A thesis on Robust Droop Controller for Accurate Proportional Load Sharing among Parallel Operated Inverters in Islanded Microgrid.

Abstract

A microgrid is a part of a distribution network embedding multiple distributed generation systems like photovoltaic panels, small wind turbines etc. and storage systems. This paper focuses on the islanded operation of microgrids. In this mode of operation, the micro-sources are required to operate autonomously to regulate the local grid voltage and frequency. To make voltage and frequency stable, there have several control method in microgrid. The conventional droop control is typically used to achieve this autonomous voltage and frequency regulation. But conventional droop control has real and reactive power sharing limitations. To share the load accurately in proportion to their power ratings two condition should have met. The condition are the droop controllers must have same per unit output impedance and have same voltage set-point for the inverters. But it is difficult to meet in practice. In this paper, the inherent limitations of the conventional droop control scheme are revealed. That’s why robust droop controller is proposed which can share the load accurately without meeting the above conditions. It also help to reduce voltage drop due to load effect and droop effect. The robust works against numerical errors, disturbances, parameter drifts and component mismatches. In simulation part, the output shows the proportional load sharing among inverters.