Improved Response of Finite Time Settling Control with Softening Filters

Abstract

The FTSC (Finite Time Settling Control) algorithm previously developed by Y. Takahashi and M. Tomizuka has the following advantages;
(1) The parameters of the process model may be easily obtained by measuring the S-shaped step responses typical in many industrial processes.
(2) The off-line computation of the control parameters and the on-line control operations are very simple.
(3) The control algorithm may be implemented by utilizing the microcomputers.
Furthermore this FTSC algorithm has been put to some practical uses. However, it is known that an extensive overshoot is generated which is called a ‘wind-up phenomenon’ caused by the saturation of the control inputs where integral action is contained in the feedback control system. Y. Takahashi and M. Tomizuka pointed out that FTSC algorithm with a first-order (or one-step) softening filter is effective to diminish these overshoots. But the optimal determination of the filter parameter was not discussed in detail. Thus, in this paper a new design method is proposed to determine optimally the parameters of the softening filters as follows;
(1) The first-order filter is extended to an L-th order filter.
(2) The parameters of the filter are adjusted so as to minimize the settling time under the amplitude limitations of the control inputs.
The proposed method here may be considered as a practical and effective one to improve the extensive overshoots of the output responses in the FTSC systems.