Stability Analysis of Cascaded H-Bridge Power Electric Transformer-Boost Converter Cascade System

With the development of distributed energy, more and more attention has been paid to the research of micro-grid system. It may cause system oscillation or even instability because of the cascading of converters in micro-grid system. Aiming at the instability of the cascaded system, this paper takes the cascaded H-bridge power electronic transformer(PET) and boost converter system as the research object. The impedance analysis method to determine the system stability is adopted in this paper. The input impedance and output impedance models of the system are established by the state space method. The frequency characteristic curve of impedance model under different parameters is analyzed, which provides the basis for selecting parameters for system stability. It can be seen that the low frequency band of port impedance frequency characteristic curve of PET and boost converter will be gradually reduced with the increase of filter capacitance. The stability of the system is judged by whether the ratio of the input impedance to the PET output impedance meets the Nyquist stability criterion.