Multiobjectives Integrated Division-Summation Method for <i>LCL</i>-Type Three-Level Grid-Connected Inverter Considering Low-Frequency Common Mode Voltage

The LCL-type three-level grid-connected inverter is extensively employed in photovoltaic (PV) power generation systems, which has multiple individually controlled objectives. To this end, an integrated division-summation (I-D-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Sigma $ </tex-math></inline-formula>) control strategy is proposed in this article, which can consider grid-connected current tracking, neutral-point potential (NPP) balance control, resonance suppression, and low-frequency common mode voltage (CMV), simultaneously. To compensate for the fact that the dual-division-summation (D-D-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Sigma $ </tex-math></inline-formula>) method only considers grid-connected current and resonance suppression, a virtual zero potential point is added for NPP balance control. Additionally, a low-frequency CMV estimation method based on fully connect-convolutional neural network (FC-CNN) is proposed, which perfectly avoids the unobservability of sensorless CMV. The I-D-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Sigma $ </tex-math></inline-formula> method can effectively reduce the low-frequency CMV, which is compensated by the low-frequency CMV. The effectiveness of the proposed strategy was verified through comparative experimental results.