Joelianto, E., and P. H. Sitanggang. “A Substractive Clustering Based Fuzzy Hybrid Reference Control Design for Transient Response Improvement of PID Controller”. Journal of Engineering and Technological Sciences, vol. 41, no. 2, Sept. 2013, pp. 167-86, doi:10.5614/itbj.eng.sci.2009.41.2.6.