Improved phase-locked loop for distributed power generation systems

Distributed power generation systems (DPGS) based on renewable energy sources need accurate grid phase angle information in order to achieve different control algorithms usual for this application. Phase-locked loop (PLL) is the most modern and most common method for determination of the phase angle and frequency of the grid voltage. However, there are still serious limitations of reported PLL algorithms in real grid voltage conditions, such as unbalanced and distorted distribution grid. This paper proposes improved PLL which gives excellent and almost perfect grid voltage phase angle and frequency in unbalanced and distorted grid. This is achieved by a cascade of finite impulse response filters which eliminates characteristic harmonic components and extracts only fundamental harmonic signal. In that way, proposed PLL allows setting of higher bandwidth frequency of the PLL filter and much faster response which is especially important during grid voltage sags and frequency variations. Performance has been evaluated in details through simulation in Matlab/Simulink.