An Improved Droop Control Scheme for Enhancing Dynamic Current Sharing Performance in Autonomous DC Microgrids

Droop control is a basic control method for load current sharing in autonomous dc microgrids, but the conventional droop control method suffers from some inherent drawbacks. First, there is always a dc bus voltage deviation caused by virtual resistors and line resistors. Second, the dynamic current-sharing performance is degraded due to the difference between the actual output impedance and the desired output impedance of distributed generation (DG) units. Especially during the dynamic process of load current changes, the dynamic performance of certain DG units will deteriorate, and there may be a significant overshoot in their output currents. This may cause unfavorable overcurrent in certain DG units. However, this problem is often overlooked. In this paper, an improved droop control scheme is proposed to enhance the operational performance of dc microgrids. Compared with the conventional droop control method, the proposed droop control scheme can not only achieve accurate load current sharing among different DG units, but also greatly enhance the dynamic performance of DG units during the dynamic process. Moreover, the proposed droop control scheme can achieve dc bus voltage restoration and retain the conventional droop controller's advantage that does not require communication networks or central controllers, which can reduce the system's cost and improve the system's reliability and flexibility. The effectiveness of the proposed droop control scheme is verified by hardware-in-the-loop real-time simulations.