A study of fuzzy logic controller robustness using the parameter plane

An attempt is made to obtain a quantitative analysis of fuzzy logic controller robustness using parameter plane techniques. The method requires the controller, which is modelled as a multilevel relay, to be represented by a describing function. Therefore, the analysis can only be applied to systems where the input to the non-linearity is sufficiently close to a sinusoid to justify this representation. It is found that, although general quantitative results cannot be obtained, the method does produce a good indication of controller robustness for the plant investigated.