Average Modelling of Medium Frequency DC–DC Converters in Dynamic Studies

摘要

This paper studies the average value modelling (AVM) of medium frequency (200 Hz–2000 Hz) dc–dc converters, which are becoming increasingly important in high-power dc grids and distributing microgrids. The most convenient modelling is based on transfer function and power components which are available in common simulation platforms, such as PSCAD/EMTDC. However, these models are found to require very small simulation steps and the achieved time-domain accuracy is not satisfactory for medium frequency converters. The core issue of accuracy loss is identified and corresponding improvement is proposed. User written state-space models in the frame and the frame are analyzed in depth. Different solvers, including the Dommel's method, the Heun's method, and the Runge-Kutta method were adopted and compared in solving the state-space models. A high-power 2-kHz LCL dc-dc converter is taken as the test system. It is found that the AVM in the rotating frame based on the Runge-Kutta solver is able to generate very accurate time-domain responses compared to the detailed switching model with almost 100 times improvement in simulation speed. It is demonstrated that a dc-dc converter with 2-kHz inner ac circuit frequency can be accurately simulated at a 50-s time step.