PWM Strategy for Parallel Operation of Three Phase Converters Tied to Grid

When three phase converters operate, tied to the grid, interleaved PWM with coupled inductor can be used to enhance current quality. As the results, the harmonics of the output current are reduced significantly because of the increased equivalent switching frequency due to interleaving operation. However, the circulating current increases between converters. The coupled inductor is employed to suppress this circulating current. In this system, optimization of PWM pulse pattern by interleaved carrier would be the best strategy to enhance harmonics characteristics of output voltage and current. In this paper, based on harmonics analysis of PWM, a new PWM strategy for interleaved PWM is proposed and an offset voltage of each converter is optimized in terms of the harmonics of output voltage and current. As the results, the grid side inductor can be significantly reduced by decreasing voltage and current harmonics of the system to the grid. The validity, feasibility and effectiveness of the proposed method have been confirmed by computer simulation and experimental results.