A True Open-Loop Synchronization Technique

Synchronization techniques can be broadly classified into two major categories: Closed-loop and open-loop methods. The open-loop synchronization (OLS) techniques, contrary to the closed-loop ones, are unconditionally stable and benefit from a fast dynamic response. Their performance, however, tends to worsen in the presence of frequency drifts. To deal with this problem, two approaches are often recommended in the literature: Adapting OLS techniques to grid frequency variations by feeding back the frequency estimated by them or using the frequency estimated by a secondary frequency detector in a parallel manner. In the presence of the frequency feedback loop, nevertheless, the OLS technique may not be truly open-loop, which makes a deep study of stability necessary. Using the secondary frequency detector, on the other hand, increases the computational effort and implementation complexity. Another drawback of most of the available OLS techniques is that their implementation involves the computation of sine and cosine functions, which is undesirable from the computational standpoint, particularly when the implementation with low-cost digital signal processors is intended. The aim of this paper is to develop a true OLS (and therefore, unconditionally stable) technique without any need for the calculation of sine and cosine functions. The effectiveness of the proposed synchronization technique is confirmed through the simulation and experimental results.