The growth and development of populations worldwide led to an increase in the consumption of energy resources, raising serious sustainability issues. In this context, Power Engineering is assuming a crucial importance in numerous aspects regarding the efficiency and effectivity of power generation, transmission, and distribution, as well as from the perspective of the utilization of electrical apparatus by the end users. In addition, the significance of Power Engineering is also decisive for the paradigm of decentralized energy resources. Therefore, new technologies are emerging, especially for the successful operation of future Smart Grids and Smart Cities, encompassed with the production and utilization of Sustainable Energy.