The Northwind 2.2 incorporates several novel features, including an in-house design permanent magnet generator (PMG) and in-house developed FlexPhase full power converter. Fitted with these modern power electronics, the turbine is claimed to be capable of meeting the latest grid-voltage-ride-through demands. The turbine concept has also been developed with a focus on transport and serviceability. The pitch-controlled variable speed Northwind 2.2 further features a 93-metre rotor diameter in order to optimise energy yields at high altitudes and under high-turbulence wind conditions.
NPS President of Utility Scale Wind division Troy Patton said the Northwind 2.2 product history dates back to 2000 when the US Department of Energy (DoE) awarded NPS a product development grant. He said: "Supported by this funding we started developing a 1.5MW technology demonstrator turbine that was extensively tested at DoE’s facilities during 2005. Based upon these positive outcomes the turbine, generator and power conversion system were further developed and up scaled to the current 2.2MW power rating."
He added that during the process, NPS’ R&D team specifically focused at achieving high product quality and reliability, and optimised power generation under low and medium wind speed conditions.
Liquid and air-cooling
The search for solutions offering maximised systems efficiency among others resulted in a multi-pole generator with the operating temperatures controlled by a combination of liquid and air-cooling. The power converter located in the nacelle is liquid cooled. Patton continuing: "The generator and power converter system have been optimised for a highest partial-load efficiency in the 6 – 9m/s range, common conditions for IEC WC II and WC III wind sites."
NPS in this highly specialised power electronics field can draw from its fast experience with full power converter technology employed for non-wind situations like grid stabilizing. "When New York City for instance faced serious grid issues in 2003 we were called in to help manage grid stability," he adds.
Another major over another experience the company can draw from is multiple wind-diesel systems operating under remote cold-temperature "island grid" conditions in Alaska. These remote community projects typically lack a central grid system, whereas reliable stable grid conditions still have to be guaranteed.
Backbone of these hybrid wind systems is a 100kW direct drive wind turbine, the Northwind 100. This rather unusual stall regulated (fixed blade angle) variable speed turbine model features a 21-metre rotor diameter, and a relatively uncomplicated load optimised cast main chassis with frontal mounted ring generator. The product specifically aims at so-called "Community Scale Wind" applications like powering schools, community centres and small businesses. An Arctic product version for cold-weather applications and a wind-diesel hybrid system for remote regions supplement the standard Northwind 100 model for grid connection.
Since two years Northwind 100 turbines are fitted with a new in-house developed permanent magnet generator, with a maximum 97 – 98% efficiency explained Patton further: "Besides a high efficiency these turbines have also proven their worth in terms of reliability. This May we shipped the 100th Northwind unit, and as a company increasingly benefit from favourable support schemes for wind turbines with about 80 - 350kW power rating. Two key export markets in Europe are the UK and Italy. Equally favourable for NPS is the fact that it has only very few real competitors in the 80 – 100 kW segment.
Finally, the Northwind 2.2 prototypes have to prove their validity in a much-depressed home wind market situation. Based upon recently released AWEA figures the 2010 US wind market could be down with as much as 70% compared to boom year 2009.