A control hierarchy of interconnected mini-grids

Distributed generation (DG) is recently integrating conventional power systems to assist main power plants to satisfy customer need. A control hierarchy to interconnect DG systems to conventional power systems is required to improve reliability and quality of power supply systems. The main task is to control the frequency and voltage of the systems. This task is currently done by using synchronous generators in many interconnected power systems. Therefore, their control strategy of conventional power systems can be based and adapted to be implemented into other DG technologies through their interface unit to the grid, namely the inverter. The inverter is the primary interface unit between the energy source and the grid. This paper presents a flexible control hierarchy of interconnected mini-grids based on inverters.