Generic closed loop controller for power regulation in dual active bridge DC-DC converter with current stress minimization

This paper presents a comprehensive and generalized analysis of the bidirectional dual active bridge (DAB) DC/DC converter using triple phase shift (TPS) control to enable closed loop power regulation while minimizing current stress. The key new achievements are: a generic analysis in terms of possible conversion ratios/converter voltage gains (i.e. Buck/Boost/Unity), per unit based equations regardless of DAB ratings, and a new simple closed loop controller implementable in real time to meet desired power transfer regulation at minimum current stress. Per unit based analytical expressions are derived for converter AC RMS current as well as power transferred. An offline particle swarm optimization (PSO) method is used to obtain an extensive set of TPS ratios for minimizing the RMS current in the entire bidirectional power range of - 1 to 1 per unit. The extensive set of results achieved from PSO presents a generic data pool which is carefully analyzed to derive simple useful relations. Such relations enabled a generic closed loop controller design that can be implemented in real time avoiding the extensive computational capacity that iterative optimization techniques require. A detailed Simulink DAB switching model is used to validate precision of the proposed closed loop controller under various operating conditions. An experimental prototype also substantiates the results achieved

Modular multilevel converter with modified half-bridge submodule and arm filter for dc transmission systems with DC fault blocking capability

Although a modular multilevel converter (MMC) is universally accepted as a suitable converter topology for the high voltage dc transmission systems, its dc fault ride performance requires substantial improvement in order to be used in critical infrastructures such as transnational multi-terminal dc (MTDC) networks. Therefore, this paper proposes a modified submodule circuit for modular multilevel converter that offers an improved dc fault ride through performance with reduced semiconductor losses and enhanced control flexibility compared to that achievable with full-bridge submodules. The use of the proposed submodules allows MMC to retain its modularity; with semiconductor loss similar to that of the mixed submodules MMC, but higher than that of the half-bridge submodules. Besides dc fault blocking, the proposed submodule offers the possibility of controlling ac current in-feed during pole-to-pole dc short circuit fault, and this makes such submodule increasingly attractive and useful for continued operation of MTDC networks during dc faults. The aforesaid attributes are validated using simulations performed in MATLAB/SIMULINK, and substantiated experimentally using the proposed submodule topology on a 4-level small-scale MMC prototype

Adaptive Communication for Wireless Massive MIMO Systems

The demand for high data rates in wireless communications is increasing rapidly. One way to provide reliable communication with increased rates is massive multiple-input multiple-output (MIMO) systems where a large number of antennas is deployed. We analyze three systems utilizing a large number of antennas to provide enhancement in the performance of wireless communications. First, we consider a general form of spatial modulation (SM) systems where the number of transmitted data streams is allowed to vary and we refer to it as generalized spatial modulation with multiplexing (GSMM). A Gaussian mixture model (GMM) is shown to accurately model the transmitted spatially modulated signal using a precoding framework. Using this transmit model, a general closed-form expression for the achievable rate when operating over Rayleigh fading channels is evaluated along with a tight upper and a lower bounds for the achievable rate. The obtained expressions are flexible enough to accommodate any form of SM by adjusting the precoding set. Followed by that, we study quantized distributed wireless relay networks where a relay consisting of many geographically dispersed nodes is facilitating communication between unconnected users. Due to bandwidth constraints, distributed relay networks perform quantization at the relay nodes, and hence they are referred to as quantized distributed relay networks. In such systems, users transmit their data simultaneously to the relay nodes through the uplink channel that quantize their observed signals independently to a few bits and broadcast these bits to the users through the downlink channel. We develop algorithms that can be employed by the users to estimate the uplink channels between all users and all relay nodes when the relay nodes are performing simple sign quantization. This setup is very useful in either extending coverage to unconnected regions or replacing the existing wireless infrastructure in case of disasters. Using the uplink channel estimates, we propose multiple decoders that can be deployed at the receiver side. We also study the performance of each of these decoders under different system assumptions. A different quantization framework is also proposed for quantized distributed relay networking where the relay nodes perform vector quantization instead of sign quantization. Applying vector quantization at the relay nodes enables us to propose an algorithm that allocates quantization resources efficiently among the relay nodes inside the relay network. We also study the beamforming design at the users’ side in this case where beamforming design is not trivial due to the quantization that occurs at the relay network. Finally, we study a different setup of distributed communication systems called cell-free massive MIMO. In cell-free massive MIMO, regular cellular communication is replaced by multiple access points (APs) that are placed randomly over the coverage area. All users in the coverage area are sharing time and frequency resources and all APs are serving all UEs while power allocation is done in a central processor that is connected to the APs through a high speed backhaul network. We study the power allocation in cell-free massive MIMO system where APs are equipped with few antennas and how the distribution of the available antennas among access points affects both the performance and the infrastructure cost

Effect of Rest Period on the Buckling of the 304 Stainless Steel under Increasing Loading

