Droop Control Method with Virtual Output Impedance for Parallel Operation of Uninterruptible Power Supply Systems in a Microgrid

In this paper, a novel droop control scheme applied to distributed UPSs forming a microgrid is proposed. The control architecture consists of two levels of hierarchy: 1) the P/Q droop control method of every UPS unit and 2) the management of the microgrid through the control of the setpoints of the units and the intelligent switch connected to the strong grid. This second level of control let us to connect or disconnect the microgrid to the utility mains, resulting in two scenarios: grid-connected and islanding operation mode. Also, it is taken into account the seamlessly transition between both operation modes, the possibility to share power with the utility grid, and the energy management of the overall system.