New Perspectives on Droop Control in AC MicroGrid

Virtual impedance, angle droop and frequency droop control play important roles in maintaining system stability, and load sharing among distributed generators (DGs) in microgrid. These approaches have been developed into three totally independent concepts, but present strong relevance. In this letter, their similarities and differences are significantly revealed. Some new findings are established as follows: 1) angle droop control is intrinsically a virtual impedance method; 2) virtual impedance method can also be regarded as a special frequency droop control with a power derivative feedback; 3) the combination of virtual impedance method and frequency droop control is equivalent to the proportional–derivative (PD) type frequency droop, which is introduced to enhance the power oscillation damping. As a whole, these analogous relationships provide the new insight into the design of these three controllers.