Primary and Secondary Control of Dispatchable Virtual Oscillator-Controlled Grid-Forming Inverters
MS student T.G. Roberts with advisor A. Domínguez-García
Grid-forming inverters (GFMs) are a promising technology for replacing synchronous generators to sustain system voltage and frequency in microgrids with low inertia. In the U.S. bulk power grid, inertia from rotating generators helps resist sudden changes or fluctuations in frequency. Current grid-following inverters (GFIs) do not possess the capability to regulate their own frequency or voltage, which can lead to grid instability on grids with a high percentage of renewables. GFM inverters however are able to regulate their own voltage and frequency output. Applications of GFMs range from replacing synchronous machines to creating fully renewable microgrids. This research focuses on primary and secondary control of dispatchable virtual oscillator controlled (dVOC) GFMs. We first develop a power-flow model for a three bus microgrid with a dVOC-based inverter at each bus. Afterwards, we create a reduced-order dynamical model with a distributed slack bus. We then propose a secondary control architecture for regulating frequency and voltage using multiple integral controllers. This approach is novel, as previously only frequency control for GFMs has been extensively developed, and adding secondary voltage control will provide increased stability as the percentage of renewables on the grid rises. This research is funded by the U.S. Department of Energy.