| AC/DC hybrid power grid is the key technology to solve the problem that traditional AC distribution network can not effectively accept DC power supply and load.It has obvious technical advantages in accepting new energy sources and meeting multiple loads.The DC/DC converter is an important support for establishing AC/DC distribution network,and it is the main carrier for AC/DC hybrid power distribution.Therefore,it is of great significance to model and analyze the switching transient characteristics of DC/DC converter.Zhangbei flexible substation is an important engineering practice for solving the core problem of traditional AC distribution network.This dissertation combines the switching transient characteristics of DC/DC converter unit modules based on multi-winding intermediate frequency transformer coupling in actual engineering.This dissertation first proposes a wideband modeling method for multi-winding medium frequency transformers.The capacitive effect is fully considered to make the model still effective at medium and high frequencies,satisfying the actual operational requirements of the DC/DC converter.Then,a detailed circuit simulation model is built for the power module of the unit module,including the behavior model of the IGBT device and the fast freewheeling diode.At the same time,the parameters of the stray inductance in the DC/DC converter loop and the internal stray inductance of the module are extracted.Finally,a model which can better characterize the transient characteristics such as overvoltage and oscillation during the operation of DC/DC converter is established.The effectiveness of the model and parameter extraction method is verified by the no-load experiment and simulation comparison.In this dissertation,the transmission characteristics of DC/DC converter are studied by theoretical and simulation analysis.The mechanism of overvoltage and high frequency oscillation in the switching process of DC/DC converter is revealed.The simulation model is used to verify the theoretical.The results show that the parameters of stray inductance in the circuit are the main factors affecting the magnitude of overvoltage,and the different stray inductance in the circuit will lead to the unbalanced voltage of IGBT in the whole bridge during commutation.The unbalanced voltage of IGBT is solved by optimizing the structure of DC bus.Related research work has a certain guiding role in the optimization design of DC/DC converter and the suppression of electromagnetic disturbance. |
PDF Full Text Request