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Flexible Medium-Voltage Perturbation Injection Converter for AC and DC System Identification

Power systems 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 dc nature a flexible device capable of ac or dc measurements is 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. Moreover, through the hardware and control reconfiguration it is possible to address the needs of both ac and dc applications. This paper presents the flexible medium voltage Cascaded H-Bridge converter for impedance/admittance measurement of ac and dc systems. The effectiveness and flexibility of the topology is shown through a case study where the terminal characteristics of a Modular Multilevel Converter are measured.