Power Loss Mitigation of Parallel-Connected Distributed Energy Resources in DC Microgrids Using a Dual-Ascent Hierarchical Control

In this paper, the distribution power loss of DC microgrids comprising both line loss and converter loss is modelled as a quadratic function of current allocation coefficients, which is a convex function with constraints. On basis of convex optimization theory, the optimal current allocation coefficients are on-line calculated by dual ascent method. In the centralized iterative approach, the incremental of current allocation coefficients are moved in the direction of minimizing the augmented loss function. Then, an adaptive droop control is proposed to achieve the given current-sharing rate. In the proposed control, the current-sharing error generates additional adaptive bus voltage term. By sharing one common bus, the function between reference voltages and output currents of DERs can be obtained by ohm's law. By sampling data of two control periods, the line resistance can be identified in real time. In this way, the real-time efficiency optimization control of DC microgrid can be realized, regardless of line resistance variations. The effectiveness of the proposed control strategy is validated by simulation studies.