Control tester automates control testing

The modular architecture of a real-time-test program lets wind-turbine engineers automate the task of verifying many control ideas by including hardware components in their test loop. That includes embedded-control software for wind turbines. To write the program, Siemens wind-turbine engineers selected NI TestStand, LabVIEW Real-Time, LabVIEW FPGA modules, and the NI PXI platform, all from National Instruments, Austin, Texas, (ni.com). The test system now simulates the behavior of real wind-turbine components by running simulation models that supply simulated signals to the control hardware and software under test.

“The modular architecture let us scale-up the system to meet the growing requirements of a rapidly evolving industry,” says Siemens Testing and Control Software engineer Samir Bico. “The modularity and flexibility make it is easy to improve, adapt, and develop further. The system under test can be quickly swapped with another and without changes in the test-system architecture. Remote control and simple replications have the flexibility to copy the system to other sites as our operations expand.”

The testing task is no simple matter because the control system interfaces with many turbine components through hundreds of I/O signals and multiple communication protocols. The most complex part is the embedded control software executing the control loops.

Developers for the control software regularly release new versions for testing, to verify that the releases execute reliably. “With every software release we perform factory acceptance testing before the software can be used in the field. This new test system automates the process,” says Bico.

The previous and 10-year old test system was based on other software and PCI data acquisition boards. Its architecture and performance did not meet new requirements for test time and scalability. In addition, the system was difficult to maintain and had insufficient automation.

Wind turbines use many custom communication protocols because standards are few. “Using an NI PXI-7833R FPGA-based multifunction RIO module with the LabVIEW FPGA Module, lets us interface with and simulate these protocols. In addition, we are using the device to simulate magnetic sensors and for accurate three-phase voltage and current simulations. Another FPGA board connects to an NI 9151 R Series expansion chassis to further increase the system channel count,” says Bico. WPE

NREL adds two Multimegawatt Turbines

The clean wind energy industry must expand significantly in the next two decades to fulfill a strategy of generating 20 percent of the nation’s electricity. To provide the technological foundation for that dramatic growth, the National Renewable Energy Laboratory (NREL) is embarking on significant improvements at its National Wind Technology Center.

Engineers are installing the two largest turbines ever tested at the laboratory — a 1.5 MW turbine manufactured by General Electric and a 2.3 MW turbine from Siemens Power Generation.

Both turbines are being erected on the NWTC’s eastern perimeter for commissioning and operations in October. They will run for years under close observation and elaborate instrumentation. With data from these experiments, researchers will be working with the wind industry to increase turbine performance, improve durability and decrease loads.

The new turbines also allow NREL to take a significant step forward in generating its own clean electricity and meeting the Laboratory’s aggressive sustainability goals and reduce greenhouse gas emissions for its expanding research campus and support facilities. The new turbines are expected to generate twice as much energy as the NWTC uses. The U.S. Department of Energy (DOE), NREL and Xcel Energy are working to define an agreement that will allow surplus energy to be exported and sold to the local utility grid.

DOE purchase for NWTC

DOE purchased the 1.5 MW turbine for the NWTC. Crews using a crane assembled it over three days. The rotor was expected to fly — or be attached — on August 21.

The DOE turbine will operate atop a 262-foot steel tower. The diameter of its rotor will reach 253 feet.

“The DOE turbine is a national asset for the NWTC to operate as a test bed for wind energy research and development said NWTC assistant director for Testing and Operations, David Simms. “They would like us to offer it as a test bed for the best and brightest researchers from universities, laboratories and companies around the country.”

The DOE turbine was manufactured by GE and is a workhorse of the domestic wind power industry. More than 10,000 now operate at commercial wind farms around the nation, accounting for about 50 percent of the U.S. market. Because of its market share, NREL researchers say it is important to more fully understand the turbine’s performance in the field and look for ways to help advance its design.

Among the questions researchers will address are the microclimate in which the turbine operates, the aerodynamics of the turbine design and the effects of turbulence on its load and performance — and how all these factors may combine in potentially unforeseen ways. The NWTC was located at the base of the Rocky Mountains to take advantage of particularly gusty, challenging winds in order to challenge turbine designs in conditions not typically seen at commercial locations.

“If we could improve performance, thousands of turbines could remain in operation for years beyond the industry’s original expectations,” said NREL senior project leader Jim Green.

Additional trucks will be delivering the Siemens wind turbine, the cranes, and other installation equipment in August and September. The Siemens turbine will use a second tower of the same height, but its rotor diameter is 331 feet, or more than 30 percent bigger than the DOE turbine. The Siemens turbine employs an advanced new rotor design that needs field testing in the NWTC’s gusty and challenging conditions. Siemens has opened a research office in Boulder to provide engineering support and maintenance.

Siemens turbine among the largest in the U.S.

“It’s as large as any turbine in North America,” said project leader Lee Jay Fingersh. “The final design is different than most turbines with a different blade shape. Land-based turbines are getting larger to meet the demand for wind energy. This is the direction of the wind industry and we want to understand the aerodynamics of these new, larger machines.”

