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Control Theory & Applications, IET

Issue 13 • Date September 6 2012

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Displaying Results 1 - 20 of 20
  • Combined optimal pulse width modulation and pulse frequency modulation strategy for controlling switched mode DC–DC converters over a wide range of loads

    Page(s): 1973 - 1983
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1454 KB)  

    This paper develops a combined optimal pulse width modulation (PWM) and pulse frequency modulation (PFM) strategy for controlling switched mode DC-DC converters. The peak ripple magnitudes of both the output-voltages and -currents during all operating modes over a wide range of loads are minimised subject to specifications on the minimum efficiency bounds of the converters. This problem is posed as a multi-objective functional inequality constrained optimal control problem. By expressing the initial state of each operating mode at the steady state as a function of the switched time instants, as well as applying the time scaling transform method and the constraint transcription method, the multi-objective functional inequality constrained optimal control problem is converted to a conventional optimal control problem. Finally, a control parameterisation technique is applied to solve the problem. Computer numerical simulations show that the combined control strategy could achieve low peak ripple magnitudes of both the output-voltages and -currents for all operating modes over a wide range of loads and guarantees the satisfaction of the specifications on the minimum efficiency bounds of the converter over a wide range of loads. View full abstract»

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  • PID controller adjustment using chaotic optimisation algorithm for multi-area load frequency control

    Page(s): 1984 - 1992
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1060 KB)  

    The early aim of the automatic generation control is to regulate the power output of the electrical generator within a prescribed area in response to changes in system frequency, tie-line loading, so as to maintain the scheduled system frequency and interchange with the other areas with predetermined limits. The purpose of this study is to propose a PID optimised by the lozi map-based chaotic algorithm (LCOA) to solve the load-frequency control (LFC) problem. The PIDs tuned by the LCOA are used in each area for a two-area power system. The simulation results are used to demonstrate the effectiveness and performance of the proposed controller. It is shown that optimised PID is able to solve the LFC problem and also the performance of the system in each area is satisfactory. In addition, a comparative study is carried out between the results obtained from PID tuned by the LCOA and the other optimisation algorithms. View full abstract»

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  • Robust H/spl infin/ control in nano-positioning

    Page(s): 1993 - 2001
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (855 KB)  

    This study considers the use of robust H tracking control in a nano-positioning system. The nano-positioning system uses a high-performance monolithic multilayer piezoelectric stack actuator connected in series with an external capacitor, which is used to provide a measured voltage proportional to the charge on the piezoelectric actuator. The electrical energy applied to the piezoelectric actuator is transferred to mechanical energy leading to nano-scale motion. The mechanical part of this system consists of a spring mass mechanical system and a capacitive sensor is used to measure the displacement. The design of the controller takes into account the existence of hysteresis in the piezoelectric actuator by representing it as a sector-bounded uncertainty. The parameters in a non-linear model of the system are obtained from experimental measurements on the system. Experimental results show that the robust H controller yields accurate tracking of displacement and significantly reduces the hysteresis. View full abstract»

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  • Adaptive leader-following consensus control of multi-agent systems using model reference adaptive control approach

    Page(s): 2002 - 2008
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1602 KB)  

    This study is devoted to the adaptive consensus problem of multi-agent systems with partly unknown parameters and bounded external disturbances, under the guidance of an active leader with a reference input signal. Firstly, a distributed adaptive protocol is proposed for the system without disturbances by adopting the model reference adaptive control method. Then it is extended to the disturbed system by adding an adaptive disturbance compensator, based on the estimated upper and lower bounds of unknown disturbance. For the above two cases, sufficient conditions are, respectively, given to ensure that all agents can eventually track the prescribed leader. A numerical simulation illustrates the effectiveness of the proposed adaptive consensus protocol. View full abstract»

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  • Decentralised adaptive output feedback synchronisation tracking control of spacecraft formation flying with time-varying delay

    Page(s): 2009 - 2020
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1081 KB)  

