Robust Nonadaptive Three-Phase Quasi-Type-I PLL Approach under Distorted Grid Voltage Conditions

In this article, a three-phase non-adaptive pre-filtered quasi-type-I (QTI) phase-locked loop (PLL) approach is proposed for fast detection of fundamental positive sequence components. For this purpose, a non-adaptive pre-filtering architecture that relies on Lyapunov estimation theory is investigated. It is noted that the Lyapunov's principle-based QTI-PLLs are sensitive to the presence of fundamental negative sequence (FNS), harmonics, and DC-offset components. Thus, it requires additional efforts to resolve the aforementioned issues. Since the internal state-variable feed-backs in the Lyapunov's demodulation approach leads to poor dynamic performance, an improved immunity against DC-offset, harmonics and the FNS are achieved by avoiding state-feedback paths. Consequently, the demodulated error signals in the dq-frame can further reduce the number of state variables and efficiently reject the FNS components. Finally, the numerical results demonstrate the efficacy of the proposed method with respect to an enhanced QTI-PLL approach.