Current balancing control of high power parallel-connected AFE with small current ripples

Parallel connected Active Front End (AFE) voltage converters are widely employed in high-power grid interfaces for renewable energy applications. With parallel connected two level power converters, the power rating of the system can be easily increased with higher stability and less control efforts than multilevel power converter based solutions. However, due to unmatched modules, unbalanced currents inevitably happen to different modules of the same phase, which seriously impacts the efficiency and performances of the converter. This paper presents an improved current balancing control methods for a high power (600 kVA) parallel connected AFE for wind energy applications. The proposed current balancing method is integrated within a well-known Voltage Oriented Control Scheme with few implementation efforts. The simulation results show that with the proposed strategy the current ripples of each parallel-connected converter leg decrease evidently and the THDs are therefore decreased. Moreover, the effectiveness of the proposed method is also confirmed by experimental results with a grid-code compatible testing set-up.