Multipath Architecture for Ground Fault Detection in DC-Links of High-Voltage AC Drives Using Neutral-Point Voltage

Ground fault detection in DC-links of high-voltage AC drives is challenging because faults may not produce large currents, while neutral-point voltage monitoring can lose sensitivity under nearly balanced pole-to-ground conductances. This paper develops a physics-based mathematical model and a multipath detection framework for the 5 kV DC-link of the GE MV7306 drive. A closed-form expression for the neutral-point voltage VDC0 is derived using Kirchhoff’s current law in terms of equivalent pole-to-ground conductances. A normalized conductance asymmetry index characterizes near-balanced conditions, and logarithmic resistance sensitivity identifies the characteristic transition, Gfault=Gref, beyond which the neutral-point voltage approaches saturation. The analytical model is also used to relate the fixed voltage threshold to the corresponding fault conductance and fault resistance boundaries. A multipath architecture combining fixed-threshold and robust adaptive-threshold paths is then developed. Circuit-model-based simulations consider degradation–recovery, variable-resistance surface leakage, and near-symmetric conductance oscillation scenarios. The proposed method detects all three scenarios with delays of 1.213, 0.031, and 0.141 s, respectively. For the two scenarios detected by both the proposed method and the fixed-threshold baseline, the mean detection delay decreased from 0.822 to 0.622 s, a 24.3% reduction. The results establish a direct link between the conductance model, nonlinear sensitivity characteristics, and multipath ground fault detection.