A PD-like self-tuning fuzzy controller without steady-state error

This paper presents a PD-like self-tuning fuzzy controller (STFC) based on the tuning of scaling factors. A two-stage tuning method including a direct tuning stage and indirect tuning stage is proposed. For most linear controlled plants, application of the direct tuning stage alone is enough to yield satisfactory system responses. The proposed STFC can automatically detect the operating ranges of input variables and then adjust the scaling factors. In the indirect tuning stage the back-propagation algorithm can be directly applied to fine-tune the scaling factors when a more complicated plant is controlled. Furthermore, a simple but efficient method for fully compensating for steady-state error, which is the main problem in a PD-like fuzzy logic control system, is proposed so that tuning for fuzzy logic rule bases is unnecessary. Simulation results with linear time-invariant systems and a nonlinear unstable system as the controlled plants show that the proposed technique yields zero steady-state error responses very quickly without overshoot or oscillatory behavior. (C) 1997 Elsevier Science B.V.