Load Frequency Controller Design Based on the Direct Synthesis Approach Using a 2DoF-IMC Scheme for a Multi-Area Power System

Abstract

To maintain reliable and sustainable power supply, the frequency should be kept constant under varying load conditions. The two degrees of freedom internal model control (2DoF-IMC) scheme is a robust control technique and is efficient for load-disturbance rejection problems in industrial process control. The asymmetry of IMC compared to other methods regarding controller design is that it does not guarantee the stability of the system by itself but is based on the stability of the controlled system. For the control of less-stable and unstable systems, it is therefore usually supplemented with an additional controller, establishing two degrees of freedom in the overall design. In this manuscript, the load-frequency-regulation problem was investigated using a 2DoF-IMC scheme for a single-area as well as a multi-area power system. In the 2DoF-IMC scheme, two controllers are used to control the set-point response and load-disturbance response separately. The set-point controller is designed through the internal model control (IMC) principle, whereas the load-disturbance rejection controller is designed via the direct-synthesis (DS) approach. In the DS approach, the closed-loop transfer function of the system model is matched with the desired closed-loop transfer function of the system and the disturbance-rejection controller is approximated at a very low-frequency point to obtain the proportional–derivative (PD) controller parameter. The simulation results of the proposed method provide satisfactory performance for load-frequency control (LFC) in the single-area power system and extended to two-area and four-area power systems. The effect of non-linearity, such as generation rate constraint (GRC), was investigated in the single-area power system to establish the efficacy of the proposed method. A random step loading pattern was also considered to confirm the robustness of the proposed method. The overall performance of the proposed control scheme is comparatively better than the recently reported work.