Load frequency control of a hydro-thermal system under deregulated environment using biogeography-based optimised three-degree-of-freedom integral-derivative controller

This study presents the load frequency control of an interconnected two-area power system under deregulated environment with area1 as a thermal system having two generating companies and area2 as hydro-thermal system. Appropriate generation rate constraint, and governor dead band are provided in the areas. Three-degree-of-freedom integral-derivative (3DOF-ID) controllers are used as secondary controllers in the areas whose performance is compared with that of two-degree-of-freedom integral-derivative (2DOF-ID) and single-degree-of-freedom controllers such as integral (I), integral-derivative (ID). Biogeography-based optimisation (BBO) technique is used for simultaneous optimisation of controller gains and electric governor parameters. Analysis of the dynamic responses reveal the superiority of 3DOF-ID controller over I, ID, and 2DOF-ID controllers, in terms of settling time, peak deviation and magnitude of oscillation. Sensitivity analysis proved that, BBO optimised parameters obtained at nominal conditions are robust. 3DOF-ID controller parameters obtained at nominal distribution companies participation matrix (DPM) are healthy enough and not necessary to optimise for change in DPMs. Variation in frequency bias coefficient (B) concludes that the best selection for B is equal to area frequency response characteristics. Similarly, selection of governor speed regulation parameter (R) infers higher value for thermal-system, while hydro-system should be kept comparatively low.