Stability analysis and improvement of solid state transformer (SST)-paralleled inverters system using negative impedance feedback control

Abstract

In this paper, the stability of solid state transformer (SST)-paralleled inverters system is investigated by using the unified impedance-based stability criterion (UIBSC). Theoretical analysis reveals that the output impedance characteristics of SST are frequency-dependent and multiple resonances can happen in the SST-paralleled inverters system. A lead-lag controller and a negative impedance feedback controller are developed to mitigate the resonances within and beyond the current control loop respectively. Without additional sensors, the proposed negative impedance feedback control is able to achieve better damping function in a much wider frequency range compared to other methods. In addition, the proposed control method is less sensitive to the time delay. Simulation results are provided to validate the functionality of proposed methods.