Comments on "H/sub /spl infin// tracking design of uncertain nonlinear SISO systems: adaptive fuzzy approach" [with reply]

The objective of H/sub /spl infin// disturbance attenuation problem is to attenuate the effect of disturbance to the prescribed level and achieve performance robustness. Chen, Lee and Chang (Fuzzy Syst., vol.4, p.32-43, 1996) proposed an adaptive fuzzy H/sub /spl infin// disturbance attenuation algorithm. The fuzzy approximation error, which is influenced by the control input, is taken as the disturbance signal in the proposed algorithm. The authors argue that, because of the tradeoff between the attenuation level and the control input, performance robustness cannot be achieved by the proposed algorithm. The original authors agree that the approximation error will influence the performance robustness, especially in the case without external disturbance and with very small attenuation level. However, in practical control applications, very small attenuation levels are avoided in order to prevent high-gain control.