Tidal stream turbine fault-tolerant control

This chapter presented fault tolerance strategies in the context of marine current turbine. FTC system allows tolerating faults in the MCT while maintaining system stability with low or no performance degradation. In MCT, fault resilience can be implemented at design stage by using polyphase generators, redundant legs power converters, redundant sensors, cables, embedded control systems, and communication networks. Moreover, fault-tolerant control approaches can be implemented with no additional hardware usage. Two approaches have been reviewed and pros and cons discussed: active and passive FTC. Some studies propose the use of hybrid FTC allowing to take advantage the two previously presented methods at the expense of higher complexity and higher computational cost.A robust fault-resilient control approach for a tidal turbine system experiencing permanent magnets demagnetization case study has been presented. In this context, the magnetic equivalent circuit method has been used for magnet failures modeling in a synchronous generator. The preliminary simulation results have illustrated the tidal turbine power generation and dynamic performances high level of degradation when using conventional PI controllers. Therefore, high-order sliding modes have been used for resilience purposes, while maintaining the tidal turbine optimal power and dynamic performances. Simulations that were carried out with real tidal velocities at the Raz de Sein site in France have clearly shown the second-order sliding mode control advantages and superiority in terms of magnet failure resilience.A second case study has been presented, which considers FTC strategies for sensors-faults resilience. Flow-meter and generator rotational speed/position transducers failures have been investigated. Extensive simulations have been carried out on a direct-drive fixed-pitch marine current turbine based on permanent magnets synchronous generators. The FTC strategies have been assessed in terms of energy conversion efficiency, torque ripples, robustness against parameters uncertainty, and computational cost. Regarding, flow-meter sensors fault, simulation results show that turbine parameters-based FTC strategies outperform the other techniques in terms of response time, reduced torque ripples, and energy conversion efficiency. However, their accuracy depends on the turbine parameters knowledge. In the case of rotational speed/position speed fault, EKF-based methods achieve better performance but their implementation in real-world applications is highly constrained by their higher computational burden.All case studies presented within this chapter could be used as guidelines by industrial and researchers in academia for the choice of the most appropriate fault-tolerant strategy in the marine current turbines context and beyond. Indeed, these approaches could be generalized to all power conversion systems in electrical energy production based on renewables, its conversion, distribution, and consumption. It is worth to mention that the choice of the adapted strategy for fault-resilience is not an easy task and various FTC methods could be appropriate depending the context and the constraints of the energy conversion system.