This paper presents a structure of robust adaptive control for biped robots, which includes balancing and posture control for regulating the centre-of-mass (COM) position and trunk orientation of bipedal robots in a compliant way. First, the biped robot is decoupled into the dynamics of COM and the trunks. Then, the adaptive robust controls are constructed in the presence of parametric and functional dynamics uncertainties. The control computes a desired ground reaction force required to stabilise the posture with unknown dynamics of COM and then transforms these forces into full-body joint torques even if the external disturbances exist. Based on Lyapunov synthesis, the proposed adaptive controls guarantee that the tracking errors of system converge to zero. The proposed controls are robust not only to system uncertainties such as mass variation but also to external disturbances. The verification of the proposed control is conducted using the extensive simulations.

This study derives a least-squares-based iterative algorithm and a gradient-based iterative algorithm for Hammerstein systems using the decomposition-based hierarchical identification principle. The simulation results confirm that the proposed two algorithms can give satisfactory identification accuracies and the least-squares-based iterative algorithm has faster convergence rates than the gradient-based iterative algorithm.

A novel planar path following control method for an underactuated stratospheric airship is presented in this study. Firstly, the Guidance-Based Path Following (GBPF) principle and the Trajectory Linearisation Control (TLC) theory are described. Then, dynamic model of the stratospheric airship is introduced with kinematics and dynamics equations. Based on this model, a path following control strategy integrated GBPF principle and TLC theory is deduced. The designed control system possesses a cascaded structure which consists of guidance law subsystem, attitude control loop and velocity control loop. Stability analysis shows that the controlled closed-loop system is asymptotically stable. Finally, simulations for the stratospheric airship and flight experimental results for a low-altitude airship to follow typical paths are illustrated to verify effectiveness of the proposed approach.

In this study, we consider the distributed output regulation (DOR) problem of linear multi-agent systems subject to input saturation with switching topology. Owing to the input saturation elements, the considered systems is non-linear. It is natural to take the semiglobal frame for it which allows one to use distributed linear feedback controller. The basic problem is to design distributed feedback controller for the considered multi-agent systems in order to have all agents to track an active leader and/or distributed rejection with disturbance signals. Both the leader and the disturbance signal are modelled as the exogenous system with different dynamics and unmeasurable variables. A systematic distributed linear design approach based on the solvability condition is proposed for the considered DOR problem.

The most crucial step in manufacturing organic electronic devices is the deposition of the active organic layers. This deposition is mostly achieved by thermal evaporation of special organic materials out of an evaporation cell in a high-vacuum environment. The major goal is to produce a thin layer with a well-defined deposition rate. In this study, a mathematical model of the deposition process is presented and a procedure for identifying the unknown model parameters is given. The model covers the transient evaporation of organic materials as well as the thermal behaviour of the evaporation source. A control law based on the concepts of differential flatness turned out to be superior to conventional control strategies. The controller is tested on a real world high-vacuum system using two different evaporation materials. Finally, it is demonstrated, that the proposed approach yields improved layer morphologies that are the basis of outstanding device characteristics.

The problem of adaptive robust state observer design is considered for a class of uncertain non-linear dynamical systems with multiple time-varying delays. It is assumed that the upper bounds of the non-linear delayed state perturbations are unknown and that the time-varying delays are any non-negative continuous and bounded functions, which do not require that their derivatives have to be less than one. In particular, it is only required that the non-linear uncertainties, which can also include time-varying delays, are bounded in any non-negative non-linear functions, which are not required to be known for the system designer. For such a class of uncertain non-linear time-delay systems, a new method is presented whereby a class of memoryless adaptive robust state observers with a rather simpler structure is proposed. It is also shown that by employing the proposed adaptive robust state observer, the observation error between the observer state estimate and the true state can be guaranteed to be uniformly exponentially convergent towards a ball, which can be as small as desired, in the presence of significant uncertainties and time delays. Finally, a numerical example is given to demonstrate the validity of the results.

Stabilisation of sampled-data systems with time-varying and uncertain sampling periods via dynamic output-feedback controllers is considered. Extending the existing discrete-time approaches to the more general setup of output-feedback control, sufficient linear matrix inequalities conditions are developed for the design of linear, constant-parameter controllers. The applicability of the proposed design method is demonstrated through numerical examples, which also indicate improvement with regards to the other approaches.

This article studies output synchronisation of a set of non-linear interconnected systems and general linear interconnected systems. It will be shown that output synchronisation of the systems can be achieved by adding a new coupling interconnections (consensus algorithm) to the existing interconnections if the input and output relationship of the given system is passive. The output synchronisation scheme will then be applied to a class of interconnected non-linear systems with the special structure of port-controlled Hamiltonian (PCH) dynamics. Since the structure of the PCH systems is restrictive, we further present a synthesis of state feedback controller to overcome the restriction. This result will be applied to multi-machine power systems. As the second part of this paper, the output synchronisation of general linear interconnected systems will be ensured. In the case of linear interconnected systems, the synchronisation can be achieved by a decentralised observer-based output feedback control scheme. The controller and observer gains will be calculated from decentralised linear matrix inequality conditions. Simulation tests are conducted to evaluate the performance of the proposed methods.

An integrated design of the adaptive robust control and the fault identification for a linear system with actuator faults is proposed. When actuators suffer from unpredicted faults, the proposed control strategy can track the actuator fault parameters adaptively without any prior fault information, and guarantee the robustness of the faulty system. An unknown input observer is designed to decouple the disturbance and the actuator faults. Then an adaptive control law with projection is presented to track the fault parameters. A new definition of robust H _∞-like performance is proposed to ensure that the system is robust for both exogenous disturbance and unpredicted faults. Then the adaptive robust control law is designed to guarantee the system satisfying the robust H _∞-like performance. Finally, the effectiveness of this control strategy is illustrated through the fault-tolerant longitudinal control of the simplified F-18 aircraft model.

