Frequency superimposed robust coordinated control in a hybrid microgrid

Abstract

The paper presents a frequency superimposed robust coordinated control technique for the precise power bifurcation among the multiple energy storage elements. In the proposed control principle, a dynamically computed low voltage virtual frequency is injected into the dc control network. According to the total power demand, and the energy density of the battery units, the virtual frequency is computed in the master controller units. Further, with respect to the measured virtual frequency and their specified drooping gain, the slave units interact. In consequence of the conditional drooping factors, the slave units can locally decide their spell of execution. Thus, the proposed scheme ensures a precise power management among the multiple energy storage elements without introducing any virtual resistance in the dc network. In an addition, accounting the system stability, the proposed scheme controls the amount of ac grid interference into the dc microgrid. Considering two numbers of battery as master controllers and a compressed air storage as a slave unit, the performance and the stability are evaluated and found to be satisfactory.