A Ground Fault Location and Severity Estimation Method for Modular Multilevel Converters

Resumen

The need of efficient electric transmission systems, the rise of renewable energy production, and the development of battery storage systems have driven the adoption of Modular Multilevel Converters (MMC), which offer better performance than conventional converters. However, the diagnosis of electrical faults in MMC is more challenging because more components are involved in the fault circuit. Particularly, ground faults (GF) are the most common type of faults in power systems, yet their diagnosis has not been extensively studied for AC-DC converters, where most industrial relays fail. This paper proposes a GF location method for MMCs based on the use of a high-value grounding resistor placed at the DC midpoint or AC neutral point. By measuring the voltage between its terminals and conducting frequency analysis, the fault position and fault resistance can be accurately located. The novelty of this method lies in its ability to locate the GFs on the AC side, DC side, or within a faulty submodule (SM) of the MMC. Numerous simulations were performed on a half-bridge three-phase MMC converter, yielding excellent results. Additionally, experimental tests were performed on a 60 kVA 12-level full-bridge three-phase MMC, validating the method.