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

Abstract

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- $\Sigma $ ) 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- $\Sigma $ ) 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- $\Sigma $ 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.