A Second-Order Generalized Integrator Frequency Locked Loop With Damping Ratio Adaptation

The complex and ever-changing harmonics in grid voltage will cause performance deterioration of the frequency-locked loops (FLLs). Although various measurements had been adopted to attenuate the deterioration, they had to make the tradeoff between the dynamic and steady-state characteristics generally. Consequently, a novel single-phase FLL that can adaptively adjust the dynamic and steady-state performance was proposed in this article. The proposed FLL regards the damping ratio of second-order generalized integrator-FLL (SOGI-FLL) as a time-varying parameter rather than a constant, and adjusts the damping ratio adaptively, so the proposed FLL was named SOGI-FLL with damping ratio adaptation (DASOGI-FLL). The adaptive mechanism is to decrease the damping ratio as frequency estimation error decreases and vice versa. To realize the mechanism, a novel variable was constructed to indirectly correlate the damping ratio with frequency estimation error. An objective function containing the constructed variable for damping ratio adaptation was designed, and the adaptive algorithm was derived by using the gradient ascent method. Then, the convergence analysis, parameter design, and digital implementation of the algorithm were elaborated. Finally, the results of simulation and experiment reveal that, benefits from the damping ratio adaptation, DASOGI-FLL can achieve rapid convergence, strong filtering capability, and high estimation accuracy simultaneously.