A droop controller is intrinsically a phase-locked loop

This paper demonstrates that a droop controller, which is fundamental to the operation of power systems and now the parallel operation of inverters, is intrinsically the same as a phase-locked loop (PLL), which is widely adopted in modern electrical engineering. This bridges the gap between the two communities working on droop control and PLLs. As a result, droop controllers and PLLs can be improved and further developed via adopting the advancements in the other community. This also offers insightful understanding to power systems that have inverters and generators mixed together and leads to significant technological breakthrough for the grid connection of renewable energy. For example, there is no longer a need for grid-connected inverters to have a phase-locked loop and a droop controller at the same time.