Discrete approximation and supervisory control of continuoussystems

Addresses the following hybrid control problem: a continuous plant (its state evolving in Euclidean space) is to be controlled via symbolic output feedback-both measurement and control signal “live” on finite sets of symbols. We adopt the following approach: the hybrid problem is first translated into a purely discrete problem by approximating the continuous plant model by a (nondeterministic) finite-state machine. By taking into account past measurement and control symbols, approximation accuracy can be improved and adjusted to the specification requirements. Supervisory control theory for discrete-event systems (DES) is then applied to find the optimal controller which enforces the specifications. As the behavior of the approximating automaton is guaranteed to contain the behavior of the underlying continuous plant model, the controller also forces the latter to obey the specifications     

离散事件系统的混合型Petri网控制器

考虑由具有不可控变迁的受控Petri网建模的DES的控制器综合问题.提出了兼具 DES的逻辑型和结构型二种控制器优点的混合型Petri网控制器:在系统状态的获取和跟踪上具 有结构型控制器的优点,而在控制作用的实施上则具有逻辑型控制器的优点.全文通过实例说明 了混合型Petri网控制器的设计方法.     

The real-time supervisory control of an experimental manufacturing system based on a hybrid method

In this paper, the real-time supervisory control of an experimental manufacturing system is reported based on a recently proposed hybrid (mixed PN/automaton) approach. Assuming that an uncontrolled bounded Petri net (PN) model of a (plant) discrete event system (DES) and a set of forbidden state specifications are given, the proposed approach computes a maximally permissive and nonblocking closed-loop hybrid model. The method is straightforward logically, graphically and technologically. This paper particularly shows the applicability of a hybrid (mixed PN/automaton) approach to low-level real-time DES control. To do this, programmable logic controller (PLC) based real-time control of an experimental manufacturing system is considered.     

一类混杂系统的建模与控制器设计

研究一类离散事件系统和连接时间系统相混合的混杂系统建模与控制器设计问题。首先用不同的模型方法建立混杂系统的层次模型，分析连续时间系统状态空间的离散化和系统的可控性；在此基础上利用ＤＥＳ监控理论设计控制器，以规范系统的时域和逻辑行为。最后的示例表明了层次模型与控制算法的有效性。     

Model matching for finite-state machines

The problem of model matching for finite state machines (FSMs) consists of finding a controller for a given open-loop system so that the resulting closed-loop system matches a desired input-output behavior. In this paper, a set of model matching problems is addressed: strong model matching (where the reference model and the plant are deterministic FSMs and the initial conditions are fixed), strong model matching with measurable disturbances (where disturbances are present in the plant), and strong model matching with nondeterministic reference model (where any behavior out of those in the reference model has to be matched by the closed-loop system). Necessary and sufficient conditions for the existence of controllers for all these problems are given. A characterization of all feasible control laws is derived and an efficient synthesis procedure is proposed. Further, the well-known supervisory control problem for discrete-event dynamical systems (DEDSs) formulated in its basic form is shown to be solvable as a strong model matching problem with measurable disturbances and nondeterministic reference model     

Incremental design of a power transformer station controller usinga controller synthesis methodology

The authors describe the incremental specification of a power transformer station controller using a controller synthesis methodology. They specify the main requirements as simple properties, named control objectives, that the controlled plant has to satisfy. Then, using algebraic techniques, the controller is automatically derived from this set of control objectives. In our case, the plant is specified at a high level, using the data-flow synchronous SIGNAL language, and then by its logical abstraction, called polynomial dynamical system. The control objectives are specified as invariance, reachability, ...properties, as well as partial order relations to be checked by the plant. The control objectives equations are synthesized using algebraic transformations     

Decentralized supervisory control of nondeterministic discrete event systems: The existence condition of a robust and nonblocking supervisor

This paper addresses a decentralized supervisory control problem for an uncertain discrete event system (DES) modeled by a set of possible nondeterministic automata with unidentified internal events. For a given language specification, we present the existence condition of a robust and nonblocking decentralized supervisor that achieves this specification for any nondeterministic model in the set. In particular, we show that the given language specification can be achieved based on the properties of its controllability and coobservability with respect to the overall nominal behavior of the uncertain DES. It is further shown that the existence of a nonblocking decentralized supervisor can be examined with a trajectory model of the language specification.     

