Abstract— In this paper, a design method to determine the optimal fractional proportional integral derivative (FPID) controller’s parameters is proposed for automated voltage regulator (AVR). The AVR model is obtained utilizing two model reduction techniques, namely particle swarm optimization (PSO) and biogeography-based optimization (BBO) with the assistance of MATLAB and Simulink software package. For tuning the FPID controller, invasive weed optimization (IWO) algorithm is used with four unique performance indices: integral square error (ISE), integral time square error (ITSE), integral absolute error (IAE) and integral time weighted absolute error (ITAE). The results show that the IWO-designed FPID – compared to the classical proportional integral derivative controller (PID) – offers a better performance in terms of overshoot, rise time and settling time.