In this paper, a new artificial intelligence technique, Harmony Search (HS), will be used for the optimization of a classical order PID for a two-area load frequency control (LFC) model using the participation factor concept. The HS has four main variants, these variants had been used for the optimization of classical order PID controllers in case of centralized control scheme, the results had been compared to select and recommend the best HS variant. Then, this best HS variant had been used for the tuning of PID controllers in case of decentralized scheme.