A Colorado-based company claims its axial gap, permanent magnet, direct-drive generator can produce the same torque with less than half the mass of comparably rated iron-core, direct-drive versions. The proprietary air-core stator, developed by Boulder Wind Power (boulderwindpower.com), contains no ferromagnetic material, so it eliminates all magnetic attraction between rotor and stator. This feature allows using lightweight, flexible, stator and rotor-support structures.
Boulder Wind Power Product Manager Peter Smith says the design will be simpler, more efficient, and less costly to maintain than other wind-turbine generators. The firm aims to produce electricity at a significantly lower cost than existing equipment and competitive with fossil fuels. “We’ll provide our generator and controls to wind-turbine manufacturers for incorporation into their products, along with turbine design and engineering services.”
BWP says it has also developed design tools to prescribe a stator circuit etched on a printed circuit board. Automated printed circuit-board (PCB) manufacturing provides a design, manufacturing, and assembly simplicity unique to wind-turbines. Smith says a 3-MW generator is in test now at a site in Montana, but details are proprietary.
A problem with conventional multi-MW generators is that they are manufactured using low-volume production methods that depend on skilled labor. This introduces quality control issues. BWP VP of Engineering James Smith asks: “How precisely can they control the installation and assembly loads applied to the coils?
Installation involves hammering coils into the slots of an iron-core, then pulling them out axially through the slot in each direction to apply a tape to the end turns. What ensures that the insulation has not been damaged or disturbed in the process, or afterwards when coil ends are brazed? A tiny imperfection in the insulating tape can be the difference between a generator that lasts 30 years and one that fails after five.
In contrast, James Smith adds, the BWP stator is manufactured using mature and repeatable PCB operations perfected by the electronics industry over the past 50 years. These advanced processes support the BWP insulation and conductor uniformly over the entire conductor surface. End-turn areas are encapsulated and supported in the same manner as working area conductors. BWP says this is superior to conventional construction.
James Smith also says the design eliminates iron losses associated with flux reversals in the stator. “Stator losses are limited primarily to conductive losses (I²R). The design minimizes eddy-current losses and eliminates hysteretic losses associated with all iron-core generators.” The high-torque density avoids torque limitations that constrain iron-core machines and allows large rotor diameters that deliver more than 30% more power than comparabe systems in low-wind speeds.
The BWP generator is constructed of multiple, identical segments, modularity that provides favorable logistics and lets crews make generator repairs up-tower. “The simple ‘plug-and-play’ stator segments can be replaced by a standard two-man crew without a land-based crane,” says Peter Smith.
The U.S. DoE selected the company for a grant under the DoE’s Wind Power Next Generation Drivetrain Development program. It provides up to $700,000 of funding in the first phase, during which the company will develop a design and test program for a 6 MW, offshore wind turbine. The company will also validate the scalability, feasibility, and economic advantages of its patented technology in a 10-MW offshore wind turbine. WPE
Filed Under: Generators, Offshore wind