Converter-Driven Harmonic Resonance Instability in VSC-STATCOMs

The connection of VSC-STATCOMs to high-voltage networks may introduce converter-driven, harmonic resonance interactions, ranging from hundreds of hertz up to a few kilohertz, with the rest of the network dynamic devices. Thus, to capture these phenomena, representative models of all the participating devices are necessary that are accurate up to this frequency range. In particular, special attention is required for the modeling of the different measurement filters, sampling, and control delays of the converters. In this paper, modeling guidelines for the derivation of high-quality, EMT linear models of converter-based devices that are accurate in the harmonic frequency range are presented. Specifically, the effect of the VSC delays on the system stability is studied in detail. Finally, the effect on stability of different key VSC controllers, such as the current loop and PLL, is also studied. The proposed modeling techniques are supported by linear analysis and detailed time-domain simulations.