Performance Guide

TDcoSim has the capability to scale from a single distribution feeder with a single DER to thousands of distribution feeders with a hundreds of DER. Due to difference in computing effort and memory footprint, the solution time increases.

In this guide we provide suggestions on reducing solution time for a given co-simulation project.

Solution time

The total solution time is comprised of three parts: Tsolution = Tinitialize + Tco-sim + Tpost-process Where, Tinitialize is the time take to setup the co-simulation, Tco-sim is the time taken for co-simulation time stepping, and Tpost-process is the time take for post-processing the simulation time. Not that each solution time component is comprised of multiple tasks.

• Tinitialize: Here individual components co-simulation is initialized.
  • Read JSON configuration files
  • Launch sub-processes
  • Setup DER model integrators (for dynamic simulation)
  • Initialize co-simulation to steady state
• Tco-sim: Here we do time stepping for individual component.
  • PSS/E model:
    • Solve power flow for transmission system model.
    • Perform integration for dynamic models with a time step of one half-cycle (1/120 s).
    • Write to .out file
  • OpenDSS model: Solve non-linear algebraic problem
  • PV-DER model:
    • Fast-DER: Perform integration with a fixed time step.
    • Dynamic Phasor: Perform integration with variable time step
  • Write to disk if memory threshold is exceeded.
• Tpost-process: Here we post process the output and write them to user defined file type from memory.

Solution time contributors

The solution time may also be expressed as a function of the specific T&D+DER co-simulation model. Tsolution = f(nBus) + f(nFeeder) + nDERFeeder*f(nDERperFeeder)

Solution time benchmarks on test systems

The following benchmark times were obtained for the following scenario using workstation with the recommended specifications mentioned in System requirements:

T system: IEEE 118 bus system

D feeder: IEEE 123 node feeder

Simulation time: 20.0 s

Events: Three phase fault from 0.2 s to 0.3 s

Number of T nodes with feeders and DER: 97

DER Model type	DER solver type	PV penetration (%)	DER models	Solution time/Simulation time/DER (s/s/DER)
ThreePhaseBalanced - 50 kW	DiffEqPy (CVODE_BDF)	25	1746	0.047
ThreePhaseUnBalanced - 50 kW	DiffEqPy (CVODE_BDF)	25	1746	0.054
Fast DER - 50kW	Forward Euler	25	1746	0.038