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Increasing Grid Resilience with Transactive Energy

Days ago, you predicted a relatively minor storm. Now, forecasts predict a much stronger one. Fortunately, your utility has implemented technologies and controls to enable a self-healing grid. Nevertheless, you activate your storm response team and your distribution operators are poised to employ additional switching operations to minimize potential outages. What more can you do? How about calling on customers with distributed energy resources (DERs)?

Researchers working on the Grid Modernization Laboratory Consortium’s (GMLC) Resilient Distribution System (RDS) project are focused on achieving increased resilience through self-healing concepts. The project aims to show that non-utility DERs do not interfere with the deployment of utility self-healing technologies, but instead can provide an operational resource. As discussed in two recent SEPA blogs, the OpenFMB framework included in the scope of the RDS project enables self-healing concepts through an architecture that combines centralized and distributed control of traditional utility assets and distributed energy resources. Taking this a step further, Pacific Northwest National Lab (PNNL) researchers working on the RDS project have looked at applying transactive energy to support these self-healing concepts.

Transactive energy is traditionally viewed as an approach for shifting or reducing peaks by incentivizing customers to conduct energy transactions between themselves, or between themselves and the utility. PNNL is testing several transactive energy methods at pilot projects across the country. By designing the incentive signal to shift or reduce the peak, transactive energy can provide a service to the grid and economic opportunities for customers.

The RDS project team looked at transactive energy a little differently. They believed transactive energy could provide grid reliability in addition to peak reductions, and customer incentives could provide reduced outage risk benefits to customers in addition to financial payments. PNNL analyzed how transactive energy, enabled through OpenFMB, could increase resilience under a diverse set of blue, grey, and dark sky use cases on a subset of Duke Energy’s substations and feeders.

First of its kind study
The PNNL patent pending algorithm used in their study reimagines the role transactive energy can play in providing resilience services to the grid. PNNL conducted the study on the “grey sky” Duke Energy distribution network use cases developed by the RDS project team. “Grey sky” conditions indicate abnormal conditions and faults on the feeders. The “grey sky” use case includes a self-healing grid with a microgrid and non-utility DER assets on specific feeders.

Transactive Energy
High Level Circuit Diagram

PNNL’s analysis includes the three technologies evaluated in the RDS project:

  1. A centralized self-healing system
  2. An inverter-based microgrid
  3. A transactive energy scheme (simulation only)

To develop a demand curve, PNNL used a double auction market with the utility pay curve mimicking a simplified ISO market clearing curve and its load requirements. The analysis included a large number of DER devices by assuming 20% solar penetration. The team emulated utility operating scenarios by co-simulating the power system model and the representative utility control systems, with the transactive algorithms and the communication network using a Hierarchical Engine for Large Scale Infrastructure Co-Simulation (HELICS)-based framework.

The figure below shows the conceptual framework PNNL used for its analysis. When “grey sky” conditions occur, the sequence of operations begins with the utility distribution management system (DMS) determining the optimal reconfiguration of utility-owned assets. If all loads cannot be restored, the DMS activates the transactive algorithm (TEA-1 and TEA-2) to engage non-utility assets. A transactive market calculates incentive signals to send to customers to meet utility requirements.

Transactive Energy
Conceptual Framework for Deploying Transactive. Source: PNNL

The study then assumes the utility would initiate an incentive signal to DER customers and conduct the additional switching options made feasible due to contributions from the non-utility DERs.

While PNNL only evaluated solar DER, the study approach could apply to any inverter-based DER, such as electric vehicles or energy storage.

OpenFMB is key
The OpenFMB architecture employs existing industry standards and technologies to securely and efficiently federate data at the grid edge. It can accelerate the deployment of resilient and secure distribution concepts through the flexible operation of traditional utility assets (e.g. reclosers, voltage regulators, and cap-banks) as well as non-utility assets.

Transactive Energy
The OpenFMB Harness

A layered OpenFMB-based control system employs a circuit segment-based approach to enable flexible operating strategies. SCADA controls traditional utility assets while VOLTTRON™ agents engage non-utility assets including DERs and end-use loads. VOLTTRON™ is an open-source IoT platform developed by PNNL for behind-the-meter control. Its small software system runs specially crafted agents, which communicate with one another and the outside world using tagged messages in a pub-sub (publish-subscribe) model.

Key findings
By including behind-the-meter DER with utility assets in a self-healing network, the PNNL study found that the number of switching operations for the distribution system operator could be increased by 15%, contributing to enhanced reliability. This increase is primarily due to the operational flexibility created by non-utility assets, which creates more switching options for grid operators. A control architecture of centralized and distributed controls, enabled by a framework such as OpenFMB, allows for flexible operation of behind-the-meter assets alongside traditional utility assets.

Customers, and their incentives for participating in the self-healing network, play a key role in realizing the results found in the study. Since transactive energy is an incentive signal for non-utility assets to provide reliability services, design of the incentive signal is critical. Success requires coordination of the performance changes from all actors on the system. As such, a financial incentive may not be appropriate. Instead, the incentive may be more about individual customers contributing to reliability.

Monetizing this reduced outage risk and paying customers for their contribution is the primary challenge, not the technology. The GMLC RDS project is proving that distributed intelligence concepts in an OpenFMB framework can deliver grid resilience using commercially available assets and communication networks. Leveraging the findings from the GMLC RDS project, utilities can deploy these concepts and technologies today. PNNL’s transactive energy study reveals customer assets can further add to this resilience value via the design of the proper incentive mechanism.

The GMLC RDS project will be completed in September, 2021. More information on the GMLC RDS project and its use of the OpenFMB framework will be made available throughout the year. SEPA will continue to share updates, findings, and lessons learned from this project. Stay up to date with SEPA via social media, upcoming webinars, and additional articles.