Quadrature signal generator based on all-pass filter for single-phase synchronization

Precise calculation of the grid voltage magnitude and phase is required for the operation of distributed power generation (DPG) systems. While the general concepts involved in the synchronization of single-phase and three-phase systems are the same, the practical implementation can differ substantially, the single-phase case being more challenging. Phase-locked-loop (PLL) based methods have been widely used for the synchronization of single-phase systems. These methods can be roughly grouped into methods that use a quadrature signal generator (QSG) and methods that implement a single-phase PLL. One drawback of single-phase PLL methods is that they usually produce a component at twice the fundamental frequency that needs to be removed. On the contrary, QSG methods do not induce such component, enabling therefore the use of three-phase PLLs. On the other hand, the phase error usually depends on the input magnitude for both methods. This paper proposes a QSG based single-phase synchronization technique that overcomes the aforementioned limitations of both single-phase PLLs and QSGs. It will be shown that the proposed method accurately estimates the magnitude and phase of the microgrid/grid fundamental voltage with high dynamic response, even under high distorted conditions.