Three-Phase Unbalanced Transient Dynamics and Powerflow for Modeling Distribution Systems With Synchronous Machines

Abstract

Unlike transmission systems, distribution feeders in North America operate under unbalanced conditions at all times, and generally have a single strong voltage source. When a distribution feeder is connected to a strong substation source, the system is dynamically very stable, even for large transients. However if a distribution feeder, or part of the feeder, is separated from the substation and begins to operate as an islanded microgrid, transient dynamics become more of an issue. To assess the impact of transient dynamics at the distribution level, it is not appropriate to use traditional transmission solvers, which generally assume transposed lines and balanced loads. Full electromagnetic solvers capture a high level of detail, but it is difficult to model large systems because of the required detail. This paper proposes an electromechanical transient model of synchronous machines for distribution-level modeling and microgrids. This approach includes not only the machine model, but also its interface with an unbalanced network solver, and a powerflow method to solve unbalanced conditions without a strong reference bus. The presented method is validated against a full electromagnetic transient simulation.

Interface Algorithm for Electromechanical Transient Simulation of Power System Based on PSD-Psmodel

“…According to the curve, it can be judged whether the generator unit in the system can continue to operate synchronously, that is, whether the system transient is stable or not [8].…”

Improving Distribution Resiliency with Microgrids and State and Parameter Estimation

“…During the first two years of the Microgrids as a Resiliency Resource program, the capability to simulate electromechanical machine dynamics and factor in unbalanced distribution considerations were added to the GridLAB-D platform. Details are available in previous reports and a journal publication [5]- [7]. Many existing GridLAB-D reports and papers outline the three-phase current injection method as the basis for all powerflow solutions, with those details readily available in [8].…”

“…A Norton-equivalent circuit models the device or system as a dependent current source, with a parallel impedance, as shown in Figure 1. The values in Figure 1 are calculated using the equations: Utilizing equations (1) to (5) and the details further outlined in [7], the basis for the dynamics of microgrid or islanded systems can be properly represented. Figure 2 shows the voltage results for the IEEE 13-node system with two distributed, synchronous diesel reciprocating engine generators.…”

A Matlab-Based Simulation Tool For The Analysis Of Unsymmetrical Power System Transients In Large Networks

“…• Three phase power flow calculations (Abdel-Akher et al 2005), (Kamh and Iravani 2010), (Demirok et al 2012), • Assessment of small signal stability (Salim and Ramos 2012), and • Analysis of dynamic transients in transmission networks (Saha and Aldeen, 2015) or distribution level systems (Elizondo et al 2016). The research highlighted above mainly focused on component modeling for three-phase unbalanced dynamic analysis and validating the developed models using commercial simulation tools.…”