Enhanced power frequency droop control for microgrids

This thesis develops enhancements to power frequency droop control for microgrids. Contemporary research fails to fully solve a number of problems with droop control. This thesis provides a conclusive argument that the control employed in microgrid inverters requires advancement, to address the specific problems of: imbalances in reactive power output; poor voltage regulation; increased voltage range; achieving frequency limiting and ensuring the stable operation of microgrid control algorithms. This thesis provides enhancements to droop control that solve or circumvent the specific problems noted. The five contributions to primary level control in microgrids are: the utilisation of an arctan function for the power frequency droop profile; the enhancement of the virtual output impedance concept; a PCC voltage estimation technique; a parallel voltage and current control scheme and an adaptive sliding mode controller for microgrids. The thesis discusses the theoretical basis for each of these enhancements and justifies their advantages over contemporary state of the art control schemes. Experimental and simulation results are presented from a three phase two inverter microgrid. The results confirm the performance improvements provided by each enhancement to power frequency droop control, on a case by case basis.