New Publications are available for Discrete control systems
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New Publications are available now online for this publication.
Please follow the links to view the publication.Robust stability of solar-power wireless network control system with stochastic time delays based on H2 norm
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0605
In this paper, the robust stability analysis of Solar Wireless Networked Control Systems (SWNCSs) with stochastic time delays and packet dropout is investigated. The Robust Model Predictive Controller (RMPC) technique for the SWNCS is discussed using the linear matrix inequality (LMI) technique. Based on the SWNCS model, the RMPC (a full state feedback controller) can be constructed by using the Lyapunov functional method. Both sensor-to-controller and controller-to-actuator time delays of the SWNCS are considered as stochastic variables controlled by a Markov chain. A discrete-time Markovian Jump Linear System (MJLS) with norm bounded time delay is presented to model the SWNCSs. Sufficient conditions for stochastic stability based on H_2-norm and stabilization of the fundamental systems are derived via LMIs formulation. Finally, an illustrative numerical example is given to demonstrate the effectiveness of the proposed techniques. (6 pages)Discrete hardware controllers design of a single phase PFC boost converter with FPGA
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0188
A discrete control design of a single phase PFC boost converter with FPGA is presented. The average current mode control (with current reference) and Self Control (without current reference) are analyzed when implemented with discrete hardware controller. Simulation and experimental results are shown to verify the performance of both controllers. (5 pages)Implementation of time-varying observers used in direct field orientation of motor drives by trapezoidal integration
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0162
The paper discusses the problem of implementing the state observers associated with direct field orientation (DFO) of motor drives using trapezoidal integration (Tustin method). Typically, the discrete-time equations of observers are obtained by emulating the continuous-time equations using the Euler method (forward rectangular rule). With Euler integration, the resulting equations are simple and the real-time implementation requires low computational effort. However, Euler-based observers become inaccurate if a small sampling time cannot used or if the motor drive operates at high frequency-this is because, as the sampling time increases, the Euler approximation of the integral starts losing more and more area from under the curve. The Tustin method (trapezoidal integration) offers an interesting alternative it is theoretically a more accurate integration method, however, it is more complicated. The paper discusses the emulation procedure required to discretize continuous-time observers based on trapezoidal integration. The permanent magnet synchronous motor (PMSM) is used as an example of a time-varying plant-the paper develops a trapezoidal integration based observer for the PMSM and compares this with an Euler-based observer in terms of computational complexity and performance. The two observers are simulated comparatively in order to establish the conditions when trapezoidal integration outperforms the Euler method. (6 pages)Predictive PID controller for DC-DC converters using an adaptive prediction error filter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0213
This paper presents a predictive PID controller for DC-DC converters using an adaptive prediction error filter (PEF) in the controller feedback loop. The concept of using an adaptive PEF is clearly described, and mathematical analysis of central concepts, such as the Auto-Regressive (AR) process generator and Moving Average (MA) identifier are explained in detail. The direct relationship between an adaptive PEF and a digital Proportional-Derivative (PD) controller is also presented. This leads to the development of an adaptive Proportional-Derivative + Integral (PD+I) control structure which is an effective substitute to a conventional PID controller. Experimental validation shows that the approach results in a fast adaptive controller with self-loop compensation. (6 pages)Modelling an active suspension controller for a road vehicle
http://dl-live.theiet.org/content/conferences/10.1049/cp.2010.0482
This paper presents the development of an active suspension control system which uses state space methods and the pole placement technique for a novel application on an unmanned ground vehicle (UGV). Continuous and discrete controllers are developed for both one and two degree of freedom (DOF) quarter-car active suspension systems. The response of both systems to a step input equivalent to a 10 cm bump in the ground surface is presented and the implications are discussed. A preliminary design for the construction of a physical 1-DOF active suspension experimental rig is proposed. The 1-DOF system has been suitably scaled for laboratory conditions. The experimental rig will be used to support teaching and research activities in control strategies for active suspensions, especially for unmanned ground vehicles.On a variation of the Gershgorin circle theorem with applications to stability theory
