A Ground Fault Location Method for Modular Multilevel Converters

The need of efficient electric transmission systems, the rise of renewable energy production and battery storage systems has empowered the use of Modular Multilevel Converters (MMC) which allows a better performance than convenctional converters. However, the diagnosis of electrical faults in MMC are more challenging because more components are involved in the fault circuit. Particularly, ground faults are the most common type of faults in power systems and their diagnosis has not been widely studied for AC-DC converters, where most of the industrial relays fail. This paper proposes a ground fault location method for MMC converters based on a high value grounding resistor placed in a DC midpoint or AC neutral point of the MMC. Measuring the voltage between its terminals and performing its frequency analysis the fault can be located. The novelty of this method resides in the detection of the ground fault in AC or DC side or in the faulty-submodule location if the ground fault happens inside the MMC. To corroborate the method, numerous simulations have been performed in a half-bridge three-phase MMC converter obtaining promising results.