An improved droop control method for enhanced SOC balancing in DC microgrids

This study investigates the state-of-charge (SOC) imbalance among multiple energy storage units (ESUs) operating in parallel within an islanded DC microgrid. To address this issue, an adaptive droop control strategy is proposed. The method introduces a hyperbolic tangent (tanh) function into conventional droop control to dynamically adjust the droop coefficient. By leveraging the function's bounded and continuously differentiable characteristics, the approach achieves smooth and adaptive SOC regulation. Multiple regulation factors are incorporated to collectively enhance control sensitivity under small SOC deviations, and a bus voltage compensation mechanism is included to mitigate voltage fluctuations during power redistribution, thereby maintaining DC bus voltage stability. The control establishes a nonlinear mapping between SOC and virtual impedance, enabling automatic current adjustment for balanced charging and discharging. Finally, this study constructed a simulation model based on MATLAB/Simulink and set up an experimental platform to verify the effectiveness of the proposed strategy. The results show that this method can effectively achieve the balancing of SOC, the reasonable distribution of load current and the recovery of DC bus voltage under dynamic system conditions. In contrast to conventional methods, the presented strategy markedly accelerates SOC convergence while maintaining robust system stability across a range of power fluctuations and operating conditions. • Hyperbolic tangent function enables smooth SOC-adaptive droop adjustment. • Dedicated regulation factors and bus voltage compensation enhance sensitivity and voltage stability. • The strategy outperforms existing methods in SOC balancing, convergence speed, and load sharing.