Topology and Control for Second Harmonic Current Reduction in Two-Stage Single-Phase Inverter Without Electrolytic Capacitors

Aiming for high reliability, it is necessary to remove the electrolytic capacitor from a two-stage single-phase inverter. To enforce this, the flying capacitor of the flying-capacitor-clamped (FCC) boost three-level (TL) converter was employed to buffer the second harmonic current (SHC). In this article, the topology of FCC boost TL converter was reconstructed from the viewpoint of active clamping. Based on this, different circuits in previous publications were synthesized, and a comparison of derived circuits was present. Under the condition of the front-end FCC boost TL converter regulating the dc-bus voltage, the SHC compensation method based on the modified flying capacitor voltage reference was proposed. By transformation of the control diagram, the voltage control plus load-current feed-forward scheme was derived. Finally, a 3 kW two-stage single-phase inverter was built and tested, and the experimental results verified the validity of the proposed scheme.