    This study deals with the problem of decentralised cooperative position tracking with time-varying delays of interconnect communication in the leader-follower spacecraft formation flight. More specifically, a class of low-pass linear filters is developed to derive a control law without absolute and relative velocity measurement, which is significant for practical applications with low-cost configurations of spacecrafts. Using a well-chosen Lyapunov function, it proves that the proposed control law can make the spacecrafts in formation flying achieve global convergence to the desired position and velocity relevant to the leader, in the face of modelling uncertainties, external disturbances, as well as non-uniform time-varying delays in communication links. Moreover, to release the heavy communication pressures of the leader, a modified control law is designed by introducing a finite-time sliding-mode estimator for a tree-type transformation topology of the formation, in which delays only affect the state (position and velocity) information received from neighbours of each spacecraft. Finally, simulation results are presented to demonstrate the effectiveness of the proposed control schemes. View full abstract»

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  • Block backstepping controllers design for a class of perturbed non-linear systems with m blocks

    Page(s): 2021 - 2030
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (739 KB)  

    Based on the Lyapunov stability theorem, a design methodology of adaptive block backstepping controller is proposed in this study for a class of multi-input systems with mismatched perturbations to solve regulation problems. According to the number of blocks (m) in the plant to be controlled, m-1 virtual input controllers are firstly designed from the first block to the (m-1)th block. Then the proposed robust controller is designed in accordance with the last block. Adaptive mechanisms are used in each of the virtual input controllers as well as the robust controller, so that the least upper bound of perturbations except that of the input channel is not required during the design process. Furthermore, asymptotic stability is guaranteed by the proposed control method. A numerical example is also given for demonstrating the feasibility of the proposed control scheme. View full abstract»

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  • Output-feedback quantised control of decentralised systems

    Page(s): 2031 - 2040
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    The problem of designing decentralised ℋ feedback control for a class of linear interconnected continuous-time systems with quantised signals in the subsystem control channels is fully examined. The system has unknown-but-bounded couplings and interval delays. A decentralised static output-feedback controller is designed at the subsystem level to render the closed-loop system is delay-dependent asymptotically stable with guaranteed γ-level. When the local output measurements are quantised, we develop a local output-dependent procedure for updating the quantiser parameters to attain similar asymptotic stability and guaranteed performance of the closed-loop quantised system. Several special cases of interest are derived. Simulation of two representative examples are presented to show the effectiveness of the developed approach. View full abstract»

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  • Global H/spl infin/ consensus of multi-agent systems with Lipschitz non-linear dynamics

    Page(s): 2041 - 2048
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (505 KB)  

    This study addresses the global consensus problems of a class of non-linear multi-agent systems with Lipschitz non-linearity and directed communication graphs, by using a distributed consensus protocol based on the relative states of neighbouring agents. A two-step algorithm is presented to construct a protocol, under which a Lipschitz multi-agent system without disturbances can reach global consensus for a strongly connected directed communication graph. Another algorithm is then given to design a protocol that can achieve global consensus with a guaranteed H performance for a Lipschitz multi-agent system subject to external disturbances. The case with a leader-follower communication graph is also discussed. Finally, the effectiveness of the theoretical results is demonstrated through a network of single-link manipulators. View full abstract»

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  • Tolerance of intermittent faults in spacecraft attitude control: switched system approach

    Page(s): 2049 - 2056
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (828 KB)  

    This study models a spacecraft attitude control system (ACS) process with intermittent controller faults by a stochastic switched system, whose stability is shown to be equivalent to the fault tolerability of the ACS. A `global dissipativity` concept is first introduced for the stochastic switched system to derive its stability condition, which can be checked easily via the proposed `gain technique`. Results shown in this study demonstrate that it may not be necessary to apply the fault-tolerant controller in spite of intermittent controller faults, and the attitude control performance can also be maintained. Simulation results show the efficiency of the proposed methods. View full abstract»

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  • Stabilisation for a class of non-linear uncertain systems based on interval observers

    Page(s): 2057 - 2062
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (189 KB)  

