“…Ziegler-Nichols is one of the early conventional PID tuning technique [4] ,this method is practical applied for broad range application ,however, these traditional methods have their own drawback for employing in large interconnected power system, some of the reasons are, they do not perform adequately for non-linearity and uncertainty cases and results in poor transient performance and slow in action, large overshoot, more oscillation and long settling time, for this comparison the artificial intelligent methods are better as mentioned in [6]. To enhance the capabilities, PID parameters are tuned using GA and DE for two area multi-unit thermal power plant by applying single and multi-objective optimization and an attractive result was obtained for the case of DE [3,8],the artificial intelligent technique PSO has been applied to improve the PID controller [7] besides this, optimization of nonlinear and linear time-invariant function by PSO is given in [10,13]. Many research work have been done considering AGC of having two or more interconnected areas using both single and multi-objective optimization, in [9,11] single and hybrid optimization methods was applied in AGC of two area having six units in non-reheat thermal power plant to improve the controllability of PID controller.…”