http://dl-live.theiet.org/content/conferences/10.1049/cp.2009.1687
The conclusions of the Gershgorin circle theorem are significantly extended for the special case of real matrices. The extended result is applied to the problem of the absolute stability of both continuous- and discrete-time Lur'e systems containing sector nonlinearities. Specifically necessary conditions for the existence of common unic Lyapunov functions are presented in the form of constraints upon the root locus of the linear, time-invariant component. (5 pages)Application of the discrete-time structured singular value for DC-DC converters
http://dl-live.theiet.org/content/conferences/10.1049/cp_20080644
This paper considers the application of the discrete-time structured singular value to assess the robustness of systems subject to real parametric uncertainties. Since the associated uncertainty set is strictly real, the resulting μ bounds may be discontinuous irrespective of the fineness of the frequency sweep. It is therefore necessary to seek other more reliable methods of test. One such method detailed is a discrete robust stability state-space test that is not dependent on a frequency sweep. It is shown that this is a discrete skewed structured singular value problem. For illustration purposes, a robustness analysis using both a frequency sweep and state-space transformation is performed on a forward converter with a real parameter uncertainty. The results are detailed and critically assessed.Guaranteed cost control of uncertain sampled-data systems based on state observer
http://dl-live.theiet.org/content/conferences/10.1049/cp_20070689
In order to solve the problems of state information unable to be observed or the value of sensors too high, the guaranteed cost controller of a class of uncertain sampled-data system was studied based on the state observer. A class of sufficient conditions for the guaranteed cost controller of the sampled-data system was given via solving a class of LMI constrains. The guaranteed cost controller law and state observer gain were derived. At last, a numerical example is presented to demonstrate the validity of this approach.Multi-rate sampled-data systems with decentralized control structure
http://dl-live.theiet.org/content/conferences/10.1049/cp_20070691
This paper presented the mathematical formulation of the decentralized multi-rate controller design problem based on a lifting technique, taking account of stability and input-output performance. The design procedure includes both the analysis of the overall system and the controller synthesis for individual subsystems. Also an approach to the optimal stabilization via a decentralized control law is proposed and the main result presents a scheme for constructing a class of decentralized controllers, which stabilizes the system and is optimal with respect to a quadratic performance index.Control Theory
http://dl-live.theiet.org/content/books/ce/pbce064e
<p xmlns="http://pub2web.metastore.ingenta.com/ns/">This fully revised and updated edition of Control Theory: a guided tour addresses recent developments in the field. It discusses how the rise of Hoo and similar approaches has allowed a combination of practicality, rigour and user interaction to be brought to bear on complex control problems and has helped bridge the gap between control theory and practice. The book also examines the effects of the rise of artificial intelligence techniques and the increasing availability of comprehensive software packages.</p>Using statistical methods to simplify control system selection
http://dl-live.theiet.org/content/conferences/10.1049/ic_20040647
The PowerPoint presentation is about the initial measurement method provided by the General Motor Power Train Group and further use of statistics. Determinism, is defined, hard and soft real-time are explained, PID control and discrete control requirements are explored in the presentation. The presentation also explains the operation of the programmable logic controller (PLC), outlines the evolution of the open control system (OCS), introduces 3S, CoDeSys and the automation alliance, and contrasts the performance of the PLC versus the Pentium. Control platforms that were tested are outlined and their weaknesses are suggested. The test code used is explained and the data acquisition method used is shown.Tuning of field-oriented controller for induction machines
http://dl-live.theiet.org/content/conferences/10.1049/cp_20020139
A scheme for tuning controllers based on Indirect Self Control (ISC) for induction machines is presented. It is shown that the closed loop system can be approximated by a simple linear system, where the controller parameters can be directly expressed in terms of motor data and performance requirements. The results are verified through simulations and power lab measurements.Associative reinforcement learning for discrete-time optimal control
http://dl-live.theiet.org/content/conferences/10.1049/ic_20000342
