Maximizing output power of linear generators for wave energy conversion

SUMMARY The aim of wave energy converters is to extract energy from ocean waves and turn it into electricity. Since the earliest developments, optimal control strategy has been considered the one that optimizes the power extracted from the oscillating system. This technique requires energy exchanges between the oscillating system and an auxiliary storage energy system, and has been shown to be potentially capable of substantially increasing the amount of energy absorbed. Nevertheless, it requires very efficient devices due to the huge losses, which occur when operating conditions are far from the natural frequency of the oscillating system. Moreover, this optimization criteria cause large heave excursions in the oscillating system and high peak-to-average power ratios of the system. In this paper, a point absorber converter that uses a linear direct-drive generator and power electronics converters jointly is considered. This article presents a novel method of control, which optimizes the power transferred from the generator to the power electronic converter considering the copper losses in the electric generator. This approach of the optimization method allows a significant increase in the wave energy converter's capacity of energy conversion. Applying the proposed control strategy, power exchanges between the oscillating system and the generator can be reduced, and in consequence, system efficiency significantly increases. In addition, the oscillating system's heave excursions and the peak-to-average power ratio decrease. The formulation of the proposed method is presented as well as numerical simulations in irregular waves. Copyright © 2013 John Wiley & Sons, Ltd.