A clever generator design that uses printed-circuit-board technology for lower weight and manufacturing simplicity has passed a 3.0 MW proof of concept and is headed to a nacelle for further testing. Developer Boulder Wind Power (BWP) has also expanded its electromagnetic design team to support the prototype generators with assembly and service tooling.

Stiffening ribs on the proof-of-concept generator carry loads from the permanent magnets. Under normal operating conditions, analysis shows magnetic loads in the generator approaching 1,000,000 lb.

“Having proven the fundamental design approach for our generator and power converter and validated our design tools, we are now in the process of designing units for incorporation into a clients’ multi-megawatt wind turbine for prototype testing,” says BWP CEO Andris Cukurs. The company began testing on its 3.0 MW proof-of-concept generator in March of 2012. Final test results have proven the axial-flux air core design works as efficiently and reliably as predicted. Brian Sullivan, Principal Electromagnetics Engineer at BWP, added, “The results obtained from BWP’s proof-of-concept testing have shown a high degree of correlation with our analyses, demonstrating the accuracy of our advanced 3D electromagnetics modeling methods. As an example, our predictive models for open circuit voltage were within 2% of measured data throughout the operating range.”

Most conventional generator designs follow a set of empirically validated design rules dating back to Nikola Tesla’s time for producing new machine designs. Understanding and leveraging detailed electromagnetic finite element analysis is not a standard practice across the industry, yet.

However, the novel BWP axial flux air core design presented its designers with a white sheet of paper, a limited set of empirically validated design rules, and a truly unique set of geometric constraints. Consequently, an advanced 3D electromagnetic simulation capability was a requirement early in the design process.

BWP committed to the use of a 3D electromagnetic simulation package and invested in finding and training talented engineers to achieve the analytical accuracy required. This represents a radical advancement over the rest of the wind industry, which is just beginning to embrace simpler 2D simulation methods. Although less accurate, these 2D methods are effective for their applications since most electromagnetic finite element analysis efforts are directed at understanding specific issues that are readily represented in a 2D “slice” of conventional machines. Through its investment in team and tools, BWP is building a capability that is unique in this industry – namely, taking white sheet electromagnetic design challenges completely through a full 3D simulation design process which gives BWP unique insight into the interactions between magnetic and electric fields and enables the discovery of new solutions that have broad applicability.

Open-circuit voltage measurements collected on Boulder Wind Power’s full-scale proof-of-concept generator shows good correlation with a prediction from by detailed 3D electromagnetic finite-element analysis.

In addition to using this tool to model and predict the electromagnetic performance of BWP’s full-scale 3.0 MW proof-of-concept generator, the analytical methods were leveraged extensively to model the magnetic forces encountered during each step of the generator assembly process, as well as the static forces on various components once the generator is fully assembled. According to Jim Smith, Vice President of Engineering at BWP, “It is critical that we fully understand all of the magnetic forces between the generator components, sub-assemblies and assembly tooling during each step of the process to ensure personnel safety while leveraging the inherent manufacturing simplicity of this design.” For example, the attractive forces between each opposing back-iron segment were calculated using the same set of simulation tools to engineer these components to minimize the weight yet provide the required stiffness.

Boulder Wind Power

www.boulderwindpower.com