Transmission impedance shows the characteristics of variety in microgrid. Under different transmission impedance types, virtual impedance, angle droop control, and frequency droop control play important roles in maintaining system stability and load sharing among distributed generators (DGs). These approaches have been developed into three totally independent concepts, but a strong correlation exists. This chapter reveals their similarities and differences. Finally, introducing a unified droop control unifies these three independently developed droop control methods into a generalized theoretical framework.