Frequency response of California and WECC under high wind and solar conditions

The frequency behavior of North American grids has recently been the subject of considerably heightened concern. Reports by the North American Reliability Corporation show that “frequency response”, that is, the severity and recovery of grid frequency following large disturbances (typically trip of large thermal generation plants) has been declining over the past two decades. The addition of substantial amounts of wind power plants, and in the near future large amounts of solar photovoltaic generation, complicates the issue. A typical wind plant appears to the grid as a substantially different generation source than a conventional power plant. Without special controls, a wind plant does not inherently participate in the regulation of grid frequency. By contrast, synchronous machines always contribute to system inertia, and a fraction of the synchronous generation in operation at any point have governor controls enabled. When wind and solar generation displaces conventional synchronous generation, the mix of the remaining synchronous generators changes and has the potential to adversely impact overall frequency response. The paper summarizes results from a recent study of system frequency response in California and the Western US. Impacts of wind and solar generation on frequency response are shown. Various aspects impacting frequency response, including fraction of generation providing governor response, governor response withdrawal, and use of frequency responsive wind plant controls are presented.