Results: Volt-Watt

Distribution Grid with BESS

We based our evaluation on a San Diego Gas & Electric Company 

(SDG&E) feeder in which a lithium-ion-based BESS has been installed. 

Our research was encouraged by SDG&E in light of their need to comply 

with the California Public Utilities Commission’s requirement to meet a 

target of 165 MW of cost-effective grid storage by year 2020. 

The simulated distribution feeder is a reduced-order representation of the 

full network. The full SDG&E 2,174-node feeder model was reduced to an 

equivalent 7-bus model. It is a 12-kV feeder with a peak load of 7.5 MW. 

The loads are modeled as dynamic loads. Two capacitor banks, both 

rated at 1.2 MVar, are used to regulate the voltage. 

A 1.2-MW PV system is connected at the end of the feeder, and a 1-

MW/3-MWh BESS is connected upstream of the PV system. The loads 

are modeled as dynamic power sinks, and they are controlled by 

multiplying a per-unit load profile by a fixed load. 

IEEE PES General Meeting 2018

Portland, Oregon

August 5–9, 2018

NREL/PO-5D00-72147

Overview of the distribution feeder with BESS integration

Evaluating the Impacts of Battery Energy Storage 

System Functionalities on Distribution Systems 

Using Power Hardware-in-the-Loop Simulation 

Annabelle Pratt1, Jing Wang1, Nathan Ainsworth2, Kumaraguru Prabakar1, Murali Baggu1, Tom Bialek3, and Martha Symko-Davies1

1Power Systems Engineering Center, National Renewable Energy Laboratory, Golden, Colorado, USA

2Nhu Energy, Inc., Tallahassee, Florida, USA 

3San Diego Gas & Electric Company, San Diego, California, USA 

This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. 

Funding provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE 

or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to 

publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

Conclusions

Two functionalities—peak shaving and volt-watt—are simulated, and the 

experimental results are presented. These results demonstrate how a 

PHIL simulation platform can provide a valuable evaluation prior to field 

installation. Information from the PHIL simulations can be used by utility 

operators to determine how to operate their utility assets most effectively 

under different scenarios in the field presented.

Abstract

A battery energy storage system (BESS) can provide various grid support 

services, including voltage regulation, peak shaving, and photovoltaic 

(PV) smoothing. This paper presents results from a power hardware-inthe-loop (PHIL) simulation that was performed to test and demonstrate 

the impacts of BESS functionalities on a distribution feeder. 

The PHIL platform includes a simulated distribution grid in a real-time 

digital simulator (RTDS), AC and DC power amplifiers, and a battery 

inverter as the device under test. Guidelines on how to set up a PHIL 

platform to evaluate the impact of grid integrated systems are provided. 

Accelerated time-series PHIL simulations of peak shaving and volt-watt 

functionalities were performed using a 540-kVA BESS. These 

experimental results illustrate how PHIL simulations can be used to 

evaluate the impact of BESS functionalities on the distribution grid prior to 

installation in the field. 

Hardware-in-the-Loop Platform

Prior to the installation of a BESS in the field, proper evaluation must be 

performed to understand how the BESS can impact the grid. The most 

popular hardware testing approach is hardware-in-the-loop testing, which 

has several benefits, such as repeatability, relatively low cost, and reliable 

results. PHIL combines the advantages of a complete numerical 

simulation method and actual hardware, and PHIL testing allows 

hardware devices to be evaluated in an environment that emulates 

various realistic field conditions. 

The distribution feeder was simulated in an RTDS with a time step of 50 

μs. The PV system is modeled as a controlled current source. The input 

to the PV model specifies the output active power of the PV system, and 

the PV controller regulates the current to match the PV output active 

power to this input. We implemented an augmented ideal transformer 

PHIL interface method, and we present the design of the PHIL interface 

compensation algorithm to ensure stable and accurate PHIL simulation.

Schematic diagram of implemented PHIL simulation

PHIL loop with the interface compensation

Results: Peak Shaving

The peak day load and PV data sets were used. The BESS was inactive 

for the baseline test case, and it was operated to track a precalculated 

real power profile for the peak shaving test case. The BESS sinks real 

power (charging the battery) in the early morning near the minimum 

power, and it sources power (discharging) in the evening to reduce the 

peak. As a result, the peak source power is reduced. 

Feeder power profile results for peak load day with peak shaving

Comparison of voltage at BESS with and without volt-watt

The minimum day load and PV data set were tested 

with and without the BESS performing volt-watt 

compensation with no deadband. The BESS 

provides active power to compensate the morning 

and evening voltage dips. For this feeder, the BESS 

provides voltage support, but it is not of a sufficiently 

high rating to significantly impact the voltages.

Volt-watt curve

PHIL hardware in NREL’s Energy Systems Integration Facility