Fuzzy Unknown Input Observers Design for Four-Wheel Independently Actuated Electric Vehicles

The four-wheel independently actuated (FWIA) electric vehicle model, an extremely complex three-degree-of-freedom vehicle model, has challenging modeling and many nonlinear terms. This makes it challenging to obtain the state variables and unknown inputs for the FWIA electric vehicle model, however, in our study, the estimation using the unknown input (UI) observer approach has good results. In the design process of the observer, a unique Takagi-Sugeno (TS) fuzzy form is used, which separates the unmeasurable nonlinear terms from the nonlinear variables. This approach avoids the problem of unmeasurable premise variables and effectively reduces the conservativeness of the observer in the design process. At the end of the observer design, the sufficient conditions for the design of the UI observer are solved by using Lyapunov's stability theorem and linear matrix inequalities(LMI) and verified by simulation.