Complex Domain Analysis-Based Fault Detection in VSC Interfaced Multi-terminal LVDC System

In voltage source converter-based low-voltage dc systems (LVDC), the fault current of the dc-link capacitor is considerably high and destructive to system infrastructure. It is necessary to develop effective fault detection methods with sufficient sensitivity and accuracy. To achieve these targets, a complex domain analysis-based fault detection method is proposed in this article. Specifically, the proposed method first fits the transient current into a linear combination of exponential functions, which is solved in the Z-domain-based on the Padé approximation. Second, exponents of the fitted function are projected into the complex plane. A state circle centered on the origin is defined on the complex plane to detect dc faults according to the position of projection points relative to the state circle. The proposed method can differentiate several typical situations via theoretical analysis, including fault line transients, healthy line transients, and load switching. The performance of proposed method is validated with an experimental multiterminal LVDC system to reveal its effective performance compared with present frequency domain based methods, including the wavelet transform, the short-time Fourier transform, the S transform, and the Hilbert–Huang transform.