Comprehensive Electromagnetic Transient Simulation of AC/DC Grid With Multiple Converter Topologies and Hybrid Modeling Schemes

HVDC projects and renewable energy sources are increasingly being integrated into traditional AC grids, forming a more complex and yet sustainable power system. This paper focuses on the comprehensive electromagnetic transient (EMT) simulation of an AC/DC grid, which is composed of CIGRÉ dc grid test system, IEEE 39-bus AC system, and wind farms. The AC/DC converters are composed by different topologies of voltage source converters, including modular multilevel converters (MMCs), three-level neutral-point-clamped converters, and two-level converters. Piecewise polynomial curve fitting is proposed to the insulated gate bipolar transistor modules in the MMC. Furthermore, hybrid modeling schemes are proposed with different levels of complexity on the AC/DC grid to obtain accurate and efficient EMT simulation on PSCAD/EMTDC. Three-zone partition schemes based on distance, node number, and network coupling are also proposed and compared. The performance of the proposed schemes is presented and verified with a DC fault case study.