World's largest wind turbine test facility aims to resolve stresses of more wind generation

Clemson University created what it calls the world's largest 15-megawatt (MW) Wind Turbine Drivetrain Test facility to create new technologies for the energy market. The facility, which opened November 2013, uses National Instruments (NI) integrated hardware and software tools.

05/07/2014


This photo in front of the Clemson University 15 MW dynamometer test stand gives a small indication of the huge project size. The gearbox is larger than the ones on Navy destroyer ships, Clemson representatives told NI. Courtesy: National InstrumentsThe U.S. Dept. of Energy expects wind power to meet 20% of U.S. power needs by 2030 (up from 4.2% today), which requires advancing the technologies used to develop and test wind turbines and their interactions with the power grid. Using NI integrated hardware and software tools, Clemson University unveiled the world's largest 15 MW Wind Turbine Drivetrain Test facility in November 2013 to help design and test new technologies for the energy market. The facility has expanded to include a grid simulation lab so manufacturers can test the mechanical and electrical characteristics of wind turbine machines in a controlled environment. With this advanced testing center, companies can test any utility scale distributed energy resource, up to 15 MW, while checking the reliability and robustness of the equipment, before deploying it to the actual power grid. This approach, known as power hardware-in-the-loop (HIL) testing, can accurately mimic the dynamic behavior and interaction between the grid and the device under test while it's running full power. However, because the grid is simulated, the response of the equipment can be validated in a complete range of simulated test conditions that would be impossible to produce using the actual power grid, National Instruments explained. 

Cyber-physical systems

Successfully integrating wind power into the existing electric power grid is a complex challenge that relies on distributed, interconnected cyber-physical systems (CPS), which are proliferating within the engineering industry, according to NI. In the 2014 NI Trend Watch, NI provides more on "Cyber-Physical Systems-Developing systems that continuously and dynamically interact with their environment through coupling of distributed computational and physical components." 

Photo of the Teco inverters: Each row is 5 MW and includes 17 NI Single-Board RIO inverter control system boards. Courtesy: National InstrumentsThe document gives an example of the complexity of systems testing today, explaining, in part, "Modern engineered systems are rarely designed once, rarely designed in isolation, and rarely ever complete. The braking mechanism in your car evolved from the mechanical lever brake on horse carriages and was soon enhanced with hydraulics to improve braking power and stability. Electrical components were introduced with the advent of power-assisted brakes. Antilock brakes began as mechanical feedback control systems to prevent airplane wheels from locking and eventually migrated to automobiles."

NI believes a platform-based design approach that leverages holistic development solutions and commercial off-the-shelf hardware can help engineers achieve better CPS designs, speed design iterations, and test complex system interactions. NI offers the LabVIEW reconfigurable I/O (RIO) architecture, which is optimized to address the needs of cyber-physical systems designers. 

CPS questions, answers

CFE Media (Control Engineering and Plant Engineering) asked Brian MacCleery, principal product manager for clean energy, NI, about the facility.

Q. Can you please tell us about the facility?

Instrumentation racks (inside) contain NI PXI equipment for measuring and recording all of the data from the wind turbines during testing. This is the instrumentation room for the 7.5 MW test stand. Courtesy: National InstrumentsA. I have been working with the Duke Energy Electric Grid Research, Innovation and Development (eGRID) Center for several years on inverter control and high-speed microgrid simulation technologies for a 15 MW (20,000 hp) grid simulator. The scale of the facility is mind-boggling-I was like a kid in a candy store when touring the facility during a recent visit. The cyber-physical systems test facility is truly unique in that it covers all aspects of the wind turbine generator, including interactions with the grid. That includes the mechanical torsion of the wind turbine shaft and the complex electromechanical interactions between the control software, generator, gearbox, power electronics converters, and the power grid. There's a strong need for this type of scientific, reproducible testing, since the DOE's plan is to expand U.S. wind generation to 20% of the total by 2030, a significant expansion from around 4% now. Gear boxes need to extend their life span to 20 years, up from about 7-10 years at present. Meanwhile, electrical system failures are five times more frequent than gear box failures according to DOE data. The mechanical, electrical, and control software aspect of the wind turbine all have an impact on the lifetime of the machine, and therefore the cost of the energy produced. The new facility will enable the industry to scientifically study all of those complex multi-domain interactions to identify cause and effect.