Buckling plays a very important role in the design of slender columns. When the members are long, the loading, which is lower than yielding, may be large enough to cause the member to deflect laterally. It is well established that the mechanical surface treatments, e.g. shot peening, plasma peening and laser peening are effective method to enhance the resistance of metallic material. In this work, the main aim is to estimate the optimum improvement of dynamic behavior of medium carbon steel alloy due to shot peening experimentally. The behavior of rotating arcular column buckling of steel alloy under compression loading showed significant improvement due to shot peening time (SPT) at 25 mints. Which gave higher resistance against buckling and increasing the buckling time, after that the improvement tends to be reduced

Interaction between lead crystal glass (24 % PbO) and acetic acid

On commercially available lead crystal glass tumblers (24 % PbO), the interaction between their bulk and grain forms and aqueous Solutions of various concentrations of acetic acid at different temperatures (22 to 95 °C), and for different times (30 min to 300 d) was studied. The extent of interaction was evaluated by determining the concentrations of K⁺, Na⁺, Pb²⁺ and Si⁴⁺ ions extracted by acetic acid, the change in the pH value of aqueous acetic acid Solutions and the weight loss of glass grains. The results showed that: a) Pb²⁺ was released from the glass studied under the Standard testing conditions in concentradons that were smaller than those specified in the various Standard specifications. b) The extraction of the different cations was significantly affected by the form of the test sample; glass grains were more reactive than the bulk form. c) Extraction of modifier cations, K⁺, Na⁺ and Pb²⁺, during short times of attack, up to 6 h at temperatures u p to 95 °C or during long-time attack up to 20 d at 22 °C, could be represented by a straight-line relationship when plotted against t^(1/2).Deviation was observed for times longer than 20 d but the straight-line relationship could be restored by plotting the extraction data against t. Such behaviour indicates that the leached layer became sufficiently thick after 20 d, so that the leaching and etching reactions proceeded at equal rates. d) The dissolution of glass increased with increasing temperature of attack up to 95 °C, but the mechanism of attack remained essentially of the leaching type. e) The extraction of K⁺, Na⁺, Pb²⁺ and Si⁴⁺ ions was affected by changing the concentration of acetic acid, which was correlated with the corresponding change in its pH value. f) The quantities of Pb^^ ions released by 4 % acetic acid Solution were several Orders of magnitude greater than that released by 40% ethyl alcohol Solution indicating that the Standard 4 % acetic acid test Solution is quite suitable for Pb²⁺ release safety

THE TECHNOLOGY OF MANUFACTURING FUEL FOR OIL LAMPS IN THE HELLENISTIC PERIOD: AN APPLIED STUDY THROUGH THE FINDINGS OF THE ALEXANDRIA NECROPOLIS PROJECT OF SHATBY, ALEXANDRIA [2020–2023]

تكنولوجيا صناعة وقود إضاءة المسارج بالعصر الهلينستي «دراسة تطبيقية من خلال مكتشفات مشروع جبانة الشاطبي بالإسكندرية 2020-2023 [Ar] يقدم هذا البحث دراسة تطبيقية وتجريبية لما تم الكشف عنه من بقايا مادة وقود الإضاءة التى كانت تستخدم للمسارج فى الفترة الهلّينستية، وكذلك دراسة بقايا لفتيل محترق عثر عليه ضمن مشروع ترميم وتطوير وحماية جبانة الشاطبى الأثرية، والذى نفذته جمعية الآثار بالإسكندرية بتمويل من مؤسسة أ.ج. لفنتيس القبرصية فى الفترة من 2020-2023م. تضمن المشروع إعادة استكشاف الجبانة الأثرية بإزالة الرديم المتراكم بها عبر الزمن. وجادت الجبانة بالعديد من القطع الأثرية تمثلت فى مسارج وأطباق فخارية وأوانى الحضرة وبقايا عظام بشرية. أثبتت التحاليل والفحوص أن الصخر الذى نحتت فيه الجبانة الأثرية أحد أنواع الحجر الجيرى، وأن المياه الجوفية الموجودة بالجبانة هى مياه تترواح نسبة المعادن الذائبة بها بين 1,7جم/لتر ودرجة أس هيدروجينى pH 7.1 . تم تحليل مادة الوقود بالتحليل الكروماتوجرافى الغازى المزود بمطياف الكتلة، حيث أثبت أن مادة الوقود ذات أصل بترولى. واستخدم الفحص بالميكروسكوب الإلكترونى الماسح لفحص بقايا عينة الفتيل المتفحم، وتبين أنها جزء من ساق نبات البوط، وتم تأكيد النتيجة بفحص التركيب التشريحى لساقى نباتى البردى والبوط كجانب تجريبى. [En] This paper is an applied and experimental study on the remains of the fuel material that was used in oil lamps in the Hellenistic period, as well as the remains of a burning fuel and oil lamp wick. These remains are among the finds of the project of restoration, development, and protection of the archaeological cemetery of Shatby, conducted by the archaeological Society of Alexandria (2020-2023), funded by the A.G. Leventis foundation, Cyprus. The entire cemetery of Shatby is hewn in the a type of limestone called Calcarenite, which is a sedimentary rock. The groundwater at the site is slightly alkaline (pH 7.1), with the total dissolved solids (TDS) at 1.7 g/L. Remains of lighting fuel were found during the removal of the accumulated rubble in the ancient cemetery, where they were analyzed using gas chromatography mass spectrometry (GC-MS) analysis which proved that they are composed of crude oil. Using a scanning electron microscope to examine the traces of wick ash, it appeared that the wick was made of the culm of Cyperus articulate. Based on experimental work, this was also proven by light microscopy examination of the culms of Cyperus articulate and Cyperus papyrus

Petrological and Geochemical Analyses and economic potential of some Milestones and Siliceous rocks in northern United Arab Emirates.

