversal and DC fault conditions. A low scale prototype substantiates the theoretical analysis and simulation results

A morphological generator for the indexing of Arabic audio

This paper presents a novel Arabic morphological generator (AMG) for Modern Standard Arabic (MSA) which is designed and implemented using Prolog. The AMG is used to generate inflected forms of words used for the indexing of Arabic audio. These words are also the relevant terms in the Arab authority system (library information retrieval system) used in this study. The AMG generates inflected Arabic words from the root according to pre-specified morphological features that can be extended as needed. The Arabic word is represented as a feature structure which is handled through unification during the morphological generation process. The inflected forms can then be inserted automatically into a speech recognition grammar which is used to identify these words in an audio sequence or utterance

Modified variable step-size incremental conductance MPPT technique for photovoltaic systems

A highly efficient photovoltaic (PV) system requires a maximum power point tracker to extract peak power from PV modules. The conventional variable step-size incremental conductance (INC) maximum power point tracking (MPPT) technique has two main drawbacks. First, it uses a pre-set scaling factor, which requires manual tuning under different irradiance levels. Second, it adapts the slope of the PV characteristics curve to vary the step-size, which means any small changes in PV module voltage will significantly increase the overall step-size. Subsequently, it deviates the operating point away from the actual reference. In this paper, a new modified variable step-size INC algorithm is proposed to address the aforementioned problems. The proposed algorithm consists of two parts, namely autonomous scaling factor and slope angle variation algorithm. The autonomous scaling factor continuously adjusts the step-size without using a pre-set constant to control the trade-off between convergence speed and tracking precision. The slope angle variation algorithm mitigates the impact of PV voltage change, especially during variable irradiance conditions to improve the MPPT efficiency. The theoretical investigations of the new technique are carried out while its practicability is confirmed by simulation and experimental results

Comparing the Effect of Foliar Spraying by Calcium and Boron on Productivity and Quality of Strawberry Fruits under Organic Hydroponic System

The availability of slow-moving elements within the plant is very important for the growth and productivity of crops, the most important of which are calcium and boron, and the deficiency of any of them leads to a significant imbalance in growth and productivity. This experiment was conducted inside a greenhouse at the National Organic Agriculture Center, Unaiza, Qassim, Ministry of Environment Water and Agriculture, Saudi Arabia to investigations made on the effects of foliar applications levels of calcium (Ca) and boron (B) on yield and quality of strawberries (Fragaria X ananassa Duch.). Factorial experiment was used in a randomized complete block design (RCBD) with four levels of calcium (Ca1=100, Ca2 = 200, Ca3= 400 mg/l), and four levels of boron (B1= 5, B2= 10, B3= 20 mg/l), as well as control treatment (C=0), each treatment was replicated three times. Different treatments with different combinations of both elements were studied. Addition of B and Ca influence vegetative growth parameters, yield attributes and fruit quality parameters significantly compare to the control such as the percentages of Glucose%, Fructose%, vitamin C and Sucrose%. Therefore, results indicated that sprays of mixture contained calcium and boron at different levels of Ca2B1, Ca1B1 and Ca3B1 increased fruit diameter, fruit length, weight /plant, and total weight (g), while with Ca3B1 and Ca3B2 were showed high increment of sugar percentages. According to results authors recommended foliar application of combination of calcium and boron as follow Ca2B1, Ca3B1 and Ca3B2 to improve yield attributes and fruit quality parameters. Keywords: Strawberry, Foliar application, Calcium, Boron, Organic hydroponics DOI: 10.7176/JBAH/13-18-03 Publication date:October 31st 202

Rational Approximations for Oscillatory Two-Parameter Mittag-Leffler Function

The two-parameter Mittag-Leffler function $E_{\alpha, \beta}$ is of fundamental importance in fractional calculus. It appears frequently in the solutions of fractional differential and integral equations. Nonetheless, this vital function is often expensive to compute. Several attempts have been made to construct cost-effective and accurate approximations. These attempts focus mainly on the completely monotone Mittag-Leffler functions. However, when $\alpha > 1$ the monotonicity property is largely lost and as such roots and oscillations are exhibited. Consequently, existing approximants constructed mainly for $\alpha \in (0,1)$ often fail to capture this oscillatory behavior. In this paper, we construct computationally efficient and accurate rational approximants for $E_{\alpha, \beta}(-t)$, $t \ge 0$, with $\alpha \in (1,2)$. This construction is fundamentally based on the decomposition of Mittag-Leffler function with real roots into one without and a polynomial. Following which new approximants are constructed by combining the global Pad\'e approximation with a polynomial of appropriate degree. The rational approximants are extended to approximation of matrix Mittag-Leffler and different approaches to achieve efficient implementation for matrix arguments are discussed. Numerical experiments are provided to illustrate the significant accuracy improvement achieved by the proposed approximants.Comment: 20 pages, 14 figures and 5 table

