This review article aims to provide an in-depth analysis of the literature along with comprehensive bibliography on automatic generation control (AGC)/load frequency control investigations. Different control perspectives concerning frequency and power control have been featured. Diverse linear, non-linear power system models are discussed under conventional and deregulated environments considering various power generation sources, including conventional, renewable energy sources (RES), and realistic RES. Moreover, AGC literature briefly explains various secondary controllers like integer order, fractional order, intelligent, cascade, and some recently used controllers. To obtain the optimum values of secondary controllers, various optimization strategies such as numerical approach, heuristic, and meta-heuristic techniques for AGC issues are mentioned. Also, AGC studies concerning power transmission, considering inertia and phase-locked loops in high voltage direct current (HVDC) and accurate HVDC models are discussed. Further, AGC literature integrated with flexible alternating current transmission system devices in loaded transmission lines and energy storage devices due to intermittent power generation in RES is deliberated. Furthermore, various performance index criteria (PIC) such as standard PIC and hybrid peak area (HPA)–PIC for controller optimization with algorithms are also conferred.

This article investigates the impact of phase-locked loop (PLL) systems along with virtual inertia on system dynamics of a parallel AC/HVDC tie-line integrated two-area automatic generation control (AGC) system under a deregulated scenario. The multi-area AGC system comprises two thermal and hydro-gas in area-1, 2. An attempt is made to utilize a new secondary controller named the two-degree-of-freedom tilt-integral-derivative (2DOF-TID) controller. Its gains and PLL parameters are optimized by a novel meta-heuristic algorithm called a bird swarm algorithm (BSA). The system dynamics corresponding to the proposed 2DOF-TID are compared with 2DOF-PID, 2DOF-PI explored better system dynamics with a 2DOF-TID controller. The system dynamics are compared with AC alone, AC/HVDC, AC/HVDC tie-line incorporating with PLL, virtual inertia revealed the better performance of the latter. Moreover, the effect of variation in PLL parameter on the system dynamics are also analyzed and studies suggested that the obtained response at the nominal value of natural frequency (ω_n) and damping coefficient (ζ) reduces the subsequent oscillation and provides better dynamics other than varying condition.

This article presents the hybridization of crow-search algorithm with particle swarm optimization (hCA-PSO) in automatic generation control (AGC) studies. A new controller termed by integral-minus-tilt-derivative-control with filter (I-TDN) is proposed and its dynamics are compared with PIDN and TIDN. The proposed controller parameters are optimized by the proposed hCA-PSO technique and are compared with CA, PSO algorithms and are found to be better in terms of settling time, oscillation magnitude. Moreover, the integration of HVDC tie-lines improves system dynamics over AC tie-line. Further, sensitivity analysis suggests that system dynamics with I-TDN controller optimized by hCA- PSO technique obtained at diverse and nominal conditions are robust.