Adiwinata Gani

Isolation and handling of actuator faults in nonlinear systems

This work considers the problem of control actuator fault detection and isolation and fault-tolerant control for a multi-input multi-output nonlinear system subject to constraints on the manipulated inputs and proposes a fault detection and isolation filter and controller reconfiguration design. The implementation of the fault detection and isolation filters and reconfiguration strategy are demonstrated via a chemical process example.

A switched systems approach for the analysis and control of mode transitions in biological networks

This work presents a methodology for the analysis and control of mode transitions in biological networks. The proposed approach is predicated upon the notion of orchestrating switching between the domains of attraction of the steady-states of the constituent modes. Initially, the overall network is modeled as a switched nonlinear system that consists of multiple modes, each governed by a set of continuous-time differential equations. The transitions between the continuous modes are triggered by discrete events (changes in model parameters that correspond to alterations in physiological conditions). Then, following the characterization of the steady-state behavior of each mode, Lyapunov techniques are used to characterize the domains of attraction of the steady-states. Finally, by analyzing how the domains of attraction of the various modes overlap with one other, a switching rule is derived to determine when, and if, a given mode transition at a given time results in the desired steady-state behavior. The proposed approach has implications both for understanding the outcome of naturally-occurring mode transitions and for the ability to manipulate network behavior by enforcing mode transitions. The proposed approach is demonstrated using a model of a biological network that arises in the bacteriophage /spl lambda/-switch system.

Fault-Tolerant Control of Nonlinear Processes: Performance-Based Reconfiguration and Robustness

This work considers the problem of control system/actuator failures in nonlinear processes subject to input constraints and presents two approaches for fault-tolerant control that focus on incorporating performance and robustness considerations, respectively. In both approaches, first a family of candidate control configurations, characterized by different manipulated inputs, is identified for the process under consideration. Performance considerations are first incorporated via the design of a Lyapunov-based predictive controller that enforces closed-loop stability from an explicitly characterized set of initial conditions (computed using an auxiliary Lyapunov-based nonlinear controller). A hierarchical switching policy is derived, that uses stability considerations (evaluated via the presence of the state in the stability region of a control configuration) to ascertain the suitability of a candidate backup configuration and then performance considerations are again considered in choosing between the suitable backup configurations. Next, we consider the problem of implementing fault-tolerant control to nonlinear processes subject to input constraints and uncertainty. To this end, we first design a robust hybrid predictive controller for each candidate control configuration that guarantees stability from an explicitly characterized set of initial conditions, subject to uncertainty and constraints. A switching policy is then derived to orchestrate the activation/deactivation of the constituent control configurations

Fault-tolerant control of nonlinear systems: fault-detection and isolation and controller reconfiguration

This work considers the problem of implementing fault-tolerant control on a multi-input multi-output nonlinear system subject to multiple faults in the control actuators and constraints on the manipulated inputs. We design output-feedback fault-detection and isolation filters and output-feedback controllers via a combination of state-feedback fault-detection and isolation filters and controllers, and state estimators. The fault-detection and isolation filters essentially capture the difference between fault-free evolution of the system and the true evolution of the system to detect and isolate faults in the control actuators. The state estimates are used in devising the reconfiguration rule that determines which of the backup control configurations should be implemented in the closed-loop system. Specifically, a configuration is chosen that 1) does not use the failed control actuator, and 2) guarantees stability of the closed-loop system starting from the system state at the time of the failure (this is ascertained via the use of feedback controllers that provides an explicit characterization of the output-feedback stability region). The implementation of the fault-detection and isolation filters and reconfiguration strategy is demonstrated on a chemical reactor network example

Fault-Tolerant Control of Nonlinear Systems Subject to Sensor Data Losses

This work considers the problem of control of nonlinear process systems subject to input constraints and sensor faults (complete failure or intermittent unavailability of measurements). To clearly illustrate the importance of accounting for the presence of input constraints, we first consider the problem of sensor faults that necessitate sensor recovery to maintain closed-loop stability. We address the problem of determining, based on stability region characterizations for the candidate control configurations, which control configuration should be activated (reactivating the primary control configuration may not preserve stability) after the sensor is rectified. We then consider the problem of asynchronous measurements, i.e., of intermittent unavailability of measurements. To address this problem, the stability region (that is, the set of initial conditions starting from where closed-loop stabilization under continuous availability of measurements is guaranteed) as well as the maximum allowable data loss rate which preserves closed-loop stability for the primary and the candidate backup configurations are computed. This characterization is utilized in identifying the occurrence of a destabilizing sensor fault and in activating a suitable backup configuration that preserves closed-loop stability. The proposed method is illustrated using a chemical process example

