This document provides an overview of intentional islands, otherwise known as microgrids. The topics covered include common types of microgrid configurations, high level summaries of standards that address some aspect of microgrid implementation and interconnection, and a discussion of specific standards that apply during specific the islanding operational stages of parallel operation, transition to islanding, islanding operation and transition back to parallel operation.

The focus of this document is to provide a summary of the requirements related to unintentional islanding in the IEEE 1547 standard, and to provide the reader with basic knowledge and background information to improve the understanding and utilization of the requirements specified.

Renewable energy has become a viable solution for reducing the harmful effects that fossil fuels have on our environment, prompting utilities to replace traditional synchronous generators (SG) with more inverter-based devices that can provide clean energy. One of the biggest challenges utilities are facing is that by replacing SG, there is a reduction in the systems’ mechanical inertia, making them vulnerable to frequency instability. Grid-forming inverters (GFMI) have the ability to create and regulate their own voltage reference in a manner that helps stabilize system frequency. As an emerging technology, there is a need for understanding their dynamic behavior when subjected to abrupt changes. This paper evaluates the performance of a GFMI when subjected to voltage phase jump conditions. Experimental results are presented for the GFMI subjected to both balanced and unbalanced voltage phase jump events in both P/Q and V/f modes.

This document reports on the Grid Modernization Laboratory Consortium effort to identify gaps in standards for the interconnection and interoperability of distributed energy resources (DERs). The project extended a 3-year period from 2017 to 2019. Under the work plan, the team identified standards and test procedures related to interconnection and interoperability, grouped under the broad headings of their primary applicable technology domain: automotive, responsive loads, photovoltaic inverters, inverter-based energy storage, machine-based DERs, and microgrids. The team then conducted a gap analysis by comparing the current standards to the expected future requirements needed for specific grid services. Overall, gaps could be any activity needed to harmonize requirements among standards development organizations, minimize conflicting requirements among technology domains, or streamline conformance test procedures.

Grid codes around the world are requiring grid-support functions (GSFs) and standardized interoperability interfaces for distributed energy resources (DERs) to address the rapid increase of renewable energy. However, these new GSFs need to be assessed to ensure the desired power and communication capabilities exist in the field. The IEEE 1547.1 standard outlines the conformance test procedures for DER devices and is currently undergoing a major revision to align it with IEEE 1547-2018. Once it is published (anticipated in mid-2020), GSFs in commercial PV inverters in USA and Canada will be certified to the IEEE 1547.1 conformance test procedures. Several international research laboratories are collaborating to develop a versatile open-source DER testing platform that performs automated testing of DER devices. This community of laboratories is developing open-source IEEE Std. 1547.1 test scripts to lower barriers to DER vendor internal equipment evaluations, ease product compliance testing at certification laboratories, and provide research institutions a tool to study DER behaviors. In this work, test scripts were used for test verification of GSFs, including limit active power, constant reactive power, active power-reactive power (watt-var), and prioritization of GSF response for several DER devices. Sample test results for these DER GSFs and test protocol recommendations are presented in this paper.

Photovoltaic (PV) inverters connected to electrical grids are required to detect and respond to Unintentional Islanding (UI) conditions appropriately. The IEEE Std 1547.1-2020 specifies test procedures, based on resonant parallel RLC loads, to evaluate the ability of PV inverters to detect and disconnect under UI conditions. This paper proposes a prototype Power Hardware-in-the-Loop (PHIL) UI testing console with a Human Machine Interphase (HMI) and a virtual RLC load to evaluate the IEEE Std 1547.1-2020 UI Cat. B tests. Traditional UI testing procedures rely on physical RLC elements, which are potentially expensive, large, and heat-generating sources. Using PHIL techniques, the UI test procedure itself, and the RLC load were implemented virtually within a simulation environment. The virtual console could potentially reduce testing costs, decrease execution time and pave the way for automated testing. This paper presents promising preliminary results from the virtual console prototype.

