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Controllable Grid Interface

NREL's controllable grid interface (CGI) test system at the National Wind Technology Center significantly reduces the time and cost of evaluating and refining energy system response.

Photo of a man walking towards several long buildings.

The CGI can simulate faults and allows manufacturers and system operators to conduct certification tests in a controlled laboratory environment.


The CGI test system is central to NREL's grid integration research, and it is the only system in the world that is fully integrated with two dynamometers. It can extend that integration to renewable energy devices in the field and to various electronic and mechanical storage devices that are located nearby on the same test site.

Specific CGI capabilities include:

  • Voltage fault ride-through
  • Frequency response
  • Continuous operation under unbalanced voltage conditions
  • Simulation of grid condition (strong and weak)
  • Simulation of grid voltage distortions
  • Testing of reactive power, power factor, and voltage control
  • Testing of the protection system, including overvoltage, undervoltage, and frequency limits
  • Islanding operation
  • Subsynchronous resonance conditions
  • 50-hertz tests.