Fault-tolerant control of a polyethylene reactor

This work focuses on fault-tolerant nonlinear control of a gas phase polyethylene reactor. Initially, a family of candidate control configurations, characterized by different manipulated inputs, are identified. For each control configuration, a bounded nonlinear feedback controller, that enforces asymptotic closed-loop stability in the presence of constraints, is designed, and the constrained stability region associated with it is explicitly characterized using Lyapunov-based tools. A switching policy is then derived, on the basis of the stability regions, to orchestrate the activation/deactivation of the constituent control configurations in a way that guarantees closed-loop stability in the event of control system faults. Closed-loop system simulations demonstrate the effectiveness of the fault-tolerant control strategy

Fault-Tolerant Control of Multi-Unit Process Systems Using Communication Networks 1

Abstract This work proposes a methodology for the design of fault-tolerant control systems for chemical plants with distributed interconnected processing units. Bringing together tools from Lyapunov-based non linear control and hybrid systems theory, the approach is based on a hierarchical architecture that integrates lower-level feedback control of the individual units with upper-level logic-based supervisory control over communication networks. The local control systems consist each of a family of control configurations connected, via a local communication network, to a local supervisor that orchestrates switching between them on the basis of the stability regions in the event of failures. The local supervisors communicate, through a plant-wide communication network, with a plant supervisor responsible for monitoring the different units and coordinating their responses in a way that minimizes the propagation of failure effects. The communication logic is designed to ensure efficient transmission of information between the units while respecting the inherent limitations in network resources. The proposed approach provides explicit guidelines for managing the various interplays between the tasks of feedback control, switching and communication. The efficacy of the proposed approach is demonstrated through a chemical process example.

Fault-Tolerant Control of Process Systems: Integrating Supervisory and Feedback Control Over Networks

Abstract This work proposes a methodology for the design of fault-tolerant control systems for nonlinear processes with actuator constraints. The proposed approach is predicated upon the idea of integrating supervisory and feedback control over networks. Initially, a family of candidate control configurations, characterized by different manipulated inputs, are identified. For each control configuration, a bounded nonlinear feedback controller, that enforces asymptotic closed-loop stability in the presence of constraints, is designed, and the constrained stability region associated with it is explicitly characterized. A switching policy is then derived, on the basis of the stability regions, to orchestrate the activation/deactivation of the constituent control configurations in a way that guarantees closed-loop stability in the event of control system failures. The switching laws are implemented by a higher-level supervisor that constantly monitors the process and communicates with the various control configurations over a network. The effects of delays in fault-detection, network communication and actuator activation are taken explicitly into account in executing the switching logic. The efficacy and implementation of the proposed approach are demonstrated through a chemical process example.

Control of a Polyethylene Reactor: Handling Sensor Faults

This work considers the problem of control of a gas phase polyethylene reactor subject to intermittent data losses. A fault-tolerant controller is designed that utilizes reconfiguration (switching to an alternate control configuration) in a way that accounts for the process nonlinearity, the presence of constraints and the occurrence of sensor faults. To this end, control configurations are first identified that can be utilized as backup configurations in the event that the primary control configuration is unable to stabilize the system (due to sensor faults). The stability properties of the control configurations, specifically, the set of initial conditions as well as the maximum allowable data loss rate that preserves stability, are explicitly characterized using Lyapunov-based tools. This characterization is utilized in identifying the occurrence of a destabilizing sensor fault in the polyethylene reactor and in preserving closed-loop stability via reconfiguration.

Integrated fault-detection and fault-tolerant control of process systems

Abstract This work considers the problem of fault-tolerant control of nonlinear processes with input constraints subject to control system/actuator failures, and presents and demonstrates an approach to fault-tolerant control predicated upon the idea of integrating fault-detection, feedback and supervisory control. Specifically, a nonlinear observer is initially designed to generate estimates of the states that are used to implement Lyapunov-based state feedback controllers and a fault-detection filter. The fault-detection filter uses the state estimates to compute the expected closed-loop behavior in the absence of faults, and detects the occurrence of faults by comparing the expected behavior of the process variables with the estimates. A switching policy is then derived to orchestrate the activation/deactivation of the constituent control configurations to achieve fault-tolerant control in the event that a failure is detected. Finally, simulation studies are presented to demonstrate the implementation and evaluate the effectiveness of the proposed fault-tolerant control scheme.