A linear-generator topology is proposed for wave-energy applications. The main significance of the generator topology is that the relative position of the magnets, copper, and steels has been chosen so that there are no magnetic attraction forces between a stator and a permanent-magnet (PM) translator. The lack of magnetic forces and the modular nature of the generator topology make the manufacture and assembly of the generator easier than a conventional iron-cored PM linear generator. Analytical modeling techniques are described with a genetic-algorithm optimization method. The proposed topology is implemented to an Archimedes-wave-swing wave-energy converter. A 50-kW prototype has been built to prove the concept, and the no-load- and load-test results are presented.

It is well known that slotting harmonics exist in most of the electrical machines. So far, these harmonics are mainly identified using spectral estimation techniques. However, this approach requires long sampling and computation periods. In this study, a novel speed and position estimation method based on identification of rotor slot harmonics (RSH) that does not require any kind of spectral analysis is proposed. The required information is extracted by demodulating the information available in an external search coil (or in phase current). The algorithm used for this purpose is fast and can be applied within a typical control cycle of a vector controlled drive algorithm. In the application of the method here, higher order RSH have been utilized. In this manner, the position estimation resolution increases and also possible effect of harmonics stemming from other sources are avoided. The approach is explained in the paper and illustrated with experimental results.

In this paper, a novel and non-invasive stator inter-turn short circuit (ITSC) online detection method is presented for an induction machine (IM), driven by a two-level voltage source inverter (2L-VSI) via finite control set model predictive control (FCS-MPC). The main idea of the proposed method is to utilize the controller itself as an observer: under the presence of a fault, the distribution of inverter switching states significantly deviates from the original balanced case. Therefore, by inspecting the inverter switching vectors, which are the outcomes of the online optimization procedure of the FCS-MPC routine, a stator fault can be detected efficiently. It is observed that both the zero-vector allocation over the complex plane and the allocation among the active vectors are influenced by the presence of a stator short-circuit fault. The proposed fault detection strategy introduces little to no extra burden for processor and memory. Experimental results verify the proposed method and inter-turn short circuits of two and three turns are confidently detected and located for a 500 W, two-pole IM.

Air-cored machines offer benefits in terms the elimination of magnetic attraction forces between stator and rotor. With no iron in the stator there is not a good thermal conduction path for heat generated by Joule losses in the stator winding. Results from both models and experimental tests are provided in this paper to investigate different methods of cooling air-cored windings, including natural air-cooling, direct liquid cooling and the use of heat pipes.

The C-GEN is a novel permanent magnet generator aimed at reducing overall system mass in direct drive power takeoff applications. The design of a C-GEN generator requires the combination of electromagnetic, structural and thermal models. Models used in the development of design tools applicable to both rotary and linear C-GEN generators are described in this study. The design tool is verified with the experiment results obtained from a 15 kW prototype. A genetic optimisation algorithm is developed combining the analytical model with economical issues to search for most suitable designs for specific applications. Designs are presented using the optimisation design tool for two marine renewable applications: a wave device called Oyster developed by Aquamarine Power and a tidal current device developed by Scotrenewables.

Superconducting generators have the potential to reduce the tower head mass for large (∼10 MW) offshore wind turbines. However, a high temperature superconductor generator should be as reliable as conventional generators for successful entry into the market. Most of the proposed designs use the superconducting synchronous generator concept, which has a higher cost than conventional generators and suffers from reliability issues. In this paper, a novel claw pole type of superconducting machine is presented. The design has a stationary superconducting field winding, which simplifies the design and increases the reliability. The machine can be operated in independent modules; thus even if one of the sections fails, the rest can operate until the next planned maintenance. Another advantage of the design is the very low superconducting wire requirement; a 10 MW, 10 rpm design is presented which uses 13 km of MgB ₂ wire at 30 K. The outer diameter of the machine is 6.63 m and it weighs 184 tonnes including the structural mass. The design is thought to be a good candidate for entering the renewable energy market, with its low cost and robust structure.