A fast three-phase synchronization technique with parallel structure

Abstract

For many grid-connected equipment, the phase and frequency of grid voltage are crucial synchronization information. A phase-locked loop (PLL) is usually employed to obtain the information. In distorted grid, adding additional filter is a convenient and effective approach to enhance the harmonic rejection capability of the PLL. Most filters cannot simultaneously block the inter-harmonics, sub-harmonics and other order harmonics. Adaptive notch filter (ANF) can accomplish such task, since multiple ANFs can be flexibly cascaded. Generally, ANFs works as an in-loop filter in a PLL. When the notch frequency of an ANF is very low or multiple ANFs are cascaded in the control loop, the slowing down of the PLL response speed may be unacceptable in some applications. To deal with this problem, this paper proposes a parallel structure for the ANF-PLL to improve the response speed. In the proposed structure, a group of ANFs are placed in a front-stage synchronous reference frame and work as a prefilter, and a conventional ANF-PLL is used as a parallel frequency feedback loop (FFL). The effectiveness of this technique is verified through experimental results.