Robust and Unified Fractional Order AGC-AVR Scheme for Hydropower Plant

Hydropower plants are well known for their nonlinear and non-minimum phase behavior, which poses significant challenges in automatic generation control (AGC) and automatic voltage regulation (AVR). Although integrated AGC-AVR methods are common for thermal power plants, there's still a need for robust, unified solutions tailored to hydropower systems. This paper proposes a simple and unified fractional-order frequency-shifted PID controller with a fractional filter (FS-FPIDF) to address this gap. A fractional-order model of a non-reheated hydropower plant is derived and then frequency-shifted to design the FS-FPIDF controller, featuring a single tuning parameter optimized via integral square error (ISE) minimization of voltage and frequency deviations. The proposed control scheme demonstrates robustness against sudden load changes, nonlinearities, model uncertainties, and stealthy cyber-threats, including false data injection (FDI) and denial of service (DoS). Additionally, the methodology is scalable and has been evaluated on a renewable-integrated IEEE 39-bus hydro-thermal system to assess its performance in maintaining frequency and voltage stability amidst the stochastic nature of renewable energy sources. Practical feasibility of this proposal is ascertained using OPAL-RT-based hardware-in-loop validation. Compared to conventional integer-order control methods, the proposed FS-FPIDF controller ensures superior regulation without increasing design complexity.