Ride through of OWC-based wave power generation plant with air flow control under symmetrical voltage dips

The suitability of distributed power generation systems working at medium and high capacity as it is the case of wave power generation plants, requires a reliable Fault-Ride-Through capability. When a grid fault occurs on the transmission system, the speed of the turbo-generator group increases uncontrolled, the induction generator injects large peak currents that can potentially damage the rotor converters and the plant tends to increase the reactive power consumption, so that it might intensify the voltage dip and contribute to the collapse of the power network. A simple solution would be the automatic disconnection of the plant from the grid in response to the power fault, but this policy could lead to a series of chain disconnections that would produce a massive power network failure. This is why new Grid Codes oblige the distributed power generation systems to remain connected to the power network, even in case of balanced voltage dips. In this paper, an Oscillating Water Column (OWC)-based wave power generation plant equipped with a Doubly Fed Induction Generator is modeled and controlled to overcome these balanced grid faults. The improvement relays on the implementation of a control scheme that suitably coordinates the air flow control, the crowbar, the rotor and the grid side converters to allow the plant to remain in service during the grid fault, and to contribute to its attenuation by supplying reactive power to the network. The simulated results show how it is obtained a great reduction in the rotor currents, improving the transient power stability and avoiding the rotor acceleration, complying with new Grid Codes requirements.