EMD-based filter bank IEC standards T1-995 TA1-2040 Wave Hub augmented sliding mode observer control strategy control system current harmonic distortion design optimization direct drive direct-drive dynamic loading energy storage fault reconstruction fault-tolerant control flywheel flywheel energy storage system (FESS) horizontal-axis tidal turbine irregular waves marine current turbine modelling multibrid concept multiplicative fault detection ocean energy oscillating water column permanent magnet generator permanent magnet linear generator point absorber power quality