Dongik Lee

Nonlinear sliding mode high-gain observers for fault estimation

A robust high gain observer for state and unknown inputs/faults estimations for a special class of nonlinear systems is developed in this article. Ensuring the observability of the faults/unknown inputs with respect to the outputs, the faults can be estimated from the sliding surface. Under a Lipschitz condition for the nonlinear part, the high gain observers are designed under some regularity assumptions. In the sliding mode, the convergence of the estimation error dynamics is proven similar to the analysis of high-gain observers.

PID control for a distributed system with a smart actuator

Abstract The emergence of distributed architectures based on smart components and fieldbus networks is promoting changes in proportional-integral-derivative (PID) controller design issues. This paper explores how PID control can benefit from smart actuator and fieldbus technologies. Firstly, this paper discusses a smart actuator scheme to improve the efficiency of PID controller retuning, as well as an implementation using a low-cost stepper-motor. Then, the smart actuator is applied to on-line adaptation of PID parameters using a standard pole-placement design method. Finally, experimental validation of the proposed approach is conducted using a controller area network (CAN) bus-based distributed architecture demonstrator.

Sliding mode high-gain observers for a class of uncertain nonlinear systems

Abstract A robust high-gain observer for state and unknown input estimations for a special class of single-output nonlinear systems is developed in this article. Ensuring the observability of the unknown input with respect to the output, the disturbance can be estimated from the sliding surface. In the sliding mode, the convergence of the estimation error dynamics is proven similar to the analysis of high-gain observers.

A CANbus-based safety-critical distributed aeroengine control systems architecture demonstrator

Abstract Recent advances in microelectronics coupled with ever decreasing costs mean that it is now possible to produce very compact and cheap intelligent modules. For instance, it is now quite common for cars to use a number of intelligent units with intercommunication to implement complex functions such as traction control. There has also been a move towards embedding processing in sensors and actuators directly with application to the process control, automotive and aerospace sectors. When considering aerospace applications there are major benefits to be gained by adopting a distributed controller. However, this has to be carried out within the strict design constraints for safety-critical systems. This paper discusses design tools and a distributed system demonstrator that has been developed to explore future distributed control systems.

Rotor Speed-Based Bearing Fault Diagnosis (RSB-BFD) Under Variable Speed and Constant Load

This paper addresses the application of rotor speed signal for the detection and diagnosis of ball bearing faults in rotating electrical machines. Many existing techniques for bearing fault diagnosis (BFD) rely on vibration signals or current signals. However, vibration- or current-based BFD techniques suffer from various challenges that must be addressed. As an alternative, this paper takes the initial step of investigating the efficiency of rotor speed monitoring for BFD. The bearing failure modes are reviewed and their effects on the rotor speed signal are described. Based on this analysis, a novel BFD technique, the rotor speed-based BFD (RSB-BFD) method under variable speed and constant load conditions, is proposed to provide a benefit in terms of cost and simplicity. The proposed RSB-BFD method exploits the absolute value-based principal component analysis (PCA), which improves the performance of classical PCA by using the absolute value of weights and the sum square error. The performance and effectiveness of the RSB-BFD method is demonstrated using an experimental setup with a set of realistic bearing faults in the outer race, inner race, and balls.

Improving driver's visual field using estimation of curvature

When driving at night, it is difficult to detect obstacles such as pedestrian and wild animals on the opposite lane which is out of sight. Adaptive front lighting system (AFS) can be used to avoid accidents with obstacles that are difficult to detect with a conventional lighting system. The basic concept of AFS is to collect the information such as vehicle speed, yaw rate, steering angle, suspension height and driving mode from vehicle sensors. This information is applied to calculate an optimal angle of irradiation and used to change beam pattern and position according to the current radius of curvature. However, the driver may have to turn quickly on a sharp curve, in which the optimal angle of irradiation cannot be achieved before entering the opposite lane because swivel mode on AFS reacts based on the current radius of curvature. This paper presents a method to improve drivers visual field by using the pre-calculated curvature information on the road ahead. The effectiveness of the proposed method is evaluated with a set of experiments in the real environment.

Priority-based scheduling of dynamic segment in FlexRay network

FlexRay is an in-vehicle communication network for safety-critical automotive applications such as network-based braking or steering systems. The FlexRay protocol offers various benefits over the existing in-vehicle networks by using a hybrid approach integrating the static segment and the dynamic segment. While the static segment is based on time division multiple access (TDMA) to achieve deterministic behavior, the dynamic segment adopts so-called flexible TDMA (FTDMA) to achieve flexible and efficient use of the network. Therefore, scheduling of the dynamic segment in an optimal manner is critical for designing an efficient FlexRay-based system. This paper presents a scheduling method, named recursive qualification (RQ), for the dynamic segment in FlexRay. The proposed method is based on the multiple-slot assignment so that the dynamic segment can be used to efficiently transmit the messages with bounded delays. An index of bus accessibility (BA) is also adopted to determine the priority of each node. The effectiveness of the proposed method is verified through a set of experiments.

Fault-tolerant control strategy based on control allocation using smart actuators

This paper presents a networked fault-tolerant control strategy based on control allocation which is applied to a modern aircraft. The proposed method utilizes the benefits of networked control system architecture in which smart sensors/actuators are interconnected through a bi-directional digital communication network. A smart actuator, the paper focuses on, is capable of providing the supervisor level with various information on the device itself. This information on the device condition is then used to tolerate faulty actuators by re-allocating redundant actuators. Simulation results with an aircraft show that the proposed method can achieve a fast and effective compensation in the presence of actuator faults.

PID Control for a Distributed System with a Smart Actuator

Abstract Recent advances in smart actuator and fieldbus technologies are promoting changes in PID controller design issues. By employing a built-in microprocessor a smart actuator, in general, is capable of self-validation and compensation. In this paper, online retuning of PID controller for a distributed system that contains a smart actuator is explored. The on-line controller retuning is carried out using a set of validation data generated by a smart actuator. The proposed approach is investigated by means of a distributed architecture demonstrator which consists of a set of PCs and a stepper-motor based smart actuator interconnected through fieldbus network.

A concurrency characteristic in Petri net unfolding

Unfolding, originally introduced by McMillan (1995), is gaining ground as a partial-order based method for the verification of concurrent systems without state-space explosion. However, it can be exposed to redundancy, which may increase its size exponentially. So far, there have been trials to reduce such redundancy resulting from conflicts by improving McMillans cut-off criterion. In this paper, we show that concurrency is also another cause of redundancy in unfolding, and we present an algorithm to reduce such redundancy in live, bounded and reversible Petri nets, which is independent of any cut-off algorithm.