Current sharing and voltage restoration based on determination of transmission line resistance considering constant power loads in direct current microgrids

Maintaining proper current sharing among distributed generation (DG) units while regulating the output voltage is a challenging control issue in DC microgrids. The conventional droop control is widely used at the primary level of control to tackle this issue, but this method faces some limitations in voltage control and current sharing. To address this problem, this paper presents a new distributed secondary control method that determines the resistance of transmission lines by injecting an external pulse to the reference voltage of each converter and measuring output voltage and current changes. The proposed secondary control signal, denoted as Ui$$ {U}_i $$, enables simultaneous proportional current sharing and voltage restoration in the DC microgrid by correcting the droop coefficients based on the determined resistances. In order to ensure the stability of the proposed method, the small signal stability analysis of the closed-loop system is conducted, considering various parameter changes. In contrast to similar methods, the proposed method introduces a new hybrid technique of voltage setpoint shifting and droop parameter adjustment that achieves precise proportional current sharing and voltage restoration, even when faced with varying resistive loads and constant power loads (CPLs). Additionally, the proposed method demonstrates outstanding characteristics, such as high convergence speed, the ability to determine transmission line resistances instead of assuming them to be known, and robustness in plug-and-play scenarios and communication system failures. The simulation results in MATLAB and experimental tests confirm the effectiveness of the proposed method. This paper proposes a new distributed secondary control method for achieving precise current sharing and voltage restoration in DC microgrids. By injecting an external pulse and measuring changes in output voltage and current, the method determines transmission line resistances and adjusts droop coefficients accordingly. Simulation and experimental results confirm the effectiveness of the proposed method.image