Flexible alternating current transmission system devices and energy storage devices have great potential to support frequency regulation in power system. Hence, the impact of interline power flow controller unit and redox flow battery unit in the load frequency control (LFC) of six-area power system having different power plant units has been investigated in this paper. The multi-verse optimizer (MVO) is proposed to tune the parameters of the proportional–integral and derivative (PID) controller. Further, the efficacy of the multi-verse optimizer tuned proportional–integral (PI) controller is also equated with the recently developed sine-cosine algorithm tuned PI controller in the investigated power system. The encouraging role of interline power flow controller (IPFC) unit and redox flow battery (RFB) unit has been confirmed for system frequency and tie-line power regulation. The investigation validated that multi-verse optimizer based proportional–integral–derivative controller with an interline power flow controller unit and redox flow battery unit give better dynamic response during sudden load disturbances.