Robust and nonblocking supervisory control of nondeterministicdiscrete event systems using trajectory models

This note considers the robust supervisory control problems of uncertain nondeterministic discrete-event systems (DESs). The uncertain DES to be controlled is assumed to be modeled as a set of some possible nondeterministic automata. Then, the control objective is to achieve a given language specification and guarantee the nonblockingness of any nondeterministic automata of the set which are controlled by a robust nonblocking supervisor. Based on trajectory models, this note presents the necessary and sufficient conditions for the existence of a robust nonblocking supervisor for a given uncertain nondeterministic DES     

Linear parameter varying PID controller design for charge control of a spark-ignited engine

This paper presents the design and experimental test of a fixed-structure LPV controller for the charge control of a spark-ignition engine. A nonlinear model of the plant is transformed into an affine LPV model in the form of an LFT representation. Using a hybrid evolutionary-algebraic synthesis approach that combines LMI techniques based on K-S iteration with evolutionary search, a scheduled PID controller is designed. To reduce conservatism, the technique of quadratic separators is used in the analysis step. To improve tracking behavior, the gain scheduled feedback controller is supported by an LTI feedforward controller. The controller has been implemented on a standard electronic control unit, and experimental results on a test car illustrate that it meets the performance requirements in a wide range of operation.     

ON THE DESIGN OF AN ADAPTIVE CONTROLLER FOR UNCERTAIN PLANTS VIA LIAPUNOV SIGNAL SYNTHESIS METHOD

This paper presents an adaptive design approach for controlling a class of unknown nonlinear multivariable plants operating in an uncertain environment. The approach uses a “two-level” control technique, with a feedforward controller on its first-level, and a conditional feedback controller on its second-level. The procedure employs a Liapunov type signal synthesis approach. By introducing a characteristic vector, which is characteristic of the unknown plant and its environment, the design of the controller bypasses the rigid requirements of explicit identification of the plant and its environment as needed in the implementation of a controller using conventional techniques.

The applicability of this control approach is demonstrated by means of hybrid computer simulation studies which were carried out on a number of unknown plants; however, in this paper we present some simulation results for an exothermic chemical reactor.     

Reduced Order Robust Gain‐Scheduling Control Of The Diesel Apu For Series Hybrid Vehicles

This paper presents a reduced order robust gain‐scheduling approach for the control of the diesel auxiliary power unit (APU) for series hybrid vehicles. The nonlinear plant dynamics are converted into a linear parameter‐varying (LPV) form with parametric uncertainties, in which only partial information of the plant states is available. For this type of LPV system, a new reduced order robust gain‐scheduling synthesis method is proposed based on partial state feedback. The parametric uncertainties are considered using multipliers to reduce the conservatism. The reduced order synthesis problem is solved offline by means of linear matrix inequalities (LMIs), and the synthesis result requires much simpler online computation than the explicit controller formulas do. The synthesis method is applied to the diesel APU controller design, and simulation results are given to demonstrate the controller performance.     

Optimal hybrid fault recovery in a team of unmanned aerial vehicles

This paper introduces and develops an optimal hybrid fault recovery methodology for a team of unmanned vehicles by taking advantage of the cooperative nature of the team to accomplish the desired mission requirements in presence of faults/failures. The proposed methodology is developed in a hybrid framework that consists of a low-level (an agent level and a team level) and a high-level (discrete-event system level) fault diagnosis and recovery modules. A high-level fault recovery scheme is proposed within the discrete-event system (DES) supervisory control framework, whereas it is assumed that a low-level fault recovery designed based on classical control techniques is already available. The low-level recovery module employs information on the detected and estimated fault and modifies the controller parameters to recover the team from the faulty condition. By taking advantage of combinatorial optimization techniques, a novel reconfiguration strategy is proposed and developed at the high-level so that the faulty vehicles are recovered with minimum cost to the team. A case study is provided to illustrate and demonstrate the effectiveness of our proposed approach for the icing problem in unmanned aerial vehicles, which is a well-known structural problem in the aircraft industry.     

Fault tolerant control design via hybrid petri nets

This paper proposes a novel fault tolerant control (FTC) scheme for hybrid systems modeled by hybrid Petri nets (HPNs). The HPNs model consists of discrete and continuous PNs. The faults are represented by unobservable discrete transitions or the normal observable discrete transitions with abnormal firing time in discrete PNs. First, an observer‐based fault diagnosis method is proposed to estimate the marking in discrete places with unknown initial marking and diagnose the faulty behavior simultaneously. Then, an adaptive fault tolerant controller is designed to maintain the general mutual exclusion constraints (GMEC) of discrete PNs, and a scheme that adjusts firing speeds of continuous transitions is provided to maintain the optimality of continuous PNs. Finally, an example of an intelligent transportation system consisting of automated vehicles on a bridge is included to demonstrate the effectiveness of our developed techniques. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Modular Supervisory Control with Equivalence-Based Abstraction and Covering-Based Conflict Resolution

