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Energy Systems and Infrastructure Analysis

A Tool Suite to Improve Reliability and Performance of Combined Transmission-Distribution Under High Solar Penetration

Software tools that impart a holistic understanding of the steady-state and transient behavior of transmission-distribution interaction under high PV penetration levels

Project Objective

Achieving very high penetrations of solar PV envisioned by SunShot will imply important changes to power system planning and operation. Of particular concern are the needs to improve understanding of transmission-distribution interactions, awareness of real-time distribution system operating conditions, and capture time series dynamics across multiple scales within associated tools. To overcome such technical barriers/issues, the project team will develop a suite of software tools that imparts a holistic understanding of the steady-state and transient behavior of transmission-distribution interaction under high PV penetration levels along with real-time monitoring of the distribution system and integration of system protection.


  • Development of a transmission-distribution steady-state co-simulator
    • Software used
      • PFLOW, IGMS, GridLAB-D, CAPE
    • Technical approach
    • Modeling assumptions
  • Development of a transmission-distribution dynamics co-simulator
    • Software used
      • TS3PH, CYME
    • Technical approach
    • Modeling assumptions
  • Development of a distribution system state estimator
    • Technical approach
    • Modeling assumptions

Software Developed



  • Approach
    • Run a transmission-distribution co-simulation and collect the voltage magnitude at T&D interface. Then run a T-only and D-only simulation using the obtained interface variables. Compare the results between T&D co-simulation versus T-only and D-only approach.
  • Metrics
    • Less than 2 percent difference in voltage magnitude as asserted by utility advisory group.

Use Cases

One of the fundamental questions for this work is to identify whether a co-simulation is needed for a particular power system analysis. The use-cases help answer that question in a quantifiable manner.

  • DER Impacts on Bulk Reliability
    • Measure bulk power system reliability as a function of area control error (ACE). Study how high solar penetration levels play a factor in ACE.
  • Reactive Power Limits for Steady-State Voltage Stability at the T-D Interface
    • This use-case finds the static voltage stability limit on the seam between transmission and distribution system.
  • Impact of High PV Penetration on System Protection
    • High solar penetration scenarios under certain conditions result in a phenomenon called reverse power flow. This use case studies the said phenomenon and its effect on power system from system protection viewpoint.
  • Frequency response use-case
    • The basic idea is to study high-penetration PV impacts on dynamic frequency response following a major transmission disturbance. Under such conditions, the system may lose substantial PV inverter power generation, which could cause a decline in frequency and initiate a cascading outage. The initial disturbance in the transmission grid could affect the performance of the PV inverters, especially at high-penetration levels. Then, the reduced PV output on the distribution feeders could affect the transmission grid. In other words, there will now be a feedback loop that links T&D. A key aspect of this use-case is to investigate when and how the aggregated T-only models can be used versus when and how the combined T&D models need to be used.

Funding Acknowledgment

This work is supported by U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Solar Energy Technologies Office, under contract DE-EE0001748.