Zhiqiang Pu

A Class of Adaptive Extended State Observers for Nonlinear Disturbed Systems

This paper proposes a novel class of adaptive extended state observers (AESOs) that significantly expand the applications of extended state observers (ESOs) to nonlinear disturbed systems. An AESO is designed as a linear time-varying form that, as a result, combines both the advantages of theoretical completeness in a conventional linear ESO (LESO) and good practical performance in a conventional nonlinear ESO (NESO). To tune the time-varying observer gains, AESO error dynamics is first transformed into a canonical (phase-variable) form. Then, time-varying PD-eigenvalues are assigned for the canonical system based on differential algebraic spectral theory. Theorems for stability and estimate error bounds of the AESO are given in the presence of unknown disturbances. These theorems also offer some important guidelines for assigning the PD-eigenvalues. To demonstrate the effectiveness of this new observer, two representative applications, including a numerical single-input-single-output example and a practical multiple-input-multiple-output hypersonic vehicle application, are exemplified, and comparison simulations are conducted among AESO, LESO, and NESO. Future work is pointed out in the end.

Design of entry trajectory tracking law for a hypersonic vehicle via inversion control

A nominal altitude-velocity longitudinal entry trajectory is planned and tracked for a Generic Hypersonic Vehicle (GHV) in this paper. The entry corridor is presented which is defined by the dynamic pressure, normal acceleration, heating constraints, and the so-called Quasi-Equilibrium Glide Condition (QEGC). The flyability of the vehicle along the nominal trajectory is carefully analyzed for further validation of the selected nominal trajectory. The control scheme mainly consists of two loops: a guidance loop and an attitude loop, of which the latter is separated into the slow and fast loops with the time-scale separation theory. Inversion control is employed in these three loops, and an integration feedback approach is especially added into the inversion controller to eliminate the tracking error. Simulations demonstrate that the nominal trajectory is designed appropriately and tracked well.

Advanced inversion control for a Hypersonic Vehicle based on PSO and Arranged Transient Process

A high-order curve-fitted model which is suitable for a large flight envelope is adopted for the aerodynamic coefficients of the Generic Hypersonic Vehicle (GHV). As a supplement, the expressions of the thrust coefficients for the whole hypersonic flight range are presented in this paper. Based on this model, a general Nonlinear Dynamic Inversion (NDI) controller is designed with the feedback linearization theory for the velocity and altitude tracking purpose. However, the robustness of this general NDI controller needs to be improved, particularly when a large step command is given. For these reasons, an advanced inversion controller is designed, where both the Particle Swarm Optimization (PSO) algorithm and Arranged Transient Process (ATP) technique are applied. The PSO is used to optimize the feedback coefficients of the inversion controller, while the ATP technique is employed to guarantee that the system has better dynamic performance and control quality. Simulation results demonstrate that the advanced inversion controller has better tracking performance and robustness in a large envelope of flight condition.

Robust trajectory linearization control of a flexible hypersonic vehicle in the presence of uncertainties

This paper addresses the design of a robust trajectory linearization control (TLC) scheme for a flexible air-breathing hypersonic vehicle model with multiple uncertainties. Because of the model complexity, the flexibility effects and open-loop behaviors are analyzed, offering insights on the vehicle features and guidelines for control design. Based on the analysis, a basic TLC frame, including an adaptive time-varying bandwidth algorithm, is firstly constructed. As for the inevitable uncertainties in hypersonic flight, a uniform nonlinear uncertainty model is explored which lumps all external disturbances and typical internal uncertainties such as propulsive perturbations and variations in control effectiveness together. Then extended state observer (ESO) technique is integrated into the basic TLC frame to estimate and compensate these uncertainties, forming a robust TLC scheme. Two flight cases are conducted, through which the robust scheme exhibits great tracking performance and uncertainty rejection ability.

Optimal UAVs formation transformation strategy based on task assignment and Particle Swarm Optimization

A nested optimization strategy based on task assignment and Particle Swarm Optimization (PSO) is proposed to solve the optimization problem of formation transformation. Both the corresponding assigned target positions of interchangeable UAVs from initial formation to target formation and the relative position relationship between two formations are investigated in this paper. The Hungarian algorithm is used to rapidly solve the assignment problem, while the PSO is adopted to compute the optimal relative position relationship iteratively. To demonstrate the effectiveness and the universality of the proposed strategy, simulation results considered different situations are presented.

Time-varying spectrum based active disturbance rejection control for hypersonic reentry vehicle

This paper proposes a robust attitude control strategy for hypersonic reentry vehicles which combines novel time-varying spectrum based active disturbance rejection control techniques with a basic stabilizing controller. These techniques include time-varying tracking differentiator (TTD) and time-varying extended state observer (TESO). By adopting time-varying bandwidth, TTD can adaptively arrange transient processes for either abrupt or smooth reference commands. Also by designing time-varying bandwidth logic, TESO can not only estimate total disturbance well, but also suppress peaking phenomenon resulting from initial reentry condition dispersion. Several simulations are conducted which demonstrate that the proposed control strategy exhibits both good attitude tracking ability and great design flexibility.

Robust Trajectory Linearization Control of Hypersonic Entry Flight Using Extended State Observer and Time-Varying Bandwidth

Abstract A robust trajectory linearization control (TLC) scheme is presented for a generic hypersonic vehicle (GHV) entry flight. The basic TLC frame constructs a baseline controller for the GHV attitude system, providing local closed-loop exponential stability along nominal trajectories. Then two strategies are integrated with the basic TLC for robustness enhancement. For one thing, to cope with diverse perturbations, extended state observer is designed to yield a compensation control law. For the other, an adaptive time-varying bandwidth algorithm is developed, which can not only avoid actuator saturation and integrator windup, but most importantly, also improve system robustness when huge dynamic pressure variation occurs during entry flight. This integrated robust TLC scheme can guarantee a better control performance and a larger stability domain. At last, the great advantages of the proposed robust TLC scheme is demonstrated via three groups of simulation, including a three-DOF attitude tracking, a BTT-180 maneuver simulation, and a six-DOF integrated guidance and control test.