This paper investigates the application of associative reinforcement learning techniques to the optimal control of linear discrete-time dynamic systems. Associative reinforcement learning involves the trial and error interaction with a dynamic system to determine the control actions that optimally achieve some desired performance index. The methodology can be applied either online or off-line and in a model based or model free manner. Associative reinforcement learning techniques are applied to the optimal regulator (LQR) control of discrete-time linear systems. Adaptive critic designs are implemented and the convergence speed compared for the different approaches. These methods can determine the optimal state and state/action value function and the optimal policy without requiring system models. (4 pages)Discrete sliding mode control of a boost converter for output voltage tracking
http://dl-live.theiet.org/content/conferences/10.1049/cp_20000271
This paper proposes the design of a discrete sliding control of a boost DC-DC power converter for the output tracking of a sinusoidal reference signal. The discrete sliding surface is designed by imposing a desired dynamic behavior on the system, which allows to determine the main parameters of the sliding mode controller. This procedure leads to a discrete-time switching surface, which provides robustness with regards to external disturbances and a good dynamic response of the output voltage.Model predictive control using Dynamic Integrated System Optimisation and Parameter Estimation (DISOPE)
http://dl-live.theiet.org/content/conferences/10.1049/ic_19990536
DISOPE is a technique for solving optimal control problems where there are differences in structure and parameter values between reality and the model employed in the computations. The model reality differences can also allow for deliberate simplification of model characteristics and performance indices in order to facilitate the solution of the optimal control problem. The technique was developed originally in continuous time and later extended to discrete time. The main property of the procedure is that by iterating on appropriately modified model based problems the correct optimal solution is achieved in spite of the model-reality differences. Algorithms have been developed in both continuous and discrete time for a general nonlinear optimal control problem with terminal weighting, bounded controls and terminal constraints. The aim of this paper is to show how the DISOPE technique can aid receding horizon optimal control computation in nonlinear model predictive control. (4 pages)1D models for class of 2D linear systems
http://dl-live.theiet.org/content/conferences/10.1049/ic_19980170
The basic unique control problem for repetitive processes arises from the explicit interaction between successive pass profiles. In particular, the output sequence of pass profiles can contain oscillations that increase in amplitude in the pass to pass direction. Such behaviour is easily generated in simulation studies and in experiments on scaled models of industrial examples such as long-wall coal cutting. In long-wall coal cutting this problem appears as severe undulations in the newly cut floor profile which means that cutting operations (i.e. productive work) must be suspended to enable their manual removal. This problem is one of the key factors behind the stop/start cutting pattern of a typical working cycle in a coal mine. In general, this problem cannot be removed by standard, i.e. 1D, control action. The basic reason for this is that such an approach essentially ignores their inherent 2D systems structure. Motivated by this key fact, Rogers and Owens (1992) have developed a stability theory for repetitive processes with linear dynamics and a constant pass length. This theory is based on an abstract model in a Banach space setting which includes all such processes as special cases. The results of applying this theory to a range of special cases are also known including discrete linear repetitive processes which are the subject of this paper. (4 pages)Solution to the Shell standard control problem using genetic algorithms
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980466
The proposed scheme includes two discrete-time PID controllers with integral anti-windup and a Smith predictor to provide the required regulation, while the minimisation problem is analytically solved online, by estimating the unmeasured disturbances present in the process and solving the associated linear program. This, as well as the presence of constraints in the process manipulated variables results in a complex, nonlinear closed-loop system and hence, the manual tuning of the two PID controllers according to some given performance objectives, becomes a difficult task. GAs are successfully applied to the automatic tuning of the PID controllers, and simulation results are presented to demonstrate the effectiveness of the proposed control scheme.Supervisory control design for real-time discrete event systems
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980338
This paper deals with the development of algorithms for a software tool that derives the supervisory controller of a real-time discrete event system modelled using timed automata. An example and graphical abstractions are used to demonstrate the algorithmic work, methodology and design environment.Robust synthesis by fictitious Bayesian identification approach
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980371
