Oskar Danielsson

Experimental results from sea trials of an offshore wave energy system

A full-scale prototype of a wave power plant has been installed off the Swedish west coast and the overall wave energy converter concept has been verified. Initial results have been collected and s ...

Catch the wave to electricity

The ocean are largely an untapped source of energy. However, compared to other energies, power fluctuations for ocean waves are small over longer periods of time. This paper present a grid-oriented approach to electricity production from ocean waves, utilizing a minimal amount of mechanical components.

Detailed study of the magnetic circuit in a longitudinal flux permanent-magnet synchronous linear generator

We present the results of a theoretical study of the magnetic circuit of a longitudinal flux permanent-magnet synchronous linear generator. In our study, we used a coupled field and circuit model solved by a time-stepping finite-element technique to analyze the machine. We investigated the effects of different permanent-magnet shapes and sizes, as well as different stator steel geometries. We noted a significant difference in performance for different magnet shapes. Our results also illustrate how small changes, on a millimeter scale, will affect the flux path, and thereby the overall performance of the machine, highlighting the importance of stator steel geometry.

Electromagnetic forces in the air gap of a permanent magnet linear generator at no load

The basis for the work is the slow speed energy conversion of ocean wave energy into electricity using a direct-drive three-phase permanent magnetized linear generator. One of several important issues is the normal forces in the air gap, which is critical when designing the support structure of the generator. The electromagnetic forces in the air gap have been analyzed using Maxwell stress tensor method implemented in a two- dimensional finite element code. Simplified analytic calculations are made in order to validate the results from the extensive computer calculations. The normal electromagnetic forces in the air gap, Fδ, are analyzed for a two-sided linear generator at no load. An unstable condition of the global force on the piston occurs due to the fast increasing normal force as the air gap width decreases. A horizontal displacement of the piston from a neutral position with 3mm air gap on both sides produces a resulting horizontal force on the piston, increasing with the displacement. A displacement of 1mm gives a resulting horizontal force on the piston of 5.5kN per pole and meter of core length, which is increased to 9kN per pole and meter of core length for a displacement of 1.5mm. Furthermore, the normal force varies due to cogging as the piston moves vertically. At a constant air gap width of 3mm the normal forces per pole are varying between 9.9 and 11.3kN∕m of core length as the piston is moving from one pole to the next.The basis for the work is the slow speed energy conversion of ocean wave energy into electricity using a direct-drive three-phase permanent magnetized linear generator. One of several important issues is the normal forces in the air gap, which is critical when designing the support structure of the generator. The electromagnetic forces in the air gap have been analyzed using Maxwell stress tensor method implemented in a two- dimensional finite element code. Simplified analytic calculations are made in order to validate the results from the extensive computer calculations. The normal electromagnetic forces in the air gap, Fδ, are analyzed for a two-sided linear generator at no load. An unstable condition of the global force on the piston occurs due to the fast increasing normal force as the air gap width decreases. A horizontal displacement of the piston from a neutral position with 3mm air gap on both sides produces a resulting horizontal force on the piston, increasing with the displacement. A displaceme...

A direct drive wave energy converter : Simulations and experiments

A novel wave energy converter concept is developed at Uppsala University, Department of Engineering Science. The concept is based on a synchronous permanent magnet linear generator, placed on the seabed. The piston of the generator is directly connected to a surface-floating buoy with a rope. The tension in the rope is maintained with springs that pull the piston downward. The three-phase current induced in the stator coil has a varying amplitude and frequency and a conversion is therefore necessary. Research has been carried out in three main areas: generator design, dynamic behavior and grid connection. The generator is modeled by full physics numeric simulations, based on a 2-dimensional finite element formulation of the time dependent electromagnetic field. A first set up is built to experimentally verify the simulated results. The impact of different parameters are estimated with mathematical models and verified by experiments. This paper includes both simulated and experimental results.Copyright

Measuring air gap width of permanent magnet linear generators using search coil sensor

A concept for a wave power plant is being developed at the Centre for Renewable Electric Energy Conversion at the A˚ngstrom Laboratory at Uppsala University. The concept is based on a permanent mag ...

Influence of Generator Damping on Peak Power and Variance of Power for a Direct Drive Wave Energy Converter

The first full-scale offshore prototype of a novel wave energy converter system has been launched off the Swedish west coast. The concept is based on a point absorber directly coupled to a linear generator located on the ocean floor. The wave energy converter is part of a research project that will study the electrical system of 10 units forming a small farm of wave power plants as they are linked and connected to an electric grid. A full scale farm will consist of a large number of interconnected units. The chosen direct drive system reduces the mechanical complexity of the converter but has repercussions on the electrical system. The output from the generator will vary with the speed of the point absorber, leading to large fluctuations of power on the second scale. This has implications on both the individual generator and on the system as a whole. The hydrodynamic behavior of the point absorber depends, to a large extent, on the damping of the generator. The damping, in turn, can be controlled remotely by changing the load resistance. It has previously been shown that this has a large influence on the power absorbed by the wave energy converter. This paper investigates the peak power, the translator speed and the variance of the power at different sea states and for different levels of damping. The peak power has an impact on the design of the generator and the required ability, for a single unit, to handle electrical overloads. The speed of the translator is directly proportional to its momentum. It is thus important for the design of the end stop. The variance of the power of one unit will have an impact on the farm system behavior. The study is based on two and a half months of experimental measurements on the prototype wave energy converter and a wave measurement buoy. The aim is to analyze whether load control strategies may influence the dimensioning criteria for the electrical system and the generator. The results are compared with previously investigated relationships between absorbed mean power and load resistance as a function of sea state. In the study it was found that the maximum power is approximately proportional to the average power while maximum translator speed and standard deviation decrease as the damping factor is increased.© 2007 ASME