Electricity network across the globe has witnessed an increase in penetration of distributed energy resources (DER) to the grid. A maiden attempt to integrate 50% loaded Combined Cycle Gas Turbine (CCGT) plant and doubly fed Induction Generator (DFIG) plant with DER is carried out for investigations to study frequency excursions in the hybrid system along with temperature excursions in the CCGT plant. A novel attempt is done to introduce modified beluga whale optimizer for tuning the controller gains and system parameters of the hybrid isolated system. This article emphasizes on the system behaviour of an isolated power system consisting of a CCGT plant and a DFIG plant integrated with distributed energy resources comprising of Diesel engine generator, wind turbine generator and battery energy storage system. Among the classical secondary controllers, comparison of system responses is carried out to select the best among proportional, proportional-integral, and proportional-integral-derivative controllers. A modified beluga whale optimization algorithm is utilized to tune the controllers. Various investigations conducted with different turbo generators confirm the control strategy to the frequency of excursions. The hybrid CCGT – DFIG - DER system is also evaluated under random load demand, change in generation rate constraints and DFIG power output.