---

DOE/GE 1.5 MW Vital Statistics

* Hub height – 80 meters (262.5 feet)
* Radius – 38.5 meters (126.3 feet)
* Total ground to tip = 118.5 meters (388.8 feet)

Siemens 2.3 MW vital statistics

* Hub Height – 80 meters (262.5 feet)
* Radius – 50.5m (165.7 feet)
* Total ground to tip = 130.5 meters (428.2 feet)

Power Generation:

* Average US home monthly electricity consumption in 2007 = 936kWh
* DOE/GE estimated production from DOE/GE turbine at the NWTC* = 1,600,000kWh/year (enough to serve 142 homes)
* Siemens 2.3 MW estimated production at the NWTC* = 2,800,000 kWh/year (enough to serve 249 homes)

*The NWTC is a testing site. Production at more typical commercial wind farm would be higher.*

---

NREL is providing the site, the foundation and the electrical connection for the turbine, the cost of delivery, installation services and expertise in field aerodynamics testing, structure and reliability testing and meteorological analysis. NREL and Siemens have signed a cooperative research and development agreement that is expected to continue into 2014.

The Siemens turbine was selected for testing by the DOE after a national competition.

More than meets the eye

As considerable as the new turbines are, NREL researchers are equally interested in what is required beneath the ground in order to support such imposing machines, which can weigh more than 300 tons.

NREL engineers worked with Renewable Energy Systems Americas, Inc., to pour the large customized concrete foundations for the turbines. The concrete was delivered in July in an impressive convoy of more than 80 trucks.

NREL and RES Americas have signed a cooperative research and development agreement to study the design and performance of turbine foundations to increase the reliability of non-turbine components and lower the cost of wind-generated power. RES Americas recently established its U.S. headquarters in Broomfield, Colo., near the NWTS.

Research questions include structural loads on foundations of operating wind turbines, thermal performance of underground collection system electrical cables, and side-by-side comparisons of alternative wind speed measurement systems.

“This CRADA will result in some of the first-ever measurements of loads inside and under the foundation of an operating wind turbine,” Green said.

After the two new turbines are operating, NWTC engineers will erect two new meteorological towers to the west of the turbines. Each tower will stand 440 feet high and feature more than 60 instruments to collect the most advanced information on the wind, temperature, dew point, precipitation and other weather features that can influence the performance and lifespan of a wind turbine.

NREL and the wind energy industry are turning to taller towers to characterize the wind resources and conditions higher up where new, larger turbines operate.

The new towers also will feature LED lights that require virtually no maintenance and use a fraction of the energy of conventional lights.

After the towers are completed this fall, crews will remove the red flashing warning lights atop the new wind turbines and three of the existing meteorological towers, too, leaving the NWTC with a total of three lighted towers.

NREL

HVDC cable could trim most grid losses

High voltage dc transmission lines are one way to reduce the amount of power lost in transmission grids from the current average of about 8% to an estimated 1 to 2%, according to Wolfgang Dehen, chief executive of Siemens’ energy unit.

Traditional lines typically lose 8% of power in transmission, leading to higher costs and lower earnings for energy companies. New technology, such as high-voltage direct current, trims the amount of power lost so associated costs also drop, according to Dehen.

He says it is possible to connect cities with distant renewable wind and water farms, and cited the 2,000 km HVDC transmission lines under construction in China. The line will link the Xiangjiaba hydro-electric power plant in the south west to Shanghai on the north-east coast by year’s end. “It’s definitely a higher cost cable, but it’s the only way to bridge the distance and transport large amounts of power from a generation center to users,” he says.

Scratch the tower. Let the turbines float

Norway’s StatoilHydro and its new division Hywind have towed and anchored a floating 2.3-MW wind turbine to a spot about 10 km off the southwest coast of Norway. A 100-m buoyancy section of the tower keeps the rest of the unit floating upright. It’s anchored to the seabed with cables. The turbine can be placed at depths from 120 to 700 m. The Hywind, built by Siemens, combines technologies from the wind farming industry and oil and gas sectors, and will serve as a two-year test bed.

“This should help move offshore wind farms out of sight and away from where they cause disruption,” says Statoil spokesperson Alexandra Beck Gjorv. This would benefit military radar operations, the shipping industry, fisheries, bird life, and tourism.

“Taking wind turbines to sea presents new opportunities,” adds Gjorv. “Wind is stronger and more consistent and the areas are large.” Floating wind farms will be connected to mainland grids by cables on the seabed.

Offshore wind farms cost considerably more than wind farms on land, and initially floating ones will be more expensive than static offshore installations. But over time, says Gjorv, the floating designs should not cost more than fixed ones. Statoil plans to target markets where there is an ability to pay along with a growing demand for energy. Floating wind farms could be established off the coasts of North America, the Iberian peninsula, Norway, and the U.K. she said. Floating wind farms could also provide an additional source of energy for countries that have run out of space for their onshore wind farms, or where there is not enough wind on land.

“The global market for such turbines is potentially enormous, depending on how low we can press costs,” she said, though she was not able to quantify them or to outline a timescale for when floating wind farms would become commercially available.

StatoilHydro is investing around NOK 400 million in the construction and development of the pilot. The public corporation Enova SF, whose aim is to promote the transition to environmentally friendly energy use and energy production in Norway, has granted NOK 59 million in support.

A few specs for the floating turbine