Impedance Modeling and Stability Analysis of VSG Controlled Grid-Connected Converters with Cascaded Inner Control Loop

Yunyang Xu, Heng Nian, Yangming Wang and Dan Sun
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Yunyang Xu: College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China
Heng Nian: College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China
Yangming Wang: College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China
Dan Sun: College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China

Energies, 2020, vol. 13, issue 19, 1-21

Abstract: This paper develops the impedance models of grid-connected converters under the virtual synchronous generator (VSG) strategy with a cascaded inner control loop and analyzes the system stability of VSG controlled converters with different kinds of weak grid. Different from existing small-signal models with high dimensions, a single-in-single-out (SISO) impedance model with simple mathematical expression is obtained in this paper, which is applied to identify the influence of the cascaded control loop on impedance characteristics and system stability. It is found that the impedance characteristics of VSG controlled converters can become capacitive below the fundamental frequency, and it is mainly caused by the voltage controller in the cascaded control loop of the VSG strategy. Impedance-based stability analysis shows that the capacitive impedance characteristics can benefit the compatibility of converters operated with the series-compensated weak grid, but may deteriorate the system stability with the inductive weak grid, which can be avoided by increasing the proportional coefficients of the cascaded voltage and current controllers or applying a larger virtual resistor to reduce the negative resistance in the capacitive frequency range. Experiments based on the control-hardware-in-loop (CHIL) platform were carried out to verify the developed analytical models and possible system instable cases.

Keywords: impedance model; small-signal modeling; system stability; virtual synchronous generator (VSG); weak grid (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2020
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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