Distributed Finite-Time Secondary Control for DC Microgrids With Virtual Impedance Arrangement

In direct current (DC) microgrids, the accurate current sharing could be achieved by regulating the virtual impedance (droop coefficient) and the output voltage average value of each distributed generator (DG) could be restored by regulating the voltage reference value with a secondary controller. However, there is a coupling relationship between the current sharing and the voltage restoration process. In this paper, a distributed finite-time secondary control strategy is proposed aiming at overcoming the coupling effect. The proposed controller consists of four control loops, which are the current sharing controller (CSC), the virtual impedance average value restoration controller (AIRC), the reference voltage consensus controller (RVCC), and the voltage average value restoration controller (AVRC). With the proposed controller, the coupling effect is eliminated and the virtual impedance of each DG is only determined by the system load distribution. Besides, a simplified control strategy is also proposed which only contains the CSC and AIRC, and the reference voltage value can be calculated using the local information. The stability of the proposed controller is analyzed using the Lyapunov method. At last, the proposed controller is simulated in MATLAB/Simulink to verify its effectiveness.