A Novel Beat Frequency Modulated Single-Stage Soft-Switched Microinverter

In this paper, a novel single-stage single-phase microinverter with a beat frequency modulation (BFM) and fully soft-switching operation is presented for photovoltaic (PV) applications. To convert the low-level DC voltage of the PV panel to the desired AC voltage of the grid, a DC-AC converter is required to amplify the input DC voltage and also make a sinusoidal AC voltage at the output. The proposed microinverter is configured based on a resonant LLC converter to provide both amplification and isolation. A new frequency modulation is applied to the converter to provide a pure sinusoidal waveform at the output of the microinverter. The soft-switching conditions are provided for all switches of the converter due to the utilization of the resonant elements. The rectifier and unfolder at the output stage of the microinverter are merged to utilize the minimum number of semiconductors. A new control strategy is employed to provide the output current regulation based on a single-phase DQ current controller. The proposed beat frequency modulation and topology derivation of the microinverter are discussed in this paper. To validate the theoretical analysis, a 250W prototype is implemented and experimental results are represented.