A Method Without Stability Issue for Robust Estimation of Three-Phase Grid Frequency

The grid frequency estimation using a recursive signal or an integrator-based method may suffer from a stability issue due to an accumulation or discretization error. To avoid these shortcomings and also to obtain a robust estimation of three-phase grid frequency under unbalanced and distorted conditions, this letter proposes a demodulation-based method without using a recursive signal and integrator. The proposed demodulation-based approach relies on the Clarke transform and fixed transport delay-based relatively simple finite-impulse-response filters. It includes an open-loop structure, thus unconditionally stable. It also does not demand the real-time evaluation of the trigonometric or inverse trigonometric function. Moreover, it generates improved accuracy as compared with a frequency-locked loop and phase-looked loop.