In this paper, a novel graphical approach for stability and robustness analysis in commensurate and incommensurate fractional-order systems (FOS) is proposed. The approach can determine zero distribution of system characteristic equations with commensurate and incommensurate fractional-orders in right-half plane (RHP) and imaginary axis in the complex plane. The approach proposed is derived and generalizd from Routh-type test for polynomials with the commensurate fractional and integer orders. In addition, the novel graphical approach can treat robustness issues of some certain systems. Furthermore, some examples are given to demonstrate the effectiveness of the approach.Finally, a proof is given to verify the correctness of the criterion.

In order to achieve a straight ballistic trajectory of missile and reduce the update frequency of the missile normal acceleration for the interception of maneuvering target, a backstepping-based parallel approaching guidance method is designed with nonlinear disturbance observer (NDO) technique and event-triggered (ET) mechanism in this paper. In order to suppress the adverse effect of target maneuver, the NDO is designed to estimate the target maneuvering acceleration. Then, the NDO-based backstepping method is used to obtain the normal acceleration of missile and realize the parallel approaching guidance. In order to reduce the update frequency of missile normal acceleration, the ET mechanism is employed in the parallel approaching guidance method. If the missile trajectory is relatively straight, the normal acceleration of missile remains unchanged. On the contrary, if the missile trajectory is not straight, the normal acceleration of missile is updated to make the missile trajectory straight. In this way, the ET-based parallel approaching guidance can be obtained. Furthermore, a determined method for the initial missile flight-path angle is proposed to keep the normal acceleration of missile at zero in the initial stage of interception. Besides, Lyapunov stability analysis method is used to prove that all signals in the closed-loop guidance system are uniformly ultimately bounded. Finally, simulation results show the effectiveness of the proposed guidance method.

In this paper, the problem of the post‐stall pitching maneuver of aircraft with lower deflection frequency of control actuator is studied by considering the unsteady aerodynamic disturbances (UADs). A nonlinear disturbance observer is employed to estimate the UADs in order to suppress their adverse effects. And the nonzero equilibrium adaptive dynamic programming (NEADP) control method derived from the reinforcement learning is adopted to achieve the optimal control of aircraft. Simultaneously, a critic neural network is constructed to approximate the value function in the Hamilton‐Jacobi‐Bellman equation so as to realize adaptivity. Furthermore, the event‐triggering (ET) scheme with an improved triggering condition is applied in the control method in order to decrease the deflection frequency of control actuator. In addition, the Lyapunov stability analysis method is used to prove that all signals in the closed‐loop control system are uniformly ultimately bounded. And the proof by contradiction is applied to confirm that the Zeno behavior is excluded with the analysis of the minimum dwell time. Finally, simulation results verify the effectiveness of the improved ET‐based NEADP control method.

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To intercept a maneuvering target in a two-dimensional plane, the inverse optimal guidance law based on zero effort miss (ZEM) and disturbance observer (DO) is studied in this paper. Firstly, the relative kinematics equation is simplified to obtain the missile-target ZEM and its dynamics. In order to enhance the robustness of the inverse optimal guidance law, the integral of the ZEM is introduced as a new state to form an augmented system with the original system based on the idea of proportional integral (PI) control. Then, the target maneuver acceleration is assumed as the unknown external disturbance of the guidance augmented system, which is estimated by the DO. Based on the estimated value of DO and the backstepping method, the inverse optimal guidance law is designed to reduce the adverse effect of the disturbance on the guidance system. Finally, simulations are designed to verify the effectiveness of the inverse optimal guidance method based on DO.

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