System Stability and Short Circuit Contribution as Discordant Targets in Cascade Connected DC Microgrids: a Design Procedure

Advanced DC microgrids design requires considering interdependent aspects. In these flexible grids with large penetration of high-bandwidth controlled converters, both system stability and short circuit limitation are crucial aspects to be attained. The design of filtering stages directly affects both: on one side the stability is beneficially influenced by a large filter capacitor, while on the other the short circuit current increases with oversized capacitors. Thus, voltage stability and filter’s short circuit contribution are discordant goals, which need to be carefully balanced by the designer. To solve this issue, a design procedure for sizing the LC filtering stage and the main bus voltage in a cascade-connected DC power system is proposed. The aim is to ensure meeting both voltage/current ripple requirements, as well as accomplishing system stability and limiting the energy supplied into a fault. Final tests on a Hardware-In-the-Loop system and electro-magnetic transients’ simulations are used to verify the effectiveness of the filter’s designing procedure.