Medium-Voltage Cascaded H-Bridge Perturbation Injection Converter for AC and DC System Identification

The power system have lately seen a tendency of increasing share of renewable energy sources and integration of power electronics equipment. The concept of distributed power generation introduces various stability-related challenges into the power system operation. Consequently, safe and reliable operation imposes the need to understand, describe and estimate the system stability through impedance-admittance measurements and identification. As in a present day network configuration the sources and loads can either be of ac or de nature a flexible device capable of ac or de measurements in required. The 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 measurements. Mover through the hardware and control reconfiguration it is able to operate both as an ac or a de device. This paper presents the flexible medium voltage Cascaded H-Bridge converter for impedance / admittance measurement. The effectiveness and flexibility of the topology is shown through a case study where the terminal characteristics of a Modular Multilevel Converter are measured and the influence of different parameters on the shape of the characteristics is evaluated.