Hisayoshi Muramatsu and Seiichiro Katsura :
“An Adaptive Periodic-Disturbance Observer for Periodic-Disturbance Suppression,”
IEEE Transactions on Industrial Informatics, vol. 14, no. 10, pp. 4446-4456, Oct. 2018.
http://ieeexplore.ieee.org/document/8288655/