Line Force and Damping at Full and Partial Stator Overlap in a Linear Generator for Wave Power

• Main Authors: Liselotte Ulvgård, Linnea Sjökvist, Malin Göteman, Mats Leijon
• Format: Article
• Language: English
• Published: MDPI AG 2016-11-01
• Series: Journal of Marine Science and Engineering
• Subjects: wave power; force measurement; line force; power take-off; damping
• Online Access: http://www.mdpi.com/2077-1312/4/4/81

A full scale linear generator for wave power has been experimentally evaluated by measuring the line force and translator position throughout the full translator stroke. The measured line force, in relation to translator speed, generator damping and stator overlap, has been studied by comparing the line force and the damping coefficient, γ , for multiple load cases along the translator stroke length. The study also compares the generator’s behavior during upward and downward motion, studies oscillations and determines the no load losses at two different speeds. The generator damping factor, γ , was determined for five different load cases during both upward and downward motion. The γ value was found to be constant for full stator overlap and to decrease linearly with a decreasing overlap, as the translator moved towards the endstops. The decline varied with the external load case, as previously suggested but not shown. In addition, during partial stator overlap, a higher γ value was noted as the translator was leaving the stator, compared to when it was entering the stator. Finally, new insights were gained regarding how translator weight and generator damping will affect the translator downward motion during offshore operation. This is important for power production and for avoiding damaging forces acting on the wave energy converter during operation.