    Feedback stabilisation for a class of non-linear uncertain systems is devoted in this study. An interval observer is given to estimate admissible values of the state. A linear control law is designed such that the equilibrium point of the interval observer is asymptotically stable. By the linear control law, the uncertain system is asymptotically stable at the equilibrium point. An application of the proposed technique to linear parameter varying systems is developed. Finally, an ecological example is used to illustrate the effectiveness of the proposed design technique. This method allows us to stabilise a wider kind of non-linear uncertain systems. View full abstract»

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  • Approximate dynamic programming for continuous-time linear quadratic regulator problems: relaxation of known input-coupling matrix assumption

    Page(s): 2063 - 2075
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    This study proposes an approximate dynamic programming (ADP) scheme which solves approximately the continuous-time (CT) infinite horizon, linear quadratic (LQ) optimal control problems (OCPs) online for CT linear time-invariant (LTI) systems whose model is not exactly given a priori. In order to relax the assumption of the perfectly known input-coupling matrix, a cheap OCP consisting of a dynamic controller and a modified quadratic performance index is formulated from the conventional LQ OCP. Then, the CT ADP technique based on policy iteration is embedded in the controller as an adaptive element for iteratively solving this cheap OCP in online fashion. By solving the cheap OCP, the near-optimal solution of the original LQ OCP can be obtained, which is proven in this study. The proposed scheme guarantees the stability and convergence to a near-optimal solution, and does not require the knowledge regarding system dynamics during the iterations. Finally, the simulation results are provided to verify the applicability and effectiveness of the proposed control scheme. View full abstract»

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  • Estimating the stability domain of spacecraft attitude with delayed feedback

    Page(s): 2076 - 2082
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    This study deals with the estimation of the stability domain of the spacecraft attitude control system with delayed feedback. For autonomous functional-differential equations, by using the invariance principle, a general estimation theorem is established to explicitly estimate the stability domain. Furthermore, based on the estimation theorem and an applicable Lyapunov functional, an estimation criterion of the stability domain for the spacecraft attitude control system with delayed proportional-derivative (PD) controller is obtained. It is worth noting that the estimation criterion can be described as a generalised eigenvalue problem and thus can be solved by linear matrix inequality (LMI) optimisation techniques. Finally, numerical examples show the effectiveness of the estimation criterion. View full abstract»

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  • Non-linear decoupling control of vehicle plane motion

    Page(s): 2083 - 2094
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (531 KB)  

    This article studies the decoupling control strategies for a quasi-linearised vehicle model consisting of three degrees of freedom. The key feature of the model is that it preserves strong non-linearities and inherent coupling effects between longitudinal acceleration/braking force, steering angles and state variables of the vehicle, based on which two kinds of decoupling controllers are presented. Firstly, a control law for approximate decoupling of longitudinal, lateral and yaw motions is derived, which requires small control magnitude. Next, by selecting the virtual control inputs, a new input-output map is built, and the input-output decoupling controller is proposed. Furthermore, according to the characteristics of the vehicle model, an exponentially stable observer is designed. Several simulations are included to illustrate the proposed control scheme. View full abstract»

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  • Control of linear discrete-time systems by quantised feedback

    Page(s): 2095 - 2102
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (499 KB)  

    In this study the authors, we investigate the problem of designing quantised H feedback control for a class of discrete-time systems with and without bounded uncertainties. The quantiser has arbitrary form. A linear matrix inequality-based method using static and dynamic quantised output-feedback controller are designed to render the closed-loop system asymptotically stable with guaranteed γ-level. The authors illustrate the theoretical developments by numerical simulations. View full abstract»

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  • Task priority approach to the coordinated control of a team of flying vehicles in the presence of obstacles

    Page(s): 2103 - 2110
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1077 KB)  

