Evaluating Constant DC-Link Operation of Wave Energy Converter

Abstract

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.

Optimal Constant DC Link Voltage Operation of a Wave Energy Converter

“…The simulation has to be performed in time-domain for handling the non-linear system effects, like the electric rectification, the translator hitting the end-stops of the generator and the flexible wire connection between the buoy and the translator. The system model is based on MatLAB Simulink, and has been verified with experimental results in e.g., [15,16]. The model constitutes of four major subsystem blocks.…”

Grid Connection of Wave Power Farm Using an N-Level Cascaded H-Bridge Multilevel Inverter

“…Considering the small-scale nature of the WECs, a simpler strategy may be advantageous. In [8], passive rectification onto a constant DC-bus is evaluated, where the optimal DC-voltage is a function of the sea state.…”

Control of offshore marine substation for grid-connection of a wave power farm

“…Ekström, R., Leijon, M. (2014) Control of offshore marine substation for grid-connection of a wave power farm. …”

“…For WECs with a more modest power output, a simpler strategy may be advantageous. In [28,15], passive rectification onto a constant DC-bus is evaluated, where the optimal DC-voltage is a function of the sea state. Since the DC-bus is common for all the WECs, the WEC control strategy becomes very simple, and is allocated to the grid-side control of the marine substation.…”

“…This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the original published paper (version of record):Ekström, R., Leijon, M. (2014) Control of offshore marine substation for grid-connection of a wave power farm. …”