Adaptive robust constraint-following control for electromechanically driven vector deflection system emphasis on time-varying uncertainty and input limit

Electrification is the development trend of future aircraft, by which exploration on effective control strategy for electromechanical actuator (EMA) in aero-engine system is significant. For this, this paper focuses on an adaptive robust control strategy for EMA-driven nozzle deflection system in consideration of complex (maybe nonlinear time-varying) uncertainty, including modeling error, external disturbances, variable loads, and so on. First, a nonlinear dynamic modeling of EMA actuation system is constructed, based on which a set of angle constraints on the actuator motors is constructed to represent the nozzle deflection command, and then an angle constraint-following error is defined to measure the satisfaction degree of constraints. By this, the problem of nozzle deflection control is transformed into another constraint-following control. Second, to handle complex uncertainty, an adaptive law is developed to estimate the unknown bound online, and then a robust controller is designed. By combining the two, an adaptive robust control strategy is formulated to render the angle constraint-following error to be uniform bounded and uniform ultimate bounded, that means the nozzle deflection actuation system can track the nozzle deflection command in real time. Finally, to handle the conflict between the control commands and the actual execution capability of the actuator, a homeomorphic differential transformation on the control input is carried out to limit the input peak. By this, the control input can be limited to an expected range that is determined by the maximum execution capacity of the electromechanical actuator. In summary, this paper realizes three-layer control objectives of nozzle vector deflection control, complex uncertainty control and control input limitation by one adaptive robust control strategy.