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.

Auf dem Gebiet der mobilen Arbeitsmaschinen und Nutzfahrzeuge zeigen aktuelle Arbeiten weltweit ein verstärktes Interesse an leistungsverzweigten Antriebskonzepten auf Basis elektrischer und hydraulischer Hybridlösungen. Die Kombination beider Technologien verspricht wartungsarme, energieeffiziente Antriebssyteme mit hoher Steuer- und Regelbarbeit sowie hoher Kraftdichte. Die primär erzeugte mechanische Antriebsleistung der Wärmekraftmaschine kann meist für die Arbeitsprozesse und zur Versorgung zugehöriger Hilfsfunktionen nicht direkt verwendet werden. Diese muss je nach Anforderungen gewandelt bzw. angepasst oder bedarfsgerecht mittels zusätzlichen, wiederaufladbaren Speichern bereitgestellt werden. Solche hybriden Lösungsansätze führen jedoch gegenüber konventionellen Antrieben zu einer steigenden Komplexität sowie einem erhöhten technischen Aufwand. Nach dem Stand der Technik erfolgt die Erzeugung hydraulischer und elektrischer Leistung mit Hilfe mindestens dreier Komponenten: Verbrennungsmotor, Hydraulikpumpe und Generator. Für künftige antriebstechnische Innovationen ist daher aus funktionellen und energetischen Gründen ein einfaches, preiswertes Primäraggregat zur gleichzeitigen, bedarfsgerechten Bereitstellung hydraulischer und elektrischer Leistung wünschenswert, welches unnötige Umwandlungsverluste vermeidet und zusätzlich Kosten spart. Das Forschungsprojekt „Theoretische Grundlagen zur Verknüpfung von thermohydraulischer und thermoelektrischer Leistungswandlung in einem Aggregat – Thermohydraulischer Lineargenerator“ befasst sich mit einer belastbaren Abschätzung der technischen Realisierbarkeit und des technischen Aufwands eines derartigen neuen Antriebskonzeptes mit frei wählbarer Bereitstellung hydraulischer und elektrischer Leistung auf Basis des Freikolbenprinzips. Die grundlegenden Untersuchungen widmen sich der Kopplung zweier unterschiedlicher Leistungswandlungen, einer stabilen Prozessführung sowie der Analyse und Bewertung der physikalischen Prozessgrößen in Bezug auf eine zukünftige Auslegung eines Prototyps. Der Beitrag erklärt das Grundkonzept, zeigt den aktuellen Stand des Projekts auf und stellt die zum gegenwärtigen Zeitpunkt vorliegenden Ergebnisse vor.

The main focus of this thesis is on the power electronic converter system challenges associated with the grid integration of variable-renewable-energy (VRE) sources like wave, marine current, tidal, wind, solar etc. Wave energy conversion with grid integration is used as the key reference, considering its high energy potential to support the future clean energy requirements and due the availability of a test facility at Uppsala University. The emphasis is on the DC-link power conditioning and grid coupling of direct driven wave energy converters (DDWECs). The DDWEC reflects the random nature of its input energy to its output voltage wave shape. Thereby, it demands for intelligent power conversion techniques to facilitate the grid connection. One option is to improve and adapt an already existing, simple and reliable multilevel power converter technology, using smart control strategies. The proposed WECs to grid interconnection system consists of uncontrolled three-phase rectifiers, three-level boost converter(TLBC) or three-level buck-boost converter (TLBBC) and a three-level neutral point clamped (TLNPC) inverter. A new method for pulse delay control for the active balancing of DC-link capacitor voltages by using TLBC/TLBBC is presented. Duty-ratio and pulse delay control methods are combined for obtaining better voltage regulation at the DC-link and for achieving higher controllability range. The classic voltage balancing problem of the NPC inverter input, is solved efficiently using the above technique. A synchronous current compensator is used for the NPC inverter based grid coupling. Various results from both simulation and hardware testing show that the required power conditioning and power flow control can be obtained from the proposed multilevel multistage converter system. The entire control strategies are implemented in Xilinx Virtex 5 FPGA, inside National Instruments’ CompactRIO system using LabVIEW. A contour based dead-time harmonic analysis method for TLNPC and the possibilities of having various interconnection strategies of WEC-rectifier units to complement the power converter efforts for stabilizing the DC-link, are also presented. An advanced future AC2AC direct power converter system based on Modular multilevel converter (MMC) structure developed at Siemens AG is presented briefly to demonstrate the future trends in this area.