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| Sequence Impedance Modeling and Stability Analysis of Load Converter with Virtual Inertia Control Connected to Weak Grid |
| Liu Yifeng1, Zhou Xiaoping1, Hong Lerong1, Xia Haitao1, Tian Hao2 |
1. National Electric Power Conversion and Control Engineering Technology Research Center Hunan University Changsha 410082 China;
2. State Grid Qianjiang Electric Power Company Qianjiang 433100 China |
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Abstract Both load virtual synchronous machine (LVSM) and load converter based on DC-link capacitor virtual inertia control (DLCVIC-LC) can enhance the power system inertia. However, inevitably, there are some interaction problems like harmonic resonance in weak grids. In this paper, considering the DC-link voltage dynamics and frequency-coupling effects, the general sequence impedance formulas for three-phase load converters were derived. Then, the precise sequence impedance models were built for impedance characteristics comparison analysis of LVSM and DLCVIC-LC. The analysis shows that the positive-sequence impedance of LVSM is generally inductive, which is basically consistent with the grid impedance characteristics and hardly causes harmonic resonance. In contrast, the positive-sequence impedance of LCVIC is negative-resistive-capacitive (i.e., phase angle is between -180° and -90°) in the middle-frequency band, which is likely to cause harmonic oscillation in weak grids. Furthermore, based on the derived model and Nyquist stability criterion, the effects of grid impedance and other control parameters on the stability of the two load converters connected to the grid were analyzed. Finally, experiments were performed to validate the analysis.
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Received: 02 December 2019
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2021, Vol. 36 
