Lifetime-Oriented Droop Control Strategy for AC Islanded Microgrids

This paper presents a lifetime-oriented droop control strategy for ac islanded microgrids, which is able to perform equal thermal sharing among paralleled inverters. Electro-thermal model and temperature estimation model are first established to estimate thermal characteristics of inverters, and temperature-power droop relationships are built according to the electro-thermal model. Then, a lifetime-oriented droop controller is developed to realize equal thermal stress sharing. In addition, a small-signal model of microgrid equipped with the proposed droop control is established, and the effect of electro-thermal parameters of the power devices on the closed-loop stability of a droop controller is investigated. Simulation and experimental results show that the proposed lifetime-oriented droop control is able to perform identical thermal stress sharing among paralleled inverters automatically, which mitigates the impact of thermal stresses on average lifetime of inverters and thus enhances long-term reliability of microgrids.