Advanced Control of Grid-Connected Current Source Converter Under Unbalanced Grid Voltage Conditions

There are technical challenges when the grid-connected current source converter operates under unbalanced grid voltage conditions. The negative sequence component of the unbalanced grid voltage would result in the low-frequency ripple at dc side, as well as current harmonics at ac side. It has an adverse impact on the system operation. In order to solve the problem, the system mathematical model is established in this paper. The limitation of the conventional control strategy is clearly clarified. And then, the improved control strategy is discussed from the viewpoint of constant instantaneous active power. In order to further enhance the system performance, a new control strategy is proposed. Instead of the complicated instantaneous power theory, the proposed solution is a direct control strategy. Both the low-frequency dc-side ripple and ac-side current harmonics can be significantly reduced with a simple control structure, due to the direct control concept. Finally, the comparison evaluation of the conventional and proposed control strategies is carried out. The experimental results verify the effectiveness of the proposed solution.