Complex-Valued Multi-Frequency Admittance Model of Three-Phase VSCs in Unbalanced Grids

Yicheng Liao; Xiongfei Wang; Xiaolong Yue; Lennart Harnefors

doi:10.1109/JESTPE.2019.2963004

Complex-Valued Multi-Frequency Admittance Model of Three-Phase VSCs in Unbalanced Grids

Yicheng Liao, Xiongfei Wang, Xiaolong Yue, Lennart Harnefors

Research output: Contribution to journal › Journal article › Research › peer-review

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Abstract

This article proposes a multifrequency admittance model for voltage-source converters with three-phase unbalanced grid voltages. The model is derived with multiple complex vectors and harmonic transfer functions, which is merely dependent on its own input voltage trajectory, and can accurately capture the frequency-coupling dynamics. The dynamic effects of both the basic synchronous-reference-frame phase-locked loop (PLL) and its alternative with a notch filter of the negative-sequence voltage component are compared. It is revealed that the notch-filtered PLL significantly weakens the frequency-coupling effects, which leads to a reduced order of the admittance model. The developed model is validated by a frequency scan, and the frequency-coupling effects impacted by different PLLs and voltage unbalance factors are verified by the experimental tests. Finally, a case study on stability analysis in unbalanced grids proves the significance of the model.

Original language	English
Article number	8946704
Journal	IEEE Journal of Emerging and Selected Topics in Power Electronics
Volume	8
Issue number	2
Pages (from-to)	1934-1946
Number of pages	13
ISSN	2168-6777
DOIs	https://doi.org/10.1109/JESTPE.2019.2963004
Publication status	Published - Jun 2020

Keywords

Complex vector
frequency coupling
harmonic transfer function (HTF)
modeling
phase-locked loop (PLL)
unbalanced grid
voltage-source converter (VSC)

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Open Access articleFinal published version, 4.32 MBLicence: CC BY 4.0

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title = "Complex-Valued Multi-Frequency Admittance Model of Three-Phase VSCs in Unbalanced Grids",

abstract = "This article proposes a multifrequency admittance model for voltage-source converters with three-phase unbalanced grid voltages. The model is derived with multiple complex vectors and harmonic transfer functions, which is merely dependent on its own input voltage trajectory, and can accurately capture the frequency-coupling dynamics. The dynamic effects of both the basic synchronous-reference-frame phase-locked loop (PLL) and its alternative with a notch filter of the negative-sequence voltage component are compared. It is revealed that the notch-filtered PLL significantly weakens the frequency-coupling effects, which leads to a reduced order of the admittance model. The developed model is validated by a frequency scan, and the frequency-coupling effects impacted by different PLLs and voltage unbalance factors are verified by the experimental tests. Finally, a case study on stability analysis in unbalanced grids proves the significance of the model.",

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AU - Wang, Xiongfei

AU - Yue, Xiaolong

AU - Harnefors, Lennart

PY - 2020/6

Y1 - 2020/6

N2 - This article proposes a multifrequency admittance model for voltage-source converters with three-phase unbalanced grid voltages. The model is derived with multiple complex vectors and harmonic transfer functions, which is merely dependent on its own input voltage trajectory, and can accurately capture the frequency-coupling dynamics. The dynamic effects of both the basic synchronous-reference-frame phase-locked loop (PLL) and its alternative with a notch filter of the negative-sequence voltage component are compared. It is revealed that the notch-filtered PLL significantly weakens the frequency-coupling effects, which leads to a reduced order of the admittance model. The developed model is validated by a frequency scan, and the frequency-coupling effects impacted by different PLLs and voltage unbalance factors are verified by the experimental tests. Finally, a case study on stability analysis in unbalanced grids proves the significance of the model.

AB - This article proposes a multifrequency admittance model for voltage-source converters with three-phase unbalanced grid voltages. The model is derived with multiple complex vectors and harmonic transfer functions, which is merely dependent on its own input voltage trajectory, and can accurately capture the frequency-coupling dynamics. The dynamic effects of both the basic synchronous-reference-frame phase-locked loop (PLL) and its alternative with a notch filter of the negative-sequence voltage component are compared. It is revealed that the notch-filtered PLL significantly weakens the frequency-coupling effects, which leads to a reduced order of the admittance model. The developed model is validated by a frequency scan, and the frequency-coupling effects impacted by different PLLs and voltage unbalance factors are verified by the experimental tests. Finally, a case study on stability analysis in unbalanced grids proves the significance of the model.

KW - Complex vector

KW - frequency coupling

KW - harmonic transfer function (HTF)

KW - modeling

KW - phase-locked loop (PLL)

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Complex-Valued Multi-Frequency Admittance Model of Three-Phase VSCs in Unbalanced Grids

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Keywords

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Impedance Modeling and Stability Analysis of Grid-Interactive Converters

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