A Multifunctional Control Strategy for Oscillatory Current Sharing in DC Microgrids

In this paper, a multifunctional control strategy is proposed for an accurate sharing of oscillatory and dc components of load currents among distributed generation (DG) units in a dc microgrid. The proposed controller is composed of a voltage control loop and a multiloop current control unit. The voltage control loop is used to regulate the microgrid voltage as well as to share the dc component of load current through the conventional droop scheme. The current controller includes two main units to simultaneously (1) manage the oscillatory current sharing, (2) improve the stability of control unit, (3) diminish the voltage ripples, and (4) protect the DG units against overloads. In this paper, the idea of virtual conductance is introduced to modify the output impedance of converters for oscillatory current sharing among DG units. To restrict the instantaneous current of DG units under overload conditions, a maximum current limiter unit is introduced to the control system. The compensation signals of these units are eventually applied to the inner current control loop. This scheme guarantees the microgrid voltage to be maintained within the tolerable range under a variety of oscillatory conditions. The stability of the system is studied using small signal analysis. The proposed control scheme is examined in two different microgrid configurations of radial and ring structures. The effectiveness of the proposed method is evaluated through simulation studies.