GridSweep Simulation: Measuring Subsynchronous Impedance Spectra of Distribution Feeder

TL;DR

This paper introduces GridSweep, a new instrument for measuring the subsynchronous impedance spectra of distribution feeders, which helps assess oscillation risks associated with inverter-based resources.

Contribution

The paper presents a simulation model of GridSweep and demonstrates its ability to measure impedance spectra and identify oscillation modes in a distribution feeder with IBRs.

Findings

Peaks in impedance spectrum align with system oscillation modes.

GridSweep can effectively measure subsynchronous impedance spectra.

Simulation validates measurement capability for IBR-equipped feeders.

Abstract

Peaks and troughs in the subsynchronous impedance spectrum of a distribution feeder may be a useful indication of oscillation risk, or more importantly lack of oscillation risk, if inverter-based resource (IBR) deployments are increased on that feeder. GridSweep is a new instrument for measuring the subsynchronous impedance spectra of distribution feeders. It combines an active probing device that modulates a 120-volt 1-kW load sinusoidally at a user-selected GPS-phase locked frequency from 1.0 to 40.0 Hz, and with a recorder that takes ultra-high-precision continuous point-on-wave (CPOW) 120-volt synchrowaveforms at 4 kHz. This paper presents a computer simulation of GridSweep's probing and measurement capability. We construct an electromagnetic transient (EMT) simulation of a single-phase distribution feeder equipped with multiple inverter-based resources (IBRs). We include a model of the GridSweep probing device, then demonstrate the model's capability to measure the subsynchronous apparent impedance spectrum of the feeder. Peaks in that spectrum align with the system's dominant oscillation modes caused by IBRs.