The problem of designing Luenberger-like observer for non-linear Lipschitz systems is addressed. Based on using the coordinate transformation, the author classify many practical approaches of observer synthesis into direct and indirect methods. A generalised Lipschitz condition and the related stability condition are then employed to establish a general framework in designing the Luenberger-like observer dealing with both methods. Moreover, the proposed framework is interpreted in terms of some linear matrix inequalities (LMIs) which allows using numerical techniques to obtain a reduced order observer. Finally, some simulation examples are given to exhibit the effectiveness of the proposed observer synthesis approach.

This study aims to develop an iterative learning control (ILC) approach to solving finite-time output consensus problems of multi-agent systems. The communication topologies among agents are considered to dynamically change in two directions (along both time axis and iteration axis), for which a framework is presented to construct effective distributed protocols. It is shown that a protocol can be derived through ILC to enable multi-agent systems to accomplish the finite-time consensus, which moreover can possess an exponentially fast convergence speed. In particular, for any desired terminal output that is available to not all of but only a portion of agents, multi-agent systems can be guaranteed to achieve the finite-time consensus at the desired terminal output. Simulation tests are given to demonstrate the performance and effectiveness of the obtained consensus results.

The problem of controlling cascade systems, involving in series a saturating actuator and a linear plant, is revisited. Presently, the actuator is described with a more realistic model that accounts not only for its saturating nature but also for its dynamics. Furthermore, the considered model emphasises the internal feedback interaction (between saturation and dynamics) that characterises most real-life actuators. The control objective is 2-fold: (i) stabilising the whole actuator-plant association; (ii) and enforcing the plant input de accurately match any bounded reference signal. To this end, a two-loop controller is developed following a backstepping-like design procedure. Accordingly, the outer regulator is first synthesised, to meet the output-reference tracking objective. During this synthesis stage the actuator output is considered as a virtual control signal. The control law obtained at this stage will serve as a reference trajectory for the actuator output. In the second stage, the inner regulator is designed to make the actuator output tracks its reference trajectory. The cascade controller thus developed is formally shown to meet its control objectives, that is, bounded input bounded output (BIBO) stability and perfect asymptotic matching of any reference signal that is compatible with the actuator saturation.

This study achieves compensation of a physical twin rotor multiple-input and multiple-output system in two steps: (i) input–output decoupling its transfer function model, obtained by linearising its non-linear model around an operating point, using an open-loop, minimal precompensator and (ii) effecting 2-degree of freedom single-input and single-output (SISO) compensations for the resulting SISO-decoupled units. While step (i) ensures decoupling in the responses, the other performances (such as robustness, tracking, disturbance rejection, etc.) can be achieved using SISO compensations in step (ii) above. The performances of the compensated system in respect of decoupling, loop robustness and disturbance rejection are verified through simulations and experiments. The results are also compared with the existing ones.

This study investigates ℒ₂-induced gain from the input disturbance to output of discrete-time switched linear systems subject to actuator saturation. With the state feedback gains adopted beforehand, the authors establish the linear matrix inequalities formulation which estimates the restricted ℒ₂-induced gain for this class of switched systems by dwell-time approach. Then the authors investigate the influence of parameter variations on the restricted ℒ₂-induced gain, and present a state feedback design method for a fixed dwell time and an upper bound of restricted ℒ₂-induced gain. In addition, the authors investigate the qualitative relationship between disturbances rejection capability and dwell time. A numerical example is provided to illustrate the effectiveness of our obtained results.

The problems of finite-time analysis and design for a class of Markov jump systems with Gaussian transition probabilities (TPs) are investigated in this study. Gaussian TP density function is introduced to quantise the stochastic uncertain information of TPs. Mode-dependent and variation-dependent controller is designed to make the resulting closed-loop systems finite-time bounded and finite-time stabilisable for all admissible unknown external disturbances and random uncertain TPs. It is shown that the approach proposed in the paper dealing with TPs outperforms available ones in literature to date, which is also confirmed by a numerical example.

This study addresses the problem of global stabilisation by output feedback for a class of uncertain non-linear systems whose output functions are not precisely known. To solve the problem, the authors first construct a new observer and then use the adding one power integrator technique to design a linear controller to globally stabilise the uncertain non-linear system. It is shown that global exponential stability of the closed-loop system is guaranteed by an appropriate choice of the design parameters.

This study is devoted to the consensus protocols design for a set of fractional-order heterogeneous agents, which is composed of two kinds of agents differed by their dynamics and the fractional-order α satisfies 0 < α < 2. Distributed state feedback consensus protocols are constructed for the two kinds of agents, respectively. Based on the Kronecker product technique and the fractional-order stability theory, sufficient conditions are derived to ensure the consensus of heterogeneous multi-agent systems in terms of linear matrix inequalities (LMIs). These can be solved numerically by LMI toolbox in Matlab. Finally, a simulation example is employed to validate the effectiveness of the theoretical results.

In this study, we address a leader–follower coordination problem with noise in a multi-agent system. In order to minimise the mean-square deviation of the individual state of followers from the state of the leader, we develop a strategy to select a subset of followers to connect with the leader. We adopt the method of convex optimisation to solve both constant edge weight and different edge weight case. Furthermore, we propose optimised algorithms to find the fastest convergence speed. We also study optimisation problems for leader–follower system with a dynamic leader, and also provide a sufficient condition for the convergence of the expected value of the total mean-square deviation. Examples and applications of the developed methodology are also discussed.