Richard Crozier

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

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.

Modelling and first order optimisation of the air-cored tubular PM machine using polynomial approximation

Finite element analysis remains the most reliable method of simulating electromagnetic systems. When attempting to optimise a system, FEA can be computationally expensive and time consuming. This paper demonstrates the use of polynomial approximation to FEA results to minimise the necessary number of FEA simulations. Using this method, a simulation is developed, capable of accurately reproducing the magnetic field above one pole in the air-cored tubular permanent magnet machine for any combination of machine parameters in a pre-chosen design space. The same method is also employed to optimise the machine parameters to produce the maximum reaction force for a fixed current. A second optimisation is also presented based on the capital cost per average power produced per unit length of translator in a typical wave motion.

A new MATLAB and octave interface to a popular magnetics finite element code

FEMM (Finite Element Method Magnetics) is a free, open source, high quality 2D finite element modelling tool extremely popular in academia for both research and teaching, particularly in the field of electrical machine design. However, FEMM suffers from being tied to the Microsoft Windows platform, and having a slow interface to external programs. This paper presents a successful project to extract the core algorithms from FEMM, make them cross-platform and compile them into a set of libraries and command-line programs. In addition the creation of a new Matlab and Octave interface with direct access to the libraries is described with an example of its use. The libraries use only the C++ standard template libraries for maximum portability. For students and researchers, the tools can be used without knowledge of C++, but for more advanced students and those who might want to add further improvements, the code has also been substantially reorganised for clarity. The new C++ toolbox is referred to as “xfemm”, and the interface “mfemm”.

Hydrodynamic and electromechanical simulation of a snapper based wave energy converter

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.

Comparison of permanent magnet synchronous and induction generator for a tidal current conversion system with onshore converters

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.