On the Enhancement of Generalized Integrator-based Adaptive Filter Dynamic Tuning Range

Many phase-locked loop (PLL) or frequency-locked loop (FLL) use quadrature signals (directly or indirectly) as the input variables. Generalized integrator (GI) is a popular quadrature signal generator (QSG) available in the literature. GI is also widely used in various industrial applications. In addition to being a QSG, GI also works as a kind of bandpass filter. However, due to structural limitations, the dynamic tuning range is limited for the standard GI. The limitation arises from using only one gain in the direct-phase estimation dynamics, while quadrature phase estimation dynamics does not use direct feedback of the filter estimation error. Some attempts have already been made to overcome this limitation by adding direct feedback of the filter estimation error to quadrature-phase dynamics as well. However, we have demonstrated in this article that this kind of implementation has some frequency domain limitations. In this article, we propose a novel GI-type adaptive filter using coordinate transformation. The resulting structure maintains the same kind of filtering property of the standard GI at the transformed coordinates level while at the same time enhancing the dynamic tuning range of standard GI. Details of the proposed technique, stability analysis, and discussion on gain tuning are provided in this article. Finally, comparative experimental results are provided with respect to GI-FLL to show the dynamic performance improvement. Experimental results demonstrate the suitability of the proposed technique.