An Enhanced Discrete-Time Oscillator-Based PLL-Less Estimation of Single-Phase Grid Voltage Parameters

This article presents a robust single-phase phase-locked loop (PLL)-less frequency, phase, and amplitude estimation technique. The proposed scheme, unlike PLL approaches, does not require a rigorous design and tuning process in order to attain a better stability margin. It is important to note that an improved discrete-time oscillator is obtained by involving a comb filter, which helps improve the dc-offset rejection capability and transient response time. Moreover, the notch-filter-like behavior and the introduction of imaginary zeros ensure better harmonic removal ability when compared to a known nonadaptive discrete-time oscillator. The proposed scheme relies on an open-loop frequency estimation technique that does not involve an inverse trigonometric function for the estimation of fundamental frequency deviation. The feedbackless architecture of the scheme and the avoidance of inverse trigonometric function, therefore, assist in reducing the real-time implementation complexity. However, under off-nominal grid frequency deviations, the amplitude and the phase of the output of the prefilter will suffer from errors. These errors are compensated by employing a mathematical regression approach. The results are experimentally validated and compared in order to prove the robustness and usefulness of the proposed scheme for single-phase applications.