H∞ output tracking fuzzy control for nonlinear systems with time-varying delay

► A Takagi-Sugeno (T-S) fuzzy model represents the nonlinear system with time-varying delay. ► A fuzzy observer design estimates immeasurable state. ► Third, a virtual desired variable (VDV) based tracking controller design guarantees H∞ control performance for the overall system. ► Using Lyapunov-Krasovskii's stability analysis, we obtain sufficient conditions for stability of estimation, control, and robustness. ► We allow unknown time-varying delay, ensure robust output tracking, provide relaxed conditions via a three-steps procedure to find observer and controller gain.