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Design of a Modular and Scalable Small-signal dq Impedance Measurement Unit for Grid Applications Utilizing 10 kV SiC MOSFETs

Fig. 1. The proposed Perturbation Injection Unit (PIU) topologies for shunt (left) and series (right) injection.
The tremendous increase in employment of power electronics in the energy production, transfer, and consumption not only enables a sustainable future, it undoubtedly brings a major energy savings and stimulating improvements to people's quality of life. But not for "free". This trend is considerably changing the nature of the sources and the loads in the electrical grid, altering their mild properties, and inflicting low-frequency dynamic interactions that did not exist before in the conventional power system. To be able to understand, analyze, design, and dynamically control the existing and future power systems, it is unarguably required that one must develop concepts and tools that offer better insights into the system-level behavior and stability of the grid.

This paper shows the impedance measurement unit (IMU) that can characterize in-situ source and load impedances of the sub-transmission medium-voltage networks (up to 69 kV and 250 MVA). The IMU injection circuit can be designed using the power electronics building block (PEBB) concept, in Fig. 1, as it offers a high-scalability and allows for numerous power conversion topologies to be implemented by a series/parallel connection of building blocks.

This paper further shows a unique impedance measurement unit prototype, shown in Fig. 2, built for 4.16 kV, and capable of characterizing medium-voltage distribution systems in 4.16 kV networks at the power level of up to 2.2 MVA. With extraordinary advantages featured by the power electronics building block modular concept, and unconventional power processing benefits offered by state-of-the-art SiC semiconductors, development of the unit shown in this paper unquestionably offers unique capabilities that could lead to a much better understanding of the power system small-signal stability margins, not only under high penetration of power electronics, but in general as well.

Fig. 2. Medium-voltage IMU prototype.
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