Single-phase dual-stage isolated multilevel inverter applied to solar energy processing

This paper presents a grid-connected mono-phase PV system. The electronic processing of the photovoltaic array energy was managed by a dual-stage inverter through high-frequency galvanic isolation. The DC-DC three-phase Series Resonant Converter works with switching frequencies equal to the resonant frequency. The main objective of the DC-DC converter is providing a bus with an equally divided voltage to the inverter. The DC-AC stage consists of a mono-phase NPC (Neutral Point Clamped) inverter, responsible for the grid current control and capacitive bus control. Two different modelling methods were used in order to obtain the inverter control loops. Through its operation stages the internal transfer function was obtained, and considering the reverse energy flow, the external transfer function could also be assessed. This paper presents the theoretical analysis, according to the following specifications: 2kW output power; 400V input voltage, 127 V rms AC output voltage; 20kHz switching frequency.