We examine a new robust control procedure in order to ensure the best trade-off performance/parametric robustness. This study extends the research performed into an analysis method called PRABI (parameter robust analysis Bayesian identification). Its basic idea was the close relationship between quality of fictitious parametric Bayesian identification in closed-loop and stability robustness against variations of inherent parameters. The algorithm detailed below generalizes the concept in parametrizing the synthesis step for the study of performance robustness. Robust control design of a flexible system is demonstrated to prove the relevance of the theoretical methodology, which is easy to implement.Analytical solution to the polynomial diophatine equation: development and application to generalised predictive control analysis
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980332
The techniques of predictive control are based on building a prediction about the future plant behaviour. One way to obtain such a prediction requires solving a polynomial diophantine equation (PDE). There are different methods to solve such an equation, which are good for design purposes but present some restrictions when studying the behaviour of solutions and the performance of the methods in which they are applied. In this article an analytical solution for the PDE is developed, which constitutes a new analysis tool for predictive methods. Also, first results are briefly described on the application of this solution to the analysis of the generalised predictive control method.Robust stability for nonlinear sampled-data control systems and Aizerman's conjecture
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980305
The robust stability criterion for sampled-data control systems with a sector nonlinearity was presented in our previous papers (1996, 1998). Although it is applicable only to the sampled-data control system of a certain class, a usual discrete-time control system belongs to this type of class. The criterion contains the robust stability condition in regard to the nonlinear allowable band (sector) for continuous-time systems and the linear allowable gain band (interval set) for discrete-time systems. The paper focuses primarily on the concept of robust stability in order to analyze a nonlinear element by the linear gain band, in other words, the validity of Aizerman's conjecture extended into discrete-time systems.On the control of nonholonomic systems in power form
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980441
We develop discontinuous controllers for stabilizing n-dimensional nonholonomic mechanical systems given in power form. We show that the stabilization of the whole system turns out to be a simultaneous stabilization of (n-3) driftless subsystems. The control strategy is based on the technique of invariant manifolds. Moreover, it is shown that we could improve the rate of convergence of the state vector by the use of dynamic controllers. A numerical procedure is proposed to filter the noisy measurement without affecting the dynamic of the controller.Design of reduced-order feedforward controller
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980228
The design of a linear, reduced-order, continuous or discrete-time feedforward controller (FFC) is presented. The FFC is located in the reference value branch of a linear feedback system of any order which is designed according to the damping optimum. The aim of the FFC is to decrease the control system reference response time, while retaining a low overshoot and a well-damped form of the reference step response. This is achieved by locating the FFC zeros with the aid of the extended magnitude optimum, which is provided in the continuous or discrete-time variant. The influence of a suboptimally designed feedback system with a reduced-order feedback controller on feedforward control is analyzed. Reduced and full-order FFCs are compared.Evolutionary design of process controllers
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980444
The genetic programming (GP) architecture offers a potentially powerful framework for `intelligent' controller design due to its inherent matching of structure to utility. The article describes the use of GP to design discrete time single loop controllers for two different processes: a linear auto-regressive exogeneous (ARX) type system and a non-linear simulated continuous stirred tank reactor (CSTR), both with constraints on the actuator outputs. It is demonstrated that the GP methodology is capable of designing recursive controllers that, for a specific class of control objectives, offer similar performance to PID controllers on the nominal systems. The advantages and disadvantages of controllers designed in this way are also discussed.Multi-rate sampled-data feedback system synthesis via a long-range predictive control approach
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980296
A polynomial modelling technique is utilised to synthesise predictive control laws for multi-rate sampled-data systems. Subsequently, the effect on feedback system performance of deploying alternative sampling strategies is examined.A priori information in network design
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980317
