Evaluating Constant DC-Link Operation of Wave Energy Converter

A Wave Energy Converter (WEC) based on a linear generator and a point-absorbing buoy has been developed at Uppsala University. Interconnecting an array of WECs in parallel requires a point of common coupling, such as a common DC-bus. The DC voltage level seen by the generator is directly linked to the electromagnetic damping of the generator. A lower DC-level results in a higher damping factor and is important for increased absorption of the wave power. The drawback is increased losses in generator windings and cable resistance. There will be an optimal DC-level for maximum power output. This is a function of not only generator and buoy characteristics, but the current sea state. Experimental results of the full-scale system have been carried out, and used as validation of a simulation model of the system. The model is then used to evaluate how the DC-level seen by the generator influence the power output. The results indicate that higher DC-levels should be used at higher sea states, and power output may vary by up to a factor five depending on which DC-level is chosen.