Results

Background

In Phase 1 of this DOE project, EPRI developed a dedicated PV System model in the OpenDSS. In addition to this model, EPRI also developed a new control model in the OpenDSS that gave the PV system the ability to provide volt/var control, as defined in an industry-wide effort lead by EPRI, DOE, Sandia, and SEPA .

In Phase 2 of this project, EPRI examined two field demonstration cases of high PV penetration on existing utility distributions. Stochastic analysis of thousands of PV deployment scenarios as well as time series analysis was performed on both feeders. The results showed that feeder impacts vary greatly depending upon the particular feeder, how much PV is added, size of the PV (customer kW-class vs. utility MW-class) and most importantly, where it is located on a feeder. By taking these factors into account, EPRI’s detailed modeling and simulation approach was able to quantifiably determine PV hosting capacity for each feeder. In particular, one of the two distribution feeders EPRI modeled was found to have a much lower hosting capacity for PV due to voltage related issues.

A number of research projects have addressed the need for developing and applying advanced inverter capabilities for PV. Combining Phase 1 and Phase 2 efforts, EPRI’s Phase 3 has taken research in this area one step further by demonstrating, through simulations, how effective changes in the PV inverter controls can increase the distribution feeder’s hosting capacity.

The analysis approach in this phase determined the potential improvement in PV hosting capacity from utilizing rather straightforward changes in PV inverter controls. While other research efforts have focused more on single PV systems and the use of advanced inverter functions for providing grid support, this effort targeted large numbers of PV systems spread throughout an entire feeder. This focused on the potential aggregate impact of each PV system’s contribution to help support the grid through smart inverter controls and therefore increase the amount of PV that can be accommodated on the feeder (hosting capacity).

Specific grid-support functions that were considered included fixed power factor, intelligent volt/var, dynamic reactive current, and volt/watt controls. These grid-support function definitions were updated in a second phase of the EPRI/DOE/Sandia/SEPA-led project mentioned previously. Task 11 of this project took the single voltage-constrained feeder that was modeled in Phase 2, applied these grid-support functions to all the PV in the model, and determined potential improvements to hosting capacity. In addition to the volt/var function added under Phase I, as part of a separate, EPRI-funded project, the additional advanced inverter functions listed above were added to the OpenDSS. Since the OpenDSS is open-source and freely available, once implemented these new inverter control models become immediately available for public use.

The results of the Phase 3 effort have demonstrated, through simulation, how implementation of smart inverter functions in the PV inverter controls can increase a distribution feeder’s hosting capacity for PV.