Increasing solar energy penetrations may create challenges for distribution system operations because production variability can lead to large voltage deviations or protection system miscoordination. Instituting advanced management systems on distribution systems is one promising method for combating these challenges by intelligently controlling distribution assets to regulate voltage and ensure protection safety margins. While it is generally not the case today, greater deployment of power system sensors and interoperable distributed energy resources (DER)e.g., photovoltaic (PV) inverters, energy storage systems (ESS), electric vehicles (EVs)will enable situational awareness, control, and optimization of distribution systems. In this work, a control system was created which measures power system parameters to estimate the status of a feeder, forecasts the distribution state over a short-term horizon, and issues optimal set point commands to distribution-connected equipment to regulate voltage and protect the system. This two-year project integrated multiple research innovations into a management system designed to safely allow PV penetrations of 50% or greater. The integrated software was demonstrated through extensive real-time (RT) and power hardware-in-the-loop studies and a field demonstration on a live power system with a 684 kVA PV system.

Historically, photovoltaic inverters have been grid-following controlled, but with increasing penetrations of inverter-based generation on the grid, grid-forming inverters (GFMI) are gaining interest. GFMIs can also be used in microgrids that require the ability to interact and operate with the grid (grid-tied), or to operate autonomously (islanded) while supplying their corresponding loads. This approach can substantially improve the response of the grid to severe contingencies such as hurricanes, or to high load demands. During islanded conditions, GFMIs play an important role on dictating the system's voltage and frequency the same way as synchronous generators do in large interconnected systems. For this reason, it is important to understand the behavior of such grid-forming inverters under fault scenarios. This paper focuses on testing different commercially available grid-forming inverters under fault conditions.

This is the final report for a project to support the development of systems integration standards. The scope of work undertaken by the multi-laboratory team was to facilitate standards development and to help expedite the process in three important standards identified under the SunShot National Laboratory Multiyear Partnership (SuNLaMP) grid performance and reliability topic area. Specifically, the standards addressed are IEEE 1547, IEEE 1547.1 and UL 1741.

The anticipated high penetration of distributed photovoltaic (PV) energy sources is expected to lead to significant changes in utility interconnection requirements for PV systems. These changes will include provisions for voltage and frequency regulation capability, as well as better voltage and frequency ride through requirements. For distributed energy resources (DER), in particular PV, to provide grid support, it must participate in frequency and voltage regulation. Frequency and voltage ride through allows inverters to remain connected to ensure robust recovery in the event of voltage and frequency disturbance. Implementing these advanced capabilities is essential to mitigating the negative impacts of high penetration PV, but their integration into a typical distribution system presents significant technical challenges, one of which is the increased risk of unintentional islanding. In this paper, an island detection method is presented that relies on a continuous subharmonic signal, a power line carrier permissive (PLCP), that is injected at the transmission level or at the substation and detected by any type of DERs in any combination. Absence of the signal indicates loss of utility and possible island condition. Laboratory and simulation experiments were done to investigate feasibility of the method. The PLC system discussed herein is novel in that it utilizes a power electronics based series voltage injection method. Advantages include the ability to use a smaller and less expensive transformer and enhanced flexibility in the amplitude, waveform and frequency of the injected signal.

The high penetration of photovoltaic (PV) distributed energy resources (DER) facilitates the need for today’s systems to provide grid support functions and ride-through voltage and frequency events to minimize the adverse impacts on the distribution power system. These new capabilities and its requirements have created concerns that autonomous unintentional islanding (UI) algorithms are not sufficient to prevent a condition were the loss of utility is detected. Type tests in IEEE 1547-2018 have evolved to thoroughly evaluate DER capabilities and a new method includes power hardware-in-the-loop (PHIL) testing. Sandia National Laboratories is performing a detailed laboratory comparison of the tuned Resistive, Inductive, Capacitive (RLC) circuit method using discrete elements and the PHIL that applies the PV inverter equipment under test (EUT), real-time simulator, and a power amplifier. The PHIL method allows UI assessments without the need for potentially expensive, large, heat generating discrete loads.

