DC fault isolation study of bidirectional dual active bridge DC/DC converter for DC transmission grid application

Fast isolation and detection of DC faults is currently a limiting factor in high power DC transmission grid development. Recent research has shown that the role of DC/DC converters is becoming increasingly important in solving various DC grid challenges such as voltage stepping, galvanic isolation and power regulation. This paper focuses on an additional important feature of bidirectional dual active bridge (DAB) DC-DC converters which make it attractive for future DC grids; it's inherent fault isolation capability which does not need control intervention to limit fault current in case of the most severe DC faults. Detailed analytical, simulation and experimental study are performed by subjecting the converter to DC short circuit faults at its DC voltage terminals. The results obtained have shown significant advantage of DAB where fault current is less than rated current during the fault duration. Thus no control action is necessary from the non-faulted bridge to limit fault current and no external DC circuit breakers are required. This advantage makes DAB converter feasible for DC grid integration

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

Linearized large signal modeling, analysis, and control design of phase-controlled series-parallel resonant converters using state feedback

This paper proposes a linearized large signal state-space model for the fixed-frequency phase-controlled series-parallel resonant converter. The proposed model utilizes state feedback of the output filter inductor current to perform linearization. The model combines multiple-frequency and average state-space modeling techniques to generate an aggregate model with dc state variables that are relatively easier to control and slower than the fast resonant tank dynamics. The main objective of the linearized model is to provide a linear representation of the converter behavior under large signal variation which is suitable for faster simulation and large signal estimation/calculation of the converter state variables. The model also provides insight into converter dynamics as well as a simplified reduced order transfer function for PI closed-loop design. Experimental and simulation results from a detailed switched converter model are compared with the proposed state-space model output to verify its accuracy and robustness

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

Modeling and simulation of a 3-ф induction motor based on two types of WFA

This paper has been proposed to simulate the transient model of 3-Ф cage rotor induction motor based on winding function approach (WFA). According to this method the motor is assumed to be consist of an electrical circuits on both stator and rotor. The magneto motive forces (MMF) that have been generated by these circuits play a role for coupling them together. Then mutual and self-inductances will be easily computed using WFA. Two types of WFA have been used to build and simulate the model of the induction motor. In the one part type, it’s assumed that the coupling MMF between stator and rotor have a non-sinusoidal shapes according to the actual windings distribution over the motor slots. While in second part type the generated MMF in are assumed to have sinusoidal waveform. The suggested models may be used to simulate the dynamic as well as steady state performance of a faulty and non-faulty motor. A simulation of the suggested models that consists of m-rotor bars and n-stator phases multiple coupled circuit-based has been performed using matlab m.file and the results of the motor current have been proved in its nonlinear way by using WFA

Effect of Yoghourt Starter Culture and Nickel Oxide Nanoparticles on the Activity of Enterotoxigenic Staphylococcus aureus in Domiati Cheese

Domiati cheese is the most popular type of white soft cheese in Egypt. Staphylococcus aureus is a common microorganism that can easily contaminate Domiati cheese during processing and distribution. Enterotoxigenic S. aureus strains produce staphylococcal enterotoxins (SE) that have been involved in food poisoning outbreaks worldwide. The aim of the present study was to examine the inhibitory effect of yoghourt starter culture and nickel oxide nanoparticles (NiO NPs) on the development of the enterotoxigenic S. aureus together with the enterotoxin production during the manufacturing and storage of Domiati cheese. Fresh cow’s milk was inoculated with S. aureus in a count of six log CFU/mL with the addition of either yoghourt starter culture or NiO Nps. The cytotoxicity of NiO NPs on normal human epithelial cells (HEC) was assessed using the MTT assay. In the current study, the inoculated milk was used for making Domiati cheese and the survival Weibull and log-linear models were fitted to the observed data. The obtained results showed that the mean log count of S. aureus decreased one week earlier by using yoghourt starter culture. Staphylococcal enterotoxin A (SEA) was identified only in the control cheese. Notably, Domiati cheese contained MIC of NiO NPs (35 µg/mL), which resulted in a significant decrease in S. aureus counts since at day 21 of cheese ripening it was not detected (<10 CFU/g). Overall, the current study indicated that the addition of yoghourt starter culture and NiO NPs during the processing of Domiati cheese could be useful candidates against S. aureus and enterotoxin production in the dairy industry

Radiological changes and progress in patient with pulmonary Tuberculosis following treatment with daily versus intermittent short course regimens

This is a prospective comparative randomized study carried out at Kosti teaching hospital 2006-2008.Objectives: to determine the radiological findings and to evaluate the radiological progress in patient with pulmonary Tuberculosis treated with daily versus intermittent short course regimens.Methodology: A total of 275 smear positive new cases of Tuberculosis were enrolled and randomized in to two groups, intermittent group (A) and daily regimen group (B) .X-Ray film was done initially and at the end of treatment for each patient.Results: It was found that 31% of the X-Ray films were normal.  Concerning the progress of minimal lesion significantly high percentage improved to normal X-Ray 58% in group A and 53 % in group B , 42 % in group A and 40 % in group B stayed as minimal lesion. The results of faradvanced lesion revealed that intermittent regimen improved 16.6% of the films to normal and minimal lesion , 8.3 % to moderate lesion, 33.3 % moderately advanced lesion and 25 % remained unchanged, while in the daily regimen , 21 % improved to normal and minimal lesion , 5.2 % tomoderate lesion , 27 % to moderately advanced lesion and 27.6 %. Statistical analysis revealed a significant difference between the two groups.Conclusion: Conversion of minimal lesions to normal X-Ray was  significantly higher in the intermittent group and the conversion of far advanced lesions to normal was significantly higher in the daily regimen