Adaptive synchronization of utility in abnormal voltage conditions

Synchronization is a key issue of an inverter-dominated distributed generator to enhance its uninterrupted operation ability in abnormal utility voltage conditions. In this paper, an adaptive-filter-oriented algorithm is proposed to fast and effectively synchronize the positive- and negative-sequence fundamental, even the desired harmonic components of utility voltage. The proposed method consists of two parts. One part is a robust digital phase-locked loop associated with a Sliding-Goertzel-Transform-based filter to track the frequency of utility. The other part is an adaptive module to separate the desired synchronous voltage components from the abnormal utility voltage. Firstly, the mathematical model of the proposed algorithm is established and explained in detail. Then, some useful analysis on the tradeoff between the stability and the convergence of the adaptive module is investigated. Finally, the simulated results by using MATLAB and experimental results performed on a 32-bit fixed-point DSP platform have verified the validation and feasibility of the proposed method, in the cases of distorted and imbalanced utility voltage, frequency step, one-phase or three-phase voltage drops to zero.