Improved PLL for Power Generation Systems Operating under Real Grid Conditions

摘要

Distributed power generation systems (DPGS) basedon renewable energy sources need accurate grid phase angleinformation in order to achieve different control algorithms usualfor this application. Phase-locked loop (PLL) is the most modernand most common method for determination of the phase angleand frequency of the grid voltage. However, there are still seriouslimitations of reported PLL algorithms in real grid voltageconditions, as in unbalanced and distorted distribution grid. Thispaper proposes improved PLL which gives excellent and almostperfect grid voltage phase angle and frequency in highlyunbalanced and distorted grid. This is achieved by a cascade offinite impulse response filters which eliminates characteristicharmonic components and extracts only fundamental harmonicsignal. In that way, proposed PLL allows setting of higherbandwidth frequency of the PLL filter and much faster responsewhich is especially important during grid voltage sags andfrequency variations. Performance has been evaluated in detailsthrough simulation in Matlab/Simulink.