A positive and negative sequences detecting method based on an improved PQ theory for power grid synchronization

This paper proposes a modified PQ theory for detecting the positive and negative components of the utility voltages under faulty grid conditions. Fast and exact detecting of those sequences is important to achieve the operating at unity power factor integration of distributed generations into the main grid and for other uses. A detailed description of the proposed method has been accomplished. A phase lockedloop on synchronous rotating frame (SRF PLL) is commonly used to detect the exact phase angle; nevertheless this solution failed immediately to extract the two sequences under unbalanced and distorted conditions. The FMV filter constitutes a very interesting alternative to obtain the phase angle precisely and instantaneously; in this way, different kind of filters with a narrow bandwidth have been used for the separation of positive and negative components; however the response time is extended and an important phase delay is generated. the calculation of the mean value of the instantaneous power is a way to eliminate the AC component with a time response less than one of half of period. The obtained simulation results have been confirmed experimentally using a Dspace 1104 platform.