Operations and Development of Practical Control Approaches for the Borrego Springs Microgrid

The purpose of this article is to provide an in-depth examination of Borrego microgrid operations, the U.S.s first utility-scale microgrid, and to develop control approaches that are robust, simple, and practical such that they can be readily implemented within the existing Borrego microgrid converters while minimizing hardware retrofits. Borrego is located in the state of California and includes, (i) A solar PV farm with a capacity of 26 MW, (ii) Two sets of battery energy storage (BESS) rated at 0.5 MW, and 1.5 MW, (iii) Two sets of diesel generators (DG) each rated at 1.8 MW, and (iv) A number of community loads accumulating to 13 MW. Borrego microgrid is capable of operating in standalone islanded mode and also offers grid connection to a 92-kV local grid in California. This article proposes three control strategies while the intention is their applicability and implementation to the Borrego microgrid, namely, (1) DC voltage-current (I-V) control applied to each source, where PV farm and DG serve as main sources for addressing load demand that aligns closely with the real-world scenarios observed in Borrego microgrid, and the BESS compensating for the fluctuations in load, (2) An individual d-q control for each solar PV array for achieving maximum power point tracking (MPPT) as the load varies, and (3) A droop control approach that manages parallel connection of multiple sources within the microgrid. The droop control applies the power sharing between the sources based on the deviation of the grid frequency from the reference frequency. As the grid frequency decreases, more power is drawn from the parallel sources up to their rated power, and after that the voltage drop has been observed to meet the further increase in load demand. The analyses of simulation results provide valuable insights into the effectiveness of the proposed controls and their applicability in real-world scenarios.