A new active power controller in dual active bridge DC-DC converter with a minimum-current-point-tracking technique

This article proposes a new controller for power regulation in dual active bridge (DAB) dc-dc converter based on a new scheme that tracks minimum RMS current to ensure minimum losses. The proposed controller is based on an implementation of perturb and observe (PO) tracking method that enables minimum current point tracking (MCPT) at any desired level of active power transfer and dc voltage ratio. The PO is embedded in a closed-loop control scheme which simultaneously regulates active power in DAB converter. The nonlinear I - V characteristic of DAB presents the basis for this proposed controller and the rationale of using PO algorithm. The proposed controller does not require complex nonlinear converter modeling and is not circuit parameter dependent. Design procedure of the proposed controller is presented, and extensive simulation is carried out using MATLAB/Simulink to validate the effectiveness of the proposed MCPT closed-loop controller. An experimental prototype also substantiates the results achieved

A genetic programming hyper-heuristic for the multidimensional knapsack problem

Purpose: Hyper-heuristics are a class of high-level search techniques which operate on a search space of heuristics rather than directly on a search space of solutions. The purpose of this paper is to investigate the suitability of using genetic programming as a hyper-heuristic methodology to generate constructive heuristics to solve the multidimensional 0-1 knapsack problem. Design/methodology/approach: Early hyper-heuristics focused on selecting and applying a low-level heuristic at each stage of a search. Recent trends in hyper-heuristic research have led to a number of approaches being developed to automatically generate new heuristics from a set of heuristic components. A population of heuristics to rank knapsack items are trained on a subset of test problems and then applied to unseen instances. Findings: The results over a set of standard benchmarks show that genetic programming can be used to generate constructive heuristics which yield human-competitive results. Originality/value: In this work the authors show that genetic programming is suitable as a method to generate reusable constructive heuristics for the multidimensional 0-1 knapsack problem. This is classified as a hyper-heuristic approach as it operates on a search space of heuristics rather than a search space of solutions. To our knowledge, this is the first time in the literature a GP hyper-heuristic has been used to solve the multidimensional 0-1 knapsack problem. The results suggest that using GP to evolve ranking mechanisms merits further future research effort. © Emerald Group Publishing Limited

Modified Q-f droop curve method for islanding detection with zero non-detection zone

In this paper, a modified Q-f droop curve method for the inverter-based distributed generator is proposed. The proposed method has merits such as detecting islanding with zero non-detection zone, negligible effects on power quality, and simple implementation. A new parameter is embedded in the reactive power reference to accelerate the frequency deviation at the point of common coupling until the islanding is detected. Therefore, a passive under/over frequency relay will be simply sufficient to detect islanding within the permissible limit. The proposed method is modelled with a computer-aided design SIMULINK/MATLAB environment. The proposed method is analyzed for operation with unity and non-unity power factors. The performance is validated for various loading quality factors with a negligible change in detection time. In addition, it is confirmed that the proposed system is stable under unbalanced loading and switching conditions. The proper operation of the proposed islanding detection method under multi distributed generators connection is validated. The results of the hardware experimentations are presented to confirm the proposed method analysis and simulations

Evaluation of IR Spectral Analysis and Dyeing Parameters for Plasma and /or Nano-Silver Treatments of Polyester and Nylon Fabrics

In our work of this paper, we study the effect of surface modification of polyester and nylon fabrics induced by DC plasma discharge and/ or nano-siliver treatments .DC plasma discharge was employed at first, as a function of plasma device parameters including different time, different current and different hydrostatic pressure using chemically inert working gas: argon or nitrogen. Optimization of the performance of the applied DC plasma discharge with various applied conditions were performed using Fourier Transform Infra-Red (FTIR) Spectroscopy spectral analysis, by following up the changes in the peak intensity values of the characteristic functional groups that characterize polyester fabric. Then the dyeing properties of different pretreated fabrics with plasma by the best conditions are subjected to nano-silver treatment by concentration 50 ppm under the effect of different dye concentrations, different dyeing temperature and different dyeing time. Finally, the fastness properties to light and washing for the treated samples were studied. The results obtained showed that both of the dyeing parameters and fastness properties were highly improved by the treatment of fabrics by either individual plasma treatment or combined DC cold plasma and nano-silver treatments