Modeling of grid-connected converter-based sources as equivalent impedances for symmetrical and asymmetrical short-circuit calculation

Abstract

The study of electrical systems under fault conditions provides fundamental information for proper system protection design and coordination. These studies are traditionally performed in the phasor domain and based on the physical behavior of the synchronous generators directly connected to the grid. However, the increase of converter-based renewable sources (CBRSs) connections to the grid have created the need for new short-circuit (SC) calculation methods, since, unlike the synchronous generators, the converter SC contribution depends only on its Fault Ride Through (FRT) and active power injection requirements. In this paper, a comprehensive approach for steady-state SC calculation in power systems with CBRSs is proposed. The proposed approach is based on the bus impedance matrix and can be used for symmetrical and asymmetrical SC calculation considering both positive and negative sequence currents from converters as required in the grid codes of many countries. The proposed approach is demonstrated with a 17-bus test system containing converter-controlled photovoltaic (PV) and wind generation submitted to the Brazilian Electric Grid code requirements. By comparing the obtained results with the grid code requirements, the effectiveness of the proposed iterative approach in the estimation of the steady-state SC current contribution from CBRSs is verified.

Keywords

• short-circuit analysis
• full-scale converters
• distributed generation
• type iv wind turbine
• photovoltaic generators.