Circulating current controller for parallel interleaved converters using PR controllers

To cope with power from large-scale renewable systems, more and more power electronic converters are used in parallel. Typically, carrier interleaving is used, thus leading to a decrease in filtering requirements. However, this causes additional circulating current to flow between the modules of the converter. The modules of the parallel converters are Voltage Source Converters (VSC). Usually, a coupled inductor (CI) is used to suppress the circulating current. However, the CI can be sensitive to the low order harmonic content of the circulating current which can appear owing to parameter mismatches between the converters. If the value of the low frequency circulating current is too high, this can saturate the CI. In order to ensure stable operation of the converter, this article presents a circulating current control based on the Proportional Resonant (PR) controller, which reduces the value of the low frequency circulating current. Furthermore, a specially designed sampling method is also presented, which ensures that only the fundamental component of the circulating current is fed to the circulating current controller.