Abstract-The introduction of microgrids in distribution networks based on power electronics facilitates the use of renewable energy resources, distributed generation (DG) and storage systems while improving the quality of electric power and reducing losses thus increasing the performance and reliability of the electrical system, opens new horizons for microgrid applications integrated into electrical power systems. The hierarchical control structure consists of primary, secondary, and tertiary levels for microgrids that mimic the behavior of the mains grid is reviewed. The main objective of this paper is to give a description of state of the art for the distributed power generation systems (DPGS) based on renewable energy and explores the power converter connected in parallel to the grid which are distinguished by their contribution to the formation of the grid voltage and frequency and are accordingly classified in three classes. This analysis is extended focusing mainly on the three classes of configurations grid-forming, grid-feeding, and gridsupporting. The paper ends up with an overview and a discussion of the control structures and strategies to control distribution power generation system (DPGS) units connected to the network.

This paper presents a power control study of a Wind Energy Conversion System (WECS) based on a DoublyFed Induction Generator (DFIG) connected to the electric power grid. Proportional-Integral (PI) and Sliding Mode (SM) controls are used to compare the system's performances in terms of reference tracking and robustness to disturbance rejection and with respect to the machine parameters variation. The DFIG control method is based on vector direct control loop with stator flux orientation and the active and reactive powers are controlled PI and sliding mode Simulation studies were performed using Matlab/Simulink/ SimPowerSystems software.

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