Fault transient analysis in microgrid using discrete wavelet transform

Microgrid is an effective means to integrate distributed generations and manage their power flows. Since the high penetration rate of DGs in microgrid and its capability to operate in grid-connected mode or islanded mode, the fault patterns of microgrid are not that obvious as those shown in the traditional low voltage distributed networks. Thus an extensive knowledge of fault transient characteristics is beneficial to design effective protection schemes for microgrid. Since conventional methods have difficulties in analyzing transient signals, discrete wavelet transform is employed in this paper to identify fault patterns from fault current/voltage signals. Aiming to provide a solution to the problems arise from applying wavelet in microgrid with short line segments, this paper proposed an improved wavelet transform method that using Daubechies complex wavelet with cubic spline interpolation. A modified benchmark microgrid network is modeled in Matlab/Simulink to verify the proposed method. Four types of fault cases in bus-bar and feeder are investigated respectively, and the simulation results indicate the unique fault patterns in the form of modulus maxima and wavelet energy.