ABSTRACT
Tidal energy is renewable and also highly predictable; however, access for maintenance operations on devices is limited and very expensive. The immense forces impacting on tidal current turbines (TCT) may cause component failures which have the potential to result in loss of power generation. Fault tolerant control offers the potential for the TCT to continue operating in the event of failures in components such as tidal velocity sensors. This paper presents a fault tolerant control methodology for maximum power point tracking in the event of a tidal velocity sensor failure with simulation results demonstrating the capability of the technique.
Renewable energy is making a greater contribution than ever in supplying global energy demand. Due to the predictability and capacity of the tidal currents, the position of tidal energy in the renewable energy mix has significantly increased with tidal current energy starting to make contribution (Benbouzid et al., 2011).
Tidal current turbines capture energy from tidal currents using technology which is very similar to the wind turbine capture of energy from moving air (Clarke et al., 2006). The water density is significantly higher than that of the air, so tidal current turbines operate at lower speeds but higher torques compared with wind turbines. In tidal current turbine systems, there is the potential for certain faults to cause failure of the whole system because the devices are subjected to large forces from strong tidal currents. Such failures would generally require retrieval of the device to carry out maintenance on shore but the time window to access a device is limited both by the weather and the tidal currents themselves (Sousounis et al., 2016). In order to reduce the maintenance time and increase the energy capture, fault tolerant control is essential in tidal current turbine systems.
Fig. 1 shows the percentage breakdown of failures that occurred during the period 2000-2004 in Swedish wind power plants, from this figure it can be seen that the sensor faults accounted for 14.1%, faults in electric systems 17.5% and faults in control system 12.9%. These are the most common faults that might occur in the electrical side of the system (Amirat et al., 2009). The electrical control system of a tidal current turbine is sufficiently similar to that of the wind turbine for the fault data of wind turbines to be considered as a reference for tidal current turbines.
