Efficient network fault analysis method for unbalanced microgrid systems

A novel network short-circuit fault analysis method based on graph theory and a complex short-circuit MVA representation is proposed as an alternative method for unbalanced microgrid systems. The proposed algorithm is based on the branch-path incidence matrix K and the newly defined augmented incidence matrix Kℓ of a power network, as opposed to the traditional Z-bus building algorithm and inverse Y-bus matrix with the lower and upper triangular matrix (LU) method. To simplify the unit transformation among different voltage levels, all network components are represented in a short-circuit MVA form with their own infinite bus. Moreover, two major types of distributed generation (DG) models have been successfully implemented using the proposed method; therefore, the contributions of DG to the fault currents can be easily addressed in a microgrid system. The results indicate that the proposed algorithm is accurate and performs better than other methods, particularly with respect to large-scale unbalanced microgrid distribution systems with hybrids of single-, two-, and three-phase.