Colorado-based Boulder Wind Power (BWP) is accelerating the development of a new permanent magnet generator, through use of advanced electromagnetic design software from Cobham Technical Services. Based on a permanent magnet, direct drive design, BWP's generator uses a unique axial flux, air-core architecture that increases efficiency and reliability, and, according to the company, will ultimately reduce the cost of wind generated electricity to compete at parity with fossil fuels.
In support of the initial engineering studies taken on at the company’s formation in early 2010, BWP chose to use the 3D version of the Opera electromagnetic simulator from the Vector Fields Software range of Cobham Technical Services. BWP cites the software’s accuracy, the ease with which its analytical capabilities can be adapted to suit specific requirements, and Cobham’s willingness to collaborate in further developing key areas such as dynamic modelling as the primary factors behind its choice.
Like all permanent magnet direct drive wind turbines, the generator rotor of BWP’s 3.0MW design turns at about 13 revolutions per minute, necessitating a high pole count. Opera’s advanced solvers allow high periodicity to be leveraged, so that the analytical model can be a fraction of the size of the complete generator – significantly reducing simulation times. This is particularly important for BWP because it makes exclusive use of the 3D version of Opera, which is necessarily more computationally demanding than the 2D version. While many wind turbine designers employ two-dimensional simulation for the main components in a generator, and only use three-dimensional simulation for elements such as the end turns on windings, BWP’s designers must use full 3D simulation at every stage, in order to model the generator’s novel architecture as accurately as possible.
Brian Sullivan, principal electromagnetics engineer at BWP, commented: ‘The physics engine and computational solvers in Opera-3D provide an excellent foundation for the detailed analyses that we perform for our design optimisation. Combined with Opera’s extensive scripting capabilities, which are far more flexible than the pre-programmed templates offered by competitive electromagnetic design packages, this software is enabling us to develop new analytical techniques for our unique machine architecture.
‘In addition, the results obtained from prototype testing have shown a high degree of correlation with our analyses, demonstrating the accuracy of the software. As an example, our predictive models for open circuit voltage in Opera were within 2 per cent of measured data. We are now working with Cobham to build on these exceptional results by enhancing dynamic and transient modelling capabilities, which will enable us to take the next big step in accelerating our design analysis and optimisation.’