Three-phase phase-locked loop for grid voltage phase estimation under unbalanced and distorted conditions

Abstract

This paper proposes a signal reforming algorithm based three-phase phase-locked loop (PLL) to estimate the phase angles of an unbalanced and harmonics affected three-phase voltage system. This technique transforms the unbalanced waveforms into a balanced one by first attenuating the harmonic components and then balancing the voltage waveforms so that any conventional synchronous reference frame (SRF) PLL can accurately estimate the phase angle of the system. The harmonics attenuation technique is simple and fast. The signal reforming algorithm is effective in all possible unbalanced conditions. The proposed technique solves the difficulties of phase-estimation of the conventional SRF-PLL working under harmonics affected unbalanced grid conditions and avoids the use of three single-phase PLLs for phase-angle estimation of a three-phase voltage system. MATLAB/Simulink software has been used to carry out all the simulations and verify the performance of the proposed algorithm.