Q. What is the total cost of the testing facility?

A. The drivetrain was $98M and the grid simulator cost another $12M, bringing the entire building cost to a total $110M.

Q. Have any tests resulted in design changes yet?

Instrumentation racks (outside) contain NI PXI equipment for measuring and recording wind turbine data during testing. This is the instrumentation room for the 7.5 MW test stand. Courtesy: National InstrumentsA. No tests have actually run yet, so there are no design changes to share at this time. They are still working through commissioning and will begin testing in the next few months. Unfortunately, we will not be able to share specifics on design changes in the short term based on confidentiality and competitive reasons.

Q. In general, what are the expected impacts of the facility?

A. Clemson University said that when tying drivetrain testing with the electrical testing, those using the facility are looking at how to model interactions that cross the mechanical and electrical parts of the wind turbine. This includes 1) performing full wind model simulations in real time, 2) driving the mechanical test bench from these wind field simulations, and 3) simulating an electrical grid in real time, while making it possible for a generator to interact with the system too. They expect that this real-time simulation of the wind field and the electrical grid will make it possible to look at higher level wind turbine control challenges that are the result of similar time constants in mechanical and electrical systems. An example might be sub-synchronous resonance on the electrical grid interacting with the pitch control system of a wind turbine. These are the types of developments that can be fully explored in this facility.

Q. How is NI involved?

It takes three tanker trucks full of hydraulic fluid to fill the supply tanks. These are for the hydraulic actuators that mechanically A. NI LabVIEW reconfigurable I/O (RIO) embedded control software and hardware are used in the 15 MW power amplifier inverter used to simulate the power grid, which was developed by the TECO Westinghouse Motor Company. The 4160 V modular multi-level power converter uses a series connected H-Bridge topology and phase shift carrier pulse width modulation (PWM) to provide 12 kHz of amplifier bandwidth and very low total harmonic distortion (THD). This is achieved through the synchronized control of 69 FPGA-based NI Single-Board RIO control systems coordinating via serial fiber optic links. The TECO bi-directional inverters can also be easily reconfigured for different voltage and current ratings. In addition, NI LabVIEW software and PXI instrumentation equipment is used to acquire the mechanical and electrical system measurements, as well as to record and analyze the massive amounts of data generated during testing.

Q. Cyber-physical systems (CPS) aren't new. How are these concepts helping here and in other high-tech applications?

A. Originally, it was only a mechanical drivetrain test facility. However, electrical grid simulation was determined to be one of the biggest needs. There are many complexities related to harmonics and control stabilities that cross the boundary between mechanical and electrical, as well as cyber and physical. NI is developing a new class of real-time simulators that is fast enough to accurately mimic the high-bandwidth nature of cyber-physical systems. It's only today that we are able to achieve the simulation speeds necessary for this kind of CPS validation and verification. It opens up the possibility of designing much more complex CPS that have been fully validated and verified so they can perform reliably in the field.

Software shows cutaway concept of Clemson University’s 15-MW Wind Turbine Drivetrain Test facility, which opened in November 2013 and uses National Instruments (NI) integrated hardware and software tools. Courtesy: Clemson University, National InstrumentsQ. Simulators were available previously; how is this different?

A. For combustion engines, no automotive company would ship a car that is not fully HIL tested, yet with wind turbines and similar grid tied equipment, simulation bandwidths in the 500 kHz to 1 MHz range have not been readily available. NI has invested in R&D over the last five years to develop real-time simulators for high-speed electric power applications. As a result, we can now demonstrate how an FPGA-based simulator captures the full frequency response of electrical equipment on a microgrid. A month ago, we released the NI electric motor simulation toolkit. As an example, a new hybrid vehicle power electronics control system was comprehensively validated and verified using these new tools.

Q. What lessons could others learn in other control and monitoring applications?

A. New, full power testing technologies can provide rigorous test coverage for complex cyber-physical systems. Such testing capabilities mean that power grid equipment can be as fully verified as the control systems used in automobiles and aircrafts. Although students may not have been taught in school that such HIL testing is part of the embedded control system design process, we're trying to bring this formal design process to the power grid industry.

- Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering, mhoske(at)cfemedia.com.

ONLINE

www.controleng.com/archives

May has more information and answers under this headline.

www.ni.com

See the NI article: Controlling a hardware-in-the-loop grid simulator for the world's most powerful renewable energy test facility

ONLINE extras

Nov. 22, 2013, Clemson test facility dedication information

TECO technical presentation on the 20 MW inverter control using NI Single-Board RIO; it simulates the grid connection of the wind turbine.

NI provides reference designs and tutorial videos at 

Department of Energy 20% wind report shows (page 76 of 248-page PDF) that electrical system failures occur five times more frequently than gearbox failures. 

And see prior articles on wind power, below.

http://www.20percentwind.org/20percent_wind_energy_report_revOct08.pdf



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