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In high power applications the maximum switching frequency is limited due to thermal losses. This leads to highly distorted output waveforms. In such applications, it is necessary to filter the output waveforms using bulky passive filtering systems. The recently presented selective harmonic mitigation technique (SHMPWM) produces output waveforms where the harmonic distortion is limited fulfilling specific grid codes when the number of switching angles is high enough. The related technique has been previously presented using a switching frequency equal to 750Hz. In this paper, a special implementation of the SHMPWM technique optimized for very low switching frequency is studied. Experimental results obtained applying SHMPWM to a three-level neutral point clamped converter using a switching frequency equal to 350Hz are presented. The obtained results show that the SHMPWM technique improves the results of previous selective harmonic elimination (SHEPWM) techniques for very low switching frequencies. This fact highlights that the SHMPWM technique is very useful in high power applications leading its use an important reduction of the bulky and expensive filtering elements.

Abstract-Multilevel converters have received increased interest recently as a result of their ability to generate high quality output waveforms with a low switching frequency. This makes them very attractive for high power applications. A Cascaded HBridge converter is a multilevel topology which is formed from the series connection of H-Bridge cells. Optimized pulse width modulation techniques such as Selective Harmonic Elimination (SHE-PWM) or Selective Harmonic Mitigation (SHM-PWM) are capable of pre-programming the harmonic profile of the output waveform over a range of modulation indices. Such modulation methods may however not perform optimally if the DC links of the Cascaded H-Bridge Converter are not balanced. This paper presents a new SHM-PWM control strategy which is capable of meeting grid codes even under non-equal DC link voltages. The method is based on the interpolation of different sets of angles obtained for specific situations of imbalance. Both simulation and experimental results are presented to validate the proposed control method.

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To examine the congenital nature of the geographic form of focal/multifocal retinal dysplasia, we carried out a retrospective analysis of the medical records of dogs produced in a closed colony of service dogs who receive very thorough ophthalmologic examinations early in their life, and later, when they return for training. Medical records were reviewed from all dogs produced by The Seeing Eye, Inc. between October 1991 and September 1998, and which had a diagnosis of geographic retinal dysplasia coded. We identified 23 dogs of five different breeds or interbreed crosses that comprise the breeding and production program (Golden Retrievers, German Shepherds, Labrador Retrievers, Labrador Retriever/Golden Retriever cross and German Shepherd/Labrador Retriever cross) in which the results of at least two complete ophthalmic examinations were documented, the first before 10 weeks of age, and the second when the dog was a young adult. Of the 23 dogs, only one was identified as affected with the geographic form of retinal dysplasia when examined at 5-6 weeks of age. The remaining dogs were normal. Our findings indicate that, in most cases, the geographic form of retinal dysplasia is not present in dogs prior to 10 weeks of age. These findings indicate the need to revise recommendations for early screening of dogs for retinal dysplasia.

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Large digital integrated circuits designed to solve space applications, have to be designed following standards that recommend to include hardening techniques against Single Event Phenomena caused by harsh radiation environments. It is specifically important in the case of modern deep-submicron technologies. Single Event Effects are phenomena related to the effects of radiation when ionizing particles hit the surface of semiconductors in certain critical areas, where the consequences are mainly data corruption or unexpected behavior with no permanent damage. Fault injection studies are a valuable methodology to evaluate the robustness of the circuit mainly in the early stages of the design. This paper introduces the second generation of the emulation-based fault injection platform FT-UNSHADES supported by the European Space Agency, where new features have been included to fulfill with the demands of a growing community of users.