State of charge balancing for distributed batteries in DC microgrids without communication networks

State of charge (SoC) balancing and accurate power sharing have been achieved among distributed batteries in a DC microgrid without a communication network by injecting an AC signal. The frequency of the generated signal is proportional to the SoC of a predefined master battery and it is used for the other batteries as a common variable to estimate the SoC and output power of the master battery. Based on modified droop control, the distributed batteries realize a balanced SoC and accurate power sharing regardless of the differences in the line resistance. A communication system is not required. Thus, the system cost is notably reduced. Moreover, to guarantee system reliability, a new master battery selection method is provided to replace the master battery under fault conditions. The effectiveness of the proposed strategy was verified by simulations and experimental results.