Uppsala, Sweden
Uppsala, Sweden
Time filter
Source Type

Rahm M.,Uppsala University | Bostrom C.,Uppsala University | Bostrom C.,Seabased | Svensson O.,Uppsala University | And 3 more authors.
IET Renewable Power Generation | Year: 2010

In this study, the design, construction, deployment and operation of an offshore underwater substation is discussed. The seabed placed substation interconnects three linear generator wave energy converters (WECs) at the Swedish Lysekil wave energy research site. The power from the WECs fluctuates because of their direct-driven topology. The generator voltage has varying electrical frequency and amplitude. To reduce the fluctuations, the individual voltages of the WECs are rectified and the power is added on a common DC-bus in the substation. The voltage is inverted, transformed and power is transmitted to an on-shore resistive load. The substation was retrieved on two occasions since the deployment in the spring of 2009. The functionality of the substation is validated by comparing voltage and current wave forms from Simulink with measured results from laboratory experiments. In addition, a sample of results from real offshore operation is illustrated and discussed. With a proportional-integral-derivative (PID)-regulator in the inverter control, the small fluctuations in the DC-bus voltage could be minimised. However, this would reduce the energy storage capability of the DC-link smoothing capacitors. © 2010 © The Institution of Engineering and Technology.

Hong Y.,Uppsala University | Eriksson M.,Seabased | Castellucci V.,Uppsala University | Bostrom C.,Uppsala University | And 2 more authors.
IET Renewable Power Generation | Year: 2016

Within the Lysekil wave energy research project at the Swedish west coast, more than ten Wave Energy Converters (WECs) prototypes have been developed and installed in an ocean based test site. Since 2006 various experiments have been conducted and the generated electricity was delivered to shore at a nearby island. While experiments are essential for the development of wave energy converters, theoretical studies and simulations are an important complement - not only in the search for advanced designs with higher efficiency, but also for improving the economic viability of the studied concepts. In this paper a WEC model is presented. The model consists of three subsystems: i) the hydrodynamic source, ii) the linear generator model, and iii) the electrical conversion system. After the validation with the experimental results at the research site, the generator model is connected to three passive load strategies - linear resistive load, passive rectification and resonance circuit. The paper focuses on analysing the operation of the model coupled with three load cases. The results prove that the WEC model correctly simulates the linear generator developed in the Lysekil Project. Moreover, the comparison among different load cases is made and discussed. The results gives an indication of the efficiency of energy production as well as the force ripples and resulting mechanical loads on the wave energy converters. © 2016 The Institution of Engineering and Technology.

Bostrom C.,Uppsala University | Ekergard B.,Uppsala University | Waters R.,Uppsala University | Waters R.,Seabased | And 2 more authors.
IEEE Journal of Oceanic Engineering | Year: 2013

This paper describes a linear direct driven generator used for wave energy utilization. The generator is placed on the seabed and connected to a buoy on the ocean surface. Due to the reciprocating motion of the translator, an electrical conversion system is needed between the wave energy converter (WEC) and the grid. Depending on how the conversion system is designed, the generator will be subjected to different loads. A novel conversion system is presented in this paper where the voltage from the WEC is rectified in a resonance circuit. Both simulations and experiments are performed on the circuit. The results from the simulations show that a higher power absorption and power production can be achieved with the resonance circuit compared to a WEC connected to a passive rectifier. A WEC, L9, developed by Uppsala University (Uppsala, Sweden) was used in the experiment. Significantly higher power absorption was obtained for L9 compared to power data from the first installed WEC, L1, at the Lysekil research site. © 1976-2012 IEEE.

Hong Y.,Uppsala University | Waters R.,Uppsala University | Waters R.,Seabased | Bostrom C.,Uppsala University | And 4 more authors.
Renewable and Sustainable Energy Reviews | Year: 2014

Renewable energy techniques are now gaining more and more attention as the years pass by, not only because of the threat of climate change but also, e.g. due to serious pollution problems in some countries and because the renewable energy technologies have matured and can be depended upon an increasing degree. The energy from ocean waves bares tremendous potential as a source of renewable energy, and the related technologies have continually been improved during the last decades. In this paper, different types of wave energy converters are classified by their mechanical structure and how they absorb energy from ocean waves. The paper presents a review of strategies for electrical control of wave energy converters as well as energy storage techniques. Strategies of electrical control are used to achieve a higher energy absorption, and they are also of interest because of the large variety among different strategies. Furthermore, the control strategies strongly affect the complexity of both the mechanical and the electrical system, thus not only impacting energy absorption but also robustness, survivability, maintenance requirements and thus in the end the cost of electricity from ocean waves. © 2013 The Authors.

Waters R.,Uppsala University | Waters R.,Seabased | Rahm M.,Uppsala University | Eriksson M.,Seabased | And 6 more authors.
IET Renewable Power Generation | Year: 2011

The ability of a wave energy converter to capture the energy of ocean waves has been studied in offshore experiments. This study covers 50 days during which the converter was subjected to ocean waves over a wide range of frequencies and amplitudes as well as three different electrical loads. The results present the wave energy converter's energy absorption as a function of significant wave height, energy period and electrical load. It is shown that the power generated overall continues to increase with wave amplitude, whereas the relative absorption decreases towards the highest periods and amplitudes. The absorption reached a maximum of approximately 24 with the used combination of buoy, generator and electrical load. Absorption to cover for iron and mechanical losses has not been included. A brief study of the nature of the electromagnetic damping force has also been included in the study. The wave energy converter is of the technology that is being researched at Uppsala University and experimented on off the Swedish west coast at the Lysekil wave energy research site. © 2011 The Institution of Engineering and Technology.

Seabased | Date: 2010-05-28

The invention relates to a stator frame (12) for a submerged linear generator. According to the invention the stator frame (12) includes a cylindrical tube of metal with mounting means (13, 14, 15, 16) for mounting stator packages to the inside wall of the tube. The stator frame (12) also is the external circumferential wall of the linear generator. The invention also relates to the use of such a stator frame (12) and to a method for manufacturing a linear generator with such a stator frame (12).

Seabased | Date: 2010-12-09

The invention relates to an electric device with a winding (12) and means for inducing a current in the winding. A bridge circuit (400) electrically connects the winding (12) to a load (13). According to the invention the bridge circuit (400) includes capacitor means (401, 402), which is adapted for obtaining resonance with the impedance of the winding (12)

The invention relates to a wave power unit with a floating body (1), a submerged station (2) and flexible connection means (3) connecting the floating body (1) to the submerged station (100). The submerged station (100) has a stator 5 (5) and a moving part (6). According to the invention the flexible connection means (3) is provided with a damper (12). The damper (12) is arranged to absorb tensile forces in the flexible connection means (3). The invention also relates to a use of such a wave power unit and to a 10 method for producing and supplying electric energy.

Engstrom J.,Uppsala University | Isberg J.,Uppsala University | Eriksson M.,Seabased | Leijon M.,Uppsala University
Journal of Renewable and Sustainable Energy | Year: 2012

The total instantaneous energy transport can be found for polychromatic waves when using the deep water approximation. Expanding this theory to waves in waters of finite depth, we derive an expression for the total instantaneous energy transport for polychromatic fluid gravity waves based on potential theory with linearized free surface boundary conditions. We present the results for time series of wave elevation measured at the Uppsala University wave energy research test site. We show that a significant proportion of the total instantaneous energy transport is not accounted for when using the deep water theory. This is important since many wave energy conversion devices under development will operate in waters that do not fulfil the deep water criteria. © 2012 American Institute of Physics.

Loading Seabased collaborators
Loading Seabased collaborators