Performance In Presence Of Faults Research Articles

Fault tolerance evaluation of model-free controllers with application to unmanned aerial vehicles

Although important improvements in the area of robust control of nonlinear systems have been presented in the literature, most of the developed controllers suffer from complexity and large dependency on accurate mathematical formulation of the models. Recently, model-free robust control techniques were introduced and have shown good performance when applied to multi-input–multi-output systems. The model-free approach is characterized by the nonuse of any prior knowledge about the underlying structure and/or associated parameters of the dynamical system. Therefore, the major criteria for assessing the effectiveness of these controllers are related to their ability to handle unknown inputs and disturbances, as well as achieving the desired tracking performance in presence of faults and malfunctions. This work considers the development of robust fault-tolerant controllers based on the model-free approach and their application to multirotor unmanned aerial vehicles’ (UAVs) systems. The different controllers based on intelligent proportional-derivative (iPD), intelligent backstepping (iBackstepping), and adaptive control are compared in terms of performance, ease of implementation and parameters tuning. The simulated results, tested on Matlab/Simulink on a full nonlinear model of a hexarotor UAV, validate the theoretical advantages of the adaptive approach with respect to multiple criteria such as improved tracking performance in case of existence of actuators faults when compared to the iPD and iBackstepping control methods at the cost of increased complexity.

Aging Resilience and Fault Tolerance in Runtime Reconfigurable Architectures

Runtime reconfigurable architectures based on Field-Programmable Gate Arrays (FPGAs) allow areaand power-efficient acceleration of complex applications. However, being manufactured in latest semiconductor process technologies, FPGAs are increasingly prone to aging effects, which reduce the reliability and lifetime of such systems. Aging mitigation and fault tolerance techniques for the reconfigurable fabric become essential to realize dependable reconfigurable architectures. This article presents an accelerator diversification method that creates multiple configurations for runtime reconfigurable accelerators that are diversified in their usage of Configurable Logic Blocks (CLBs). In particular, it creates a minimal number of configurations such that all single-CLB and some multi-CLB faults can be tolerated. For each fault we ensure that there is at least one configuration that does not use that CLB. Second, a novel runtime accelerator placement algorithm is presented that exploits the diversity in resource usage of these configurations to balance the stress imposed by executions of the accelerators on the reconfigurable fabric. By tracking the stress due to accelerator usage at runtime, the stress is balanced both within a reconfigurable region as well as over all reconfigurable regions of the system. The accelerator placement algorithm also considers faulty CLBs in the regions and selects the appropriate configuration such that the system maintains a high performance in presence of multiple permanent faults. Experimental results demonstrate that our methods deliver up to 3.7× higher performance in presence of faults at marginal runtime costs and 1.6× higher MTTF than state-ofthe-art aging mitigation methods.

Reconfigurable Direct Torque and Flux Control with Torque Ripple Reduction

AbstractThis work presents a reconfigurable direct torque and flux control strategy which guarantees good performance in presence of faults in the actuator, the voltage source inverter. It is based on a new quantification of the stator flux vector position means a new definition of sectors on the ab-plane. The main outcome of this quantification, which takes into account the fact that the voltage vectors available at the output of the faulty inverter have different magnitudes than those of the healthy inverter, is a switching table producing less torque ripple than the table based on the standard sector definition.Simulations results are presented that demonstrate the continuous operation of the system after the occurrence of a fault as well as its good dynamic response. A frequency analysis shows the torque ripple reduction.