Cobham Technical Services is helping Colorado-based Boulder Wind Power (BWP) accelerate development of a radical new permanent magnet generator through use of advanced electromagnetic design software. 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 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 three-dimensional (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.
According to Brian Sullivan, Principal Electromagnetics Engineer at BWP: “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 preprogrammed 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% 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.”
Unlike conventional permanent magnet generators, the air-core stator in the BWP design does not use electrical steel laminations wound with conductors, and contains no ferromagnetic materials. This breakthrough has several advantages including eliminating iron losses associated with flux reversals in the stator and eliminating the magnetic attraction between the generator’s rotor and stator. Together these enable higher efficiencies and higher torque levels for a given mass of generator.
According to Andris Cukurs, CEO of BWP: “Having proven the fundamental design approach for our generator and validated our design tools, we are now in the process of designing units to be incorporated in our clients’ multi-megawatt wind turbine designs for prototype testing. We believe our technology will provide wind turbine manufacturers with the innovative design advantages they are looking for to better compete in the global wind market.”
Kevin Ward, Director of Cobham Technical Services – Vector Fields Software, points out that wind power is at a critical point of development: “Wind turbines currently account for about 5 percent of the world’s installed capacity for electricity generation, providing ample opportunity for growth. We are delighted to be working with BWP to help them develop this highly innovative generator which is being designed to make the future of wind power more accessible.”
BWP’s generators will be available for testing in prototype turbines in 2013, with full commercial availability expected in 2014.
Press release, October 22, 2012; Image: Cobham