A parallel control strategy for the cascaded multi-level inverters in the distributed generation system

In the distributed generation systems, three-phase inverters are the basement because they are used as power electronics interface between the generators and the grid. Cascaded multi-level H-bridge inverters are widely used for industrial application due to the simple topology and good power quality. However, unbalanced power source problem will easily happen in such an application. In this paper, a parallel control strategy for three-phase cascaded multi-level H-bridge inverters is proposed. The voltage and current inner control loops are introduced to deal with unbalanced power source problem. The droop method with the virtual impedance loops is introduced in order to share power between parallel inverters. Besides, a secondary control method is added to remove the frequency and amplitude deviation produced by the droop control. The performance and robustness under Islanded operation mode are validated by the simulation results.