Generalized Configurations for the Synchronization System Based on Transfer Function Approach

This paper presents our research on deriving all the generalized forms for the grid synchronization system of an inverter in the grid-connected applications. The transfer function approach is introduced in order to obtain the generalized second-order and third-order synchronization systems. This approach is based on the orthogonal property of two outputs from the second-order generalized-integrator (SOGI) technique that these two outputs are always 90° difference in phase but only equal in magnitude at the grid frequency. The proposed approach then can provide the generalized forms of any high-order synchronization system, including the second-order and the third-order systems. It is interesting to see that the systems derived from this approach include all the previous synchronization systems in the literature. The simulation results have confirmed that these generalized systems are able to generate two perfectly orthogonal outputs to determine the grid information, i.e. voltage magnitude and phase angle. In addition, the generalized third-order system shows its excellent performance in removing harmonics under the distorted grid condition, and thus its ability to accurately detect the grid information.