Grid-Voltage Synchronization Algorithms based on Phase-locked Loop for Power Converter under Balanced and Unbalanced Conditions

Rapid integration of non-conventional energy sources connected to grid and distribution systems with electronic power circuits has altered the planned grid specifications to ensure adequate grid failure efficiency. One of the essential control unit’s components is phase locked loop(PLL),where power converter grid is connected it. A synchronous reference frame (SRF) PLL approach is proposed in this research for obtaining correct phase knowledge for unbalanced grid voltages. The PLL efficiency was tested for abnormal grid conditions like unbalance, voltage sag, phase jump etc. This paper presents SRF PLL's analysis for the non-ideal grid conditions, where SRF-PLLs are implemented with pre-filters. Exact measurement of grid’s fundamental frequency and phase angle is important for grid connected power converter circuit’s control algorithm. The pre-filters which are used with SRF-PLL are band pass filter and low pass filter, in which band pass filters can be used to minimize input harmonics and low pass filter can reduce input noise. The implementation has been done through MATLAB software.