In this paper, a new approach is proposed for the robust PID controller design for load frequency control (LFC) problem in a multi-area power system having different turbines. The proposed approach is based on Kharitonov's theorem and stability boundary locus. In this paper, first of all, four-area power system model for LFC problem is presented in the form of a linear uncertain system with fixed lower and upper bounds in the coefficients. Then, stability analysis is carried out using Kharitonov's theorem and lastly a robust controller is designed for each control area of multi-area power system. The beauty of the proposed approach is that the fixed PID controller is taking care of uncertainty in the each control area. The efficiency and efficacy of the proposed approach is tested through two examples and results are compared with few recently proposed approaches. (C) 2016 Elsevier Ltd. All rights reserved.