Increasing Grid Resilience Under Differing Distributed Control Architectures

Recently, we’ve written about PNNL’s innovative work to demonstrate how a utility power system can safely operate using a control system integrated with the Open Field Message Bus (OpenFMB) framework to increase system flexibility and resiliency. PNNL has successfully tested these concepts in a laboratory setting, and have analyzed how OpenFMB concepts can support innovative transactive energy schemes for increasing resilience. As this technology progresses towards commercial use, these project concepts will now be deployed in the field to generate real, tangible results in an operating utility distribution network.

These successes are part of the Grid Modernization Laboratory Consortium (GMLC) Resilient Distribution System (RDS) project entitled, “Increasing Distribution System Resiliency using Flexible DER and Microgrid Assets Enabled by OpenFMB.” In October 2020, we highlighted accomplishments from the project’s completion of laboratory-based co-simulations and its testing of utility operational concepts in an emulated environment. These activities were in preparation for a field validation of project concepts on a subsection of host utility Duke Energy’s network.

To prepare for field validation, the project team created an integrated assessment plan (IAP), which defines the testing required to meet the objective of the original research proposal to the Department of Energy (DOE). The IAP includes an operational demonstration execution plan to execute the field demonstration, and an operational assessment plan which describes the data collection process during the demonstration. The project team aims to validate OpenFMB’s ability to augment centralized systems and execute coordinated and autonomous control of grid edge devices in an active distribution network. When paired with results from simulations and lab demonstrations, the team will have evaluated the entire scope of the RDS project.

The field demonstration focuses on increasing resiliency using a specific example of fault location isolation and service restoration (FLISR), solar photovoltaic (PV), battery energy storage, and microgrids. The exhibited resiliency will be evaluated through increased operational flexibility, as measured by the following:

• Autonomy: Each segment on a distribution system will have the ability to support a level of autonomous operations, in coordination with the distribution management system (DMS)
• Coordinated Control: Distributed Energy Resources (DERs) will be able to make local high-speed decisions in support of centralized systems that have access to more information
• Distributed DER Intelligence: The system will engage DERs as active elements to support the segment-based operation of the system
• Dynamic network configuration: The system will recognize, validate, and evaluate the specifications of new devices, as well as compensate for those that cease to operate or communicate

The IAP documents eight demonstration scenarios ranging from relatively benign operations, such as observing how OpenFMB works with existing equipment and systems, to more operationally complex, such as the coordination of protection settings between distribution SCADA and OpenFMB. For each scenario, distribution operations staff will install OpenFMB adapters in all protection and control equipment and in DER/microgrid controllers. These devices will publish time-stamped reading and status profiles that include real-time phasor measurements, such as voltage, currents, real and reactive power, and power factor. OpenFMB nodes will subscribe to this data as it is published, allowing distributed processing of messages.

New opportunities to apply OpenFMB concepts
Duke Energy will complete the field demonstration defined in the IAP once all regulatory approvals are obtained and supporting equipment is installed. Additionally, Duke Energy has indicated it will spend up to $302 million on expanding the deployment of self-optimized grid (SOG) technologies. As quoted in their PUC filing (NC Dockets E-2 sub 1219 and 1193), the new SOG system must address the fact that “…when privately owned roof-top solar becomes widespread, a dynamic, automated, capacity-enabled two-way power flow grid will be essential.” The Duke-RDS project, and the concepts developed as part of it, provides Duke Energy with new technical capabilities to complement and enhance the coordination of SOG in regions with medium-to-high penetration of grid-tied distributed energy resources.

While Duke Energy will utilize the IAP to demonstrate project concepts in the field, the GMLC project team also wants to ensure project learnings and IAP concepts are carried forward. DOE, PNNL, and Duke Energy project representatives discussed how to best leverage these learnings and concepts in lieu of a culminating field demonstration. These discussions yielded the decision to apply the OpenFMB concepts to a different GMLC project just getting underway – the Citadels Project.

The GMLC Citadels Project is focused on how networked microgrids, and their component DERs, can operate using collaborative autonomy concepts implemented in an OpenFMB architecture. Citadels uses the concept of consensus algorithms – a common technique used in distributed computing. It includes a number of agents that communicate with each other to achieve a global objective in a distributed way, without containing a single point of failure. Citadels will apply this concept to self assembly of networked microgrids, with the microgrids acting as the agents. The architecture treats each microgrid’s controller as an agent that reaches a decision on how best to meet the objective function. Each controller then communicates with others to produce a consensus decision. The goal is to demonstrate that, when networked, these microgrids can operate longer than when islanded, thus providing an increased resilience benefit.

While Citadels will implement a peer to peer control strategy, as the GMLC RDS project did, it is fundamentally different. Selecting an OpenFMB framework enables a flexible control architecture. The RDS project team proved that OpenFMB is sufficiently mature and flexible to support peer to peer communications, and to do so with off-the-shelf equipment. Likewise, it also proved that OpenFMB is a flexible framework that supports any sort of messaging through both distributed and centralized control architectures. These findings confirm OpenFMB and IAP concepts from the RDS project as a perfect fit for the Citadels project.