Modeling and Control of Zero-Sequence Circulating Current in Parallel Converters With Space Vector Modulation

The use of parallel converters is one of the most practical solutions to solve the problem of transmitting bulk power generated in megawatt wind turbines to the grid. In spite of several advantages of paralleling, some considerations must be taken into account. Zero-sequence circulating current flowing between parallel converters is one of these concerns. Characteristic differences and discrepancy of zero-axis duty cycles of the parallel converters are considered as the main origins of this current. This paper investigates another source of this phenomenon in space vector modulation controlled converters. This unnoticed source is the notable third-harmonic voltage generated in the conventional SVM. This claim is confirmed analytically and by simulations. Accordingly, several methods for reduction of this third-harmonic voltage and mitigation of the resultant zero-sequence circulating current are proposed. The performances of these methods are verified analytically and by simulations. Finally, the experimental results are presented to verify the effectiveness of the proposed methods.