Frequency instability is one of the fundamental problems in power systems that occurs when a disturbance, increase in demand, or change in system structure causes a progressive and uncontrollable drop in frequency. Research has shown that the use of simple-structured controllers with fewer degrees of freedom, like proportional-integral control (PI) and proportional-integral-derivative control (PID), cannot achieve the desired characteristics of the system, such as the speed of response to disturbance and robustness to system changes. This paper presents a new two-degree-of-freedom proportional-integral-derivative-accelerative (2DOF-PIDA) control method for the load frequency control problem of the power systems to enhance the dynamic response and robustness in the presence of the generation rate constraint and the governor dead-band. The control parameters are adjusted using an improved particle swarm optimization (IPSO) algorithm. In addition, to further improve the control performance, a modified objective function including Integral Time multiplied Absolute Error (ITAE), the settling time, and the maximum overshoot of the frequency and tie-line power deviations with appropriate weighting coefficients was used. The performance of the proposed controller was studied using simulation on an interconnected two-area power network and compared with that of PI and PID controls. The results show that the proposed 2DOF-PIDA method performs better in comparison with PI and PID controllers in terms of the dynamic response and maximum response deviation, as well as robustness to parameter changes.