A Single-Phase Transformerless Grid-Connected Inverter for Photovoltaic Applications Based on Switched Capacitors

Abstract

This article studies the control strategy of photovoltaic power generation inverters,
establishes a dual-loop control strategy for the stability of output power and builds the
entire photovoltaic microgrid system model based on modeling and simulation. The
stability of the inverter is studied with a double-loop strategy to maximize the output
power of the photovoltaic power generation system through the inverter. Generally
speaking, there are many kinds of photovoltaic inverter topologies, which can be roughly
divided into unipolar and bipolar inverters. At present, the single-pole mid-interleaved
flyback micro-inverter is generally selected, which has simple circuit, low cost and high
efficiency, which is beneficial to the promotion of household photovoltaic power
generation. The interleaved flyback inverter topology is mainly composed of dual
flyback converters, power frequency polarity reversal bridges and filter circuits. The
dual-circuit flyback converter is connected in parallel on the output side of the
photovoltaic module to control its output voltage and realize the MPPT function. Parallel
dual flyback converters can also increase the power level, reduce current ripple and
improve power quality. The power frequency polarity reversal bridge has the function of
inverter and is connected to the grid after the filter circuit. Through simulation
experiments, the grid-connected current and voltage of the system can maintain the same
frequency and phase stably, the output power of the solar photovoltaic power generation
panel increases and the output power of the inverter is stable and controllable. We can
verify the effectiveness of the dual-loop control strategy through verification.