The high penetration of emerging power electronics-based distributed energy resources into electric grids has raised control, management, and stability issues. Besides, the electrical grids have been converted to multiinput multi output cyber-physical systems (CPSs) that need advanced communication infrastructure to be monitored and optimally controlled. The smart grid (SGs) concept has been introduced as the platform that facilitates dealing with the challenges of modern electric grids. Monitor and control capacities, automatic grid control, and active consumer participation in the energy industry expand the SGs influence. Mentioned emphatic features of SGs have been achieved by combining power system technologies with emerging power electronics and digital telecommunications technologies. Since almost all the distributed energy resources (DERs) technologies, such as renewable energy resources, micro sources, and energy storage systems, use the power electronic interfaces, it is vital to match the characteristics of the DERs with the grid requirements. On the other hand, power electronics provide 2more flexibility, controllability, and better power quality, which are essential factors in SGs. However, with the rapid progression of physical systems in power electronics applications to interface DERs combined with cyber frameworks, the threats of cyber have a significant impression on SG security and performance. A comprehensive study of the vital power electronic role in SGs as CPSs to provide sustainable/reliable energy resources is provided in this chapter. Specifically, cyber-attacks in power electronics systems are studied briefly.