Dynamic Co-Simulation Methods for Combined Transmission-Distribution System and Integration Time Step Impact on Convergence

TL;DR

This paper analyzes the convergence of co-simulation methods for combined transmission-distribution systems, proposing two approaches and demonstrating the superior stability of the series computation method at larger time steps.

Contribution

It introduces two novel co-simulation methods for CoTDS and provides a rigorous convergence analysis, validating the methods against total system simulation and commercial software.

Findings

Series computation method shows better numerical stability at larger time steps.

Validated co-simulation methods against total system simulation and EMTP software.

Series method achieves remarkable correspondence with commercial software.

Abstract

Combined Transmission and Distribution Systems (CoTDS) simulation for power systems requires development of algorithms and software that are numerically stable and at the same time accurately simulate dynamic events that can occur in practical systems. The dynamic behavior of transmission and distribution systems are vastly different, especially with the increased deployment of distribution generation. The time scales of simulation can be orders of magnitude apart making the combined simulation extremely challenging. This has led to increased research in applying co-simulation techniques for integrated simulation of the two systems. In this paper, a rigorous mathematical analysis on convergence of numerical methods in co-simulation is presented. Two methods for co-simulation of CoTDS are proposed using parallel and series computation of the transmission system and distribution systems. Both these co-simulation methods are validated against total system simulation in a single time-domain simulation environment. The series computation co-simulation method is shown to have better numerical stability at larger integration time steps. The series computation co-simulation method is additionally validated against commercial EMTP software and the results show remarkable correspondence.