Adaptive Clarke Transformation for Robust Estimation of Three-Phase Grid Frequency.

A grid-synchronization algorithm for grid-tie inverters must be precise, accurate, robust to noise and harmonic distortion and fast to react to grid voltage disturbances to facilitate stable operation in a modern distribution grid network. Unlike traditional synchronization algorithms such as the phase-locked loop (PLL), the harmonic version of the Aboutanios and Mulgrew (HAM) algorithm performs well in all these characteristics. However, both the three-phase HAM estimator and three single-phase HAM estimators generate some small estimation error during unbalanced grid voltage conditions. This paper proposes a method that combines the adaptive Clarke transform (ACT) with the HAM estimator to reduce this error and cause convergence to the Cramèr Rao Lower Bound in noisy environments under both balanced and unbalanced conditions. Simulated results confirm that the proposed method generates improved performance when compared to several similar competing estimators.