Jørgen Hals

Wave Prediction and Robust Control of Heaving Wave Energy Devices for Irregular Waves

This paper presents a comparison of different existing and proposed wave prediction models applicable to control wave energy converters (WECs) in irregular waves. The objective of the control is to increase the energy conversion. The power absorbed by a WEC is depending on the implemented control strategy. Uncertainties in the physical description of the system as well as in the input from irregular waves provide challenges to the control algorithm. We present a hybrid robust fuzzy logic (FL) controller that addresses the uncertainty in the model and the short-term tuning of the converter. The proposed robust controller uses the energy from the power take off as input, while the FL controller portion is used for short-term tuning. The FL controller action is based on a prediction of the incoming wave. Simulation results indicate that the proposed hybrid control yields improved energy production, while being robust to modeling errors.

Power electronics as grid interface for actively controlled wave energy converters

Off the coasts of Europe, the potential for power generation from offshore renewable energy is huge and the technology for offshore wind power is already becoming available. Achievement of a cost-effective technology is the main concern for commercial development of wave energy converters (WEC). It is widely recognized that some kind of active control of the primary conversion is needed in order to increase the electricity production and hence improve the economical payback. Moreover, if high penetration levels are going to be reached with offshore renewables, barriers to interconnection will be encountered. These barriers need to be identified and the technologies that will mitigate the impacts on the power system stability need to be investigated. Power electronics will be the enabling interface that will permit wave farms to act as one large power plant. This paper presents known approaches for maximizing production from wave power through active control, and discusses how these can be implemented by power electronics controllers used as interface with the power network. Three alternatives of power electronics interface are presented through three case studies for active control of WEC, power conditioning, and stability. Simulation results indicate the role of the power electronic interfaces in the active control of the wave energy converters and in network interactions.

Wave prediction and fuzzy logic control of wave energy converters in irregular waves

This paper presents a short comparison of different existing and proposed wave prediction models, which in turn are used to control wave energy converters (WEC) in irregular waves. The objective of the control action is to increase the energy conversion. The prediction models are compared based on the contribution to the prediction of the individual filter weights, in an effort to reduce the filter order. The controller is based on adjusting the short term stiffness and damping of the power take off (PTO) of the WEC. The control action, which is a fuzzy logic (FL) based design, is supported by utilizing nominal damping and stiffness values determined for the given sea state and instantaneous wave using a simple genetic algorithm (GA). The WEC chosen is comprised of a spherical buoy and is modeled using the bond-graph technique. The simulation carried out indicates the proposed algorithm increases the energy conversion of WEC in irregular waves compared to the no control case.

Robust control of heaving wave energy devices in irregular waves

The power absorbed by a wave energy device is depending on the implemented control strategy. Uncertainties in the physical description of the system as well as in the input from irregular waves provide challenges to the control algorithm. In this paper we present a hybrid robust-fuzzy logic controller that allows for addressing the uncertainty in the model as well as the short term tuning of the converter. The converter is comprised of a spherical heaving buoy with a fixed reference, which could be the bottom or a body at rest. The proposed robust controller uses the energy from the Power Take Off (PTO) as input while the Fuzzy Logic (FL) controller portion is used to tune for the short term wave variation. The FL controller action is based on a prediction of the future incoming irregular wave. Simulation results indicate that the proposed hybrid control yields improved energy production, while being robust to modeling errors.

Power Absorption Measures and Comparisons of Selected Wave Energy Converters

In this study, a selection of Wave Energy Converters (WECs) with different working principle is considered. It comprises a heaving device reacting against the seabed, a heaving self-reacting two-bodies device, a pitching device, and a floating OWC device. They are inspired by concepts which are currently under development. For each of these concepts, a numerical Wave To Wire (W2W) model is derived. Numerical estimates of the energy delivery which one can expect are derived using these numerical models on a selection of wave site along the European coast. This selection of wave site is thought to be representative with levels of mean annual wave power from 15 to 88 kW/m. Using these results, the performance of each WEC is assessed not only in terms of yearly energy output, but also in terms of yearly absorbed energy/displacement, yearly absorbed energy/wetted surface, and yearly absorbed energy per unit significant Power Take Off force. By comparing these criteria, one gets a better idea of the advantages and drawbacks of each of the studied concepts.Copyright