Aiming at the problem of state-of-charge (SoC) imbalance among energy storage units in DC microgrids caused by line impedance mismatch

which can lead to overcharging or over-discharging of individual units

an adaptive droop control strategy based on successive compensation of line impedance is proposed. First

in the line impedance compensation control

the process is divided into three stages. In the first stage

the droop coefficient is updated by integrating the output current. In the second stage

the output current at the intermediate integration moment is used as the reference current to restore the bus voltage. In the third stage

the current sharing error is estimated to update the iterative signal. In addition

a switching signal is introduced to control the transitions between stages

and a consistency algorithm is used to calculate the iterative signal for updating the switching signal. Next

in the SoC balancing control

the compensated line impedance and a monotonic function associated with the SoC information are incorporated into the adaptive droop control to achieve SoC balancing and current sharing among the energy storage unit. Finally

an experimental prototype with multiple energy storage units is built to verify the feasibility and effectiveness of the proposed strategy.