Droop Control Techniques for Grid Forming Inverter

Multiple distributed energy resources (DERs) can be connected to a microgrid, and coordination of these units is necessary for meeting the increasing demand for electricity. In stand-alone mode of operation, converters should meet load requirement in addition to satisfying voltage and frequency constraints. Numerous control approaches, such as droop control, master-slave control, peer-peer control, and average current-sharing control, have been applied for parallel operation of inverters; however, droop control technique is the most well-established grid-forming method in literature owing to its high reliability, and non-dependance on communication. Thus, this study first presents a review of state-of-the-art droop control techniques adopted within a microgrid. Later, a simple droop control technique applied to an isolated two-inverter system is presented, where active and reactive powers are drooping against frequency and voltage, respectively, and a cascaded loops control structure consisting of PI controllers for inner control of voltage and current of converter are also presented. The overall system is simulated in MATLAB/Simscape software, and the results verify the effectiveness of droop control technique for grid-forming inverters in autonomous operation of a microgrid.