Modeling and Analysis of 2nd Harmonic Interaction for VSC with Transformer under Saturation Condition

Abstract

This paper investigates the mechanism behind the 2nd harmonic interaction of a transformer connected Voltage-Source Converter (VSC) under saturation conditions. The detail small-signal models of a saturated transformer and a VSC are derived considering their nonlinear behavior. It is revealed that the frequency coupling from the saturated transformer and the PLL in the VSC may form a positive feedback loop and give rise to a 2nd harmonic amplification. The harmonic amplification gain is established herein, which provides an accurate assessment of the 2nd harmonic interaction. This theoretical analysis is verified by a power hardware in the loop laboratory experiment.

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“…However, the nonlinear behavior of the saturated transformer complicates the interaction analysis. To handle this issue, the small-signal modeling at the worst-case operating point is a straightforward approach [18], [19].…”

Adaptive Anti-Saturation Control Design of Transformers in Converter-Based Grid Emulators

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