Modeling and Control of Single Phase Grid-Tie Converters

The penetration of renewable energy into the electric utility grid is growing worldwide. At the heart of these renewable sources is the power electronic systems used to convert the renewable source to an output that can be connected to the grid. In recent years, there has been a great deal of work in designing converters for grid-tie applications and is continuing to grow. With recent smart grid activities, it is not likely that this work will cease in the short term. Most of the recent research is in ancillary services that the converter can offer in addition to the normal energy transfer. With more advanced converters, the ability to provide reactive power and harmonic compensation has triggered many researchers to look at more advanced control schemes.

The work in this thesis focuses on modeling and control of single phase grid connected converters with an emphasis on grid interactions and ancillary services. While there has been a great deal of work in the modeling and control area for general converter operation, there has been little analysis in the converter’s response to grid disturbances. There are very few resources that discuss the controller design as it relates to power quality. However, these are issues that must be considered in a real design and what separates the research and commercial level converters.

In addition to control and modeling work, the author suggests two new transformerless converter topologies for photovoltaic applications. In general, these converters can be viewed as a hybrid converter topology comprised of a two level and multi-level structure. Both converters show conducted emissions improvements over the standard commercial transformerless converters while also meeting leakage current requirements.