By Dave Wilson, Academic Marketing Director, National Instruments
Wind turbines are getting much bigger and sitting higher and higher above the ground to provide clearance for the rotor blades. It’s much better to test the turbine generators before mounting them 120m (the length of one American football field!) above the ground. The DOE awarded Clemson University Restoration Institute (CURI) the largest DOE grant ever issued to build the world’s most powerful mechanical test facility for wind turbine nacelles with generating capacities to 15 megaWatts, which is three times larger than the largest nacelles in use today. This facility supports the DOE’s objective of using wind power to provide 20% of the electricity generated in the US (currently 25,000 teraWatt-hours generated annually) by 2030.
The DOE issued a separate grant to provide a 15-megaWatt grid simulator in what is now the Duke Energy Electrical Grid Research Innovation and Development (eGRID) center. With the addition of this 15 megaWatt eGRID, companies can test both the mechanical and electrical characteristics of hardware prototypes for any energy resource at utility scale in a controlled and calibrated environment before deploying these resources on an actual electrical grid.
Clemson researchers used National Instruments (NI) FPGA-based hardware programmed with LabVIEW system design software and the LabVIEW FPGA module to create a system capable of HIL (hardware in the loop) control. The FPGAs’ deterministic nature and the LabVIEW Real-Time module allow for a flexible and reliable system for data acquisition, communication, and control.
The eGRID has three components for testing high-power fault and response scenarios:
A power amplifier and reactive divider to simulate the power grid
A real-time digital simulator (RTDS) for creating realistic simulation responses
A control interface
The power amplifier and reactive divider employ an arbitrary waveform generator and 15-megaWatt inductors and resistors that can be controlled with an 83µsec update rate. TECO Westinghouse Motor Company designed and built the power amplifier, which is controlled with a custom serial communication protocol over fiber-optic communications links.
The real-time digital simulator (RTDS) simulates realistic responses of a moderately sized power grid. The RTDS used in combination with the power amplifier can generate predefined voltages representing a power system and can respond realistically to the effects of having a device under test (DUT) connected to the system, providing HIL capability. These two components simulate and test the entire cyber physical system including the wind turbine, power-grid dynamics, and control algorithms.
The control interface manages every aspect of the grid simulator. Its functions fall into three categories:
data acquisition and logging
The Clemson development team considered many options for implementing the control component of the grid simulator, and the deterministic nature, flexibility, and modularity of NI’s hardware and software made NI the alternative of choice. The control interface is built into an NI PXI chassis populated with NI R Series multifunction reconfigurable I/O (RIO) FPGA modules, GPS-synced timing cards, NI FlexRIO FPGA modules, and an NI CompactRIO expansion chassis. NI’s FlexRIO architecture is based on Xilinx Virtex FPGAs. The intuitive LabVIEW programming drastically reduced the development time of the entire system. A small development group with minimal FPGA or HDL experience quickly created the system using LabVIEW and the LabVIEW FPGA module.