An adaptive phase-locked loop structure for three-phase utility grid-connected systems

This paper proposes a phase-locked loop (PLL) structure, which is composed of non-autonomous adaptive filters (AFs) and a positive sequence detector (PSD), both operating in conjunction with the PLL based on synchronous reference frame (SRF-PLL). The AFs are used to extract the fundamental components of the utility voltages, whereas the PSD extracts the positive sequence components at fundamental utility frequency. The main purpose of the AF-based PLL is to overcome the drawbacks presented in the well-known SRF-PLL scheme, mainly in occurrence of non-ideal utility conditions, such as voltage harmonics and/or unbalances. Usually, such problems can be minimized reducing the bandwidth of the SRF-PLL system, at cost of compromising its dynamic response. Both static and dynamic performances of the AF-based SRF-PLL are compared to the conventional SRF-PLL by means of experimental tests, taking into account the following power quality problems: voltage harmonics and unbalances, voltage sags, phase-angle jumps and frequency variations.