Multiobjectives Integrated Division-Summation Method for LCL-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-Σ) control strategy is proposed in this paper, 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-Σ) 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-Σ 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.