Grid Synchronization Phase-Locked Loop Strategy for Unbalance and Harmonic Distortion Conditions

Abstract

The synthesis, design and analysis of a threephase phase-locked loop (PLL) algorithm under grid voltage uncertainties is presented. Unlike other techniques, the proposed strategy is simple but yet, robust against unbalanced and distorted voltage conditions. The method does not rely on the symmetry of the three-phase voltages, like conventional PLL implementation techniques. Under phase lock, the reference voltage and the output voltage are in synchronism, hence they cross the zero axis at the same time. The proposed PLL implementation exploits this fact, by counting the difference between the zero crossing times of the grid voltage and the output voltage waveform, and generating an error signal proportional to this difference. This error is fed into a PI regulator which forces it to zero over time. The proposed algorithm is compared against two popular PLL techniques. Simulation and experimental results show better performance of the proposed PLL implementation in unbalanced grid voltage conditions.

Fundamental frequency sequence amplitude estimator for power and energy applications

“…In obtaining (20), small-angle approximation is used, i.e., cos(x) = 1 − x 2 /2. Eqs ( 20) and ( 21) quantify the frequency deviation-induced errors when nominal frequency is used in estimating the DC offsets in (17) and (18). These errors need to be compensated in-loop to obtain error-free estimation of the signal parameters.…”

“…Phase-Locked Loop (PLL) [15][16][17][18] is another technique that is extremely popular in the literature. Out of various PLL techniques available in the literature, Synchronous Reference Frame (SRF)-PLL [15] is undoubtedly the most used one.…”

Photovoltaic inverter control using programmable logic device

“…Therefore, the reference current must be synchronized with the grid voltage in order to maximize the active power delivered from PV cells. Many solutions described in the literature use the phase-locked loop (PLL) method [13]. This voltage synchronization strategy was assumed as a standard method compared with the fuzzy logic-based (FLC) synchronization method proposed in this paper as a new solution for grid-connected inverter.…”