Conductance-frequency droop control to ensure transient stability of inverter-based stand-alone microgrids.

• Analysis of the transient stability boundaries of a stand-alone inverter-based microgrid during current limitation employing three different frequency droop controls. • The conventional P-f and Iact-f droop controls cannot guarantee the microgrid stability for all possible operating conditions. • The use of a variable defined as the equivalent conductance is proposed to carry out the frequency droop leading to the G-f droop control. • The G-f droop control provides the same satisfactory performance irrespective of the operating conditions, ensuring always the transient stability of inverter-based microgrids. Currently, inverter-based stand-alone microgrids are gaining interest due to the advantages of obtaining energy from renewable sources. To manage the operation, these microgrids include storage systems connected in parallel to the PCC through electronic inverters that are controlled as voltage sources in order to support the frequency and voltage at the PCC. For the purpose of ensuring P and Q sharing among inverters and also the synchronization stability of the microgrid, droop control is widely used, achieving a satisfactory performance in normal operation. Nevertheless, in the presence of overloads or short-circuits, the inverters must limit the current for self-protection, thereby modifying the performance of the system that then becomes prone to suffer transient stability problems. In this paper, first the performance of the inverter-based stand-alone microgrids with the conventional P - f and I act - f droops is analyzed, obtaining the stability boundaries during current limitation. In order to always ensure the synchronization stability of the system, this paper then proposes the G - f droop that consists in employing the equivalent conductance seen by each inverter for its frequency droop control. Furthermore, as this variable always correctly represents the inverter power angle, the system dynamics are not affected by the operating conditions. The theoretical results have been validated by means of simulation and Hardware-In-the-Loop results, showing the superior performance of the proposed G - f droop. [ABSTRACT FROM AUTHOR]