This study highlights the performance of the combined automatic load frequency control and automatic voltage regulator model of Power System Stabilizer (PSS) integrated three unequal area multi-source system. The system is provided with suitable generation rate constraints and governor dead band along with time delay. Fractional order PIADF controller is proposed for this model and compared the performance of the same with other classical controllers. The controller and PSS parameters are optimized simultaneously using lightning search algorithm. The investigation reflects the superior performance of PIADF to integer order controllers. Analysis of the effect of system nonlinearities shows the increased sustained oscillations of the responses. The performance of PSS is investigated and reveals that the inclusion of PSS reduces the system oscillations, which leads to better system dynamics. Sensitivity analysis established the robust performance of PIADF controller and PSS parameters obtained at base condition. © 2018 IEEE.