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. While being a perturbation injection and a measurement instrument it also needs to assure that it does not cause instabilities in the device under test. Hence, a mechanism to determine the output impedance of a single cell of a Cascaded H-Bridge converter is needed. To validate the theoretical developments, a new method to measure the single-phase output impedance in the dq-frame is proposed.