A CONTRIBUTION TO THE STUDY OF PLLs APPLIED IN ELECTRICAL POWER
SYSTEMS UNDER NON-IDEAL OPERATING CONDITIONS
This work aims to present 2 techniques for implementing PLLs in the synchronization of single-phase and three-phase networks, in the condition of faults in distribution systems, such as symmetrical and asymmetrical voltage sags, unbalance, harmonic distortions and frequency changes. The first of them uses the OCF technique as another alternative to estimate the positive sequence of the voltage vector in the stationary αβ frame. The second technique is presented as a new method to calculate the angular position of the grid voltage based on a discrete set of angles, through the use of FPS. The positive sequence voltages extracted from the OCF filter are then handled by an algorithm that is implemented with the FPS technique to estimate the phase angle. Therefore, to improve the performance of the PLL algorithm, the OCF filter is used for a filtering procedure, based on the structure of a SOGI, using this filter to filter the voltages αβ stationary data generated directly by the SOGI structure. The use of the second technique, FPS, has the advantage that SRF-PLL does not use a PI controllers and, therefore, it is not necessary to compute its gains. Results obtained on a experimental bench using signals affected by different harmonic distortions and with sag voltages similar to those obtained in power networks under fault conditions validate the contributions.