Research on Harmonic State-Space Modeling and Calculation Analysis of Low-Switching-Frequency Grid-Connected Inverter Considering the Impact of Digitization

Under low-switching-frequency condition, there is harmonic coupling in grid-connected inverter. The harmonic state-space (HSS) modeling method is an effective means to analyze the output harmonic characteristics of inverter. When the switching frequency is low, the sampling/holding and control delay make the update of pulsewidth modulation pulses more untimely, which will have a non-negligible impact on system output. However, the current relevant research fails to take these factors into account in the HSS model. In addition, the existing work fails to thoroughly study the calculation and analysis methods of HSS model, and the relevant work is insufficient. Based on this, this article studies the closed-loop HSS model and its calculation and analysis methods of three-level grid-connected inverter considering the digitization impact. First, according to the different calculation and analysis methods of the HSS model of the grid-connected inverter, the methods considering the digitization impact are proposed, respectively. Second, according to the proposed method, the harmonic characteristics of low-switching-frequency grid-connected inverter are analyzed, and the necessity of considering the digitization impact is explained. Finally, the effectiveness and accuracy of the proposed HSS-model calculation and analysis methods considering the digitization impact are verified by simulation and experiment.