Single-Current Feedback Control Strategy for Input-Parallel Output-Series LCL-Type Grid-Connected Inverter System

The multi-module input-parallel output-series (IPOS) connected inverter system, which is composed of standard modules parallel in the input side and series in the output side, have many advantages in high voltage applications. For example, in the renewable energy power generation fed to the grid, the IPOS inverter system can reduce the transformation ratio of the transformer between the inverter and grid, thus the transformer can be smaller and lighter. In order to get the high quality of grid current, the LCL filter is adopted in the output side of standard modules. Multiple objectives such as unity power factor, damping the resonant spike of LCL filter and output voltage sharing within standard modules, need to be achieved for this LCL-type IPOS grid-connected inverter system. This paper proposes a single-current feedback scheme which only samples the inverter-side current of one module to reach these goals simultaneously. It greatly simplifies the control structure and cuts down the cost sharply. In the end, the experimental results of the prototype consisting of two modules are shown to verify the effectiveness of the proposed scheme.