A control system to improve the efficiency of wave energy converters

September 18, 2018, University of the Basque Country
Credit: CC0 Public Domain

Interest in wave energy has been growing in recent years, and electric generators specially designed to generate electricity from this renewable energy source are being developed. The UPV/EHU's Advanced Control Group (GCA) has come up with a robust control system for these generators which, during the tests conducted, has been shown to substantially improve their efficiency.

The Advanced Control group of the Faculty of Engineering—Vitoria-Gasteiz (EIVG) and the UPV/EHU's EIG-Faculty of Engineering—Gipuzkoa (Eibar section), which specialises in the of electric machines, has come up with a robust control system for one of the most popular converters, the oscillating water column (OWC), together with a doubly-fed induction . "Electrical generators of this type are suited to working at variable speeds, and at the same time, what the control system we have proposed achieves is to improve the efficiency of these generators by controlling the rotational speed of the turbine, given that this speed affects the efficiency of the process to extract kinetic from the waves," explained Oscar Barambones, one of the researchers who participated in this study, which was recently published by the journal Ocean Energy.

Doubly-fed induction generators (DFIGs) are regarded as highly suitable for generating energy that comes from wave energy because they are specially designed to work under changing, unpredictable conditions. "The airflow generated by the waves that they are going to have to work with will never be known, but in these converters, the electricity generator has the capacity to control the working speed so that the system can work at its optimum speed, irrespective of the speed of the airflow received by the turbine," said the researcher.

In the study, they wanted to see whether the performance of the converter could be improved by adding to it a sliding mode control system, which is characterised by displaying correct behaviour even in changing dynamics, variable parameters and external disturbances. "What we did was to see what the effect would be if this control system were to be incorporated, firstly by means of various simulations, and secondly in some experimental tests carried out on an experimental platform that the research group designed and built at the EIG (Eibar). This is based on an actual commercial doubly-fed generator; we connected the generator to a motor, and that motor simulated the mechanical energy profile provided by the airflow that would be produced by the waves in a wave energy generation plant."

As Barambones explained, the tests conducted showed that the efficiency of the wave energy converters "was greatly improved: the control system maximises the extraction of energy from the waves, because what it does is to regulate the speed of the turbine so that the system operates with maximum efficiency. The performance of these systems is optimized when the generator is made to follow a reference which depends on the speed of the airflow so that the turbine can operate at the maximum point of efficiency." And given that they were carried out using a commercial converter, "the control system could be applied right away."

But the researcher is aware that difficulties could emerge when this control system is applied under real conditions. The main problem he believes could emerge has to do "with the inertia of the turbines. We have not worked with very large inertia, but one can assume that an actual turbine would have a considerably bigger mass and therefore, a higher inertia. And we have seen that the greater the inertia is, the more difficult it would be for the system to follow the optimum reference with increased precision, although in any case an improvement in the of the system will be achieved by controlling the speed of the . We will continue to conduct studies in this respect," he concluded.

Explore further: Electronic control to ensure photovoltaic systems always work at maximum power

More information: Oscar Barambones et al. A real time sliding mode control for a wave energy converter based on a wells turbine, Ocean Engineering (2018). DOI: 10.1016/j.oceaneng.2018.05.058

Related Stories

The wave power farm off Mutriku could improve its efficiency

December 29, 2017

The study by the UPV/EHU's EOLO (Meteorology, Climate and Environment) research group reveals that the technology used at the farm off Mutriku—a global pioneer in generating wave power—needs to improve its output to be ...

Wind turbines that learn like humans

March 27, 2012

Depending on the weather, wind turbines can face whispering breezes or gale-force gusts. Such variable conditions make extracting the maximum power from the turbines a tricky control problem, but a collaboration of Chinese ...

Recommended for you

Solid-state catalysis: Fluctuations clear the way

February 18, 2019

The use of efficient catalytic agents is what makes many technical procedures feasible in the first place. Indeed, synthesis of more than 80 percent of the products generated in the chemical industry requires the input of ...

Engineered metasurfaces reflect waves in unusual directions

February 18, 2019

In our daily lives, we can find many examples of manipulation of reflected waves, such as mirrors, or reflective surfaces for sound that improve auditorium acoustics. When a wave impinges on a reflective surface with a certain ...

Design principles for peroxidase-mimicking nanozymes

February 18, 2019

Nanozymes, enzyme-like catalytic nanomaterials, are considered to be the next generation of enzyme mimics because they not only overcome natural enzymes' intrinsic limitations, but also possess unique properties in comparison ...

Sound waves let quantum systems 'talk' to one another

February 18, 2019

Researchers at the University of Chicago and Argonne National Laboratory have invented an innovative way for different types of quantum technology to "talk" to each other using sound. The study, published Feb. 11 in Nature ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.