No abstract

During the ascent phase of a missile, a challenging problem occurs that blocks the construction of a high-precision attitude control scheme, which directly affects accurate modeling including disturbances: non-linearities of an actuator, rapidly time-varying parameters, un-modeled dynamics, etc. In order to improve the control performance, an active disturbance rejection control (ADRC) scheme, considering non-linear dynamics of the actuator and wind disturbance during the ascent phase, is proposed in this paper. An expand state observer (ESO) is planned to estimate and compensate the actuator’s non-linear dynamics, flight model uncertainties, and wind disturbance. Therefore, the complex non-linear time-varying control problem is simplified into a linear time-invariant control problem. The pitch attitude control system is controlled by the cascade method and ADRC controllers are designed for actuator close loop and attitude control loop, respectively. The simulation results show that ADRC has strong robustness under different dead-zones and external disturbances of the actuator. On the other hand, ADRC can effectively suppress the external atmospheric disturbance. Compared with the traditional gain-scheduling control scheme, the ADRC scheme can significantly reduce the overloading of the system and shows remarkable performance for tracking as well as wind resistance.

Friction nonlinearity, which is common in electromechanical actuator (EMA) systems, leads to undesired dynamic responses such as “flat top”, low-speed crawl, which brings challenges to high precision attitude control of flight vehicles. In order to improve the robustness of the actuator control system under friction nonlinearity, and suppress the chattering caused by high gain of sliding mode control (SMC), a composite SMC scheme based on modified extended state observer (MESO) is proposed. Nonlinear MESO is adopted for estimating the nonlinear friction dynamics, unmodeled disturbance, and external real-time load dynamics so as to compensate for their adverse effect. At the same time, in order to improve the robustness of EMA, and reduce the tracking error of the servo system, SMC is adopted to ensure the tracking error convergence in a finite time. The stability of the proposed method is proved, and the effectiveness is verified by simulations.