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RESEARCH

Modular Scalable Medium-Voltage Impedance Measurement Unit Using 10 kV SiC MOSFET PEBBs

Medium-voltage IMU prototype
This paper describes the design and implementation of the first functional medium-voltage im-pedance measurement unit capable of characterizing in-situ source and load impedances of dc and ac networks (4160 V ac, 6000 V dc, 300 A, 2.2 MVA) in the frequency range of 0.1 Hz - 1 kHz. It comprises three power electronics building blocks, each built using SiC MOSFET H-bridges, features great reconfigurability, and allows both series and shunt perturbation injection in order to achieve accurate impedance characterization of the Navy's shipboard power systems. With the extraordinary advantages featured by the modular power electronics building block concept, and unconventional power processing benefits offered by SiC semiconductors, the development of the unit shown in this paper unquestionably enables both improvement of existing and design of future stable and reliable electrical Navy shipboard platforms with advanced electrical energy generation and modern distribution architecture. The requirements for improved reliability and high survivability of shipboard power systems have steered development of medium-voltage ac (MVAC), and medium-voltage dc (MVDC) systems as direct replacements of conventional low-voltage generation and distribution. This is predominantly the case with the MVDC, as it is incontrovertibly seen as a key enabling technology for all electric ships. However, this shift introduces highly increased employment of power electronics in energy production, distribution, and consumption, and although it offers a necessary means for an advanced and flexible energy utilization, that trend is fundamentally changing the nature of the shipboard power system sources and loads, altering their consistently mild properties, and inflicting low- and high-frequency dynamic interactions that never before existed. As power electronics converters make loads more robust to variations of voltage and frequency, they unfortunately present a negative incremental resistance behavior known for initiating low-frequency dynamic interac-tions. To better design, dynamically control, and understand future electronic systems on all-electric ships, it is necessary to develop innovative concepts that offer better insights into converter- and system-level behavior.

Experimental results - dq source impedances obtained at 480 V
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