Grid-Forming Inverter Controls

NREL is developing grid-forming controls for distributed inverters to enable reliable control of low-inertia power systems with large numbers of inverter-based resources. 

 

Existing power systems are dominated by synchronous generators with large rotational inertia and contain a small amount of inverter-interfaced generation. Next-generation inverter controls will enable architectures that are dominated by inverter-based resources. 

Managing the stability of electric power systems is based on decades of experience with large, synchronous generators. Today’s electric power systems have increasing numbers of nontraditional sources, such as wind and solar power, as well as energy storage devices, such as batteries. In addition to the variable nature of some renewable generation, many of these resources are connected to the power system through electronic power inverters.

The operation of future power systems must be based on the physical properties and control responses of traditional large, synchronous turbine generators as well as inverter-based resources. But there is no established body of experience for operating hybrid power systems with significant inverter-based resources at the scale of today’s large interconnections. To operate such systems, the assumptions that underlie generation design and control must be reexamined and modified—or even redefined—to take account of the challenges and opportunities presented by inverter-based generation.

Most inverter controllers today are grid-following and built on the assumption that system voltage and frequency are regulated by inertial sources. Such control approaches cannot guarantee system stability in low-inertia setting and are unlikely to sustain an inverter-dominated infrastructure. This limitation has inspired an investigation into grid-forming control methods for power electronic inverters, which provide functionalities that are traditionally provided by synchronous machinery.

Focused on these challenges, NREL researchers are working to:

• Analyze the limitations of conventional grid-following controllers and develop models of low-inertia systems with traditional controllers
  
  
• Leverage the algorithmic flexibility of digital microcontrollers in designing next-generation inverter controllers for transformative impacts in systems dominated by inverter-based resources
  
  
• Ensure interoperability in hybrid systems with various inverter controls and synchronous generators.
  NREL is collaborating on grid-forming inverter control research with partners from research institutes, manufacturers, vendors, and power system operators. Multiple projects use cross-cutting research approaches that entail mathematical modeling, dynamic systems analysis, control design, hardware development, and experimentation.

Publications

Research Roadmap on Grid-Forming Inverters, NREL Technical Report (2020)

Transient Stability Assessment of Multi-Machine Multi-Converter Power Systems, IEEE Transactions on Power Systems (2019)

Reduced-Order Aggregate Model for Parallel-Connected Single-Phase Inverters, IEEE Transactions on Energy Conversion (2018)

Achieving a 100% Renewable Grid: Operating Electric Power Systems with Extremely High Levels of Variable Renewable Energy, IEEE Power and Energy Magazine (2017)

Can Smart Solar Inverters Save the Grid?, IEEE Spectrum (2016)

View all NREL publications about grid-forming inverter controls.

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