Droop Control Strategy For Input-Parallel Output-Series LCL-Type Grid-Connected Inverter System

The input-parallel output-series inverter system(IPOS) is very suitable for low input-voltage and high output-voltage applications, which is composed of multiple inverter modules connected in parallel on the input side and in series on the output side. The output voltage sharing(OVS) is the key to ensure the stable operation of the IPOS inverter system, and the existing control strategies have shortcomings such as low modularity and reliability. Therefore, this paper proposes a droop control strategy based on the droop relationship between the inverter-side inductor current and filter capacitor voltage. It realizes disturbed control with no interconnection bus between modules. In the case of inconsistent filter parameters, it can significantly improve the system output voltage sharing and ensure the stable operation of the system by increasing the droop coefficient. This paper introduces the working principle and characteristic of the droop control strategy firstly. The influence of the droop coefficient on the system stability is also analyzed, and simulation results are presented at last.