Combined microscopic, heavy mineral, X-ray diffraction and chemical analyses have been carried out on the Jurassic limestone, the upper cretaceous Hawasina cherts and the coastal and inland sand dunes in several localities in the Ras Al Khaimah Emirate. The obtained results revealed that a number of represents cherts subfacies; namely: ferruginous radiolarian ribbon chert, carbonaceous radiolarian ribbon chert, colloform ribbon chert, calcareous chert and siliceous mud stone. These rocks consist of (in order of decreasing abundance): quartz, calcite, dolomite and hematite. The carbonate rocks are made up of lime mudstone, wackestone; pack stone and, rarely, crystalline limestone. Various types of wackestone and pack stone were recorded. Mineral1ogically, these limestone consist of calcite and much lesser proportions of quartz and dolomite. Diagenesis greatly modified the original textural and compositional characteristics of the rocks especially the limestone. On the other hand, the light fractions of the coastal sand dunes contain higher concentrations of carbonate lithoclasts and skeletal grains and lower proportions of quartz and chert than those of the inland dunes. Also, the heavy fractions of the former sediments are slightly more enriched in opaques, pyroxenes, epidotes and hornblende while depleted in rutile, tourmaline, garnet and monazite. The obtained geochemical data confirm the presence of the main chert types; namely: (i) radiolarites (R), (ii) calcareous cherts (CC), and (iii) siliceous mudstones(SM). Each type has a homogeneous and characteristics major and trace element confirmed by the increase of Ti02, Al2O3), MgO, Fe203) and HFSE ( High Field Strength Elements). The cherts exhibit LREE (Light Rare Earth Elements) fractionated patterns with moderate negative Eu anomalies. R-mode cluster analysis shows three clusters. The first is for the carbonate minerals the second includes the terrigenous components and the third is the silica cluster. Factor analysis produced a two-factor model, which accounts for 85.85% of the data variability. The first is the terrigenous factor (Ti02,Al2O3) FeO, K20, P205 Rb, Ga, Zr and REE), and the second is the carbonate factor. The majority of the studied limestones and a few of the chert rocks are Compositionally similar to those presently used by the Ras Ai Khaimah Rock Company for cement Production and, consequently can be considered for possible future needs. On the other hand, the compositional characteristics of the dune sands, especially the coastal dunes, do not permit their use as a possible source of silica

Enhanced performance modified discontinuous PWM technique for three phase Z-source inverter

Various industrial applications require a voltage conversion stage from DC to AC. Among them, commercial renewable energy systems (RES) need a voltage buck and/or boost stage for islanded/grid connected operation. Despite the excellent performance offered by conventional two-stage converter systems (DC-DC followed by dc-ac stages), the need for a single-stage conversion stage is attracting more interest for cost and size reduction reasons. Although voltage source inverters (VSIs) are voltage buck-only converters, single stage current source inverters (CSIs) can offer voltage boost features, although at the penalty of using a large DC-link inductor. Boost inverters are a good candidate with the demerit of complicated control strategies. The impedance source (Z-source) inverter is a high-performance competitor as it offers voltage buck/boost in addition to a reduced passive component size. Several pulse width modulation (PWM) techniques have been presented in the literature for three-phase Z-source inverters. Various common drawbacks are annotated, especially the non-linear behavior at low modulation indices and the famous trade-off between the operating range and the converter switches' voltage stress. In this paper, a modified discontinuous PWM technique is proposed for a three-phase z-source inverter offering: (i) smooth voltage gain variation, (ii) a wide operating range, (iii) reduced voltage stress, and (iv) improved total harmonic distortion (THD). Simulation, in addition to experimental results at various operating conditions, validated the proposed PWM technique's superior performance compared to the conventional PWM techniques

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

MESI protocol for multicore processors based on FPGA

In modern techniques of building processors, manufactures using more than one processor in the integrated circuit (chip) and each processor called a core. The new chips of processors called a multi-core processor. This new design makes the processors to work simultaneously for more than one task or all the cores working in parallel for the same task. All cores are similar in their design, and each core has its own cache memory, while all cores shares the same main memory. So, if one core requests a block of data from main memory to its cache, there should be a protocol to declare the situation of this block in the main memory and other cores. This is called the cache coherency or cache consistency of multi-core. In this paper a special circuit is designed using VHDL coding and implemented using ISE Xilinx software, one protocol was used in this design, the MESI (Modify, Exclusive, Shared and Invalid) protocol. Test results were taken by using test bench, and showed all the states of the protocols are working correctly