The concept “flexibility” has been introduced to address challenges related to uncertainty in power generation (supply side), uncertainty in energy availability (demand side), the need for changing power systems planning methods, and the need for changing power systems operation approaches. In order to increase the flexibility of power systems to reliably and cost-effectively manage the variability and uncertainty of demand and supply across all relevant timescales, Distributed Generation (DG) units and Energy Storage Systems (ESSs) can be utilized. The interconnection of such systems to power grids can be via the DC-link of Custom Power devices (CUPs). The result of this interconnection, called “Flexible Distributed Energy Resources”, can affect the flexibility of power systems by controlling energy exchange, active power and voltage, and simultaneously improving power quality indices. In this presentation, challenges related to uncertainties in power generation and energy availability, as well as changes in power systems operation and planning methods, will be discussed. Discussions on power systems flexibility will be given, and then, it will be shown that it is possible to connect DG units and ESSs to power grids using the DC-link of Distribution Static Compensator (D-STATCOM), Dynamic Voltage Restorer (DVR) and Unified Power Quality Conditioner (UPQC), and control active power injected by DG units and ESSs and simultaneously improve power quality indexes. Co-sponsored by: Power and Energy Systems Research Laboratory Speaker(s): Prof. Gevork B. Gharehpetian Virtual: https://events.vtools.ieee.org/m/365992