Droop Control Strategy Without Interconnection Lines for Input-Parallel Output-Series Grid-Connected Inverter System

The input-parallel output-series (IPOS) grid-connected inverter system is suitable for low input voltage and high output voltage occasions, such as solar energy based distributed power generation systems. This letter explores to select least number of control variables to realize multiple control objectives of IPOS grid-connected inverter system, including good system stability, high power factor, and power balance. Then, to avoid interconnection lines among modules to obtain better disturbance-rejection performance, a droop control strategy without interconnection lines is derived based on the duality of input-parallel output-parallel system. Even if the modules hardware parameters are unmatched, the power balance among the modules can also be ensured by increasing the droop coefficient. Finally, the experimental results based on a two-module IPOS grid-connected inverter prototype and simulation results based on three-modulate system are provided to verify the effectiveness of the proposed method.