Modeling and control strategy of an oscillating water column-wave energy converter with an impulse turbine module

The global energy demand requires alternative resource from the fossil fuels and nuclear fission. Ocean energy should take in charge of a key role in renewable energy due to the high density and vast amount of its energy in the near future. In particular, an oscillating water column-wave energy converter (OWC-WEC) is one of the most promising devices to capture energy from the ocean waves. This kind of devices consists of a capture chamber, power take off (PTO) module such as a Wells turbine or an impulse turbine, and a generator. An overall efficiency of this device is determined by the efficiency of each component: wave to pneumatic conversion in the capture chamber, pneumatic to mechanical conversion in the PTO, and mechanical to electrical conversion in the generator. Among them, the second stage has a high nonlinearity which is a function of flow coefficient. In order to achieve the good performance, the PTO module should been operated with an optimal flow coefficient. Meanwhile, considering the grid connection, it is also important that the device provides a constant voltage. Since the induced voltage of the generator is proportional to rotor angular speed, a controller for the constant angular speed is also required.