Research on Control Strategy of Single-Phase T-type Three-Level Grid-Connected Inverter

Aiming at the power mismatch problem of single-phase T-type three-level photovoltaic grid-connected inverter in operation, this paper designs a double closed-loop control strategy based on delay-free adaptive state observer based on the analysis of the principle of double-frequency ripple generation of DC bus voltage. This method effectively suppresses the second harmonic existing in the DC bus voltage, enhances the robustness of the inverter system, and realizes the stable operation of the inverter even in the case of grid-side voltage fluctuation. The correctness and effectiveness of the control strategy are verified by simulation.