Generalized impedance model and interaction analysis for multiple grid-forming and grid-following converters

Abstract

The growing use of power electronics converters in the power system leads to emerging stability issues. However, existing impedance models are insufficient for analysis of the converter-induced stability issues in the converter-congregated local area, especially faced with the hybrid integration of both grid-following (GFL) and grid-forming (GFM) converters. In this paper, a generalized impedance model in the d q frame is developed to facilitate the impedance-based analysis of any grid node with both GFL and GFM converters. With this model, closed-loop, internal and external stability performance can be accurately described and predicted. This paper shows that the internal stability of power converters has the feature of transferability. Therefore, to facilitate the internal stability analysis of multiple-input and multiple-output systems, this paper proposes a stability analysis method that utilizes the determinant of total admittance (matrices in high dimension) for direct stability demonstration, based on the recognition of instability pattern. Finally, the procedure for integrating power converters is considered to help with the stability-oriented design. The established impedance model, the proposed stability analysis method and the converter integration procedure are validated with control hardware-in-the-loop results in a study case of a multi-terminal network with current-controlled converters and virtual synchronous generators. • Impedance model describing any local area with GFL and GFM converters is proposed. • The determinant of total bus admittance is used for internal stability demonstration. • Impacts of critical system parameters on internal and external stability are studied. • A three-step procedure is adopted to facilitate the stability-oriented design.