Analysis of AC link topologies in non-isolated DC/DC triple active bridge converter for current stress minimization

This paper presents analysis of the non-isolated DC/DC triple active bridge (TAB) converter under various purely inductor-based AC link topologies. The objective of the analysis is to find the topology that incorporates the least value of the AC link inductors which leads to reduced converter footprint in addition to minimum internal current stresses. Modelling of the TAB under each of the different topologies is presented in per unit expressions of power transfer and reactive power assuming fundamental harmonic analysis. The power expressions are used to calculate the inductor values necessary to achieve same rated power transfer of Dual Active Bridge (DAB) converter for the sake of standardizing comparison. On this basis, the topology requiring the least value of interface inductors, hence lowest footprint, is identified. Furthermore, based on phase shift control, particle swarm optimization (PSO) is used to calculate optimal phase shift ratios in each of the proposed topologies to minimize reactive power loss (hence current stress). The topology with minimum stresses is therefore identified and the results are substantiated using a Matlab-Simulink model to verify the theoretical analysis

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

Second Handed Computer Purchasing Web-Based System

In this paper we describe a web-based information system, which serves for a first contract between a university seller and buyers of second-handed computer materials. We describe advantages of an involvement of the transaction into the virtual space within a university. Our e-transaction system covers the whole sales and buys process. The objective is to make the communication between the buyer and the seller more effective and consequently to achieve considerable time and resource savings at the both parts when it comes to purchase second-hand computer material virtually

Generalized small-signal modelling of dual active bridge DC/DC converter

this paper presents a novel generalised approach of the small-signal modelling of dual active bridge (DAB) DC/DC converter. The adopted analysis is based on a per-unit fundamental frequency representation of the DAB. The outcome of the proposed modelling approach is a small signal, linearised, state-space DAB model; which is considered as a main building block for future control applications. The developed small signal DAB model includes all possible degrees of freedom affecting the performance of the DAB; this includes the voltage conversion ratio to allow the study of all DAB operation modes (i.e.: unity-gain and buck/boost modes.). Furthermore, since triple phase shift control (TPS) is used in this development work, the proposed model incorporates phase shift in addition to duty ratios. This feature allows for bridge voltage regulation, which is essential for efficient DAB operation in the case of buck/boost operation. Another key achievement is that the proposed small signal modelling methodology can be applied to any bidirectional DC-DC converter regardless of ratings, parameter values and number of ports. Extensive simulation is carried out to verify the proposed analysis

Smart integration of a DC microgrid: Enhancing the power quality management of the neighborhood low-voltage distribution network

The fast development of the residential sector regarding the additional integration of renewable distributed energy sources and the modern expansion usage of essential DC electrical equipment may cause severe power quality problems. For example, the integration of rooftop photovoltaic (PV) may cause unbalance, and voltage fluctuation, which can add constraints for further PV integrations to the network, and the deployment of DC native loads with their nonlinear behavior adds harmonics to the network. This paper demonstrates the smart integration of a DC microgrid to the neighborhood low-voltage distribution network (NLVDN). The DC microgrid is connected to the NLVDN through a three-phase voltage source inverter (VSI), in which the VSI works as a distribution static compensator (DSTATCOM). Unlike previous STATCOM work in the literature, the proposed controller of the VSI of the DC smart building allows for many functions: (a) it enables bidirectional active/reactive power flow between the DC building and the AC grid at point of common coupling (PCC); (b) it compensates for the legacy unbalance in the distribution network, providing harmonics elimination and power factor correction capability at PCC; and (c) it provides voltage support at PCC. The proposed controller was validated by Matlab/Simulink and by experimental implementation at the lab

Congenital pyloric atresia: clinical features, diagnosis, associated anomalies, management and outcome

Background: Congenital pyloric atresia (CPA) is very rare and usually seen as an isolated anomaly, which has an excellent prognosis. CPA can be associated with other anomalies or familial and these are usually associated with other hereditary conditions with poor prognosis. This review is based on our experience with 20 infants with CPA.Patients and methods: This is a review of CPA, highlighting its clinical features; associated anomalies; and aspects of diagnosis, management and outcome.Results: This review is based on our experience with 20 patients with CPA (nine male and 11 female). Their mean birth weight was 2.1 kg (1.1-3.9 kg). Polyhydramnios was seen in 13 (65%) patients. Seven patients were full-term and the remaining 13 were premature. Two were brothers and four were members of the same family. Isolated CPA was seen in seven (35%) patients and 13 had associated anomalies. Epidermolysis bullosa was seen in eight (40%) patients and multiple intestinal atresias in five (25%). Three patients had associated esophageal atresia. Pyloric diaphragm was the most common and seen in 13 patients including double diaphragms in two followed by pyloric atresia with a gap in four and pyloric atresia without a gap in three. All patients did well in the early postoperative period; however, 10 died later giving an overall survival of 40%. Sepsis was the main cause of death.Conclusion: CPA is a very rare malformation that can be familial and inherited as an autosomal recessive. It can either occur as an isolated lesion with an excellent prognosis, or be associated with other anomalies. The overall prognosis of CPA, however, is still poor, and this is due to the frequent-and often fatal-associated anomalies.Keywords: aplasia cutis congenita, congenital pyloric atresia, epidermolysis bullosa, hereditary multiple intestinal atresi

Determination of Saline Soils Specific Gravity

The existence of salts as part of the solid phase of the soil or dissolved within the pore fluid may cause significant errors in the values of specific gravity of such soils by using conventional determination methods. Errors may arise from effects of wrong measurements of weights or volumes that take place due to dissolution of the salt during testing, precipitation during drying or dehydration of the crystals of certain salts such as gypsum. To overcome this confusion, the standard procedure for specific gravity determination is reconsidered and the calculation methods are reanalyzed. Suggestions for a more adequate procedure for gypseous or other types of saline soils are presented and corrections required for computations are derived