    This study describes the application of the task priority null-space behavioural technique to the coordinated control of a team of flying vehicles with hovering capabilities, such as helicopters or quadrotors, in the presence of obstacles and no-fly zones. Once a flight mission is assigned to the team in terms of a target region to reach, each flying vehicle is required to accomplish four tasks with assigned priorities. Formation flight and collisions avoidance with other vehicles and unknown or moving obstacles tasks are formulated via analytical expressions as required by the classical null-space behavioural approach. Move to target and a priori known obstacle avoidance behaviours are obtained by solving a partial differential equation problem within the flight domain. The effectiveness of the proposed technique is discussed with regards to two-dimensional and three-dimensional numerical examples. View full abstract»

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  • Solving periodic Lyapunov matrix equations via finite steps iteration

    Page(s): 2111 - 2119
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (239 KB)  

    Periodic Lyapunov matrix equations play important roles in stability analysis and stabilisation of discrete-time periodic systems. In this paper, an iterative algorithm for solving periodic Lyapunov matrix equations is established. It is shown that the proposed iteration converges to the unique solution of the considered matrix equations at finite steps with arbitrary initial condition despite the stability of the associated discrete-time periodic linear systems. Both the reverse-time and forward-time discrete-time periodic Lyapunov matrix equations are considered. Numerical examples are worked out to illustrate the effectiveness of the proposed algorithm. View full abstract»

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  • Observer-based partial differential equation boundary control for a flexible two-link manipulator in task space

    Page(s): 2120 - 2133
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1198 KB)  

    This study addresses the problem of trajectory control of a flexible two-link manipulator on the basis of the partial differential equation (PDE) dynamic model. One of the key contributions of this study is that a novel non-linear PDE observer is proposed to estimate distributed positions and velocities along flexible links, which cannot be achieved by the typical ordinary differential equation observer. In addition, the rigidity-flexibility coupling dynamics is decomposed using the singular perturbation approach, thus providing convenience for control design. Based on the proposed observer and the decoupled PDE model, a boundary control scheme is designed to regulate the end effector along reference trajectory in task space and suppress vibration simultaneously. The asymptotic stability of both the proposed observer and the control algorithm is validated by theoretical analysis and demonstrated by simulation results, respectively. View full abstract»

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  • Global adaptive stabilisation of feedforward systems by smooth output feedback [Brief Paper]

    Page(s): 2134 - 2141
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (411 KB)  

    The authors address the problem of global output-feedback stabilisation for a class of feedforward nonlinear systems. The system satisfies linear growth condition with an unknown growth rate. Using the dynamic gain scaling technique and introducing a new adaptive law, it is proved that global adaptive stabilisation of the feedforward systems can be achieved by smooth output feedback. The gain matrices are only required to satisfy the Hurwitz condition, which makes the control law very easy to implement. Moreover, the authors show that for feedforward systems and low triangular systems with unknown linear growth rate, global adaptive stabilisation can be handled in a unifying framework, that is, the observer and the controller can be designed in a same structure just with two different adaptive laws for the dynamic gain, respectively. View full abstract»

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  • Robust cooperative output regulation problem for non-linear multi-agent systems [Brief Paper]

    Page(s): 2142 - 2148
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    In this study, the author considers a robust cooperative output regulation problem for a class of uncertain non-linear multi-agent systems. The dynamics of each agent can be represented by a non-linear system with unknown parameters. It is assumed that only some of the agents are able to access the exosystem, and thus the problem has to be solved by cooperation among different agents. An internal model-based control strategy is proposed such that, regardless of small parameter perturbations of the agent and control law, the objective of asymptotic tracking and disturbance rejection can be achieved by the control law. Moreover, this method does not require each agent to have identical dynamics. View full abstract»

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  • Relaxed inequality approach to robust H/spl infin/ stability analysis of discrete-time systems with time-varying delay [Brief Paper]

    Page(s): 2149 - 2156
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (219 KB)  

    This study aims at deriving a less conservative delay-dependent criterion for the robust H stability analysis of discrete-time systems with interval time-varying state delay. To this end, an appropriate Lyapunov-Krasovskii functional containing triple summation terms is established and a relaxed inequality approach is proposed to address the induced double summation inequality and to exploits novel relaxation variables for null sum terms. Three numerical examples are provided to illustrate the effectiveness of the derived stability criteria. View full abstract»

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