Paralleling Converters in DC Microgrids with Modified Lag I-V Droop Control and Voltage Restoration

Abstract

In stand-alone or islanded DC microgrids, sharing of the load between parallel-connected converters is usually achieved using the droop control method. Two main types of droop control are used with DC microgrids: the impedance (V-I)droop control method and the admittance (I-V) droop control method. Droop control permits the sharing of load between parallel-connected converters, but it creates a voltage deviation in the DC microgrid voltage. Voltage restoration control is then required to restore the DC microgrid voltage back to its preset value. This paper proposes a novel I-V droop control method using a modified lag compensator which combines voltage control and load sharing between the parallel-connected converters within the DC microgrid. The proposed control system is made up of two nested controllers: an inner Proportional Integral (PI) current controller and an outer modified lag compensator which controls the voltage and the droop. An addition outer loop is used for voltage restoration. The proposed control system was simulated using Simulink. Simulation results are shown for the operation of two Buck converters connected in parallel and sharing a common resistive load.