Project Background

For NERC and its many stakeholders, understanding the full-spectrum impact of distributed energy resources (DERs) on the bulk power system (BPS) is a critical component in ensuring secure and reliable grid planning and operations. A transmission and distribution (T&D) co-simulation software tool that enables transmission planners to conduct studies using their existing workflow and without the necessity to know co-simulation technique is a current need that TDcoSim is designed to address. The tool is being developed in close partnership with NERC to ensure the tool meets NERC’s requirements.

Scientific Opportunity

Current state-of-the-art transmission-only tools use aggregated DER model that captures the total response of DERs at a given transmission-distribution interface. The primary challenge stems from the fact that not all DERs in the distribution feeder follow the same standard with some of the DERs following older standards while others following newer standards. Capturing this mixed vintage of DERs accurately, while accounting for the voltage drop along the feeder is an open problem. These factors, combined with the increasing levels of DER penetration has raised fundamental questions about the way we plan and operate the electric grid. Hence, there exists a need to develop detailed models, such as transmission & distribution co-simulation, that are capable of accurately capturing the impact of DERs on BPS stability.

Research Goal

To develop transmission & distribution co-simulation software, TDcoSim, and use it to answer the fundamental questions the industry is currently facing – a) Do currently available DER models with default settings adequately capture the characteristics to validate system stability, b) Understand the limitations of transmission only positive sequence simulation tools under the context of modern power system operation with significant renewable generation. The aim of this project is to answer these questions in a quantifiable manner and provide recommendations to improve the current practices.

Research Plan

Expanding TDcoSim capabilities

• Development of individual DER models that have desired numerical properties.
• Large scale DER model integration
  • 20,000 individual DER instances were integrated and validated in T&D co-simulation.
  • The validation includes, among other metrics, comparing the response of the DERs to that of DER_A model.
  • The fast DER model is capable of emulating the behavior of BTM solar.
  • The team is currently testing out capabilities to scale the number of DER instances to 100,000. The fast DER model is non-stiff. This allows explicit numerical integration schemes to be used. Hence, large number — in the order of tens of thousands of individual DERs — can be modeled.

Using TDcoSim to understand limitations of transmission-only positive sequence simulation tools under increasing DER penetration

• Emphasis is on assessing impact of DERs on BPS stability
• Development of NERC SPIDERWG white paper — ​“Beyond Positive Sequence”
  • TDcoSim is used to compare current approaches under future DER penetration scenarios
  • Provide recommendations to better represent existing aggregated DER models in transmission planning studies.
• Answer fundamental questions that the industry is currently facing

Deliverables and Impacts

TDcoSim: Development of open-source transmission and distribution co-simulation software that is capable of accurately evaluating the impact of DERs on BPS stability. The repository can be accessed at https://​github​.com/​t​d​c​o​s​i​m​/​T​D​coSim

Industry adoption: TDcoSim takes a language and technology agnostic approach for better adoption. The user needs little to no knowledge of programming or co-simulation to use TDcoSim. The user interacts with TDcoSim using human readable and intuitively structured JSON files to setup and run complex T&D co-simulations with ease.

NERC SPIDERWG White Paper: ​“Beyond Positive Sequence” white paper. TDcoSim is used to quantify the differences between the state-of-the-art approaches and co-simulation. The differences between the approaches are viewed from the transmission planner’s perspective. The recommendations are be based on whether the current approach warrants a change under high DER penetration levels i.e. difference in results are acceptable until it becomes a deficiency. Through TDcoSim, the team also identified and provided recommendations to better represent existing aggregated DER models in transmission planning studies.

Report based on detailed studies: The team is working on detailed comparison studies between current state-of-the-art transmission-only software and TDcoSim. The said study helps answer fundamental questions that the industry is facing currently — a) Do currently available DER models with default settings adequately capture the characteristics to validate system stability, b) Understand the limitations of transmission only positive sequence simulation tools under the context of modern power system operation with significant renewable generation.

Team

• Karthikeyan Balasubramaniam (Argonne)
• Siby Jose Plathottam (Argonne)
• Sang-il Yim (Argonne)
• Kumarsinh Jhala (Argonne)
• Shijia Zhao (Argonne)

Project PI:
Karthikeyan Balasubramaniam
Principal Energy Systems Scientist
Energy Systems and Infrastructure Analysis
Email: kbalasubramaniam@​anl.​gov