R. Carbone

A short course of pegylated interferon-alpha in acute HCV hepatitis

Summary.  Acute hepatitis C virus (HCV) infection evolves to chronicity in 50–84% cases. Treatment with interferon‐α (IFN‐α) was repeatedly found to provide sustained cure rates higher than that in chronic HCV infection, but the optimal treatment strategy has not yet been defined. In a multicentre open‐label study, we investigated the therapeutic performance of a short course of pegylated (peg) IFN‐α in patients with acute HCV hepatitis. Peg IFN‐α2b, 1.0–1.5 μg/kg weekly, was administered for 12 weeks. Forty‐six patients were enrolled; 26 of them were intravenous drug users. Eleven patients had jaundice. Treatment was started within 1–90 days from the peak alanine aminotransferase. Treatment was well tolerated with a single dropout (2%). Thirty‐three of 46 patients (72%) had a sustained virological response (SVR) after a 6 months post‐treatment follow‐up, 8 (17%) relapsed after treatment and 4 were nonresponders (9%). A lower peak viraemia, receiving at least 1.2 μg/kg of peg IFN‐α, and a negative HCV‐RNA at week 4 and week 12 were predictors of SVR. Thus, in patients with early (week 4) viral response, a short course of peg IFN‐α at a weekly dose >1.2 μg/kg, may be a valuable option for the treatment of acute HCV hepatitis.

Grid-connected photovoltaic systems with energy storage

There are different interesting ways that can be followed in order to reduce costs of grid-connected photovoltaic systems, i.e., by maximizing their energy production in every operating conditions, minimizing electrical losses on the plant, utilizing grid-connected photovoltaic systems not only to generate electrical energy to be put into the power system but also to implement some other important auxiliary services normally implemented by properly conceived apparatus (electrical power quality control, load demand peak control, …), making easy the integration of different kind of renewable electrical energy resources (wind plant, fuel-cells, …).

Some considerations on the iterative harmonic analysis convergence

The convergence difficulties of the iterative harmonic analysis (IHA) methodologies are considered. Two techniques proposed to improve IHA convergence are described and their applicability limits are analyzed. To overcome the aforementioned limits, a third improvement technique is presented. A critical case study is solved by means of IHA and the three improvement techniques, and the results are analyzed and discussed. >

Modelling of AC/DC/AC conversion systems with PWM inverter

Modelling of AC/DC/AC power conversion systems with PWM inverters is considered and a new model is presented and discussed. The new model is based on the modulation function theory and uses the iterative harmonic and interharmonic analysis (IHIA), taking advantage of a new inverter model. The proposed model can be applied successfully to adjustable speed drives (ASD) for asynchronous motors, achieving better modelling accuracy with respect to approaches based on simplified inverter modelling. It also allows sensible reduction of computational burdens with respect to the time domain models. For this reason, it constitutes an attractive tool inside Monte Carlo simulations for the probabilistic analysis of harmonic and interharmonic distortion. Numerical experiments demonstrate the good performances of the proposed method and the need of accounting for the presence of interharmonics for high power PWM drives.

A new approach to model AC/DC/AC conversion systems

A new approach for modeling AC/DC/AC power conversion systems is presented and discussed. It is based on the modulation function theory and utilizes the concept of the iterative harmonic analysis (IHA), taking advantage of a two-step procedure in which two different models are utilized. The proposed approach can be applied successfully on HVDC systems and adjustable speed drives for synchronous and asynchronous motors, achieving better modeling accuracy with respect to classical modulation function approaches and reduction of computational burdens with respect to the time domain models. It constitutes an attractive tool inside Monte Carlo simulations for the probabilistic analysis of harmonic and interharmonic distortion. Comparative tests validate the proposed method and demonstrate its accuracy performances.

A new approach for the computation of harmonics and interharmonics produced by line-commutated AC/DC/AC converters

A new approach for modeling line-commutated ac/dc/ac conversion systems is presented and discussed. It is based on the modulation function theory taking advantage of a two-step procedure in which two different models are used. The goal is to achieve a reduction of the computational burden with respect to the time domain models and better modeling accuracy with respect to classical modulation function approaches. The proposed model constitutes an attractive tool inside Monte Carlo simulations for the probabilistic analysis of harmonic and interharmonic distortion. Comparative tests validate the proposed method and demonstrate its computational efficiency and result accuracy.

Recent advances on AC PV-modules for grid-connected Photovoltaic plants

The paper provides an overview on Photovoltaic (PV) AC-modules, among typical PV-modules which only produce DC output. A novel approach for designing of a new AC PV-module is also presented and discussed, being an other goal of the paper that of introducing an innovative AC PV-module simply based on a conventional DC PV-module and on a micro and distributed energy storage system. PV-plants endowed by AC PV-modules have several advantages over conventional PV-plants: lower generation losses caused by unequal PV-module generation, higher degree of flexibility in the planning and installation of PV-modules, lower price due to the economy of mass production of AC PV-modules, lower minimum system size (and hence lower barrier to the PV market entry), superior ability to site individual modules without concerning for partial shading and other kinds of mismatching conditions; furthermore, installation is safer because there are no high-voltage DC-bus connections. Based on previous researches on distributed energy storage for grid-connected photovoltaic plants, the basic idea for introducing a new AC PV-module is that of connecting a certain number of rechargeable batteries in parallel to a specifically designed number of PV-cells, according to a criterion of maximizing the PV-module generated energy and the number of voltage levels that we want to physically get as input for a multilevel inverter that is proposed to be mounted on the backside of the new AC PV-module. The use of a multilevel inverter technology introduce many advantages with respect to conventional PWM inverters: a greater efficiency, a greater reliability, a lower harmonic pollution on the AC output voltage and so on. To confirm the effectiveness of the proposed idea, the circuit configuration of the introduced AC PV-module and its operating principle are numerically tested by means of some Pspice simulations, performed under ideal operating conditions of batteries.

Probabilistic modeling of industrial systems for voltage distortion analyses

Referring to the IEEE industrial test system for harmonic modeling and simulation, the system impedance probabilistic model accounting for parameter uncertainty, load and supply variability is developed. Such a model together with the probabilistic model of the current pollution produced by an ASD is utilized to evaluate voltage harmonic and interharmonic distortion. The results, obtained by utilizing two methods characterized by different complexity and accuracy and, for each method, referring to different time scenarios, are compared among them.

A new method based on periodic convolution for sensitivity analysis of multi-stage conversion systems

A new approach for sensitivity analysis of harmonics and interharmonics in multi-stage conversion systems is presented. Each component (converter, filter, transformer, etc.) is modeled by taking advantage of periodic convolution and representing the signals by means of a discrete Fourier transform. Firstly, single component frequency coupling matrices are built up starting from the component characteristics. Then, according to the specific topology of the conversion system, single-component matrices are combined to deduce a whole-system frequency coupling matrix: it provides the coupling among the harmonics and interharmonics of voltages and currents. The operative procedure to build up the frequency coupling matrix of a complex AC/DC/AC PWM adjustable speed drive is described: it is very fast and efficient. In particular, the frequency coupling matrix is utilized to perform a sensitivity analysis of the absorbed current with respect to the supplying voltage perturbations around a fixed operating point, developed with reference to a specific case-study.

Iterative harmonic and interharmonic analysis in multiconverter industrial systems

The problem of analysing harmonic and interharmonic distortion in multiconverter industrial power systems is considered. An useful updating of the iterative harmonic analysis algorithm to include interharmonics, based on automated EMTP simulations of nonlinear loads, is presented and its capabilities are discussed, also in the perspective of utilisation in a distributed computing environment.