A Demodulation-Based Method for Instantaneous Phase-Angle Estimation of Unbalanced Three-Phase Voltage Systems

This article proposes an open-loop-based demodulation technique for the instantaneous phase-angle estimation of three phase voltage systems. The proposed demodulation-based method relies on the Clarke transform, finite-impulse-response filters, and algorithms for phase-angle and frequency deviation estimation. When compared to a frequency-locked loop (FLL) based on dual second-order generalized integrators and a phase-locked loop (PLL) relying on adaptive delayed signal cancellation operator, the proposed one does not use any integrators, recursive signals, and feedback of frequency or phase angle, thus unconditionally stable and relatively simple tuning is achieved. In addition, the proposed method is computationally efficient due to avoiding interpolation, square-root, trigonometric functions or their inverse operations. Moreover, under equal dynamic condition, the proposed one generates improved steady-state accuracy in a range of the frequency deviation specified by standard and grid code. Simulated and experimental results are presented to verify the efficacy of the proposed method.