Direct Decoupled Synchronization Method for power converters under grid disturbances

During grid faults, three-phase grid-connected converters neighboring fault points usually operate under unbalanced and distorted operation conditions. This paper proposes a Direct Decoupled Synchronization Method (DDSM) based on direct decoupling of fundamental symmetrical voltages. Specifically, after Clarke transformation of three-phase measured voltage, a decoupling scheme of positive- and negative-sequence components from reference voltage u_α, u_β is implemented, in which some advanced single phase PLL modules are used. These modules, which can generate the inphase and quadrature-phase waveforms of the input signals, can be regarded as frequency adaptive filters. DDSM can also be easily expanded to deal with low-order harmonics. In comparison to existing three phase synchronization methods, operation properties and frequency response of the proposed synchronization schemes are analyzed. The conclusions are verified by experimental results.