Total energy control system-based interval type-3 fuzzy logic controller for fixed-wing unmanned aerial vehicle longitudinal flight dynamics

Traditional longitudinal flight controllers for fixed-wing unmanned aerial vehicles (FW UAVs) assume a decoupling of airspeed and flight path angle dynamics, leading to stability degradations in challenging conditions. The total energy control system (TECS), a multi-input, multi-output (MIMO) flight controller, computes thrust commands based on the total energy requirements for the desired flight path (altitude) and airspeed while adjusting the elevators for energy distribution errors. Although it provides coupled control of flight path angle and airspeed to meet flight requirements, it faces challenges in handling model uncertainties and environmental disturbances. Therefore, this paper presents a novel interval type-3 fuzzy logic controller (IT3 FLC) for the longitudinal flight dynamics of an FW UAV. The controller consists of an inner loop with an IT3 fuzzy proportional-integral-derivative (IT3 FPID) controller for pitch dynamics and an outer loop with an IT3 fuzzy TECS (IT3 FTECS) for flight path and airspeed. The optimization of the scaling factors and all the fuzzy system parameters in the proposed controller was achieved using the grey wolf optimizer (GWO) algorithm. The proposed strategy, tested under ideal conditions, wind disturbances, model parameter variations, and a comprehensive statistical analysis under stochastic uncertainties and turbulent winds, shows superior performance in dealing with uncertainties and nonlinearities in UAV dynamics compared to a type-2 FLC (T2 FLC), a TECS, and a PID-based successive loop closure (PID-SLC). The results also demonstrate accurate tracking of the desired altitude while minimizing airspeed deviation and vice versa.