An analysis of how a priori knowledge of relative order can be applied to train a neural network effectively, is presented. In many cases only an approximate model of a system is known. The information from this model can be used to produce a more accurate one. Often this knowledge is not available or at best is inaccurate. Under these conditions, the relative order can be determined from the structure of the trained network using the rules developed here. This analysis is demonstrated with two examples.Fault detection and isolation for a three tank system based on a bilinear model of the supervised process
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980449
Time varying innovation generators combined with generalized likelihood ratio (GLR) tests are designed for detection and isolation of faults in a three tank system. This diagnosis system is based on a bilinear model of the supervised process. It is shown to work properly in a larger working range than a fault detection and isolation (FDI) system based on a linear model. As the faults enter in a bilinear way in the model, achieving exact decoupling of the residuals with respect to some of the faults is not possible. One has to resort to approximation methods such as the approach developed in Patton and Chen (1993). The whole FDI system is designed and tuned on the basis of a simulation of the three tank system. Next it is applied to actual pilot plant data and it is shown to perform well. To be able to detect temporary faults (namely fault appearance and disappearance) with the GLR test, a strategy based on the use of two Kalman filters running in parallel is used.Noise sensitivity of fast output sampling controllers
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980236
Fast output sampling controllers have been proposed as an alternative to observer-based state feedback control. However, a typical problem with this type of controller is noise sensitivity due to large feedback gains. In this paper, it is proposed to allow a small deviation from the exact solution to the design problem in order to reduce noise sensitivity. This can be achieved by posing the design problem in the form of an LMI problem. Fast output error dynamics can be included as an additional design objective. A practical design example serves to illustrate the approach. The performance of the controller is compared with observer-based state feedback, and experimental results show that in this case fast output sampling has superior performance.Finite word length stability issues of a teleoperation motion-scaling control system
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980481
We study the finite-precision implementation and the relevant stability conditions for optimal controller structures of a bilateral motion-scaling teleoperation control system. The parameterized digital controller realizations and the relevant stability robustness measures subject to word length constraints are formulated. The resulting controller structure provide an improved stability condition with minimum finite word length implementation.On identification for robust-optimal control
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980409
The design techniques of robust optimal controllers for the linear discrete-time control objects with random noise and regular parameter perturbations are given. These are based on identification approach using two auxiliary stabilizing controllers.MIMO robustness analysis of digital control systems using genetic algorithms
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980238
An approach to robustness analysis in discrete-time MIMO control systems is developed by using the closed-loop characteristic equation in the presence of gain or phase perturbations. Genetic algorithms are also proposed as the search algorithm for determining the smallest destabilizing perturbations in the form of MIMO gain and phase margins. This technique is computationally more burdensome than the calculus-based technique. However, it can deal with digital control systems, which include time delays, in the exact manner.Unified representation of predictive control algorithms for practical applications
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980329
Various forms of predictive algorithms are available in the literature. We give an unified representation of these, which includes the multivariable case. Practical considerations of boundedness of the input are taken into account. The algorithms presented are the basis for an industrial multivariable predictive controller.Numerical algorithms and issues concerning the discrete-time optimal projection equations for systems with white parameters
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980469
The discrete-time optimal projection equations for systems with white parameters are strengthened. For the class of minimal mean square stabilizing compensators the strengthened discrete-time optimal projection equations are proved to be equivalent to first-order necessary optimality conditions for optimal reduced-order dynamic compensation of systems with white parameters. The conventional discrete-time optimal projection equations are proved to be weaker. As a result solutions of the conventional discrete-time optimal projection equations may not correspond to optimal reduced-order compensators. To compute optimal reduced-order compensators two numerical algorithms are proposed. One is a homotopy algorithm and one is based on iteration of the strengthened discrete-time optimal projection equations. The latter algorithm is a generalization of the algorithm that solves the full-order problem, which in turn is a generalization of the algorithm that solves the two Riccati equations of full-order LQG control through iteration. Therefore the efficiency of these three types of algorithms is comparable. It is demonstrated that, despite the strengthening of the optimal projection equations, the optimal reduced-order compensation problem, in general, may possess multiple extrema.A formal technique for the synthesis of Petri net supervisors for discrete event systems
