Stability analysis of islanded DC microgrid for the proposed distributed control strategy with constant power loads

Abstract

Droop control by means of virtual resistance in control loop is applied for parallel operation of sources in order to minimize circulating currents. The droop control approach is widely used in DC microgrids. The conventional droop control schemes are unable to mitigate trade-off between effective equal load-sharing (in per unit) and bus voltage regulation for unequal cable line parameters. The stability analysis becomes important when constant power loads (CPLs) are applied to DC bus due to the impact of the negative impedance of CPLs. In this paper, the distributed control scheme is proposed with a digital communication link for an averaging current signal to compensate the cable line voltage drop and load sharing error. The proposed control scheme based on the hysteresis current controller is found robust in terms of simplex tuning procedure than conventional cascaded proportional integral controllers. The stability analysis of the DC microgrid is done with the effect of the proposed distributed controller and CPLs. This analysis covers a specific range of droop gain, communication time delay, and CPLs. The performance analysis of the system is done based on three source units and common CPL.