In this book the basic theory of grid connected photo-voltaic systems is explained, giving an introduction to the different aspects of system design. Starting with a look at the standards concerning grid connection of distributed resources, and working its way through how thephoto-voltaic cells work, to how photo-voltaic modules with electrical converters can be arranged. Some different converter topologies suitable for use with photo-voltaics are found, and based on these topologies, solutions for how to control these converters have been examined. These controls involve methods for utilizing the maximum power from solar panels, methods for synchronizing with the grid and methods for current and voltage control.