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980339
In this paper a formal technique for the synthesis of Petri-net-based supervisors for discrete event systems is proposed to solve the forbidden state problem. The solution has close parallels to the finite state machine approach proposed by Ramadge and Wonham (1987, 1989). The technique thus provides a Petri net equivalent method to act as further stimulus to solving the synthesis of supervisory control problems. In this paper the methodology is explained in detail by considering a discrete manufacturing system.A modified recurrent least squares algorithm for on-line closed-loop identification for processes with time delay
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980223
Focuses on an algorithm of linear digital dynamic models online identification based on recurrent parameter estimation for processes with time delay. This algorithm is efficient for adaptive control systems design. The delay of the linear part of a digital model in the S-domain is estimated as well as parameters of a numerator and denominator of a transfer function (TF) in the Z-domain. This allows us to correct the delay of a model in the Z-domain and accordingly to make a correction of the recurrent least squares algorithm. The experimental results of prop-fan engine identification are submitted. The algorithm can also be useful for checking of process model structure correctness and choosing of an optimum interval of time discretisation in digital control system design.Design of digital two steps internal model controller with simplified internal model
http://dl-live.theiet.org/content/conferences/10.1049/cp_19980468
A simple internal model controller is proposed which has a better performance and stability margin than conventional proportional-plus-integral control when used on time-delayed plants. Moreover, the controller is also easier to tune than conventional controllers and can accommodate actuator saturation in a more effective manner. The proposed two step internal model controller is particularly effective on time-delayed plants which have actuator saturation effects present.Engineering maths is alive!
http://dl-live.theiet.org/content/conferences/10.1049/ic_19970459
This paper aims to remind us of some of the reasons why engineering mathematics is vital in two senses. Firstly, as is generally acknowledged, fluency in mathematical expression is essential for the study of any scientific or technical subject. Equally though, engineering mathematics is vital in the sense that it is alive. It is a developing subject, regularly called upon to explain new phenomena or new approaches to problems. This paper examines the latter view. In the last few years some graduates employed in engineering have been asked to investigate, and report on `new' ideas which might have a part to play in the future of their companies. We give a brief introduction to these ideas in order to highlight both the excitement of engineering mathematics, and to underline the importance of firm foundations on which personal development can be based. Attention is given to the Hartley transform as an alternative to the Fourier transform and to the modelling of discrete-time systems with rapid sampling, and an application of artificial neural networks to fuzzy logic is also presented. (4 pages)Robust PIP control of multivariable stochastic systems
http://dl-live.theiet.org/content/conferences/10.1049/ic_19971286
This paper discusses the development of robust versions of multivariable non-minimal state space design procedures, for the proportional-integral-plus (PIP) control systems previously introduced by Young et al. (1994). Robust control design aims to ensure good closed loop performance under difficult conditions, such as model uncertainty and “worst case” disturbance inputs. In this regard, the practical utility of the PIP controllers are evaluated on two systems, namely a multivariable coupled drive rig and the IFAC93 benchmark. The first of these examples is a laboratory scale plant representing a materials handling system, where control of speed and tension is required; while the latter is a stochastic simulation, whose parameters vary randomly within specified ranges. (3 pages)Speed control of DC motor drives based on efficient utilization of energy and optimal performance
http://dl-live.theiet.org/content/conferences/10.1049/cp_19970602
