Here, the novel minimum order quasi-decentralized fractional observer is proposed for frequency regulation in a multi-area power system with DC Link and thyristor controlled phase shifter (TCPS) integrated with battery energy storage (BESS). While it is difficult to estimate the states of large multi-area power system, a quasi-decentralized observer controller is designed of single order with linear functional control approach and thus estimated control signal is directly utilized in each area. System performance is investigated in respect of frequency regulation vis-à-vis step and random load changes in any one area with and without AC/DC Link and TCPS coupled in the system. Results are compared and contrasted against the existing state feedback optimal controller and observer based controllers and the analysis is presented thereof. The results obtained are almost mimicking the results of state feedback optimal controller with the system dynamic performance showing improvement in respect of peak overshoot and settling time. The simulations are executed in MATLAB(R)