This paper discuss the implementation of fractional order controllers to large inter connectedpower systems with HVDC link. In recent years researchers paid much attention on application of fractional order controllers to power system stability issues. The enhanced performance of FOPI controllers oner Integer order controllers can further be improved by tuning the controller parameters. In this work improved version of DE algorithm is used to tune the FOPI controller. The effectiveness of the proposed training algorithm is tested on IEEE 9-Bus test power system using MATLAB/SIMULINK under different fault conditions.