Integrated design of direct-drive linear generators for wave energy converters

Abstract

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

Investigation of Multi-phase Tubular Permanent Magnet Linear Generator for Wave Energy Converters

“…The displacement δ is interpolated via the nodal shape function: (6) where is the nodal shape function of the node. Using (5) and (6) the visual work can be also expressed as:…”

“…Number of concepts for direct drive WEC has been presented [4][5][6][7][8][9][10][11][12][13][14][15]. Caused by the relatively low vertical speeds of the marine waves and the desire for high output power, the generators share large sizes and hence, high magnetic forces such as cogging forces.…”

Multiphase tubular permanent magnet linear generator for wave energy converters

“…Recently, number of PMLG concepts designed for direct driven WEC has been proposed [2,3]. Due to the relatively slow wave motion, the PMLGs share large sizes and hence, high magnetic forces are observed.…”