High-power high-frequency converter modelling using Dommel’s and Runge-Kutta methods in ABC and DQ frame

As the future DC grids will involve numerous converter systems, the accuracy and speed of their modeling becomes of high importance. This paper develops and compares four average models for high frequency converters like DC/DC or DC hubs: the average model in the ABC frame using Dommel's method (Model 1), the average model in the dq frame using Dommel's method (Model 2), the average model in the ABC frame using Runge-Kutta method (Model 3) and the average model in the dq frame using Runge-Kutta method (Model 4). Schematics and principles of the numerical algorithms for the four models are presented. Detailed switching model of a 500MW, 2kHz, ±200kV /±400kV DC/DC converter is taken as benchmark for comparing the four average models. It is found that Model 2 is numerically unstable. Model 1 and Model3 need the same small solution time step as the detailed switching model to give accurate results. Model 4 is the recommended average model for high frequency (1-3kHz) converter. It gives accurate result as the detailed switching model at the benefit of 100 times faster simulation speed.