Stability Analysis of Three-Port Cascaded Inverter System With Second Harmonic Current Suppression

Considering the secondary power fluctuation, usually, it is necessary to cascade the second harmonic current suppression circuit (SHCSC) in the front of the single-phase inverter. However, it may result in the cascaded system being unstable, so far, the issue has received little attention yet. In this article, the active negative capacitor (ANC) is employed to eliminate the second harmonic current (SHC) and the Middlebrook criterion is employed in the proposed cascaded DC-AC system with SHCHC. The small-signal model of each subsystem is established initially, which is more accurate than the conventional model. Correspondingly, the output/input impedance and necessary stability conditions are obtained. Based on the stability condition, the influence that comes from control and circuit parameters on the impedance of each subsystem is revealed and the parameter constraints for input filter inductor and load are given, which guides to design of a stable system. Last, the filter inductor is taken as the freedom to improve the system stability considering different load conditions. Finally, a 500W prototype is built, and simulation results are in good agreement with experimental results. The stability analysis method could be extended to any other three ports system.