Skip to main content

Virtual Oscillator Controls

NREL is developing virtual oscillator controls for distributed inverters to enable reliable control of low-inertia power systems with hundreds of gigawatts of photovoltaic (PV) integration.

In today's electric power system, large fossil fuel-driven generators provide rotational inertia that forms a rigid backbone to maintain system frequency. However, with PV forecasted to provide more than 600 GW of generation by 2050 under Department of Energy SunShot objectives, power electronic inverters will play a large role in maintaining the reliability of future systems.

Schematics of the present and future power systems showing the growth of distributed energy resources and inverters.

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

Today, risks to system stability are apparent on islands, such as Hawaii, that contain large amounts of PV generation. In these low-inertia systems, PV power is routinely curtailed to ensure frequency regulation. This approach is necessary because of a fundamental shortcoming of contemporary control strategies: Existing inverter controllers cannot guarantee grid stability.

Existing inverter controllers are grid-following and built on the assumption that system voltage and frequency are regulated by inertial sources. But prevailing control approaches cannot guarantee system stability in a zero-inertia setting and are unlikely to sustain an inverter-dominated infrastructure. The future calls for the deployment of stabilizing grid-forming controllers for decentralized inverter networks that actively regulate voltage and frequency.

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 PV-dominated networks
  • Assess the compatibility of novel grid-forming controllers on commercial off-the-shelf inverters.

This project uses a cross-cutting research approach that entails mathematical modeling, dynamic systems analysis, control design, hardware development, and experimentation. The project team comprises experts at NREL, the University of Minnesota, University of California Santa-Barbara, and SunPower.

Publications

Synthesizing Virtual Oscillators To Control Islanded Inverters, IEEE Transactions on Power Electronics (2015)

Uncovering Droop Control Laws Embedded within the Nonlinear Dynamics of Van der Pol Oscillators, IEEE Transactions on Control of Network Systems

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

Oscillator-Based Inverter Control for Islanded Three-Phase Microgrids, IEEE Journal of Photovoltaics (2013)

Synchronization of Nonlinear Circuits in Dynamic Electrical Networks With General Topologies, IEEE Transactions on Circuits and Systems I: Fundamental Theory and Applications (2014)

Synchronization of Nonlinear Oscillators in an LTI Electrical Power Network, IEEE Transactions on Circuits and Systems I: Fundamental Theory and Applications (2014)

View all NREL publications about virtual oscillator controls.

Contact

Brian Johnson

Research Engineer

brian.johnson@nrel.gov
303-275-3967