The most flexible control is obtained by means of a separately-excited DC motor, in which the armature and field circuits are provided with separate sources. The speed control in a DC motor is widely applied. The concept of control system optimization comprises a selection of a performance criterion and a design which yields the optimal control system subjective to the limits imposed by physical constraint, which will minimize some measure of deviation from ideal behaviour. In addition to considering errors as a measure of system performance, however, it must pay attention to the energy required for the control action, for efficient utilization of energy, since the control input is proportional to the required energy. If the errors are minimized regardless of the energy required, then a design may result in an overly large value of control input. The discrete optimal control theory in addition to the preview feedforward control, which depends on minimizing a selected performance index, are involved in the design of a system controller to obtain the optimal control law. Simulation results are obtained to investigate the effectiveness, the susceptibility, the feasibility and the transient response properties of the above mentioned system. An experimental set-up is built up to confirm the above obtained simulation results. A three phase six-pulse power converter is built to provide a variable DC power supply to the armature circuit, controlled either manually or automatically through an analog DC voltage applied from a microcomputer, in order to decrease power loss and improve the utilization of energy. (5 pages)Extended real-time logic for hybrid systems controller design
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961366
Summary form only given. Hybrid systems are systems which combine both continuous variable and discrete event dynamics. Their complexity has risen to the extent that traditional approaches which dealt separately with the continuous and discrete aspects of such systems have become obsolete. Instead of proposing a novel formal notation for the specification of controllers for hybrid systems we have developed extended real time Logic (ERTL) as a formal notation for the modelling and analysis of relative and absolute timing properties of hybrid systems. ERTL embeds the discrete system model of the real time logic (RTL) of Jahanian and Mok (1986, 1988) into continuous time, and adds the ability to reason about piecewise continuous functions using predicates over real valued variables. While RTL is able to formally describe the behaviour of computational entities in the time domain, ERTL also permits the formal description of the behaviour of physical entities in both value and time domains. (2 pages)Using modal analysis to guarantee the closed loop behaviour of a class of hybrid systems
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961367
Several issues in the control of a class of hybrid systems are discussed. The class of hybrid systems considered are linear time-varying plants controlled by means of switching between homogeneous controllers. In this paper modal analysis is used to analyse the behaviour of switching systems with real eigensystems. Conditions guaranteeing the stability of such systems are presented and guidelines for shaping their transient response given. It is demonstrated that for SISO systems, controlled by means of dynamic state feedback, a local state approach can be employed which results in a closed loop system with guaranteed asymptotic stability irrespective of switching frequency. The theory presented is used in the design of a hybrid speed control system for a real automobile which guaranteed nominal stability and good transient response properties. (5 pages)Modelling mode-switching systems as the limit of discrete computational processes
http://dl-live.theiet.org/content/conferences/10.1049/ic_19961364
This paper presents a theoretical outline of a new formalism for mode switching or hybrid systems in which continuous dynamics are represented as the limit of a discrete computational process. Mode switching systems are systems which are composed of continuous modes switched between by discrete transitions. Most existing mode switching formalisms treat their continuous and discrete components as distinct types of process. This new approach brings the two together and provides a platform for the investigation of the transition between continuous change and discrete events. (6 pages)A new discrete current vector regulator for torque controlled induction motor drives
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960957
The paper proposes a new current vector control strategy for torque controlled field oriented drives. The choice of the inverter switching vectors is based on the angular position of the rotor flux and on the reference and the motor current vectors in the switching vectors plane. The simulation results prove that the proposed method allows an improved DC bus utilization and lower motor phase currents THD to be obtained, compared to other current vector control techniques.A method for discrete-time linear quadratic optimal control problems of a large-scale multi-destination network and applications
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960563
We propose a new dual projected pseudo quasi-Newton method for discrete-time linear quadratic optimal control problems of a large-scale multi-destination network. Our method has successfully overcome the difficulties caused by large dimensions and inequality constraints by having a constant Hessian matrix and an efficient successive projection method, respectively. Application of our method to the congestion control of multi-destination networks is presented. Above all, it takes less than one second to obtain the solution of a large-scale discrete-time linear quadratic optimal control problem with the problem size of 2800 variables, 700 equality constraints and 2400 inequality constraints.Modular procedural control of chemical processes