As utility interconnected photovoltaic systems (PV) become integrated into the electrical power system (EPS) at an increasing rate, utilities and regulators have become concerned about the potential for increased voltage and frequency deviations as well as EPS reliability and resiliency. These concerns have initiated the need to amend the utility interconnection standard to allow advanced inverter control functionalities that provide: (1) reactive power control for voltage support, (2) real (active) power control for frequency support and (3) voltage and frequency ride- through for bulk system support. The new real and reactive power modulation are intended to reduce EPS voltage and frequency deviations by mimicking the droop and excitation controls of conventional generation. The new ride-through capabilities are needed to prevent a large quantity of generation from autonomously de-energizing or disconnecting in response to a voltage or frequency deviation. These changes, however, may have the potential to interfere with autonomous anti-islanding, especially when multiple inverters from different vendors are co-located on one bus. This report presents results from an investigation of multi-inverter autonomous anti- islanding with advanced functions, and the development of a means to mitigate adverse interaction between the two.

The proliferation of photovoltaic (PV) distributed energy resources (DER) on distribution systems have caused concerns about electric power system (EPS) protection schemes, protection configurations, and device coordination. With the EPS designed for power to flow in one direction, the high penetration of PV-based DER has created concerns of grid reliability and protection scheme efficacy. The short-circuit current characteristics of the classical synchronous generator has been well characterized for symmetrical or unsymmetrical short circuit faults, but inverter-based DER dynamic models are not as well-known and are generally specific to a single inverter manufacturer. There is also uncertainty in how advanced inverter controls like volt-var and low-voltage ride-through capabilities can impact the inverter fault currents. This paper performs laboratory tests to quantify the fault currents of single-phase, three-phase, and grid-forming inverters under a range of grid-support function operating modes. The results characterize the PV DER sub-transient, transient, and steady-state equivalents. It was found that grid-support functions affect the current contribution from PV inverters.

Most inverters for use in distribution-connected distributed energy resource applications (distributed generation and energy storage) are tested and certified to detect and cease to energize unintentional islands on the electric grid. The requirements for the performance of islanding detection methods are specified in IEEE 1547-2018, and specified conditions for certification- type testing of islanding detection are defined in IEEE 1547.1. Such certification-type testing is designed to ensure a minimum level of confidence that these inverters will not island in field applications. However, individual inverter certification tests do not address interactions between dissimilar inverters or between inverter and synchronous machines that may occur in the field. This work investigates the performance of different inverter island detection methods for these two circumstances that are not addressed by the type testing: 1) combinations of different inverters using different types of islanding detection methods, and 2) combinations of inverters and synchronous generators. The analysis took into consideration voltage and frequency ride- through requirements as specified in IEEE 1547-2018, but did not consider grid support functionality such as voltage or frequency response. While the risk of islanding is low even in these cases, it is often difficult to deal with these scenarios in a simplified interconnection screening process. This type of analysis could provide a basis to establish a practical anti- islanding screening methodology for these complex scenarios, with the goal of reducing the number of required detailed studies. Eight generic Groups of islanding detection behavior are defined, and examples of each are used in the simulations. The results indicate that islanding detection methods lose effectiveness at significantly different rates as the composition of the distributed energy resources (DERs) varies, with some methods remaining highly effective over a wide range of conditions.

Active and reactive power must be balanced between generation and load when there is a section of the area electric power system that has been disconnected, or islanded, for there to be a possibility of creating a sustained island lasting two seconds or more. The degree to which this power balance must be achieved can be expressed using several equations. These equations can be used to estimate the island voltage and frequency based upon the generation and load conditions that existed just prior to formation of the island. These equations apply to inverter based current source generation and are fundamentally different than if the island were formed using synchronous voltage source generation. Qualitative consideration of advanced inverter functions such as Volt-Var, Frequency-Watt or Volt-Watt are provided. It is proposed that Volt-Var operation will significantly reduce the possibility of sustained island operation.