Hardware-in-the-Loop Characterization of Source-Affected Output Characteristics of Cascaded H-Bridge Converter

Recent trends in power system design such as an increasing share of renewable energy sources and integration of power electronics equipment for medium voltage applications are creating 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 measurement. This paper assesses the impact that the active element on the input side has on the output side, where the injection of the perturbation signal is realized. Models of the input and output element 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 and the measurement is performed using offline and real-time simulations on a hardware-in-the-loop platform.