Performance of shunt active power filter with DSOGI-FLL Under distorted grid voltage

Proliferation of non-linear loads and power-electronics based distributed generators has aggravated the issue of harmonic and its adverse effects on the electrical utility and various equipment connected to the utility. To mitigate the effects of the harmonics, it is advisable to eliminate them or to maintain them within the statutory limits. This objective can be effectively achieved using Shunt Active Power Filter (SAPF). However, it is a challenging task to control the SAPF to effectively compensate the harmonics, especially when the grid voltage is characterized by different abnormalities like presence of harmonics, imbalance in supply, imbalance in load, dc offset etc. The SAPF's effectiveness depends on the accurate generation of the reference current. Some of the conventional methods fail to generate the desired reference current under some of these grid abnormalities, ultimately leading to deviation from a balanced set of sinusoidal grid currents. The paper presents the technique to compute the reference compensating current using second-order generalized integrator (SOGI), frequency-locked loop (FLL) and instantaneous power theory (p-q theory) to control SAPF. This approach, which obtains the reference current from the voltage and current components derived through dual SOGI-FLL, can effectively and quickly compensate the harmonics even under unbalance conditions. The system's dynamic performance is tested for a three-phase three-wire network under different grid abnormalities and the results are reported and analyzed.