M. Elsisi and  M. Soliman and  M. A. S. Aboelela and  W. Mansour,  GSA-Based Design of Dual Proportional Integral Load Frequency Controllers for Nonlinear Hydrothermal Power System.   journal   = {International Journal of Electrical and Computer Engineering}, [online]. World Academy of Science, Engineering and Technology.
    August 2015, vol. 104(8). 928 - 934
    [viewed 04 April 2020]. Available from: https://publications.waset.org/pdf/10002456.