Active Rectifier Control for Selective Fuse Tripping in a DC Microgrid

Distributed energy resources and new loads such as fast charging stations for electric vehicles are often dc-based. By using low-voltage dc microgrids to connect such systems to the grid, conversion stages can be omitted and higher efficiencies can be achieved. Challenges exist with respect to the protection of dc microgrids, where dc fuses are a viable solution but selective tripping must be ensured. The grid-forming converter must be able to supply the fault current in the case of a line-to-line short-circuit in a feeder without tripping due to over-current. To avoid expensive over-sizing, this paper proposes to use a virtual resistance in the control of the grid-forming converter to limit its output current. The range of the virtual resistance is discussed for normal grid operation and the effect of the virtual resistance on limiting the bus current during a short-circuit fault is discussed. In addition, the impedance models of the source and load systems are presented. Based on this, the influence of the virtual resistance on the system stability is analyzed. To validate the theoretical part, a switching model is simulated and the results show a good agreement with the theoretical analysis.