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960640
Procedural control theory (PCT) encompasses chemical process modelling, specification, controller synthesis and analysis. In particular, techniques have been presented for designing sequential controllers for chemical systems which are guaranteed to generate a behaviour which conforms to a functional specification and terminates in a desired process state (non blocking). Until now, the techniques within PCT have been limited to simple chemical systems modelled by no more than a few thousand states and for which the specifications are relatively straightforward. The aim of this work is to apply the same techniques to a broader category of control problems in chemical batch processing, for which the size of the state models may be many orders of magnitude greater, and the specifications quite complex. In this work, size complexity is addressed using reduced models of the process which are easily calculable within the modular approach for process modelling in PCT. A complementary method for handling specification complexity is addressed by borrowing from AI the concept of subgoals. Both decomposition techniques serve to modularise the controller synthesis problem.Sliding mode state observers for SISO linear discrete-time systems
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960661
Discrete-time sliding mode observer design for SISO systems is discussed. The sliding lattice is a new approach in sliding mode control design. For discrete-time systems sliding points exist on a hyperplane which we call the sliding lattice. Asymptotically stable observer design and the stability of reconstruction error systems using the Lyapunov direct method are presented. Techniques for finding the feedforward injection map and the external feedforward compensation signal are given.Probabilistic discrete system models for H<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">∞</sub> optimal control design
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960561
The modelling and H<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">∞</sub> control of discrete-time systems with uncertain parameters which can be represented probabilistically is considered. The polynomial based model structure is chosen so that high frequency lag terms may be introduced whose parameters have zero expected value. Similarly uncertain zeros may be considered. An H<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">∞</sub> controller can then be obtained which stabilises the nominal plant model and also provides a degree of robustness to uncertain poles and zeros.Discretization of continuous control laws
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960580
This paper presents a discretization procedure which reproduces the behavior of a continuous state feedback control scheme. This method is introduced in the SISO case and then extended to the MIMO case. For this kind of model, one has to choose among a set of solution concerning the distribution of control variables; this is illustrated by a few examples. Finally the procedure is applied to a magnetic levitation model and simulation tests show the good behavior of the controlled system.New developments in batch process input profile optimisation
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960651
A novel algorithm for solving nonlinear discrete time optimal control problems with model-reality differences is presented. The technique uses dynamic integrated system optimisation and parameter estimation (DISOPE) which achieves the correct optimal solution in spite of deficiencies in the mathematical model employed in the optimisation procedure. A new method for approximating some Jacobian trajectories required by the algorithm is introduced. It is shown that the iterative procedure associated with the algorithm naturally suits applications to batch chemical processes.Universal regulators for discrete-time systems
http://dl-live.theiet.org/content/conferences/10.1049/ic_19960822
The paper presents an approach to the problem of universal adaptive stabilization for discrete-time systems by means of switching controllers, as previously developed in different ways by Martensson (1985), Fu-Barmish (1986), Miller-Davison (1989), for continuous-time systems. It is assumed that the plant is linear, time-invariant and can be stabilized by a feedback compensator of known structure, so that the task of the switching algorithm is to search the space of possible controller parameters until stability is achieved. Since the search has to be undertaken on an infinite set, dense in the parameter space, the algorithm is designed so that, in the absence of disturbances, the switching will eventually terminate and the system will then asymptotically approach its equilibrium state. Moreover, by utilizing the internal model principle, the adaptive stabilizer can be embedded in a control scheme to track reference signals with known dynamic properties. Modifications are then considered, so as to allow for the presence of disturbances. (5 pages)