Concepts and methods in fault tolerant control with application to a wind turbine simulated system

Faults in automated processes will often cause undesired reactions and shutdown of a controlled plant, and the consequences could be damage to technical parts of the plant, to personnel or the environment. Fault tolerant control combines diagnosis withcontrolmethods to handle faults in an intelligentway. The aim is to prevent that simple faults develop into serious failure and hence increase plant availability and reduce the risk of safety hazards. Fault-tolerant control merges several disciplines into a common framework to achieve these goals. The desired features are obtained through online fault diagnosis, automatic condition assessment and calculation of appropriate remedial actions to avoid certain consequences of a fault. The envelope of the possible remedial actions is very wide. Sometimes, simple re–tuning can suffice. In other cases,accommodation of the fault could be achieved by replacing a measurement from a faulty sensor by an estimate. In yet other situations, complex reconfiguration or online controller redesign is required. This chapter gives an overview of well–established and more recent tools to analyse and explore structure and other fundamental properties of an automated system such that any inherent redundancy in the controlled process can be fully utilised to maintain availability, even though faults may occur. On the other hand, the effectiveness of the analysed solutions has been verified when applied to a wind turbine system. In fact, wind turbine plants are complex dynamic and uncertain processes driven by stochastic inputs and disturbances, as well as different loads represented by gyroscopic, centrifugal, and gravitational forces. Moreover, as their aerodynamic models are nonlinear, both modelling and control become challenging problems. On one hand, high–fidelity simulators should contain different parameters and variables in order to accurately describe the main dynamic system behaviour. Therefore, the development of fault tolerant control solutions for wind turbine systems should consider these complexity aspects. On the other hand, these solutions have to include the main wind turbine dynamic characteristics without becoming too complicated. The second point of this chapter is thus to provide practical examples of the development of robust fault tolerant control strategies when applied to a simulated wind turbine plant. Experiments with the wind turbine simulator represent the instruments for assessing the main aspects of the developed control methodologies.