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Offshore Measurement System for WavePower: Using Current Loop Feedback
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0001-6870-6729
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2016 (English)In: Electronics, ISSN 2079-9292, Vol. 5, no 4, article id 86Article in journal (Refereed) Published
Abstract [en]

This paper presents the design and testing of a measurement system for wave powergenerators. The work is part of a project to build a robust and cheap measurement system for offshoremonitoring of wave power farms. Due to the harsh offshore environment, low accessibility andhigh cost for installation and maintenance, it is of key importance to minimize power consumption,complexity and cost of each measurement unit. For the first prototype, the objective was to measurevoltage, current and translator position inside the linear wave power generator. For this, twoprinted circuit boards (PCBs) were developed, using a two wire current loop transmitter setup.They were tested separately and in a three phase setup inside a wave power generator duringonshore tests. To ensure stability, speed and accuracy in the signal transfer, the PCBs were tested forlinearity, frequency response and step response. In addition, power consumption was measured,for operational time evaluation. Results show good agreement between expected and measuredperformance, with an input range of ±1560 V and ±420 A for alternating current measurements anda bandwidth of 10 kHz and 7 kHz, for voltage and current measurements, respectively. The powerconsumption was measured to 0.5 W for each measurement unit, at 24 V feed.

Place, publisher, year, edition, pages
2016. Vol. 5, no 4, article id 86
Keywords [en]
wave power; conditional monitoring; PCB; current loop; measurement system
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-313258DOI: 10.3390/electronics5040086ISI: 000392387600008OAI: oai:DiVA.org:uu-313258DiVA, id: diva2:1066439
Available from: 2017-01-18 Created: 2017-01-18 Last updated: 2017-10-08Bibliographically approved
In thesis
1. Wave Energy Converters: An experimental approach to onshore testing, deployments and offshore monitoring
Open this publication in new window or tab >>Wave Energy Converters: An experimental approach to onshore testing, deployments and offshore monitoring
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The wave energy converter (WEC) concept developed at Uppsala University consists of a point absorbing buoy, directly connected to a permanent magnet linear generator. Since 2006, over a dozen full scale WECs have been deployed at the Lysekil Research Site, on the west coast of Sweden. Beyond the development of the WEC concept itself, the full scale approach enables, and requires, experimental and multidisciplinary research within several peripheral areas, such as instrumentation, offshore operations, and wave power infrastructure.

This thesis addresses technical challenges of testing, deploying and monitoring full scale WECs. It is divided accordingly into three topics: offshore measurement systems, onshore WEC testing and deployments. Each topic presents new or improved technical solutions to enable offshore wave power research.

For the offshore measurement systems, a new portable data acquisition unit was developed, together with a new sensor system to be installed inside the WEC. The developed system offers a cheap and flexible option for short term offshore measurement ventures, when or where site infrastructure is not available. The system has been developed and tested during both onshore and offshore experiments, with promising results.

On the topic of onshore WEC testing, the thesis presents an experimental approach for assessing the power take-off (PTO) damping of the WEC. In previous experimental studies, it has been measured via the generated electrical power, which neglects both mechanical losses and iron losses. Consequently, the full PTO force acting on the WEC has been underestimated. The thesis presents experimentally attained trends for the speed dependence of the PTO damping at different resistive loads, as measured from both generated electric power and from measurements of the buoy line force. A study was also performed on how the generator damping is affected by partial stator overlap, which varies with the translator position. In order to assess how the characterized damping behavior will affect the WEC operation at sea, two simulation case studies were performed.

Finally, the thesis presents a new WEC deployment method, which has been developed through several deployment trials. By using only a tugboat, a WEC unit is transported and deployed, together with its buoy, in less than half a day. The procedure has proven to be faster, cheaper and safer than the previously used methods.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 100
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1563
Keywords
wave power, ocean energy, linear generator, measurements, sensors, point absorber, offshore, PTO, force
National Category
Energy Engineering Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-329856 (URN)978-91-513-0077-1 (ISBN)
Public defence
2017-11-10, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-10-18 Created: 2017-09-21 Last updated: 2018-03-08
2. Automated Production Technologies and Measurement Systems for Ferrite Magnetized Linear Generators
Open this publication in new window or tab >>Automated Production Technologies and Measurement Systems for Ferrite Magnetized Linear Generators
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The interest in breaking the historical dependence on fossil energy and begin moving towards more renewable energy sources is rising worldwide. This is largely due to uncertainties in the future supply of fossil fuels and the rising concerns about humanity’s role in the currently ongoing climate changes. One renewable energy source is ocean waves and Uppsala University has since the early 2000s been performing active research in this area. The Uppsala wave energy concept is centered on developing linear generators coupled to point absorbing buoys, with the generator situated on the seabed and connected to the buoy on the sea surface via a steel wire. The motion of the buoy then transfers energy to the generator, where it is converted into electricity and sent to shore for delivery into the electrical grid.

This thesis will mainly focus on the development and evaluation of technologies used to automate the manufacturing of the translator, a central part of the linear generator, using industrial robotics. The translator is a 3 m high and 0.8 m wide three sided structure with an aluminum pipe at its center. The structure consists of alternating layers of steel plates (pole-shoes) and ferrite magnets, with a total of 72 layers per side. To perform experiments on translator assembly and production, a robot cell (centered on an IRB6650S industrial robot) complimented with relevant tools, equipment and security measures, has been designed and constructed. The mounting of the pole-shoes on the central pipe, using the industrial robot, proved to be the most challenging task to solve. However, by implementing a precise work-piece orientation calibration system, combined with selective compliance robot tools, the task could be performed with mounting speeds of up to 50 mm/s. Although progress has been made, much work still remains before fully automated translator assembly is a reality.

A secondary topic of this thesis is the development of stand-alone measurement systems to be used in the linear generator, once it has been deployed on the seabed. The main requirements of such a measurement system is robustness, resistance to electrical noise, and power efficiency. If possible the system should also be portable and easy to use. This was solved by developing a custom measurement circuit, based on industry standard 4–20 mA current signals, combined with a portable submersible logging unit. The latest iteration of the system is small enough to be deployed and retrieved by one person, and can collect data for 10 weeks before running out of batteries. Future work in this area should focus on increasing the usability of the system.

The third and final topic of this thesis is a short discussion of an engineering approach to kinetic energy storage, in the form of high-speed composite flywheels, and the design of two different prototypes of such flywheels. Both designs gave important insights to the research group, but a few crucial design faults unfortunately made it impossible to evaluate the full potential of the two designs.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 79
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1573
Keywords
industrial robotics, automation, self-sensing, calibration, ferrite, linear generator, wave energy, offshore, measurements, electronics, kinetic energy storage, reluctance motor
National Category
Robotics Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-330866 (URN)978-91-513-0095-5 (ISBN)
Public defence
2017-11-24, Polhemsalen, Lägerhyddsvägen 1, 752 37 Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2017-11-02 Created: 2017-10-08 Last updated: 2017-11-02

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