AC Ground Fault Location for DC-AC Inverters Based on a Grounding Resistor Voltage Analysis

Abstract

Ground fault diagnosis is difficult to carry out in dc–ac systems due to the presence of power electronics. Additionally, it is common that neither relays could protect efficiently these systems as ac devices are not prepared to actuate under dc currents and vice versa. Previous studies were able to detect if the fault was in ac or dc but the faulty point still being incognita. This article presents a ground fault location method for the ac side of dc–ac systems that complements previous detection methods. It is based on a grounding resistor connected between the midpoint of the dc bus and ground. Then, an instantaneous voltage window record is analyzed into a histogram, obtaining two representative voltage peaks that are correlated. These values are the one with most repetitions and the one with most amplitude. Attending to a coefficient defined by these two parameters, the fault location can be estimated. The effectiveness of this method has been corroborated with simulations and experimental tests in a 140 kW dc–ac converter, achieving promising results.