A new ac/ac modular multilevel converter (M 2 LC) family will be introduced. The new concept stands out due to its modularity and superior control characteristics.The stringent modularity results in a very cost-efficient and versatile converter construction. This new M 2 LC concept is well suited to a wide range of multiphase ac/ac converters. The basic working principle together with the static and dynamic behavior are explained in detail on a single-phase ac/ac converter enabling four-quadrant operation.It is demonstrated that this converter concept fulfils the demanding requirements for future ac-fed traction vehicles very well.

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Fig. I Traction converter concept for the operation on the ISkVI16.7Hz and 2JkVISOHr wwer lines Abstracl-A versatile prototype converter system of the new Modular-Multilevel Converter (M'LC)family will be introduced. The new concept stands out due to its stringent modular eonstruction as well as its extremely good control eharacteristics. This new M'LC concept is well suitable for a wide range of high voltage applications. The basic working principle as well as the static and dynamic behaviour are explained in detail on a single-phase AClACsonverter enabling fourquadrant operation.The M'LC-family has already been introduced and examined for applications like traction converters, operating directly on the power line, and network interties 11-41. With this prototype converter system, the characteristics of various different M'LC-topologies can be investigated, including single or three phase DClAC converters as well as multiphase ACIAC converters.The prototype converter has been designed in such a way that its configuration can be quickly changed between a wide range o f topologies. A flexible control system has been implemented, which is capable of controlling up to 32 IGBTs per converter arm. independently. Next to the presentation of the converter and its control system, measurement results will be presented including converter operation. 07803-8399-0/041$20.W 020" IEEE.

The results of studies on the biological influence of magnetic fields are controversial and do not provide clear answers regarding their impact on cell functioning. Fluoride compounds are substances that influence free radical processes, which occur when the reactive forms of oxygen are present. It is not known whether static magnetic fields (SMF) cause any changes in fluoride assimilation or activity. Therefore, the aim of this work was to determine the potential relationship between magnetic field exposure to, and the antioxidant system of, fibroblasts cultured with fluoride ions. Three chambers with static magnetic fields of different intensities (0.4, 0.6, and 0.7 T) were used in this work. Fluoride ions were added at a concentration of 0.12 mM, which did not cause the precipitation of calcium or magnesium. The results of this study show that static magnetic fields reduce the oxidative stress caused by fluoride ions and normalize the activities of antioxidant enzymes, including superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT). Static magnetic fields modify the energy state of fibroblasts, causing an increase in the ATP concentration and a decrease in the MDA concentration. These results suggest that exposure to fluoride and an SMF improves the tolerance of cells to the oxidative stress induced by fluoride ions.