Identification of Source-Affected Output Characteristics of a Four-Quadrant Cascaded H-Bridge Converter Cell

The development and integration of power electronics equipment and converters for medium voltage ac and dc application has created different subsystem interactions that require proper investigation, understanding, description and estimation of global system stability through impedance-admittance measurements and identification. Four-quadrant Cascaded H-Bridge topology features high output voltage resolution and high effective switching frequency which enables high-dynamic, high-fidelity voltage perturbation injection for medium voltage impedance and admittance measurement. This paper assesses the impact that the active converter stage on the input side has on the output side, where the injection of the perturbation signal is realized. Models of the input and output converters are developed as well as the model of the connected system. To validate the theoretical developments, a new method to measure the single-phase output dynamics in the dq-frame is proposed.