Impedance Models of Grid-Tied Converters

Due to the continuous growth in the number of grid-tied electronic power converters, it has become important to study how they can be represented from the point of view of the grid itself and the system-level problems that can arise once connected. This thesis uses linear analysis to obtain a mathematical model capable of representing the impedance of a three-phase Voltage Source Converter (VSC) expressed in a rotating d-q frame. For this reason, the Small-Signal average model of the converter under analysis will be considered to analyze its behavior when it works by injecting power into the grid or when it is uses as a rectifier, absorbing energy from the grid. The central part is to observe how the sizing of the Phase Locked Loop (PLL) affects the final results in order to understand how it could lead to instability and system shutdown in weak grid conditions.