Since the medium-voltage microgrid contains PQ-controlled distributed generations, its fault characteristics are quite different from those of the traditional grid, which brings difficulties to the formulation of protection schemes. The fault control strategy of distributed generation determines the fault characteristics of microgrid, so according to the fault control strategy, this paper improves the existing fault calculation method of grid-connected microgrid. The simulation model of microgrid is established based on PSCAD/EMTDC. According to the model of microgrid, the fault calculation program is compiled with MATLAB to calculate the characteristics of voltage, current and measured impedance of microgrid when short-circuit fault occurs. Based on the analysis of fault calculation results, this paper presents the curve of fault characteristics, analyses the influence of fault location and transition resistance on fault characteristics, finally summarizes the change rule of fault characteristics in microgrid and the applicability of characteristic quantities of protection principle in microgrid.

fault calculation,fault characteristic,control strategy,microgrid,PQ control