Active disturbance rejected predictive functional control for space vehicles with RCS

Reaction control system(RCS) is a powerful and efficient actuator for space vehicles attitude control, which is typically characterized as a pulsed unilateral effector only with two states(off/on). Along with inevitable internal uncertainties and external disturbances in practice, this inherent nonlinear character always hinders space vehicles autopilot from pursuing precise tracking performance. Compared to most of pre-existing methodologies that passively suppress the uncertainties and disturbances, a design based on predictive functional control(PFC) and generalized extended state observer(GESO) is firstly proposed for three-axis RCS control system to actively reject that with no requirement for additional fuel consumption. To obtain a high fidelity predictive model on which the performance of PFC greatly depends, the nonlinear coupling multiple-input multiple-output(MIMO) flight dynamics model is parameterized as a state-dependent coefficient form. And based on that, a MIMO PFC algorithm in state space domain for a plant of arbitrary orders is deduced in this paper.The internal uncertainties and external disturbances are lumped as a total disturbance, which is estimated and cancelled timely to further enhance the robustness. The continuous control command synthesised by above controller-rejector tandem is finally modulated by pulse width pulse frequency modulator(PWPF) to on-off signals to meet RCS requirement. The robustness and feasibility of the proposed design are validated by a series of performance comparison simulations with some prominent methods in the presence of significant perturbations and disturbances, as well as measurement noise.

Robust sliding mode control with ESO for dual-control missile

This paper proposes a novel composite dual-control bycombing the integral sliding mode control （ISMC） method basedon the finite time convergence theory with extended state observer（ESO） for a tracking problem of a missile with tail fins and reactionjetcontrol system （RCS）. First, the ISMC method based on finitetime convergence is utilized to design the control law of tail fins andthe pulse control of RCS for the dual-control system, ensuring thesystem with rapid response and high accuracy of tracking. Then,ESO is employed for the estimation of aerodynamic disturbancesinfluenced by the airflow of thruster jets. With the characteristicof high accuracy estimation of ESO, the chattering free trackingperformance of the attack angle command and the robustnessof the control law are achieved. Meanwhile, the stability of thedual-control system is analyzed based on finite time convergencestability theorem and Lyapunov’s theorem. Finally, numerical simulationsdemonstrate the effectiveness of the proposed design.

Efficient Rate Control Algorithm for Hierarchical Video Coding

For rate control (RC) of hierarchical structure coding, an independent rate-quantization (R-Q) model was proposed based on mean absolute differences (MADs) in different temporal levels (TLs). In the proposed R-Q model, a novel MAD model was developed according to the hierarchical structure. The experimental results demonstrate that the proposed algorithm provides better performance, in terms of average peak signal-to-noise ratio (PSNR) and quality smoothness, than the H.264 reference model, JM14.2, under various sequences.

Fault-tolerant control with mixed aerodynamic surfaces and RCS jets for hypersonic reentry vehicles

This paper proposes a fault-tolerant strategy for hypersonic reentry vehicles with mixed aerodynamic surfaces and reaction control systems（RCS） under external disturbances and subject to actuator faults.Aerodynamic surfaces are treated as the primary actuator in normal situations,and they are driven by a continuous quadratic programming（QP） allocator to generate torque commanded by a nonlinear adaptive feedback control law.When aerodynamic surfaces encounter faults,they may not be able to provide sufficient torque as commanded,and RCS jets are activated to augment the aerodynamic surfaces to compensate for insufficient torque.Partial loss of effectiveness and stuck faults are considered in this paper,and observers are designed to detect and identify the faults.Based on the fault identification results,an RCS control allocator using integer linear programming（ILP） techniques is designed to determine the optimal combination of activated RCS jets.By treating the RCS control allocator as a quantization element,closed-loop stability with both continuous and quantized inputs is analyzed.Simulation results verify the effectiveness of the proposed method.

Experimental studies of water hammer in propellant feed system of reaction control system

Water hammer pressure transient produces large dynamic forces which can damage the pipes and other assemblies in the feed line of a reaction control system(RCS).It has led to the failure of pressure transducers monitoring the manifold pressure in the feed line of RCS.Therefore,water hammer studies have been carried out to understand its effect in feed line.Feedline system has been simplified to develop a mathematical model and experiments have been carried out at extensive levels.The mathematical model was developed considering pipe of uniform c/s and moving liquid-gas interface.The experimental studies have been done using water as working medium instead of actual propellant.The studies showed that rate of pressurization have a very critical role on the water hammer amplitude.Sensitivity studies have been also carried out to study the effect of density,friction and initial liquid column length on water hammer amplitude.

Design of Decentralized Multi-input Multi-output Repetitive Control Systems

This paper presents the design of decentralized repetitive control （RC） for multi-input multi-output （MIMO） systems. An optimization method is used to obtain a RC compensator that ensures system stability and good tracking performance. The designed compensator is in the form of a stable, low order, and causal filter, in which the compensator can be implemented separately without being merged with the RC internal model. This will reduce complexity in the implementation. Simulation results and comparison study are given to demonstrate the effectiveness of the proposed design. The novelty of design is also verified in experiments on a 2 degrees of freedom （DOF） robot.