Modulation Theory Based Analysis on Converter Transformer Core Saturation Instability

Due to its intuition,clear physical conception and convenient to use,in the calculation of harmonics of power system more and more attentions are paid to modulation theory.In this paper the detailed derivation of current switching function is expounded,and the mechanism causing transformer core saturation instability is presented briefly.It is the first time to apply modulation theory to solve converter transformer core saturation instability and a new method to judge such a harmonic instability is proposed;then based on the data of China Southern Power Grid in 2010 and by use of PSCAD/EMTDC,a simulation model for detailed electromagnetic transient of ±800 kV DC power transmission system from Yunnan to Guangdong is built,and using the built model the simulation research on core saturation instability caused by three-phase grounding fault is performed.Simulation results verify the correctness of the proposed method.