In this chapter, modified models for analyzing the effects of RES and DC links on active power and frequency support issue in large-scale power system under power market scenarios are presented. Based on the simulation results, combination of RE sources like PV and wind will be so useful in reliability of system. In fact, their aggregation and combination can reduce the overall variability of the power produced, with all the resulting benefits in terms of improved capacity credit and improved effectiveness in the reliability of the system. Technological advances, such as the use of modern power processing systems, energy storage, and control techniques in high-power systems are very important. Also by means of global RE integration and competitive markets, it would be necessary to equip the network with several DC interconnections at high voltage level between the areas. It is necessary to do more investigation in VSC-HVDC link as a bi-directional gate and application of the last technologies in power electronics interfaces. However, more frequent use of such HVDC applications with advanced power electronic devices can be expected in the future to fulfil the requirements in deregulated power system. The results of last section of this chapter, demonstrate that proposed intelligent controller improved the dynamic response of system faster than conventional controller and provides a control system that satisfied the load frequency control requirements. It was obvious that intelligent control for coordination between RES and reserve/stored energy, certainly plays a significant role. It will not be possible to integrate large amounts of RESs into the conventional power systems without intelligent control and regulation of systems.