Fundamental Positive- and Negative-Sequence Estimator for Grid Synchronization Under Highly Disturbed Operating Conditions

The control of grid-connected power converters, such as in photovoltaic generation systems, requires a fast, accurate, and robust synchronization method, particularly during faults and when operating under highly disturbed conditions. This paper presents a method to estimate the frequency, amplitude, and phase of the positive- and negative-sequence components. A filtering stage in a rotating reference frame based on a particular type of notch filter is designed to reject the most relevant disturbances, including voltage sags, frequency variations, phase jumps, voltage imbalances, and harmonics. Furthermore, an accurate estimation of the grid frequency is also carried out. Extensive simulation and experimental results are provided to show the performance of the estimation method in different scenarios considering the aforementioned disturbances. The method is able to precisely provide the estimated values between one and one and a half cycles of the fundamental frequency. Furthermore, the computational cost of implementation of the notch filters employed is considerably small.