A modular approach to control is one way to reduce the complexity of supervisory controller design for discrete-event systems (DES). A problem, however, is that modular supervisors can conflict with one another. This paper proposes requirements on coordinating filters that will resolve this conflict. Abstractions are employed to reduce the complexity of the filter construction. Our specific approach is unique in that it employs a conflict-equivalent abstraction that offers the potential for greater reduction in model size than those abstractions employed in previous works on conflict resolution. The resulting control implemented by the modular supervisors in conjunction with coordinating filters meeting the proposed requirements is shown to be safe and nonblocking. Approaches for constructing these filters are discussed and a methodology that implements deterministic coordinating filter control laws by nondeterministic automata is presented. The covering-based filter law construction methodology presented here is further demonstrated to provide less restrictive control than existing results on state-feedback supervisory control.     

Hybrid control approach to the peg-in hole problem

Since the whole assembly process has typical phase transitions between control laws driven by the environment event, the techniques of hybrid control can be employed to specify the hybrid control properties. Finally a hybrid controller and corresponding hybrid control programs are designed using the HCSP language to describe a peg-in-hole problem     

Supervisory control of switching control systems

In this paper, the problem of designing a switching policy for an adaptive switching control system is formulated as a problem of supervisory control of a discrete-event system (DES). Two important problems in switching control are then addressed using the DES formulation and the theory of supervisory control under partial observation. First, it is verified whether for a given set of controllers, a switching policy satisfying a given set of constraints on the transitions among controllers exists. If so, then a minimally restrictive switching policy is designed. Next, an iterative algorithm is introduced for finding a minimal set of controllers for which a switching policy satisfying the switching constraints exists. It is shown that in the supervisory control problem considered in this paper, limitations on event observation are the factors that essentially restrict supervisory control. In other words, once observation limitations are respected, limitations on control will be automatically satisfied. This result is used to simplify the proposed iterative algorithm for finding minimal controller sets.     

Liveness Problem of Petri Nets Supervisory Control Theory for Discrete Event Systems

A quite great progress of the supervisory control theory for discrete event systems (DES) has been made in the past nearly twenty years, and now, automata, formal language and Petri nets become the main research tools. This paper focus on the Petri nets based supervisory control theory of DES. Firstly, we review the research results in this field, and claim that there generally exists a problem in Petri nets based supervisory control theory of DES, that is, the deadlock caused by the controller introduced to enforce the given specification occurs in the closed-loop systems, especially the deadlock occurs in the closed-loop system in which the original plant is live. Finally, a possible research direction is presented for the solution of this problem.     

Synthesis of supervisory controllers for hybrid systems based onapproximating automata

The paper concerns the synthesis of supervisory controllers for a class of continuous-time hybrid systems with discrete-valued input signals that select differential inclusions for continuous-valued state trajectories and event-valued output signals generated by threshold crossings in the continuous state space, the supervisor is allowed to switch the input signal value when threshold events are observed. The objective is to synthesize a nonblocking supervisor such that the set of possible sequences of control and threshold event pairs for the closed-loop system lies between given upper and lower bounds in the sense of set containment. We show how this problem can be converted into a supervisor synthesis problem for a standard controlled discrete-event system (DES). A finite representation may not exist for the exact DES model of the hybrid system, however. To circumvent this difficulty, we present an algorithm for constructing finite-state Muller automata that accept outer approximations to the exact controlled threshold-event language, and we demonstrate that supervisors that solve the synthesis problem for the approximating automata achieve the control specifications when applied to the original hybrid system     

Hierarchical control of aircraft propulsion systems: Discrete event supervisor approach

This paper presents an application of the recently developed theory of language-measure-based discrete event supervisory (DES) control to aircraft propulsion systems. A two-layer hierarchical architecture is proposed to coordinate the operations of a twin-engine propulsion system. The two engines are individually controlled to achieve enhanced performance and reliability, as necessary for fulfilling the mission objectives. Each engine, together with its continuously varying control system, is operated at the lower level under the supervision of a local discrete-event controller for condition monitoring and life extension; the gain-scheduled feedback controller that is used to maintain the specified performance of the turbofan engine is kept unaltered. A global DES controller at the upper level coordinates the local DES controllers for load balancing and health management of the propulsion system.