Abstract
With the increasing applications of grid-connected voltage source converters, it is important to analyze the impedance characteristic of the grid-connected system to implement the stability analysis of the grid connection operation. Compared with the three-phase three-wire system, an additional zero-sequence path exists in the three-phase four-wire system. Therefore, it is necessary to consider the influence of the zero sequence when analyzing the stability of the system. In this paper, an impedance model including positive-sequence, negative-sequence and zero-sequence impedance of the three-phase four-leg grid-connected inverter is established. Through impedance characteristic analysis, the relationships between zero-sequence impedance and positive-sequence, negative-sequence impedance can be found which are decupled. Based on the developed zero-sequence impedance model, the main factors affecting the zero-sequence impedance model are revealed. Then, the system stability consisting of the grid and three-phase four-wire inverter is investigated, and the experimental results validate the theoretical analysis.
Highlights
Grid-connected voltage source converters (VSCs) have been widely employed in power system for renewable energy generation, flexible power transmission, and energy-efficient power consumption
Reference [15] presents a stability criterion for grid-connected converters based on impedance models and Gershgorin’s theorem, which consider the effect of the non-diagonal elements
The rest of this paper is organized as follows: System description and impedance modeling of three-phase four-leg grid-connected inverter is given in Section II as a foundation of the following analysis
Summary
Grid-connected voltage source converters (VSCs) have been widely employed in power system for renewable energy generation, flexible power transmission, and energy-efficient power consumption. Many scholars have studied the stability problem in the three-phases three-wire system [13]-[17], [33]-[35], the conclusions about stability based on the impedance analysis method cannot fully reflect the situation of the system due to the neglect of zero sequence component. This paper established the impedance model of the three-phase four-leg grid-connected inverter, and the impedance models of positive-sequence, negative-sequence and zero-sequence are obtained. The rest of this paper is organized as follows: System description and impedance modeling of three-phase four-leg grid-connected inverter is given in Section II as a foundation of the following analysis.
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