TY - JOUR N2 - The proportional-integral-derivative (PID) controllers have experienced series of structural modifications and improvements. Example of such modifications are set-point weighting and fractional ordering. While the former is to achieve two-degree-of-freedom (2DOF) ability of set-point tracking and disturbance rejection, the latter is to ensure smooth control action. Therefore, this paper reviews various forms of PID controllers and provides a comparative analysis of 2DOF PID and 2DOF fractional order PID (FOPID) controllers. The paper also discusses the conversion of one PID form to another. For the comparative analysis of the various controllers, a class of unstable systems are considered. Simulation result shows that in most cases the conversion from one form to another does not significantly affect the performance of the system. It is also observed that the 2DOF controllers (2DOF PID and 2DOF FOPID) improved significantly the performance of the ordinary PID controllers. L1 - http://www.journals.pan.pl/Content/109506/PDF/ACS-2018-4-7.pdf L2 - http://www.journals.pan.pl/Content/109506 PY - 2018 IS - No 4 EP - 682 DO - 10.24425/acs.2018.125487 KW - fractional order controller KW - set-point weighting KW - 2DOF PID KW - process control KW - unstable systems A1 - Bingi, Kishore A1 - Ibrahim, Rosdiazli A1 - Karsiti, Mohd Noh A1 - Hassan, Sabo Miya A1 - Harindran, Vivekananda Rajah PB - Committee of Automatic Control and Robotics PAS VL - vol. 28 DA - 2018.12.17 T1 - A comparative study of 2DOF PID and 2DOF fractional order PID controllers on a class of unstable systems SP - 635 UR - http://www.journals.pan.pl/dlibra/publication/edition/109506 T2 - Archives of Control Sciences ER -