Modulation techniques for the cascaded H-bridge multi-level converter

This thesis investigates space-vector modulation and one-dimensional modulation applied to the cascaded H-bridge multi-level converter as a model for one port of the UNIFLEX-PM power converter system. The UNIFLEX-PM converter is a modular system including galvanic isolation at medium frequency intended to replace transformers in future distribution and transmission systems. Power converters in this application must produce good quality voltage waveforms with low power loss. In this work, modulation methods are developed using theoretical analyses and simulation studies, before being verified experimentally using a low voltage, laboratory-based power converter operating at the low switching frequencies applicable to high-power applications. Using space-vector modulation, the relationship between the phase of the sampling process and the distortion of the line voltages is used to reduce the harmonic distortion of the output voltages. Different loads are attached to the cells of the cascaded H-bridge converter and limits are derived determining the range of loads for which it is possible to equalize the capacitor voltages. An algorithm which uses redundant states to balance the capacitor voltages without increasing the switching frequency is applied to space-vector modulation and one-dimensional modulation and its performance is compared to the derived limits. The geometrical effect of capacitor voltage ripple on the space-vector diagram is used to derive the influence on the spectrum of the line-voltages. It is identified that second and fourth harmonics of the capacitor voltages contribute to fifth and seventh harmonics of the line voltages. A feed-forward scheme to compensate for the ripple of the capacitor voltage is derived and is shown to reduce the magnitude of un-wanted harmonics. All the methods developed in this thesis can be applied to converters with any number of cells

Modulation techniques for the cascaded H-bridge multi-level converter

This thesis investigates space-vector modulation and one-dimensional modulation applied to the cascaded H-bridge multi-level converter as a model for one port of the UNIFLEX-PM power converter system. The UNIFLEX-PM converter is a modular system including galvanic isolation at medium frequency intended to replace transformers in future distribution and transmission systems. Power converters in this application must produce good quality voltage waveforms with low power loss. In this work, modulation methods are developed using theoretical analyses and simulation studies, before being verified experimentally using a low voltage, laboratory-based power converter operating at the low switching frequencies applicable to high-power applications. Using space-vector modulation, the relationship between the phase of the sampling process and the distortion of the line voltages is used to reduce the harmonic distortion of the output voltages. Different loads are attached to the cells of the cascaded H-bridge converter and limits are derived determining the range of loads for which it is possible to equalize the capacitor voltages. An algorithm which uses redundant states to balance the capacitor voltages without increasing the switching frequency is applied to space-vector modulation and one-dimensional modulation and its performance is compared to the derived limits. The geometrical effect of capacitor voltage ripple on the space-vector diagram is used to derive the influence on the spectrum of the line-voltages. It is identified that second and fourth harmonics of the capacitor voltages contribute to fifth and seventh harmonics of the line voltages. A feed-forward scheme to compensate for the ripple of the capacitor voltage is derived and is shown to reduce the magnitude of un-wanted harmonics. All the methods developed in this thesis can be applied to converters with any number of cells

Optimization of switching losses and capacitor voltage ripple using model predictive control of a cascaded H-bridge multi-level StatCom

This paper further develops a Model Predictive Control (MPC) scheme which is able to exploit the large number of redundant switching states available in a multi-level H-bridge StatCom (H-StatCom). The new sections of the scheme provide optimised methods to trade off the harmonic performance with converter switching losses and capacitor voltage ripple. Varying the pulse placement within the modulation scheme and modifying the heuristic model of the voltage balancing characteristics allows the MPC scheme to achieve superior performance to that of the industry standard phase shifted carrier modulation technique. The effects of capacitor voltage ripple on the lifetime of the capacitors is also investigated. It is shown that the MPC scheme can reduce capacitor voltage ripple and increase capacitor lifetime. Simulation and experimental results are presented that confirm the correct operation of the control and modulation strategies

Earth Science Education 4. Geoliteracy Canada, A National Geoscience Education Initiative

Earth scientists are collectively responsible for ensuring that geoscience knowledge is incorporated into decisions about land use in Canada. The future of our discipline depends to a considerable extent on an educated public that realizes the value of earth science information. The vitality of earth sciences also depends on our ability to convince bright students to enter our profession. In this paper, we propose an initiative in geoscience education, Geoliteracy Canada, based on expanded delivery of, and better linkages among, four national programs and an upcoming international conference. The programs that underpin this initiative are EdGEO, EarthNet, WAT ON EARTH, and Geoscape Canada. These national programs are linked, in turn, to the many local and regional geoscience education enterprises across the country. The Canadian Geoscience Education Network, the education committee of the Canadian Geoscience Council (CGC), will provide national co-ordination of the initiative. Résumé C'est la responsabilité de tous et chacun des géoscientîques de faire en sorte que les connaissances géoscientifiques soient prises en compte lors de toute décision concernant l'utilisation des terres du Canada. L'avenir de notre discipline dépend en grande partie des perceptions d'une population consciente de la portée des informations géoscientifiques. La vitalité des sciences de la Terre dépend aussi de notre capacité à attirer les meilleurs étudiants dans notre profession. Dans le présent article, nous proposons un projet d'éducation en géoscience, « Géolittératie Canada », visant à accroître les activités et les interrelations entre quatre programmes nationaux et une prochaine conférence internationale. Les programmes formant l'assise de ce projet sont Edgeo, GéoNet, WAT ON EARTH, et Géopanorama du Canada. Ces programmes nationaux sont eux-mêmes rattachés à de nombreux projets géoéducatifs locaux et régionaux à travers lepays. Le Canadian Geoscience Education Network (Réseau canadien d'éducation géoscientifique), le comité d'éducation du Conseil géoscientifique canadien (CGC), assurera la coordination nationale de cette initiative