Component-Level Thermo-Electromagnetic Nonlinear Transient Finite Element Modeling of Solid-State Transformer for DC Grid Studies

Highly-detailed equipment models for electromagnetic transient simulation provide an accurate insight into the system characteristics and behavior. In this article, a coupled field-circuit cosimulation employing detailed component-level models is proposed for the solid-state transformer. To reveal comprehensive thermo-electromagnetic information of the equipment, a high-order nonlinear insulated-gate bipolar transistor (IGBT) model is utilized for the modular multilevel converter, while the finite element method (FEM) is adopted in modeling the transformer. The heavy computational challenge posed by the complexity of these models is alleviated by exploiting model parallelism and the subsequent processing by massively parallel architecture of the graphics processing unit, e.g., a pair of coupled voltage-current sources is adopted for reducing the order of the matrix equation in the circuit part, while in the FEM-based models, a matrix-free nodal domain decomposition solution is utilized to parallelize the overall system to the maximum. A multirate scheme is applied for a further computational burden reduction of the cosimulation due to a large disparity in the appropriate time-steps between power semiconductor switches and the magnetic component. Simulation of a multiterminal dc system including the SST is carried out, and the accuracy of proposed models are validated by offline tools such as SaberRD, ANSYS, and PSCAD/EMTDC.