The study explores the potential of redox flow battery in regulating frequency in large interconnected power system having coupled diverse links - AC and HVDC Links, and thyristor controlled phase shifter -, and compares its performance against other energy storage devices, employing linear quadratic regulator based decentralised optimal control. Also, the impact of the diverse links on frequency regulation is examined in coordination with redox flow battery. The system comprises four equal areas, containing reheat thermal turbine and electrical vehicle aggregator as generating sources in each area, step and random changes (wind and photovoltaic power uncertainties) in load as the disturbances. The suggested controller, coordinated with redox flow battery and diverse links, settles system frequency and tie-line power excursions in quickest possible duration as against conventional PI and PID control. The proposition is also tested effective against time delay non-linearity in system. Simulations are executed on MATLAB platform with results analysed and illustrated in a lucid manner.