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A coupled electromechanical and hydrodynamic time-domain simulation of a direct-drive generator connected to a heaving buoy for wave energy conversion is presented. The system is based on a novel direct-drive power takeoff unit referred to as snapper. The simulation is based primarily in MATLAB using its built-in ordinary differential equation solvers. These solvers act on the data derived from electromagnetic finite element analysis and from the WAMIT wave interaction simulation software. Test results of a generator prototype for comparison with the electromechanical simulation are presented. Results from wave tank tests of a full system incorporating the power takeoff are also provided for comparison with the hydrodynamic model.

The marine energy industry is in its early stages but has a large potential for growth. One of the most significant challenges is the reduction of operation and maintenance costs. Magnetic gears (MGs) offer the potential for long periods between maintenance intervals due to their frictionless torque transmission which could reduce these costs. This study presents a summary of the state of the art in MG technology and then investigates its potential for marine energy applications. A brief overview is given of the state of the marine energy industry and the environment in which marine energy converters (MECs) operate. A short history of MG development over the past century is then presented followed by a discussion of the leading MG technologies and their relative advantages. In order to demonstrate the potential of MGs in marine applications, the current technologies, i.e. mechanically geared and direct drive machines, are examined in terms of sizing, reliability and economic value using previous studies on a similar technology, namely wind. MGs are applied to four types of MECs to demonstrate how the technology can be incorporated. The potential to deploy at scale and potential obstacles to this are then discussed.

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Tidal current conversion systems are moving towards commercialisation. Tidal energy developers are looking to optimise their systems by testing all the available options and taking advantage of the experience from the wind energy industry. The key focus of this paper is to compare an induction generator with a permanent magnet synchronous generator in a tidal current conversion system with onshore converters. The architecture of a tidal system with onshore converters is an option for tidal sites with small distances to shore as previous research has shown. In order to investigate the two generator technologies full resource-to-grid models in MATLAB/Simulink are developed. The analysis of these models compares generator efficiency, energy capture, losses at each stage, the cost and the maintenance for each system. Results show that the tidal system with PMSG is more efficient and generates fewer losses to transmit power onshore. In addition, since both systems tested are using a gearbox, the size, cost and maintenance of the PMSG are comparable to the reliable and cost-effective option of SCIG.

A coupled electromechanical and hydrodynamic simulation of a novel generator connected to a heaving buoy for wave energy conversion has been developed. The simulation is based primarily in MATLAB using its built-in Ordinary Differential Equation (ODE) solvers. These solvers have acted on the data derived from an electromagnetic finite element analysis and from the WAMIT wave interaction simulation software, to simulate the full system in the time domain.

Linear permanent magnet generators are a potentially useful technology for wave power applications. Typically, optimisation and comparison of these generators is based on an electromagnetic analysis with limited regard for the structural and thermal analysis. This paper presents a comparison of an air-cored synchronous machine and a double-sided iron-cored synchronous machine which includes the structural and bearing requirements for a more accurate cost comparison, and a discussion of the thermal issues. It is shown that both cost and feasibility depend heavily on these issues.Index Terms-Direct-drive generator, linear synchronous machine, permanent magnet machine, wave energy. I. INTRODUCTIONAVE energy converters have working surfaces that reciprocate at low speed and operate over a wide range of loadings making conventional off-the-shelf rotary generators less suitable than in other power generation technologies. Permanent magnet (PM) generators exhibit high part load efficiencies and, while they have been demonstrated at sea to a limited extent, designs are not yet fully optimised. Using direct-drive generators reduces the number of moving parts but, because of their low speeds and consequent high forces/torques, adopting conventional machine topologies leads to large and costly generators.A number of different linear generators have been proposed for use in wave energy converters (WECs). Optimisation of cost and performance requires integrated structural, electrical and thermal design techniques to establish the cost of energy produced. Work stream 5 of SUPERGEN Marine Phase 2 explores how the design of the prime-mover, drive-train, generator and power electronic converter may be fully integrated to define lighter, cheaper machines that will operate at slow speed with improved efficiency over a wide range of loads. A. Electrical Machine Topologies Suitable for Linear GeneratorsA number of different electrical machine types have previously been compared for use in direct-drive WECs. For example, Polinder et al. looked at linear versions of induction gen-This work was supported by the UK EPSRC SUPERGEN Marine Energy Consortium (Phase 2, Work Stream 5). A. S. McDonald, R. Crozier, S. Caraher and M. A. Mueller are all with the

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