New Technologies Help Grid Stability

PXiSE, is a startup company jointly developed by California utility company Sempra Energy and utility data software vendor OSIsoft. Sempra owns and operates almost 2,400 megawatts of renewable capacity. OSIsoft is a leading data management provider that can collect grid related data from multiple sources over a wide area. Sempra Energy is beginning to manage more locations that include battery storage connected to wind and solar power generation sources. This new equipment forms interconnected microgrids where battery storage adds new capability to improve grid reliability. Sempra PXiSE takes data analytics to the next level with high speed closed loop control on the distribution side of the grid. The OSIsoft application collects relevant data from the microgrids as well as control signals from the grid operator. The data collection includes high speed synchrophasor measurements, such as those used on high voltage transmission lines. Synchrophasors are used to measure grid frequency and power factor, and have long been used control transmission lines.

The control of an electric grid is difficult because grids do not have the capacity to tolerate a large mismatch between supply and demand. We often take for granted the automatic generation control (AGC) that is adjusting the power output of multiple generators at different power plants, in response to changes in the load. Generation of power must respond very quickly changes in demand. Spinning reserves typically provide the initial response. A new load initially slows down heavy rotating turbines and generators, but these machines must regain their speed as the grid quickly dispatches needed power generation. Grid connected batteries have the advantage they can be deployed at high speed and the PXiSE control system does just that. The early signs of grid stress are typically oscillations of the grid frequency (60 Cycles per second in the US and 50 cycles per second in most of the world). Grid instability can trip frequency protecting relays leading to blackouts and low power factors can lead to excessive current in transmission and distribution lines which stresses the grid.

Sempra has developed closed loop control software that can use OSIsoft data and the synchrophasor measurements to regulate frequency and power factor in a low voltage battery inverter on the distribution side of the grid. Sempra recognized that new solid-state electronics built into the inverters of battery systems can accept command signals to adjust the frequency and power factor with a very fast response time. As more battery storage appears on the grid, this technology could become a significant source of grid stability.

When non-dispatchable wind and solar power is coupled with highly dispatchable battery systems, microgrids are formed and the Sempra PXiSE concept can use this configuration to add grid stability. Keeping electric power flowing efficiently, and reliably is increasingly important and systems like PXiSE is an innovative technology that can help.