Stability Analysis and Active Damping Control Method of DC Microgrid Based on Solid-State Transformer

Stability issues of a DC microgrid based on solid-state transformer (SST) are addressed in this paper. Firstly, the small-signal model of each converter in DC microgrid is established, and then the impedance on the bus-side of each converter is derived through the small signal model. After analyzing the bus-side impedance of each converter, low frequency oscillation phenomenon is found when constant power loads (CPL) are increasing. Secondly, in order to make the system more stable, an active damping control method using quasi-proportional-resonance (QPR) controller is proposed. Through this control method, peak value of the SST output impedance is reduced by serial active damping. The system stability is improved without changing the low-frequency amplitude of the output impedance and affecting the system steady-state power flow. Finally, the validity of the stability analysis and the proposed active damping control method are verified by simulation results of a SST based DC microgrid in MATLAB/SIMULINK.