With the increase of concerns over global warming renewable energy sources (RESs) has been the center stage of academia, industry, national and international policy makers. In power systems, with the increasing integration of these distributed energy resources (DERs) like solar and wind, microgrid (MG) concept has been a favorite topic in recent times. Microgrids (MGs) are small-scale electricity networks that integrate distributed electricity generation with consumers/prosumers and potentially with storage systems. MG is typically equipped with power converters like inverters as interfaces and has become one of the most promising active distribution networks. It is normally controlled to provide the required flexible operation (like islanded operation) and to maintain the specified power quality and energy output. With regard to multi power inverters in parallel, several decentralized control methods have been proposed, such as the power droop control method. Moreover, power droop control based hierarchical control architecture is proposed, including primary, secondary, and tertiary control levels to achieve power sharing control, synchronization control, power flow management, and economic optimization. In this thesis, centralized and distributed power droop controller based secondary controllers are developed for AC Microgrids to restore voltage magnitude and frequency deviations considering communication delays. Parameters for inner voltage and current loops, virtual impedance, and power droop coefficients are designed. Harmonic suppression method is used to reduce voltage total harmonic distortion for a three phase voltage controlled inverter with a nonlinear load. The proposed control approaches are validated by using Matlab/Simulink or dSPACE 1006 based hardware in the loop simulation platform.